ALBERT

Description: 〈p〉Publication date: 15 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 264〈/p〉 〈p〉Author(s): Antonio D. del Campo, María González-Sanchis, Alberto García-Prats, Carlos J. Ceacero, Cristina Lull〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Marginal semi-arid forests in areas currently affected by climate change are a challenge to forest management, which has to focus on key functional traits that can effectively contribute to resistance under extreme drought. We studied the effects of thinning in a marginal forest by quantifying functional responses relating to growth, carbon and water fluxes. Two experimental plots were established, one thinned in 2012 and the other one left as a control. The environmental conditions varied substantially during the 4-year study period, although dry years predominated. There were signs of dieback in the control with a decreasing inter-annual trend in LAI, as opposed to the treated plots, where LAI by the end of the study almost reached pre-thinning levels. Sap flow and transpiration were greatly enhanced by the treatment, with thinned trees transpiring 22.4 l tree〈sup〉−1〈/sup〉 day〈sup〉−1〈/sup〉 in the growing season, about twice the control figures. The seasonal patterns of transpiration and soil moisture were uncoupled, indicating a contribution of deep groundwater to the former flux. In the control, limitations to water and carbon dynamics (canopy conductance) occurred at soil moisture values below 16%, whereas in the thinned trees these limitations appeared when soil moisture dropped below 10%. Overall, oaks’ transpiration was enhanced with thinning to the point that stand-water use surpassed that of the control by the second half of the study period, averaging 24% of gross rainfall in both plots. Soil evaporation increased from 12 to 20% of gross rainfall after treatment in the overall period. The treatment had a profound watering effect in this marginal forest, led by fewer trees using the same amount of water as those in the untreated overstocked plot. This research may provide guidelines for ecohydrology-oriented silviculture in stands experiencing tree encroachment and transformation into shrublands that are more prone to global change-induced disturbances.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 264〈/p〉 〈p〉Author(s): Ren Li, Lin Zhao, Tonghua Wu, Qinxue Wang, Yongjian Ding, Jimin Yao, Xiaodong Wu, Guojie Hu, Yao Xiao, Yizhen Du, Xiaofan Zhu, Yanhui Qin, Shuhua Yang, Rui Bai, Erji Du, Guangyue Liu, Defu Zou, Yongping Qiao, Jianzong Shi〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Soil thermal conductivity (〈em〉λ〈/em〉) is one of the essential parameters relating to heat exchange, and it also plays a key role in verifying soil thermal hydrodynamics in permafrost regions. In this paper, the characteristic of in situ 〈em〉λ〈/em〉 was analyzed based on data measured from June 2004 to December 2008 at Tanggula district on the Qinghai–Tibet Plateau. The result showed that diurnal 〈em〉λ〈/em〉 strongly influenced by variation of soil moisture content. The daily 〈em〉λ〈/em〉 exhibited distinct seasonal variation; on average, the largest value of 〈em〉λ〈/em〉 occurred in summer, followed by the autumn and spring season, while the smallest value occurred in winter. As a whole, 〈em〉λ〈/em〉 values in the unfrozen state were larger than those in the frozen state. Unsaturated soil and the huge difference in soil moisture content between the unfrozen state and initial freeze resulted in the lower 〈em〉λ〈/em〉 in the frozen state. For the study area, the critical value of local soil saturation degree was about 0.37, the corresponding critical soil moisture content was about 0.195 m〈sup〉3〈/sup〉 m〈sup〉−3〈/sup〉. And soil moisture content was the main factor controlling in situ 〈em〉λ〈/em〉. Finally, an empirically-derived model was proposed for predicting daily 〈em〉λ〈/em〉, and which showed good performance in the study area.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 264〈/p〉 〈p〉Author(s): Baoqing Zhang, Amir AghaKouchak, Yuting Yang, Jiahua Wei, Guangqian Wang〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Different categories of droughts (e.g., meteorological, agricultural, hydrological), and their multi-scalar features often make description of drought onset, persistence, and termination challenging and often subjective. Here we show that a water-energy balance based indicator, named Standardized Moisture Anomaly Index (SZI), better captures multiple categories of droughts and their multi-scalar features. We globally evaluate and compare the performance of SZI with existing drought indicators that use potential evapotranspiration (PET) as a measure of atmospheric water demand including the Standardized Precipitation Evapotranspiration Index (SPEI) and self-calibrated Palmer Drought Severity Index (scPDSI). We show that while 〈em〉PET〈/em〉 is a good indicator for characterizing the climate aridity, using it as a measure of atmospheric water demand for drought analysis leads to misrepresentation of droughts, especially over water-limited (non-humid) regions where the actual evapotranspiration is primarily dominated by water availability rather than energy (or PET). The main advantage of SZI is that, instead of PET, it uses a variable termed climatically appropriate precipitation for existing conditions (〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si2.gif" overflow="scroll"〉〈mover accent="true"〉〈mi〉P〈/mi〉〈mo〉ˆ〈/mo〉〈/mover〉〈/math〉) as the atmospheric water demand metric. Investigating droughts over 32 large basins across the globe, we show that the SZI can better represent meteorological, hydrological, and agricultural droughts compared to SPEI (especially in non-humid basins; 18 out of 32 basins) and scPDSI at multiple time scales. Given that SZI is physically more reasonable in reflecting surface water-energy balance over both humid and non-humid regions, it enables better characterization of different types of droughts in different climatic regions.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 264〈/p〉 〈p〉Author(s): Ravshan Eshonkulov, Arne Poyda, Joachim Ingwersen, Alim Pulatov, Thilo Streck〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Turbulent fluxes at the land surface measured by the Eddy Covariance (EC) technique are typically considerably less than the difference between net radiation and ground heat flux. This is known as the energy balance closure (EBC) problem. It is crucial for validating land surface models as it provokes substantial uncertainty to the magnitude and partitioning of energy fluxes. The gap in the energy balance calls for searching for additional energy terms in the soil-plant-atmosphere system. To evaluate the contribution of these minor storage terms to the measured EBC, we conducted an experimental study to evaluate the contribution of these minor storage terms to measured EBC in the Kraichgau region in southwest Germany over two consecutive growing seasons (2015 and 2016). The measured and calculated minor storage terms comprised the enthalpy change in the plant canopy (〈em〉S〈sub〉c〈/sub〉〈/em〉), the air enthalpy change (〈em〉S〈sub〉a〈/sub〉〈/em〉), the energy consumption and release by photosynthesis and respiration (〈em〉S〈sub〉p〈/sub〉〈/em〉), and the atmospheric moisture change (〈em〉S〈sub〉q〈/sub〉〈/em〉). Furthermore, the soil heat storage (〈em〉S〈sub〉g〈/sub〉〈/em〉) was determined at different locations within the EC footprint and compared to the single point measurements of 〈em〉S〈sub〉g〈/sub〉〈/em〉 at the EC station. Calorimetric and harmonic analysis were performed to compute ground heat flux. 〈em〉S〈sub〉p〈/sub〉〈/em〉 had the strongest effect in improving EBC due to the high net CO〈sub〉2〈/sub〉 uptake during the productive phase of plant growth. In 2015, all minor storage terms together increased EBC by 5.0% on average, with a maximum value of 7.4% in May, while the improvement in 2016 was 6.8% on average and 8.4% in May. Ground heat flux computed with the harmonic analysis based on plate data narrowed the EBC by 3% more than the calorimetric method. In summary, a better EBC can be achieved by considering minor storage terms and applying a harmonic analysis to ground heat flux data. Regarding future research, we recommend to focus on year-round measurements of energy terms because energy stored during the growing season might be lost from the system during the rest of the year. Nonetheless, the significant contribution of minor energy terms to EBC indicates that turbulent energy fluxes are most likely overestimated when all the missing energy is assumed to be turbulent–the typical approach when fluxes are corrected by the Bowen ratio post-closure method for instance.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 264〈/p〉 〈p〉Author(s): Adrià Barbeta, J. Julio Camarero, Gabriel Sangüesa-Barreda, Lena Muffler, Josep Peñuelas〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The performance and persistence of rear-edge tree populations are relevant issues for conserving biodiversity because these stands harbor high intraspecific biodiversity and play a key role during periods of climate change. The occurrence of these populations is associated with the influence of heterogeneous topography, creating suitable refugia with regionally rare environmental conditions. Climate is changing at a global-scale, but little is known about the long-term impact on local climatic singularities and the associated taxa. We analyzed tree-ring growth chronologies of the two species (〈em〉Fagus sylvatica〈/em〉 and 〈em〉Quercus ilex〈/em〉) forming the evergreen-deciduous forest ecotone, constitutive of the rear-edge of 〈em〉F. sylvatica〈/em〉 distribution. The study area is a coastal range with frequent fog immersion, which has been hypothesized to favor the persistence of 〈em〉F. sylvatica〈/em〉 in Mediterranean peninsulas. We analyzed the long-term effect of fog on tree growth along a topographical gradient and the sensitivity of growth to rainfall and temperature. The annual number of foggy days has decreased by 62% over the last four decades, concomitant with increasing temperatures. Fog frequency was a relevant factor determining tree growth; fog during summer had positive effects on 〈em〉F. sylvatica〈/em〉 growth mainly through a temperature buffering effect. The positive effect of fog on the growth of 〈em〉Q. ilex〈/em〉, however, was likely caused by a collinearity with rainfall. 〈em〉Q. ilex〈/em〉 growth was less sensitive to climate than 〈em〉F. sylvatica〈/em〉, but growth of both species was enhanced by a positive early-summer water balance. Our results indicate that a decrease in fog frequency and an increase in temperature may generally benefit 〈em〉Q. ilex〈/em〉 in this forest ecotone. Although future changes in rainfall and temperature matter most for the fate of rear-edge tree populations, local climatic singularities such as fog should also be considered. Those can have complementary effects that can swing the balance in ecotones and rear-edge tree populations such as those studied here.〈/p〉〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0168192318303447-ga1.jpg" width="269" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 264〈/p〉 〈p〉Author(s): Nina Pirttioja, Taru Palosuo, Stefan Fronzek, Jouni Räisänen, Reimund P. Rötter, Timothy R. Carter〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉Conventional methods of modelling impacts of future climate change on crop yields often rely on a limited selection of projections for representing uncertainties in future climate. However, large ensembles of climate projections offer an opportunity to estimate yield responses probabilistically. This study demonstrates an approach to probabilistic yield estimation using impact response surfaces (IRSs). These are constructed from a set of sensitivity simulations that explore yield responses to a wide range of changes in temperature and precipitation. Options for adaptation and different levels of future atmospheric carbon dioxide concentration [CO〈sub〉2〈/sub〉] defined by representative concentration pathways (RCP4.5 and RCP8.5) were also considered. Model-based IRSs were combined with probabilistic climate projections to estimate impact likelihoods for yields of spring barley (〈em〉Hordeum vulgare〈/em〉 L.) in Finland during the 21〈sup〉st〈/sup〉 century. Probabilistic projections of climate for the same RCPs were overlaid on IRSs for corresponding [CO〈sub〉2〈/sub〉] levels throughout the century and likelihoods of yield shortfall calculated with respect to a threshold mean yield for the baseline (1981–2010).〈/p〉 〈p〉Results suggest that cultivars combining short pre- and long post-anthesis phases together with earlier sowing dates produce the highest yields and smallest likelihoods of yield shortfall under future scenarios. Higher [CO〈sub〉2〈/sub〉] levels generally compensate for yield losses due to warming under the RCPs. Yet, this does not happen fully under the more moderate warming of RCP4.5 with a weaker rise in [CO〈sub〉2〈/sub〉], where there is a chance of yield shortfall throughout the century. Under the stronger warming but more rapid [CO〈sub〉2〈/sub〉] increase of RCP8.5, the likelihood of yield shortfall drops to zero from mid-century onwards.〈/p〉 〈p〉Whilst the incremental IRS-based approach simplifies the temporal and cross-variable complexities of projected climate, it was found to offer a close approximation of evolving future likelihoods of yield impacts in comparison to a more conventional scenario-based approach. The IRS approach is scenario-neutral and existing plots can be used in combination with any new scenario that falls within the sensitivity range without the need to perform new runs with the impact model. A single crop model is used for demonstration, but an ensemble IRS approach could additionally capture impact model uncertainties.〈/p〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0168192318303241-ga1.jpg" width="355" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 265〈/p〉 〈p〉Author(s): Emma Hart, Kevin Sim, Kana Kamimura, Céline Meredieu, Dominique Guyon, Barry Gardiner〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉This paper tested the ability of machine learning techniques, namely artificial neural networks and random forests, to predict the individual trees within a forest most at risk of damage in storms. Models based on these techniques were developed individually for both a small forest area containing a set of 29 permanent sample plots that were damaged in Storm Martin in December 1999, and from a much larger set of 235 forest inventory plots damaged in Storm Klaus in January 2009. Both data sets are within the Landes de Gascogne Forest in Nouvelle-Aquitaine, France. The models were tested both against the data from which they were developed, and against the data set from the other storm. For comparison with an earlier study using the same data, logistic regression models were also developed. In addition, the ability of machine learning techniques to substitute for a mechanistic wind damage risk model by training them with previous mechanistic model predictions was tested.〈/p〉 〈p〉All models were accurate at identifying whether trees would be damaged or not damaged but the random forests models were more accurate, had higher discriminatory power, and were almost totally unaffected by the removal of any individual input variable. However, if all information relating to a stand was removed the random forests model lost accuracy and discriminatory power. The other models were similarly affected by the removal of all site information but none of the models were affected by removal of all tree information, suggesting that damage in the Landes de Gascogne Forest occurs at stand scale and is not controlled by individual tree characteristics. The models developed with the large comprehensive database were also accurate in identifying damaged trees when applied to the small forest data damaged in the earlier storm. However, none of the models developed with the smaller forest data set could successfully discriminate between damaged and undamaged trees when applied across the whole landscape. All models were very successful in replicating the predictions of the mechanistic wind risk model and using them as a substitute for the mechanistic model predictions of critical wind speed did not affect the damage model results.〈/p〉 〈p〉Overall the results suggest that random forests provide a significant advantage over other statistical modelling techniques and the random forest models were found to be more robust in their predictions if all input variables were not available. In addition, the ability to replace the mechanistic wind damage model suggests that random forests could provide a powerful tool for damage risk assessment over large regions and provide rapid assessment of the impact of different management strategies or be used in the development of optimised forest management with multiple objectives and constraints including the risk of wind damage.〈/p〉 〈/div〉

Description: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 265〈/p〉 〈p〉Author(s): Qiulin Wu, Gao Hu, Hoang Anh Tuan, Xiao Chen, Minghong Lu, Baoping Zhai, Jason W. Chapman〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Rice planthoppers (RPH) are the most serious insect pests of rice production in East Asia, frequently out-breaking in China, Korea and Japan each summer. They are unable to overwinter in temperate East Asia, and summer populations arise anew each year via northward spring migration from south-east Asia. The annual migration cycle is generally believed to be a closed loop with mass returns to south-east Asia in the autumn, but this leg of the journey and the overwintering dynamics are much less studied than the spring immigrations. Previous studies have indicated that the north-central Vietnam (NCV) region is a key location for both the spring colonisation of China and for receiving return migrants from southern China each autumn. However, NCV experiences a three-month rice-free fallow period during mid-winter, and so it cannot be the principal over-wintering region for RPH populations. In this study, the continental-scale migration patterns of RPH in East Asia were explored using data from light trap catches, field surveys and atmospheric trajectory simulations. Our results confirmed that large numbers of return migrants arrive in NCV from southern China each autumn, but that they are unable to survive there over winter. The NCV region is recolonised in the early-spring (mid-February to mid-March) of each year by migrants from winter rice-growing regions in north-east Thailand, southern Laos and south-central coastal Vietnam, which are transported on favourable high-altitude synoptic winds. The following generation initiates the colonisation of East Asia from a large source population in NCV. Our results provide a new perspective on RPH migration patterns and over-wintering dynamics in East Asia, which is governed by crop production, environmental conditions and synoptic wind patterns at a continental scale.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 265〈/p〉 〈p〉Author(s): Quanxi Shao, Michael Bange, James Mahan, Huidong Jin, Hizbullah Jamali, Bangyou Zheng, Scott C. Chapman〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Continuous measurement of canopy temperature is an important indicator of plant water status of crops and the ability to predict canopy temperature will assist in the implementation of this technology for guiding crop irrigation scheduling. By noting that canopy temperature is related to its environmental weather variables which change over time of the day and have different effect or contribution to canopy temperature, this paper presents a probabilistic model to predict canopy temperature by using weather variables which can be obtained from weather model predictions. Unlike the existing models which consider only the linear correlation, the proposed model allows the model parameters to vary according to a periodic function which is designed to capture the variation over the time of the day. The continuity of parameter changes is guaranteed by varying the model parameters periodically and smoothly. Two case studies using cotton experiments from Australia and the United States are conducted to compare the model performance with the existing published models. Using the predictions of canopy temperature an index of crop stress is also predicted in order to evaluate its influence in the irrigation scheduling. Results show that the proposed model is superior to the existing published models in its ability to predict canopy temperature into the future and has utility in assessing when crop stress will occur, to assist with irrigation scheduling. Further evaluations suggest that the air temperature is a dominate weather variable for forecasting canopy temperature but the inclusion of the other weather variables still improves the forecast.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 264〈/p〉 〈p〉Author(s): 〈/p〉

Description: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 265〈/p〉 〈p〉Author(s): Koen Hufkens, Eli K. Melaas, Michael L. Mann, Timothy Foster, Francisco Ceballos, Miguel Robles, Berber Kramer〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Smallholder farmers play a critical role in supporting food security in developing countries. Monitoring crop phenology and disturbances to crop growth is critical in strengthening farmers’ ability to manage production risks. This study assesses the feasibility of using crowdsourced near-surface remote sensing imagery to monitor winter wheat phenology and identify damage events in northwest India. In particular, we demonstrate how streams of pictures of individual smallholder fields, taken using inexpensive smartphones, can be used to quantify important phenological stages in agricultural crops, specifically the wheat heading phase and how it can be used to detect lodging events, a major cause of crop damage globally. Near-surface remote sensing offers granular visual field data, providing detailed information on the timing of key developmental phases of winter wheat and crop growth disturbances that are not registered by common satellite remote sensing vegetation indices or national crop cut surveys. This illustrates the potential of near-surface remote sensing as a scalable platform for collecting high-resolution plot-specific data that can be used in supporting crop modeling, extension and insurance schemes to increase resilience to production risk and enhance food security in smallholder agricultural systems.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 265〈/p〉 〈p〉Author(s): E. Dellwik, M.P. van der Laan, N. Angelou, J. Mann, A. Sogachev〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉This study reports simultaneous measurements of wind at single point positions up- and downstream of a tree and a numerical experiment with the aim of quantifying the interaction of a solitary tree and the wind field. Relative to the inflow velocity, the velocity deficit in the wake of the tree showed strong seasonal dependence, with wake velocities changing between 70% and 10% of the upstream value from no-leaf winter conditions to full-leaf summer conditions. Whereas for the winter tree the turbulence intensity in the wake is everywhere reduced relative to the upwind flow, for the summer tree the turbulent intensity is markedly reduced in the inner wake, but increased in the outer wake.〈/p〉 〈p〉For the numerical experiment, the combination of (i) a high-detail tree model, based on terrestrial lidar scanning, and (ii) observations of the total bending moment on the tree, taken from strain gauges mounted on the stem, provided the tree parameterization. By this approach, the drag coefficient is not calibrated to fit the observed wind speed in the wake, but the total observed bending moment. Mean wind speed observations in the wake of both the winter and summer tree were well reproduced by the model with mean absolute errors lower than or equal to 5% throughout the wake transect. Also the turbulence intensity in the wake were well reproduced for the summer tree, whereas it was overestimated for the winter tree. Effects of changing tree model and grid resolution are demonstrated and discussed. Based on the presented findings, we recommend to estimate the total bending moment (or drag force) on modelled trees to ensure transferability of results between different numerical setups.〈/p〉 〈/div〉

Description: 〈p〉Publication date: 15 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volumes 266–267〈/p〉 〈p〉Author(s): N.C. Mbangiwa, M.J. Savage, T. Mabhaudhi〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Simpler crop models simulating evaporation are needed to provide information to farmers, policy makers and decision makers on how to maximise crop yield responses to water. This is becoming important as the frequency and severity of droughts in South Africa is increasing. In this regard, prediction of yield, determination of water productivity and total evaporation (〈em〉ET〈/em〉) are increasingly becoming essential in water resource management. The overall objective of the study was to compare the FAO AquaCrop daily model output of 〈em〉ET〈/em〉 to the residual 〈em〉ET〈/em〉 for non-stressed dryland soybean in a sub-humid climate. Energy balance residual 〈em〉ET〈/em〉 estimates using an eddy covariance (EC) system and modelled 〈em〉ET〈/em〉 using AquaCrop obtained from 〈em〉Glycine max〈/em〉 (L.) Merrill grown in the midlands of KwaZulu-Natal, South Africa during the 2012/13 growing season are compared. The modelled and observed yield showed good agreement, while the residual 〈em〉ET〈/em〉 was 21.6% less than the modelled. The energy balance closure computed using the daily sums of sensible heat and latent energy fluxes against daily available energy flux for unstable atmospheric conditions was 0.77. A closure of 0.99 was achieved when the EC latent energy flux was replaced with residual latent energy flux. A good fit between the modelled and observed percentage green canopy cover was observed (slope = 0.86, intercept = 15.46%, root mean square error = 10.50% and R〈sup〉2〈/sup〉 = 0.83). Season-long daily residual 〈em〉ET〈/em〉 values were consistently low for most of the growth stages compared to the modelled, except for the maturity stage. However, the residual 〈em〉ET〈/em〉 comparisons with the AquaCrop model improved after gap-filling was applied to discarded data and for when the EC system failed.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 265〈/p〉 〈p〉Author(s): Kai Yang, Chenghai Wang〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In the soil freeze/thaw phenomenon, the soil water phase and energy budget change, which can affect the soil-vegetation-atmosphere system. Herein, the basic role of freeze–thaw–process (FTP) in soil water and heat transport and its impact on soil moisture and temperature variation were investigated using the observations and numerical experiments with and without FTP in Community Land Model version 4.5 (CLM4.5) on the Tibetan Plateau (TP). The results averaged over the whole TP revealed that no soil FTP (i.e., no water phase change occurred) resulted in lower surface soil temperature by about -1.02 ℃ in freeze-thaw (FT) period, while surface soil temperature is higher by about 0.91 ℃ and surface soil moisture is drier by about -0.02 mm〈sup〉3〈/sup〉/mm〈sup〉3〈/sup〉 in after-thaw (AT) period. Soil FTP has a water storage effect, the storage index (〈em〉SI〈/em〉) can reach 0.95 at surface layer. Without soil FTP, the surface soil water content at the AT period can be reduced by ∼10% (SI is decreased by about -0.05) as a result of enhanced evaporation; the soil moisture memory was shortened by about -20 days in March. Accordingly, surface latent heat decreased by -1.07 W/m〈sup〉2〈/sup〉, while the surface sensible heat increased by 4.72 W/m〈sup〉2〈/sup〉. The effects of FTP on soil water and heat transport at deep layer are distinguished from that at the surface layer. These imply that the biases of soil temperature and moisture simulation in models during FT period could lead to large uncertainties in estimating climate effects of TP. Under climate warming background in recent decades, with the delaying of soil freeze-beginning date and advancing of soil thaw-end date, changes of soil FTP regime would lead to loss of spring soil moisture.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 265〈/p〉 〈p〉Author(s): Vadim Mamkin, Julia Kurbatova, Vitaly Avilov, Dmitry Ivanov, Olga Kuricheva, Andrej Varlagin, Irina Yaseneva, Alexander Olchev〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Effects of clear cutting and other forest disturbances on surface radiative properties and the energy and CO〈sub〉2〈/sub〉 fluxes between land surface and the atmosphere can vary significantly depending on local climatic and moisture conditions, forest structure and species composition, soil properties and many other factors. In this study we analyzed the influence of clear-cutting on the energy, water vapor and CO〈sub〉2〈/sub〉 fluxes in the still very poorly investigated part of the boreal forest community in the European part of Russia. This issue has become particularly relevant due to intensified logging in the region during recent decades. The sensible (〈em〉H〈/em〉) and latent (〈em〉LE〈/em〉) heat, as well as CO〈sub〉2〈/sub〉 fluxes were continuously measured at recently clear-cut and undisturbed mature spruce forest sites using eddy covariance technique during the first growing season following harvest. Because of their close location they are characterized by similar meteorological conditions. The results of our field measurements showed that the clear-cut strongly influenced the energy balance and CO〈sub〉2〈/sub〉 fluxes between the land surface and atmosphere. Energy fluxes (〈em〉LE〈/em〉 and 〈em〉H〈/em〉) at the undisturbed forest site were consistently larger than at the clear-cut throughout the period of measurements. The Bowen ratio (〈em〉β=H/LE〈/em〉) varied significantly over time, though was similar at both sites. Whereas 〈em〉H〈/em〉 was almost equal to 〈em〉LE〈/em〉 at both sites in spring, the 〈em〉LE〈/em〉 significantly exceeded 〈em〉H〈/em〉 over the summer (〈em〉β〈/em〉≈0.2 - for mature spruce forest and 〈em〉β〈/em〉 = 0.4 - for clear-cut). The mean 〈em〉β〈/em〉 for the entire period was similar (〈em〉β〈/em〉≈0.5) at both sites. Analysis of CO〈sub〉2〈/sub〉 fluxes showed that the clear-cut was a consistent source of CO〈sub〉2〈/sub〉 to the atmosphere. Net ecosystem exchange (〈em〉NEE〈/em〉) at the clear-cut averaged 3.3 ± 1.3 gC∙m〈sup〉−2〈/sup〉∙d〈sup〉-1〈/sup〉 (±1 SD), while average 〈em〉NEE〈/em〉 at the undisturbed mature forest was close to zero (0.1 ± 1.9 gC∙m〈sup〉−2〈/sup〉∙d〈sup〉-1〈/sup〉). Differences in 〈em〉NEE〈/em〉 were mainly governed by differences in gross primary productivity (〈em〉GPP〈/em〉) between sites (7.0 ± 4.1 gC∙m〈sup〉−2〈/sup〉∙d〈sup〉-1〈/sup〉 and 4.1 ± 3.0 gC∙m〈sup〉−2〈/sup〉∙d〈sup〉-1〈/sup〉, for the undisturbed forest and clear-cut, respectively). Total ecosystem respiration (〈em〉TER〈/em〉) did not significantly (p 〈 0.05) differ between sites (7.1 ± 3.6 gC∙m〈sup〉−2〈/sup〉∙d〈sup〉-1〈/sup〉 at the undisturbed mature forest and 7.4 ± 3.4 gC∙m〈sup〉−2〈/sup〉∙d〈sup〉-1〈/sup〉 at clear-cut). 〈em〉TER〈/em〉 at the undisturbed forest showed higher sensitivity to changes in soil temperature, whereas 〈em〉GPP〈/em〉 at the clear-cut was characterized by higher light-use efficiency. Our measurements showed that 〈em〉TER〈/em〉 rates were relatively high in the southern taiga in comparison with other boreal sites where CO〈sub〉2〈/sub〉 fluxes were previously investigated.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volumes 266–267〈/p〉 〈p〉Author(s): Marc Peaucelle, Philippe Ciais, Fabienne Maignan, Manuel Nicolas, Sébastien Cecchini, Nicolas Viovy〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Global ecosystem models lack an explicit representation of budburst and senescence for evergreen conifers despite their primordial role in the carbon cycle. In this study we evaluated eight different budburst models, combining forcing, chilling and photoperiod, for their ability to describe spring budburst, and one model of needle senescence for temperate evergreen coniferous forests. The models’ parameters were optimized against field observations from a national forest monitoring network in France. The best fitting budburst model was determined according to a new metrics which accounts for both temporal and spatial variabilities of budburst events across sites. The best model could reproduce observed budburst dates both at the site scale (±5 days) and at regional scale (±12 days). We also showed that the budburst models parameterized at site scale lose some predictive capability when applied at coarser spatial resolution, e.g., in grid-based simulations. The selected budburst model was then coupled to a senescence function defined from needle survivorship observations in order to describe the full phenology cycle of coniferous forests. Implemented in the process-driven ecosystem model ORCHIDEE, this new conifer phenology module represented accurately the intra and inter-annual dynamics of leaf area index at both the local and regional scales when compared against MODIS remote sensing observations. A sensitivity analysis showed only a small impact of the new budburst model on the timing of the seasonal cycle of photosynthesis (GPP). Yet, due to the faster renewal of needles compared to the standard version of ORCHIDEE, we simulated an increase in the GPP by on average 15% over France, while the simulated needle turnover was doubled. Compared to 1970–2000, projections indicated an advancement of the budburst date of 10.3 ± 2.8 and 12.3 ± 4.1 days in average over the period 2060–2100 with the best forcing and chilling-forcing models respectively. Our study suggests that including an explicit simulation of needle budburst and senescence for evergreen conifers in global terrestrial ecosystem models may significantly impact future projections of carbon budgets.〈/p〉〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉 〈p〉We calibrated and implemented a new phenology module for evergreen conifers in the global model ORCHIDEE with an explicit representation of both needle budburst and senescence. The new phenology module now allows to represent the seasonality of observed leaf area for evergreen conifers at the regional scale. Sensitivity tests in ORCHIDEE show a strong impact on the simulated carbon cycle for which we highlighted a 15% increase of the growth primary productivity and a doubling of the needle turnover compared to default simulations. We argue that global ecosystem models have to simulate explicit phenological processes for evergreen species if we want to improve future projections of the carbon budget.〈/p〉 〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0168192318304015-ga1.jpg" width="475" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉 〈/div〉

Description: 〈p〉Publication date: 15 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volumes 266–267〈/p〉 〈p〉Author(s): Amanda Bunce, John C. Volin, David R. Miller, Jason Parent, Mark Rudnicki〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉Trees are the most common cause of utility damage and power outages during storms in the northeastern United States. Previous studies on tree sway and risk of wind-throw have largely been conducted in heavily managed coniferous stands, while relatively little is known for northeastern mixed temperate deciduous forests. The objective of this study was to identify factors determining tree sway frequency in northeastern forests. To this end, we monitored the fundamental vibrational frequency (FVF) of 39 trees representing nine different tree species on 3 sites in southern New England over one year, and regressed those measurements against 25 potential predictor variables.〈/p〉 〈p〉Results showed that four predictors were significant across all sites and species. The height to the base of the live crown, as well as tree slenderness, defined as diameter-at-breast height divided by tree height squared (DBH 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si4.gif" overflow="scroll"〉〈mtext〉 〈/mtext〉〈mo〉∙〈/mo〉〈/math〉 H〈sup〉−2〈/sup〉), were significant. Previous studies on coniferous trees support the significance of slenderness. The other two predictors accounted for the presence or absence of foliage and whether temperatures were above or below freezing. These findings highlight the relationship of tree shape and FVF, and indicate the relationship is similar between excurrent (e.g., coniferous) and decurrent (e.g., northeastern broadleaves) species when they are grown in closed canopy situations, regardless of species mix or location. Given this relationship, and our understanding of the relationship of FVF to wind-firmness, forest management practices designed to effect slenderness and tree shape have the potential to increase wind-firmness and reduce tree-related storm damage to utility infrastructure.〈/p〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0168192318303745-ga1.jpg" width="442" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volumes 266–267〈/p〉 〈p〉Author(s): María I. Gassmann, Natalia E. Tonti, Antonella Burek, Claudio F. Pérez〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉One of the most recommended method to estimate evapotranspiration (〈em〉ET〈/em〉) of vegetated surfaces with different soil moisture conditions is the Penman-Monteith equation (PM). Canopy and soil conditions are parameterized through the surface resistance or conductance, while the contribution of the canopy to 〈em〉ET〈/em〉 is measured by the canopy resistance. The study of natural ecosystems has gained interest because of its importance in water and carbon cycles. However, unlike monocultures, natural environments are composed of a mixture of species that make the estimation of 〈em〉ET〈/em〉 with PM troublesome. This feature makes them suitable for 〈em〉ET〈/em〉 estimation considering the contribution of both, the canopy and the soil represented by the surface resistance (〈em〉r〈sub〉s〈/sub〉〈/em〉), or the contribution of the canopy, represented by the canopy resistance (〈em〉r〈sub〉c〈/sub〉〈/em〉). This work aims to model the surface and canopy resistances using conventional meteorological, biological and pedological variables observed at a salt marsh used for livestock production in Buenos Aires province, Argentina. Twelve models (M1 to M12) based on the net solar radiation (〈em〉R〈sub〉n〈/sub〉〈/em〉), air temperature (〈em〉T〈sub〉a〈/sub〉〈/em〉), air relative humidity (〈em〉RH〈/em〉), surface wind velocity (〈em〉U〈/em〉), dew point departure (〈em〉D〈sub〉p〈/sub〉〈/em〉), aerodynamic resistance (〈em〉r〈sub〉a〈/sub〉〈/em〉), leaf area index (〈em〉LAI〈/em〉) and volumetric soil water content (〈em〉ϑ〈sub〉s〈/sub〉〈/em〉) were obtained using two different regression methodologies. Surface resistances during daytime were calculated inverting the PM equation with 〈em〉ET〈/em〉 fluxes measured with the eddy covariance method. PM-derived 〈em〉r〈/em〉〈sub〉s〈/sub〉 varied between 20 and 1000 s m〈sup〉−1〈/sup〉, with a median of 137 s m〈sup〉−1〈/sup〉. From 1620 observations, 468 were used for model calibration while 1152 for model validation. M5 and M11 with 〈em〉R〈sub〉n〈/sub〉〈/em〉, 〈em〉RH〈/em〉, 〈em〉r〈sub〉a〈/sub〉〈/em〉, 〈em〉LAI〈/em〉 predictor variables were the best models with 80.8 s m〈sup〉−1〈/sup〉 root mean square error, 0.51 determination coefficient, 0.69 and 0.65 index of agreement, respectively. The modelled resistances allowed the estimation of latent heat fluxes with a root mean quadratic error varying from 60.7 to 69.5 W m〈sup〉-2〈/sup〉. These results show the possibility to achieve 〈em〉r〈sub〉s〈/sub〉〈/em〉 from a minimum set of variables easily measured in the field which in turn, allows to estimate the 〈em〉ET〈/em〉 of salt marsh ecosystems with scarce meteorological information.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volumes 266–267〈/p〉 〈p〉Author(s): Xiaobo Gu, Huanjie Cai, Zhitao Zhang, Heng Fang, Pengpeng Chen, Peng Huang, Yupeng Li, Yuannong Li, Li Zhang, Jiaming Zhou, Yadan Du〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Ridge-furrow full film mulching (RFFM) has been widely adopted as a water-saving and yield-improving planting pattern in arid and semi-arid regions. Whether or not RFFM can replace the conventional flat planting pattern (FP) with supplemental irrigation in dryland farming has not been tested. Moreover, the effects of reducing irrigation frequency and amount on crops in dryland farms under different rainfall years (dry, normal or wet years) remain unknown. Present study selected winter rapeseed (〈em〉Brassica napus〈/em〉 L.) as a test crop for a three-year field experiment to investigate the irrigation water-saving potential of RFFM. Six treatments: 1) FP without irrigation (FP0); 2) FP with 30-mm irrigation at the overwintering stage (FP1); 3) FP with 30- and 60-mm irrigation at the overwintering and stem-elongation stages, respectively (FP2); 4) FP with 30-, 60- and 60-mm irrigation at the overwintering, stem-elongation and flowering stages, respectively (FP3); 5) RFFM without irrigation (RFFM0); and 6) RFFM with 45-mm irrigation at the flowering stage (RFFM1) were conducted to explore their effects on root and shoot biomass, nutrient uptake, yield, oil production, evapotranspiration (ET) and water use efficiency (WUE). The results indicated that RFFM0 significantly promoted root and shoot biomass accumulation and nutrient uptake. Thus it significantly improved yield by 23.7–39.0%, oil production by 26.8–43.3% and WUE by 71.3–86.5%, and simultaneously decreased ET by 21.2–29.7% in comparison to FP0 and FP1 in dry, normal and wet years. Furthermore, the yield-increasing effect in RFFM0 was nearly equal to FP3 in the normal rainfall and wet years, and was equivalent to FP2 in the dry year. Yield and oil production in RFFM1 were significantly higher than in RFFM0, and were commensurate with those in FP3 in the dry year. Therefore, RFFM reduced a two-time application with total 90 mm irrigation water in a dry year, as well as a three-time application with total 150 mm irrigation water in normal rainfall and wet years for dryland winter rapeseed. Overall, RFFM is a promising adaptive agronomic strategy to apply in dryland regions to sustain food security, and cope with water scarcity, a potential threat to dryland farming due to climate change.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volumes 266–267〈/p〉 〈p〉Author(s): Maria Quade, Anne Klosterhalfen, Alexander Graf, Nicolas Brüggemann, Normen Hermes, Harry Vereecken, Youri Rothfuss〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉Field-based quantitative observations of hydrological feedbacks of terrestrial vegetation to the atmosphere are crucial for improving land-surface model parametrizations. This is especially true in the specific context of partitioning of evapotranspiration (〈em〉ET〈/em〉) into soil evaporation (〈em〉E〈/em〉) and plant transpiration (〈em〉T〈/em〉): land surface models are able to compute 〈em〉E〈/em〉 and 〈em〉T〈/em〉 separately while observed transpiration fractions (〈em〉T〈/em〉/〈em〉ET〈/em〉) are still sparse.〈/p〉 〈p〉In this study, we present the application of an on-line non-destructive method based on gas-permeable tubing for the in-situ collection of soil water vapor. This allowed for monitoring of the hydrogen and oxygen isotopic compositions (〈em〉δ〈/em〉〈sup〉2〈/sup〉H and 〈em〉δ〈/em〉〈sup〉18〈/sup〉O) of soil water during a field campaign where 〈em〉ET〈/em〉 of sugar beet (〈em〉Beta vulgaris〈/em〉) was partitioned. 〈em〉T〈/em〉/〈em〉ET〈/em〉 estimates obtained with the non-destructive method were compared with the commonly used destructive sampling of soil and subsequent cryogenic extraction of soil water under vacuum. Finally, isotope-based 〈em〉T〈/em〉/〈em〉ET〈/em〉 estimates were compared to those obtained from a combination of micro-lysimeter and eddy covariance (EC) measurements. Significant discrepancies between the values of isotopic composition of evaporation derived destructively and non-destructively from those of soil water using a well-known transfer resistance model led in turn to significant differences in 〈em〉T〈/em〉/〈em〉ET〈/em〉. This is in line with recent findings on the systematic offsets of soil water isotopic composition values in relation to the water sampling and extraction measurement techniques and calls for further investigation of these isotopic offsets for accurate separation of 〈em〉E〈/em〉 from 〈em〉T〈/em〉 in the field. These discrepancies were, however, smaller than those observed between 〈em〉δ〈/em〉〈sup〉2〈/sup〉H- or 〈em〉δ〈/em〉〈sup〉18〈/sup〉O-based 〈em〉T/ET〈/em〉 estimates, and more than three times smaller than those between isotope-based and lysimeter-based estimates.〈/p〉 〈/div〉

Description: 〈p〉Publication date: 15 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volumes 266–267〈/p〉 〈p〉Author(s): Jia Sun, Shuo Shi, Jian Yang, Wei Gong, Feng Qiu, Lunche Wang, Lin Du, Biwu Chen〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The estimation of leaf biochemical constituents is of high interest for the physiological and ecological applications of remote sensing. The multispectral lidar (MSL) system emerges as a promising active remote sensing technology with the ability to acquire both three-dimensional and spectral characteristics of targets. The detection wavelengths of the MSL system can be geared toward the specific application purposes. Therefore, it’s important to conduct the wavelength selection work to maximize the potential of the MSL system in vegetation monitoring. Traditional strategies of wavelength selection attempt to establish an empirical relationship between large quantities of observed reflectance and foliar biochemical constituents. By contrast, this study proposed to select wavelengths through the radiative transfer model PROSPECT. A five-wavelength combination was established to estimate leaf chlorophyll and water contents: 680, 716, 1104, 1882 and 1920 nm. The consistency of the wavelengths selected were tested by running different versions of PROSPECT model. Model inversion using simulated and experimental datasets showed that the selected wavelengths have the ability to retrieve leaf chlorophyll and water contents accurately. Overall, this study demonstrated the potential of the MSL system in vegetation monitoring and can serve as a guide in the design of new MSL systems for the application community.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volumes 266–267〈/p〉 〈p〉Author(s): Hong Cheng, Weiwei He, Chenchen Liu, Xueyong Zou, Liqiang Kang, Tianle Chen, Kaidi Zhang〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The biocontrol measurement is the most effective method for land desertification control in arid and semi-arid areas where is limited by water and poor soil, and thus. Optimizations are needed for the existing biocontrol methods for anti-desertification and soil-erosion control so that the scope and scale of the biocontrol can be reduced. The premise for the optimization work is to reveal the distribution law of airflow fields around vegetation. Current studies are lack of the spatial express of airflow speed on a 2-D surface and there is no report on the transition of airflow fields from single plant to multiple plants. Based on detail experiments in a wind tunnel for the airflow fields around a single plant, a single-row forest belt with different plant spacing, a multi-row forest belt with different numbers of rows but the same plant spacing, and a double-row forest belt with various arrangements, this paper developed the horizontal model (Eq. (9)) for the airflow fields around single plant comprehensively analyzing the effect of plants characteristic parameters (such as crown width (W), height (H), porosity (β) etc.) on the horizontal and vertical air flow field partition around single plants and proposed a transition model (Eqs. (13) or 14) for airflow fields from single plant to multiple plants. These researches lay the theoretical foundations for optimum biocontrol plant configurations to address anti-desertification and soil erosion control.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volumes 266–267〈/p〉 〈p〉Author(s): Liang Liang〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The geographic applicability of most phenological models is limited because of a lack in accounting for plant genotypic variation over space. This limitation may be partly addressed by quantifying plant adaptation patterns as revealed by common garden/provenance trial research. This study delineated adaptive patterns of a widely distributed tree species in North America—white ash (〈em〉Fraxinus americana〈/em〉) using multi-year common garden observations of leaf out and leaf senescence phenology. Geographically varied phenology-climate (i.e., phenoclimatic) relationships of tree provenances were investigated both with the aid of interannual temperature variations and using process-based models. Interannual weather fluctuations likely led to varied gradients of spring phenological timing by tree origin latitude as influenced by interactions of chilling and forcing, while the latitudinal gradient of autumn phenology consistently followed a photoperiod-driven pattern. Fitted models revealed latitudinal gradients of chilling requirement (for dormancy release), forcing requirement (for bud break), and critical day length requirement (for leaf senescence) for the tree provenances. When these genotype-specific phenoclimatic relationships were accounted for in spring models, predictions closely matched the latitudinal gradient of USA-National Phenology Network (NPN) observations. On the other hand, average (non-spatial) model predictions of bud break tended to be biased in the species’ northern and southern ranges. This finding shows that introducing genotypic differences to phenological models is necessary for accurate prediction of temperate tree phenology over broad geographic regions.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volumes 266–267〈/p〉 〈p〉Author(s): Yi Li, Ning Yao, Dexiu Tang, Henry Wai Chau, Hao Feng〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉A two-year summer maize irrigation experiment was conducted in soil lysimeters under a rain-shelter to analyze the effects of water repellency on soil moisture, evapotranspiration, crop growth, and yields. Soil water droplet penetration time (WDPT) was initially 1, 7, 9, 12 and 16 s, showing wettable or slight water repellency, denoted as the treatments CK, WR1, WR2, WR3, and WR4, respectively. Soil water storage dynamics were observed using the lysimeters. The WDPT and volumetric soil water content (〈em〉θ〈/em〉〈sub〉v〈/sub〉) on surface soil was measured daily. The results revealed that WDPT values of all the five treatments increased significantly as the sowing days increased and reached peaks before the subsequent irrigation. However, the peak decreased as irrigation events increased. The maximum WDPT values of CK, WR1, WR2, WR3, and WR4 were 31, 2000, 2200, 2300 and 2355s during the entire crop growth period, and indicated more persistent water repellency than the initial conditions. During the two irrigations, 〈em〉θ〈/em〉〈sub〉v〈/sub〉 decreased with the increase of WDPT. The daily and cumulative evapotranspiration at the early growth stage differed slightly but decreased from CK to WR4 at the later crop growth stages. Likewise, soil water storage increased. The higher water consumption of summer maize in CK resulted in lower soil water storage and good plant growth, thus in soils with higher WDPTs, the lower values of LAI, the mass of roots and leaves, and root lengths were noted. The crop growth decreased regularly with the increase in initial WDPT. The main reason was due to a decrease in soil water availability for the crop and impeded root water uptake as the initial WDPT increased. The variation in initial WDPTs had a significant impact on WUE. In conclusion, more persistent water repellent soils result in a decrease in summer maize growth.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 263〈/p〉 〈p〉Author(s): Seiji Shimoda, Hiromitsu Kanno, Tomoyoshi Hirota〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Potato (〈em〉Solanum tuberosum〈/em〉 L) yield per unit area in Hokkaido, Japan used to be the highest in the world; however, it has levelled off recently. The objectives of this study were to determine how recent climate variations drive potato yields and to understand the causes for this tendency of yield to level off. We used the 1-km mesh resolution for meteorological data; aggregation was performed for each municipality based on annual potato cultivation area; yield data were obtained from crop statics of Tokachi and Okhotsk regions in Hokkaido for the years 1986–2014. Potato yield was not only determined by temperatures during plant growth, as expected, but also by temperatures before planting. Probable yield inflexion point corresponded with increase in late summer temperature from the year 2000 onward. The negative correlation between spring and summer temperatures during the years 2000–2014 resulted from patterns of warm spring/cool summer or cool spring/hot summer, linked to the Inter-decadal Pacific Oscillation. A cool spring delayed planting and germination, whereas a hot summer shortened the growth period, causing the lowest yield in the year 2010. High temperatures in summer have encouraged farmers in Japan to implement adaptation strategies, such as earlier planting. As early plantation does not necessarily reduce time to sprout nor does it promote a longer growth period, the recent climate trend exacerbated potato yield responsiveness to summer temperature. As a result, increasing temperatures in summers from the late 2000s and unaltered spring temperatures as well as a shift in cultivars have caused potato yields in eastern Hokkaido to drop below those of other countries where potato yields are high. Detection of decadal climate shift as a planned-scale strategy and enhancement of drainage as a farm-scale strategy could effectively improve regional potato yield despite climate change.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 263〈/p〉 〈p〉Author(s): Javier G.P. Gamarra, Terry V. Callaghan, Helena Bylund, Dylan Gwynn-Jones〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉With warming climate many species are predicted to shift their distributions toward the poles. However, climate change models developed to predict species distributions do not always incorporate interactions between them. The northerly shift of the boreal forest and associated dwarf shrub communities will be directly affected by warming. But warming will also indirectly affect plant communities via impacts on the intensity and frequency of associated insect outbreaks. We present a general model exploring plant host herbivory in response to the balance between insect crowding, host consumption and climate. We examined how these factors dictate the feeding preference of 〈em〉Epirrita autumnata〈/em〉 larvae during an outbreak on dwarf shrub vegetation in Sub-arctic Fennoscandia. Data were collected from an outdoor experiment investigating future climate change scenarios (elevated CO〈sub〉2〈/sub〉 and temperature) on the dwarf shrub community that included deciduous (〈em〉Vaccinium myrtillus〈/em〉) and evergreen species (〈em〉V. vitis-idaea〈/em〉 and 〈em〉Empetrum nigrum〈/em〉). We observed that larval crowding was independent of treatment under outbreak conditions. We also tested and confirmed model predictions that larvae would prefer monospecific stands of either deciduous shrubs or its evergreen competitors. For current climate conditions, larvae had a preference to consume more deciduous shrubs in mixed stands. However, at elevated temperature bilberry consumption and herbivore pressure was lower, particularly in mixed stands. Our results show that during future warming, 〈em〉E. autumnata〈/em〉 herbivory could promote the success of thermophile deciduous species and possible northward migration. Insect behaviour and preferences should therefore be considered when predicting future vegetation movements responding to warming.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 263〈/p〉 〈p〉Author(s): Tsechoe Dorji, Kelly A. Hopping, Shiping Wang, Shilong Piao, Tenzin Tarchen, Julia A. Klein〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Although studies have investigated the independent effects of warming, snow, and grazing on alpine plant community properties – including plant species richness, evenness, and diversity - the interactive effects of these climate and grazing factors have not been addressed experimentally in cold systems. We investigate the effects of these climate change and grazing factors using 5 years of data collected from a relatively long-term (2009–2015), fully-factorial field experiment in an alpine meadow ecosystem on the central Tibetan Plateau. Specifically, we investigate: 1) how experimental warming, spring snow addition, and yak grazing independently and interactively affect plant community properties, including diversity metrics and relative contributions of different plant life forms to the total plant cover, and 2) how the changes in plant community properties are associated with the proportional cover of the dominant plant species, 〈em〉Kobresia pygmaea〈/em〉 within the total vegetation cover. We found that warming reduced species richness and increased species evenness and the proportional cover of shrubs within the total vegetation cover. Snow addition also increased species evenness. Grazing increased the proportional cover of 〈em〉K. pygmaea〈/em〉 within the total vegetation cover, while decreasing that of grasses. Grazing also counteracted warming-induced increases in shrubs. Treatment-induced changes in 〈em〉K. pygmaea〈/em〉 cover were strongly correlated with the indices of plant community properties and were generally in the opposite direction of changes in species evenness and diversity. We conclude that the projected increases in spring snowstorms and maintaining moderate levels of grazing can counteract some warming effects on the plant community. Moreover, the performance of the dominant species can regulate plant community responses to climate change and livestock grazing on the central Tibetan Plateau.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 263〈/p〉 〈p〉Author(s): Junliang Fan, Wenjun Yue, Lifeng Wu, Fucang Zhang, Huanjie Cai, Xiukang Wang, Xianghui Lu, Youzhen Xiang〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Accurate estimation of reference evapotranspiration (ET〈sub〉0〈/sub〉) is of great importance for the regional water resources planning and irrigation scheduling design. The FAO-56 Penman-Monteith model is recommended as the reference model to predict ET〈sub〉0〈/sub〉, but its application is commonly restricted by lack of complete meteorological data at many worldwide locations. This study evaluated the potential of machine learning models, particularly four relatively simple tree-based assemble algorithms (i.e. random forest (RF), M5 model tree (M5Tree), gradient boosting decision tree (GBDT) and extreme gradient boosting (XGBoost)), for estimating daily ET〈sub〉0〈/sub〉 with limited meteorological data using a K-fold cross-validation method. For assessment of the tree-based models in terms of prediction accuracy, stability and computational costs, these models were further compared with their corresponding support vector machine (SVM) and extreme learning machine (ELM) models. Four input combinations of daily maximum and maximum temperature (T〈sub〉max〈/sub〉 and T〈sub〉min〈/sub〉), relative humidity (H〈sub〉r〈/sub〉), wind speed (U〈sub〉2〈/sub〉), global and extra-terrestrial solar radiation (R〈sub〉s〈/sub〉 and R〈sub〉a〈/sub〉) with T〈sub〉max〈/sub〉, T〈sub〉min〈/sub〉 and R〈sub〉a〈/sub〉 as the base dataset were considered using meteorological data during 1961–2010 from eight representative weather stations in different climates of China. The results showed that, when lack of complete meteorological data, the machine learning models using T〈sub〉max〈/sub〉, T〈sub〉min〈/sub〉, H〈sub〉r〈/sub〉, U〈sub〉2〈/sub〉 and R〈sub〉a〈/sub〉 obtained satisfactory ET〈sub〉0〈/sub〉 estimates in the temperate continental, mountain plateau and temperate monsoon zones of China (RMSE 〈 0.5 mm d〈sup〉−1〈/sup〉). However, models with three input parameters of T〈sub〉max〈/sub〉, T〈sub〉min〈/sub〉 and R〈sub〉s〈/sub〉 were superior for daily ET〈sub〉0〈/sub〉 prediction in the tropical and subtropical zones. The ELM and SVM models offered the best combination of prediction accuracy and stability. The simple tree-based XGBoost and GBDT models showed comparable accuracy and stability to the SVM and ELM models, but exhibited much less computational costs. Considering the complexity level, prediction accuracy, stability and computational costs of the studied models, the XGBoost and GBDT models have been recommended for daily ET〈sub〉0〈/sub〉 estimation in different climatic zones of China and maybe elsewhere with similar climates around the world.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 263〈/p〉 〈p〉Author(s): Patrick Vallet, Thomas Perot〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉Climate change has swept away the former general principles of long-term stability in forest productivity. New types of models are needed to predict growth and to plan forest management under future climate conditions. These models must remain robust for silvicultural practices and variations in climate. In this study, we present a new type of model development to achieve these goals.〈/p〉 〈p〉Our study focused on pure and mixed stands of 〈em〉Quercus petraea〈/em〉 and 〈em〉Pinus sylvestris〈/em〉 in central France. We used National Forest Inventory (NFI) data: respectively, 525 and 548 pure plots of 〈em〉Quercus petraea〈/em〉 and 〈em〉Pinus sylvestris〈/em〉, and 68 plots of mixed species. We also used 108 tree cores from an experimental site of the same species. The cores cover the period from 1971 to 2013, making a total of 4572 individual annual increments.〈/p〉 〈p〉We coupled two types of models. One was developed with NFI data (transversal data). This model takes into account mean diameter and stand density effects on stand growth. It includes a set of biophysical factors accounting for stand fertility. The other one was developed with the data from tree cores (longitudinal data), and provides a climate modulation thanks to the correlation between ring width and yearly climate. The model with tree core data reveals the influence of December to July rainfalls on yearly variability in stand growth for 〈em〉Quercus petraea〈/em〉 and of May to August rainfalls for 〈em〉Pinus sylvestris〈/em〉.〈/p〉 〈p〉We obtained a coupled model that allowed us to project growth up to 2100 for all the different IPCC scenarios but one; the model was outside its area of validity beyond 2060 for the RCP 8.5 scenario.〈/p〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉 〈p〉Modulation in basal area growth with climate for Quercus petraea according to three IPCC scenarios for the Orleans Forest area. Black dots correspond to IPCC historical climate values, colored dots correspond to modulation in basal area growth for three IPCC climate projections. The dashed line corresponds to smoothed model extrapolations for scenario RCP 8.5.〈/p〉 〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0168192318302879-ga1.jpg" width="277" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉 〈/div〉

Description: 〈p〉Publication date: 15 December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 263〈/p〉 〈p〉Author(s): Hong Cheng, Kaidi Zhang, Chenchen Liu, Xueyong Zou, Liqiang Kang, Tianle Chen, Weiwei He, Yi Fang〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉Plants play an important role on reducing the soil erosion rate and preventing blown sand motion. The primary cause is the airflow change around the plant, especially for the lee side of plants. Although scientist have researched this topic, significant problems remain concerning airflow around plants. Therefore, we conducted a series of wind tunnel experiments to simulate average airflow speed and turbulence intensities on the lee side of eight single plants with varying characteristics under different shear velocities by utilizing a hot film anemometer. We come to the following conclusions:〈/p〉 〈p〉(1) Variation in the airflow speed along the plant downwind direction is related to the porosity and the height-to-width ratio (H/W). The weakened degree of wind speed decreases with plant porosity, and the minimum wind speeds (〈em〉u〈/em〉〈sub〉min〈/sub〉) at different heights are different for different H/W. For large H/W (H/W ≥ 2), the values of 〈em〉u〈/em〉〈sub〉min〈/sub〉 appear at the location of 1 H in the lee side of the plant, while the location where 〈em〉u〈/em〉〈sub〉min〈/sub〉 occurs for small H/W (H/W ≤ 0.5) is related to the height. The location most frequently occurs between 3 h and 5 h.〈/p〉 〈p〉(2) This paper presented a modification for relaxation equation to express airflow recovery on the lee side of plant and developed the relationships of the minimal wind speed (〈em〉u〈/em〉〈sub〉min〈/sub〉), occurring lee-side location (〈em〉x〈/em〉〈sub〉0〈/sub〉), and the characteristic length (〈em〉l〈/em〉) in this modified relation equation, with different plant characteristic. The value of 〈em〉u〈/em〉〈sub〉min〈/sub〉 increases with the plant porosity (β) in a linear function of 〈em〉u〈/em〉〈sub〉min〈/sub〉 = 0.0183〈em〉β〈/em〉-0.65 and the location (〈em〉x〈/em〉〈sub〉0〈/sub〉) where 〈em〉u〈/em〉〈sub〉min〈/sub〉 occurs and the characteristic length for wind speed recovery are proportional to the reciprocal of the ratio of plant height-to-width. Their relationships can be expressed as 〈em〉x〈/em〉〈sub〉0〈/sub〉 = 1.68(H/W)〈sup〉−1〈/sup〉 and 〈em〉l〈/em〉 = 5.30(H/W)〈sup〉−1〈/sup〉, respectively.〈/p〉 〈p〉(3) The turbulence intensity downwind direction of the plant is several times the intensity of the incoming flow, and the peak turbulence intensity can reach up to 50%. The more significantly the wind speed weakens, the more significant the increase in the turbulence intensity. The standard deviation of the wind speed varies slightly.〈/p〉 〈/div〉

Description: 〈p〉Publication date: 15 December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 263〈/p〉 〈p〉Author(s): Fei Deng, Li Wang, Shi-Lin Pu, Xiu-Feng Mei, Shu-Xian Li, Qiu-Ping Li, Wan-Jun Ren〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Chalkiness, one of the key factors in determining the market price and quality of rice grains, is markedly influenced by the environment. This study aimed to investigate the effectiveness of shading on rice chalkiness by conducting a field experiment in Wenjiang, Sichuan, China, in 2013 and 2015. Rice cultivars IIyou 498 and Yixiangyou 2115 were selected and shaded during the grain filling period; this resulted in a 53% shading environment. The results showed that chalkiness, caryopsis and amyloplast development, amylose content, and amylopectin chain-length distribution of rice grains, were markedly affected by shading. Shading significantly increased chalky rice rate and chalkiness degree of rice grains at the bottom of the panicle, which contributed to the increase in chalkiness of the entire panicle. Shading had a greater influence on grains at the bottom spikelet positions than on those at the top and middle positions. More loosely packed amyloplasts with greater airspace and reduction in amylose content of grains at the bottom spikelet positions were possibly due to the significant delay in the development of caryopsis. Furthermore, except for the bottom spikelet positions of Yixiangyou 2115, a reduction in short-length chains coupled to an increase in long-length chains of amylopectin was noted under shading. Shading increased rice chalkiness primarily by postponing caryopsis development at the bottom spikelet positions and disturbing the starch characteristics of rice grains. Therefore, more attention needs to be focused on the grains positioned at the bottom of panicle.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 263〈/p〉 〈p〉Author(s): Pan Li, Li Zhang, Guirui Yu, Congqiang Liu, Xiaoli Ren, Honglin He, Min Liu, Huimin Wang, Jianxing Zhu, Rong Ge, Na Zeng〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Subtropical forests in the East Asian monsoon region function as considerable carbon sinks in the Northern Hemisphere. Forest ecosystems in this region have experienced intensified seasonal drought that has limited their carbon sequestration capacity, but increasing atmospheric nitrogen deposition has contrarily enhanced their capacity to act as carbon sinks. Understanding and quantifying the interactive effects of seasonal drought and nitrogen deposition on the carbon sequestration of subtropical forests is of great significance for accurately predicting future changes to the terrestrial carbon cycle. In this study, we used the Community Land Model Version 4.5 (CLM4.5) to investigate how carbon fluxes, i.e. gross primary productivity (GPP), ecosystem respiration (Re), and net ecosystem productivity (NEP), respond to seasonal drought and nitrogen deposition in an evergreen coniferous forest in southern China. Our results showed that reduced GPP during the drought in the summers of 2003 and 2007 weakened the forest’s carbon sequestration capacity. The reduction in GPP mainly occurred at the sunlit canopy due to its higher sensitivity to soil water stress, and non-stomatal limitations played an important role in limiting leaf photosynthesis. The enhanced NEP by nitrogen deposition was attributed to increased plant growth, which could, in turn, be attributed to increases in leaf area. Interactions of seasonal drought and nitrogen deposition varied with drought severity. Interactive effects of the two drivers on GPP, Re, and NEP were additive under mild and moderate drought conditions but non-additive under severe drought. Their net effects on NEP shifted from +29% under mild and moderate drought conditions to -56% under severe drought. Our study highlights the importance of accounting for the interactive effects of seasonal drought and nitrogen deposition in assessing the carbon sequestration of subtropical forest ecosystems in the East Asian monsoon region.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 263〈/p〉 〈p〉Author(s): Ozgur Kisi, Meysam Alizamir〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Evapotranspiration is an important parameter in linking ecosystem functioning, climate and carbon feedbacks, agricultural management, and water resources. This study investigates the applicability of wavelet extreme learning machine (WELM) model which uses discrete wavelet transform and ELM methods in estimating daily reference evapotranspiration (ET〈sub〉0〈/sub〉). Various combination of climatic data of temperature, solar radiation, relative humidity and wind speed from two stations, Ankara and Kirikkale, located in central Anatolia region of Turkey were used as inputs to the WELM models. The WELM estimates were compared with wavelet artificial neural networks (WANN) and single artificial neural network (ANN), ELM and online sequential ELM (OS-ELM) models. The results indicate that the models comprising four input variables as inputs provide better accuracy than the models with less inputs. Solar radiation was found to be the most effective variable on ET〈sub〉0〈/sub〉. Wavelet conjunction models (e.g. WELM and WANN) generally show better accuracy compared to the single models and WELM model is found to be the best model in estimating ET〈sub〉0〈/sub〉. The root mean square error and mean relative error accuracies of the ELM, ANN and WANN models were improved by 28–25%, 32–32% and 27–26% for the Ankara Station and by 14–14%, 58–58% and 32–36% for the Kirikkale Station.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 263〈/p〉 〈p〉Author(s): Rijan Tamrakar, Mark B. Rayment, Fernando Moyano, Martina Mund, Alexander Knohl〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The effects of structural diversity on the carbon dioxide exchange (CO〈sub〉2〈/sub〉) of forests has become an important area of research for improving the predictability of future CO〈sub〉2〈/sub〉 budgets. We report the results of a paired eddy covariance tower study with 11 years of data on two forest sites of similar mean stand age, near-identical site conditions, and dominated by beech trees (〈em〉Fagus sylvatica〈/em〉), but with a very different stand structure (incl. age, diameter distribution, stocks of dead wood and species composition) because of different management regimes. Here we address the question of how management and related structural diversity may affect CO〈sub〉2〈/sub〉 fluxes, and tested the hypothesis that more structurally diverse stands are less sensitive to variations in abiotic and biotic drivers. Higher annual net ecosystem productivity (NEP) was observed in the managed, even-aged, and homogenous forest (585 ± 57.8 g C m〈sup〉−2〈/sup〉 yr〈sup〉−1〈/sup〉), than in the unmanaged, uneven-aged, and structurally diverse forest (487 ± 144 g C m〈sup〉−2〈/sup〉 yr〈sup〉−1〈/sup〉). About two-third of the difference in NEP between the sites was contributed by a higher annual gross primary productivity (GPP, 1627 ± 164 vs 1558 ± 118 g C m〈sup〉−2〈/sup〉 yr〈sup〉−1〈/sup〉) and one-third by a lower annual ecosystem respiration (Reco, 1042 ± 60 vs 1071 ± 96 g C m〈sup〉−2〈/sup〉 yr〈sup〉−1〈/sup〉) in the homogenous forest. Spring (April – May) and summer (June – July) were the two main seasons contributing to the overall annual differences between the sites, also, the sensitivities of seasonal NEP and GPP to environmental variables were stronger in the homogenous forest during those periods. Inter-annual variation of NEP was higher in the homogenous forest (coefficient of variation (CV) = 25%) compared to the heterogeneous forest (CV = 12%). At annual time scale, the higher variability of NEP in the homogenous forest is attributed to biotic factors such as fruit production and a time-dependent growth trend, outweighing differences in environmental sensitivities.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 263〈/p〉 〈p〉Author(s): Bin Yang, Yuri Knyazikhin, Haimeng Zhao, Yuzhong Ma〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Numerous canopy radiative transfer models have been proposed based on the assumption of “ideal bi-Lambertian leaves” with the aim of simplifying the interactions between photons and vegetation canopies. This assumption may cause discrepancy between the simulated and measured canopy bidirectional reflectance factor (BRF). Few studies have been devoted to evaluate the impacts of such assumption on simulation of canopy BRF at a high-to-medium spatial resolution (∼30 m). This paper focuses on quantifying the contribution of leaf specular reflection on the estimation of canopy BRF under a black soil case using one of the most efficient radiative transfer models, the stochastic radiative transfer model. Analyses of field and satellite data collected over the boreal Hyytiälä forest in Finland show that leaf specular reflection may lead to errors of up to 33.1% at 550 nm and 32.8% at 650 nm in terms of relative root mean square error. The results suggest that, in order to minimize these errors, leaf specular reflection should be accounted for in modeling BRF.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 263〈/p〉 〈p〉Author(s): Weisheng Lin, Yiqing Li, Zhijie Yang, Christian P. Giardina, Jinsheng Xie, Shidong Chen, Chengfang Lin, Yakov Kuzyakov, Yusheng Yang〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉How warming affects the magnitude of CO〈sub〉2〈/sub〉 fluxes within the soil profile remains an important question, with implications for modeling the response of ecosystem carbon balance to changing climate. Information on belowground responses to warming is especially limited for the tropics and subtropics because the majority of manipulative studies have been conducted in temperate and boreal regions. We examined how artificial warming affected CO〈sub〉2〈/sub〉 gas production and exchange across soil profiles in a replicated mesocosms experiment relying on heavily weathered subtropical soils and planted with Chinese fir (〈em〉Cunninghamia lanceolata〈/em〉). Half of 2 × 2 m mesocosms (5 replications) was heated with cables buried at a 10 cm depth, which increased temperature in the whole soil profile by 4.5, 3.6 and 2.5 °C at 15, 30 and 60 cm soil depths, respectively. Using a combination of chamber-based and concentration gradient method (CGM) approaches, we found that warming increased soil CO〈sub〉2〈/sub〉 efflux across the whole profile by 40%. Changes were unevenly distributed across soil depth: mean CO〈sub〉2〈/sub〉 production rate decreased from 0.74 to 0.67 μmol CO〈sub〉2〈/sub〉 m〈sup〉−2〈/sup〉 s〈sup〉−1〈/sup〉 in topsoils (0–15 cm depth) whereas it increased from 0.26 to 0.73 μmol CO〈sub〉2〈/sub〉 m〈sup〉−2〈/sup〉 s〈sup〉−1〈/sup〉 in subsoils (15–60 cm depth). Warming reduced moisture more strongly in subsurface than surface soils and increased subsoil soluble N concentrations as well as fine root turnover, in line with previous temperate and boreal warming studies. This consistency indicates that overall responses of subtropical forests to warming may be similar to forests in higher latitudes.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 263〈/p〉 〈p〉Author(s): Jingyong Ma, Tianshan Zha, Xin Jia, Yun Tian, Charles P.-A. Bourque, Peng Liu, Yujie Bai, Yajuan Wu, Cai Ren, Haiqun Yu, Feng Zhang, Caixian Zhou, Wenjing Chen〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Northern China’s plantations have long played a role in providing ecological services to the people of China. Reliable detection and attribution of ecosystem water and energy exchange is a precondition to the development of strategies for the sustainable management of these plantations. Here, the seasonal and interannual variability in surface energy exchange and evapotranspiration (〈em〉ET〈/em〉) over a young pine plantation was investigated using eddy-covariance measurements collected over a four-year period (2012–2015). Seasonal patterns in net radiation (〈em〉R〈/em〉〈sub〉n〈/sub〉), latent (〈em〉LE〈/em〉) and sensible heat fluxes (〈em〉H〈/em〉) were largely similar over the four years. 〈em〉H〈/em〉 was the dominant energy component, with 〈em〉LE〈/em〉 exceeding 〈em〉H〈/em〉 only during the mid-growing season. A significant share of 〈em〉R〈/em〉〈sub〉n〈/sub〉 was allocated to 〈em〉H〈/em〉 during the 2014 summer drought. Energy exchange for the young pine plantation was characterized by high Bowen ratios (〈em〉β〈/em〉 = 〈em〉H/LE〈/em〉; 6.28, 6.42, 5.65, and 5.34 for the four years), high 〈em〉H/R〈/em〉〈sub〉n〈/sub〉 (0.37, 0.36, 0.36, and 0.30), and low 〈em〉LE/R〈/em〉〈sub〉n〈/sub〉 (0.15, 0.17, 0.17, and 0.16), with mean annual values of 5.92, 0.35, and 0.16 for 〈em〉β〈/em〉, 〈em〉H/R〈/em〉〈sub〉n〈/sub〉, and 〈em〉LE/R〈/em〉〈sub〉n〈/sub〉, respectively. Daily maximum and annual 〈em〉ET〈/em〉 were 4.8, 4.5, 4.1, and 3.3 mm day〈sup〉−1〈/sup〉 and 328, 371, 290, and 326 mm for the four years, with a mean annual value of 329 mm. Seasonal variation in 〈em〉ET〈/em〉 was strongly controlled by biological factors (i.e., bulk surface conductance and vegetation greenness and density, as characterized by the normalized difference vegetation index) regulated by soil water availability and water vapor pressure deficit (VPD). Evapotranspiration varied interannually and the evapotranspiration-to-precipitation ratio (〈em〉ET/P〈/em〉) ranged from 0.79 to 1.62. Soil water replenishment through precipitation during the non-growing period of the previous year and mid-growing season of the current year was responsible for the interannual variation observed in 〈em〉ET〈/em〉. These results clearly indicate the importance of precipitation timing and soil moisture carry-over from previous years in controlling ecosystem energy and water vapor exchange. Irrigation during the spring and dry periods of the year is highly favorable for growth of plantation trees in northern China.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 263〈/p〉 〈p〉Author(s): Mohamed Jabloun, Xiaoxin Li, Xiying Zhang, Fulu Tao, Chunsheng Hu, Jørgen E. Olesen〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Process-based crop simulation models are often over-parameterised and are therefore difficult to calibrate properly. Following this rationale, the Morris screening sensitivity method was carried out on the DAISY model to identify the most influential input parameters operating on selected model outputs, i.e. crop yield, grain nitrogen (N), evapotranspiration and N leaching. The results obtained refer to the winter wheat-summer maize cropping system in the North China Plain. In this study, four different N fertiliser treatments over six years were considered based on a randomised field experiment at Luancheng Experimental Station to elucidate the impact of weather and nitrogen inputs on model sensitivity. A total of 128 parameters were considered for the sensitivity analysis. The ratios [output changes/parameter increments] demonstrated high standard deviations for the most relevant parameters, indicating high parameter non-linearity/interactions. In general, about 34 parameters influenced the outputs of the DAISY model for both crops. The most influential parameters depended on the output considered with sensitivity patterns consistent with the expected dominant processes. Interestingly, some parameters related to the previous crop were found to affect output variables of the following crop, illustrating the importance of considering crop sequences for model calibration. The developed RDAISY toolbox used in this study can serve as a basis for following sensitivity analysis of the DAISY model, thus enabling the selection of the most influential parameters to be considered with model calibration.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 263〈/p〉 〈p〉Author(s): Rachael H. Nolan, Javier Hedo, Carles Arteaga, Tetsuto Sugai, Víctor Resco de Dios〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The moisture content of live fuels is an important determinant of forest flammability. Current approaches for modelling live fuel moisture content typically focus on the use of drought indices. However, these have mixed success partly because of species-specific differences in drought responses. Here we seek to understand the physiological mechanisms driving changes in live fuel moisture content, and to investigate the potential for incorporating plant physiological traits into live fuel moisture models. We measured the dynamics of leaf moisture content, access to water resources (through stable isotope analyses) and physiological traits (including leaf water potential, stomatal conductance, and cellular osmotic and elastic adjustments) across a fire season in a Mediterranean mixed forest in Catalonia, NE Spain. We found that differences in both seasonal variation and minimum values of live fuel moisture content were a function of access to water resources and plant physiological traits. Specifically, those species with the lowest minimum moisture content and largest seasonal variation in moisture (〈em〉Cistus albidus〈/em〉: 49–137% and 〈em〉Rosmarinus officinalis〈/em〉: 47–144%) were most reliant on shallow soil water and had the lowest values of predawn leaf water potential. Species with the smallest variation in live fuel moisture content (〈em〉Pinus nigra〈/em〉: 96–116% and 〈em〉Quercus ilex〈/em〉: 56–91%) exhibited isohydric behaviour (little variation in midday leaf water potential, and relatively tight regulation of stomata in response to soil drying). Of the traits measured, predawn leaf water potential provided the strongest predictor of live fuel moisture content (〈em〉R〈/em〉〈sup〉2〈/sup〉 = 0.63, AIC = 249), outperforming two commonly used drought indices (both with 〈em〉R〈/em〉〈sup〉2〈/sup〉 = 0.49, AIC = 258). This is the first study to explicitly link fuel moisture with plant physiology and our findings demonstrate the potential and importance of incorporating ecophysiological plant traits to investigating seasonal changes in fuel moisture and, more broadly, forest flammability.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 264〈/p〉 〈p〉Author(s): Mathias Hoffmann, Vytas Huth, Jürgen Augustin〈/p〉

Description: 〈p〉Publication date: 15 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 264〈/p〉 〈p〉Author(s): A. Rodríguez, M. Ruiz-Ramos, T. Palosuo, T.R. Carter, S. Fronzek, I.J. Lorite, R. Ferrise, N. Pirttioja, M. Bindi, P. Baranowski, S. Buis, D. Cammarano, Y. Chen, B. Dumont, F. Ewert, T. Gaiser, P. Hlavinka, H. Hoffmann, J.G. Höhn, F. Jurecka〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Climate change is expected to severely affect cropping systems and food production in many parts of the world unless local adaptation can ameliorate these impacts. Ensembles of crop simulation models can be useful tools for assessing if proposed adaptation options are capable of achieving target yields, whilst also quantifying the share of uncertainty in the simulated crop impact resulting from the crop models themselves. Although some studies have analysed the influence of ensemble size on model outcomes, the effect of ensemble composition has not yet been properly appraised. Moreover, results and derived recommendations typically rely on averaged ensemble simulation results without accounting sufficiently for the spread of model outcomes. Therefore, we developed an Ensemble Outcome Agreement (EOA) index, which analyses the effect of changes in composition and size of a multi-model ensemble (MME) to evaluate the level of agreement between MME outcomes with respect to a given hypothesis (e.g. that adaptation measures result in positive crop responses). We analysed the recommendations of a previous study performed with an ensemble of 17 crop models and testing 54 adaptation options for rainfed winter wheat (〈em〉Triticum aestivum〈/em〉 L.) at Lleida (NE Spain) under perturbed conditions of temperature, precipitation and atmospheric CO〈sub〉2〈/sub〉 concentration. Our results confirmed that most adaptations recommended in the previous study have a positive effect. However, we also showed that some options did not remain recommendable in specific conditions if different ensembles were considered. Using EOA, we were able to identify the adaptation options for which there is high confidence in their effectiveness at enhancing yields, even under severe climate perturbations. These include substituting spring wheat for winter wheat combined with earlier sowing dates and standard or longer duration cultivars, or introducing supplementary irrigation, the latter increasing EOA values in all cases. There is low confidence in recovering yields to baseline levels, although this target could be attained for some adaptation options under moderate climate perturbations. Recommendations derived from such robust results may provide crucial information for stakeholders seeking to implement adaptation measures.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 263〈/p〉 〈p〉Author(s): Lewis H. Ziska, David H. Fleisher, Steve Linscombe〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The effect of climate change on recent and projected increases in surface temperatures is well-documented. For agriculture, such changes can impact crop phenology and production, but the degree of impact will depend, in part, on contemporaneous changes in crop management. In the current study, we quantified recent (last 40 years) and projected (to 2095) changes in air temperature and associated changes in growing season duration for rice along a latitudinal north-south gradient of the lower Mississippi valley. Recent and projected climate data indicated an ongoing increase in air temperature and growing season length with latitudes above ∼31 °N. We then applied the DD50 growing degree day model to these data to determine if ratooning, a management practice that produces a second rice harvest with minimal resource input, could be employed. The model results were analyzed and used relative to the southernmost location, Cameron Parish, where the season length and daily temperatures currently allow for ratooning to be a common practice for long-grain cultivars (e.g., Cocodrie, Catahoula). The recent and projected increases in temperature and seasonality indicate that ratooning could already be adopted in Avoyelles Parish, and is potentially possible as far north as Cape Girardeau County (37 °N) by the end of the 21 st century. While additional information regarding possible effects of heat stress, water availability, rising carbon dioxide (CO〈sub〉2〈/sub〉) levels, and other factors will be necessary to fully assess ratooning potential, our research indicated that ongoing increases in temperature and season length may allow agronomic management practices, such as ratooning, to help adapt rice production to climatic uncertainty.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 263〈/p〉 〈p〉Author(s): Wei Xiao, Zhongwang Wei, Xuefa Wen〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Terrestrial evapotranspiration (〈em〉ET〈/em〉) consists of evaporation (〈em〉E〈/em〉) from canopy-intercepted water, evaporation from soil and open water, and transpiration (〈em〉T〈/em〉) from plants. Determining the contribution of 〈em〉T〈/em〉 to 〈em〉ET〈/em〉 (hereafter 〈em〉T〈/em〉/〈em〉ET〈/em〉) is challenging but necessary for improving water resource management and understanding the response of ecosystem water/energy budgets to climate change. Water stable isotopes provide unique information on ecosystem processes and can be used to partition evapotranspiration at the ecosystem scale. In this paper, the aim is to review the state of the science on the isotope method for ecosystem 〈em〉ET〈/em〉 partitioning, with a focus on uncertainties related to estimating the three isotopic end members (isotopic compositions of 〈em〉ET〈/em〉, 〈em〉T〈/em〉 and 〈em〉E〈/em〉). The published results show larger 〈em〉T/ET〈/em〉 variations during the growing season in croplands due to water management and rapid leaf area index (LAI) changes compared to in other natural ecosystems. Another robust result is that on average, grasslands have lower 〈em〉T/ET〈/em〉 than woodlands. The isotopic composition of 〈em〉ET〈/em〉 is provided by measurements, while the isotopic compositions of 〈em〉T〈/em〉 and 〈em〉E〈/em〉 are generally obtained using the Craig-Gordon model with appropriate modifications. Significant advances have been made in the techniques for estimating the isotopic composition of 〈em〉ET〈/em〉, largely due to the availability of fast-responding instruments for in situ measurements of water vapor isotopic composition. The largest source of uncertainty in the 〈em〉T/ET〈/em〉 estimation comes from uncertainties in the isotopic composition of 〈em〉ET〈/em〉. Based on published results of the uncertainties in the three end members, we estimate that a typical uncertainty range for 〈em〉T/ET〈/em〉 is ±21% (one standard deviation). This review provides background information and theoretical references for studies on isotopic hydrology, ecosystem processes and climate change.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 263〈/p〉 〈p〉Author(s): Xi Zhu, Andrew K. Skidmore, Tiejun Wang, Jing Liu, Roshanak Darvishzadeh, Yifang Shi, Joe Premier, Marco Heurich〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Leaf area index (LAI) has frequently been measured in the field using traditional optical methods such as digital hemispherical photography (DHP). However, in the DHP retrieved LAI, there is always contribution of woody components due to the difficulty in distinguishing woody and foliar materials. In addition, the leaf angle distribution which strongly affects the estimation of LAI is either ignored while using the convergent angle 57.5°, or inversed simultaneously with LAI using multiple directions. Terrestrial laser scanning (TLS) provides a 3-dimensional view of the forest canopy, which we used in this study to improve LAI estimation by directly retrieving leaf angle distribution, and subsequently correcting foliage clumping and woody effects. The leaf angle distribution was retrieved by estimating the angle between the leaf normal vectors and the zenith vectors. The clumping index was obtained by using the gap size distribution method, while the woody contribution was evaluated based on an improved point classification between woody and foliar materials. Finally, the gap fraction derived from TLS was converted to effective LAI, and thence to LAI. The study was conducted for 31 forest plots including deciduous, coniferous and mixed plots in Bavarian Forest National Park. The classification accuracy was improved by approximately 10% using our method. Results showed that the clumping caused an underestimation of LAI ranging from 1.2% to 48.0%, while woody contribution led to an overestimation from 3.0% to 31.9% compared to the improved LAI. The combined error ranged from −46.2% to 32.6% of the leaf area index (LAI) measurements. The error was largely dependent on forest types. The clumping index of coniferous plots on average was lower than that of deciduous plots, whereas deciduous plots had a higher woody-to-total area ratio. The proposed method provides a more accurate estimate of LAI by eliminating clumping and woody effects, as well as the effect of leaf angle distribution.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 263〈/p〉 〈p〉Author(s): Natalia E. Tonti, María I. Gassmann, Claudio F. Pérez〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Salt marshes are vulnerable ecosystems since they are found in locations often preferred for urban development. They produce a great amount of biomass, and also are of great interest because of the ecosystem services they provide from which carbon storage stands out. This work aims to study the energy and mass exchanged by a salt marsh located in southeastern Buenos Aires province (Argentina) and to characterize its net ecosystem production. A field campaign was carried out from February 2014 to March 2015. Sensible heat, water vapor (H〈sub〉2〈/sub〉O) and carbon dioxide (CO〈sub〉2〈/sub〉) fluxes were measured with eddy covariance technique at 6 m height over a 〈em〉Spartina densiflora〈/em〉 canopy. Fifty five percent of the data were lost and 15% more were discarded due to low turbulence conditions. This gaps were filled with a combination of techniques (look-up tables and mean diurnal variations), which allowed the estimation of monthly mean net ecosystem exchange, gross primary production and ecosystem respiration. As in other marshes, the latent heat flux consumed more than 55% of the available energy of the system, reaching up to 85% after a large flood event. This flux systematically exceeds the values of sensible heat measured throughout the study period. Unlike other environments, this southern salt marsh behaved as a CO〈sub〉2〈/sub〉 sink throughout the year. The net ecosystem production from March 2014 to February 2015 was approximately −10.5 t of CO〈sub〉2〈/sub〉 ha〈sup〉−1〈/sup〉 yr〈sup〉−1〈/sup〉 which is greater than reported results for other wetlands. These preliminary results for a southern 〈em〉S. densiflora〈/em〉 salt marsh are encouraging, although new field studies are under way to confirm their accuracy.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 265〈/p〉 〈p〉Author(s): Bernhard Schauberger, Susanne Rolinski, Sibyll Schaphoff, Christoph Müller〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉Ozone pollution can severely diminish crop yields. Its damaging effects depend, apart from ozone concentration, on crop, cultivar, water status, temperature and CO〈sub〉2〈/sub〉 concentration. Previous studies estimating global yield loss from ozone pollution did not consider all of these co-factors and climate change impact studies on crop yields typically ignore ozone pollution. Here we introduce an ozone damage module for the widely used process-based crop model LPJmL. The implementation describes ozone uptake through stomata, internal detoxification and short- and long-term effects on productivity and phenology, dynamically accounting for all listed co-factors. Using this enhanced model we estimate historical global yield losses from ozone pollution for wheat and soybeans. We divide wheat into “Western” and “Asian” to account for higher ozone sensitivities in Asian types. We apply daily ozone concentrations obtained from six chemistry-transport models provided by the ACCMIP and HTAP2 projects.〈/p〉 〈p〉Our implementation of ozone damage follows expected dynamics, for example damage amplification under irrigation. The model is able to reproduce results from chamber and field studies. Historical ozone-induced losses between 2008 and 2010 vary between countries, and we estimate these between 2 and 10% of ozone-free yields for soybeans, between 0 and 27% for Western wheat and 4 and 39% for Asian wheat.〈/p〉 〈p〉Our study highlights the threat of ozone pollution for global crop production and improves over previous studies by considering co-factors of ozone damage. Uncertainties of our study include the extrapolation from rather few point observations to the globe, possible biases in ozone data, omission of sub-daily fluctuations in ozone concentration or stomatal conductance and the averaging of different cultivars across regions. We suggest performing further field-scale experimental studies of ozone effects on crops, as these are currently rare but would be particularly helpful to evaluate models and to estimate large-scale effects of ozone.〈/p〉 〈/div〉

Description: 〈p〉Publication date: 15 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 264〈/p〉 〈p〉Author(s): Matheus Boni Vicari, Jan Pisek, Mathias Disney〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Leaf angle distribution (LAD) is an important property which influences the spectral reflectance and radiation transmission properties of vegetation canopies, and hence interception, absorption and photosynthesis. It is a fundamental parameter of radiative transfer models of vegetation at all scales. Yet, the difficulty in measuring LAD causes it to be also one of the most poorly characterized parameters, and is typically either assumed to be random, or to follow one of a very small number of parametric ‘archetype’ functions. Terrestrial LiDAR scanning (TLS) is increasingly being used to measure canopy structure, but LAD estimation from TLS has been limited thus far. We introduce a fast and simple method for detection of LAD information from terrestrial LiDAR scanning (TLS) point clouds. Here, it is shown that LAD information can be obtained by simply accumulating all valid planes fitted to points in a leaf point cloud. As points alone do not have any normal vector, subsets of points around each point are used to calculate the normal vectors. Importantly, for the first time we demonstrate the effect of distance on the reliable LAD information retrieval with TLS data. We test, validate, and compare the TLS-based method with established leveled digital photography (LDP) approach. We do this using data from both real trees covering the full range of existing leaf angle distribution type, but also from 3D Monte Carlo ray tracing. Crucially, this latter approach allows us to simulate both images and TLS point clouds from the same trees, for which the LAD is known explicitly a priori. This avoids the difficulty of assessing LAD manually, which being a difficult and potentially error-prone process, is an additional source of error in assessing the accuracy of LAD extraction methods from TLS or photography. We show that compared to the LDP measurement technique, TLS is not limited by leaf curvature, and depending on the distance of the TLS from the target, is potentially capable of retrieving leaf angle information from more complex, non-flat leaf surfaces. We demonstrate the possible limitation of TLS measurement techniques for the retrieval of LAD information for more distant canopies, or for taller trees (h 〉 20 m).〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 264〈/p〉 〈p〉Author(s): E. Castillo-Lorenzo, W.E. Finch-Savage, C.E. Seal, H.W. Pritchard〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉Functional germination traits contribute to both niche competitiveness and crop yield outcomes. However, there is little understanding of the adaptive significance of the germination thermal- and hydro-parameters in crop wild relatives (CWRs), yet these species are anticipated to be the source of adaptive traits for future agriculture. Seeds of 10 seed lots of 〈em〉Brassica〈/em〉 species, sub-species and inbred lines from across Europe, North Africa and the Middle East were subjected to a range of temperature and water potential conditions. The germination progress curves recorded were analysed using repeated probit analysis and the functional trait parameters (thermal- and hydro thresholds and times) determined. Relationships between these seed parameters (and the physical trait, seed mass) and the seed source environment were investigated.〈/p〉 〈p〉The 〈em〉Brassica〈/em〉 genus was found to have diverse seed germination phenotypes, with thermal (θ〈sub〉T〈/sub〉) and hydro times (θ〈sub〉H〈/sub〉) differing by 3 to 7-fold, base temperatures (T〈sub〉b〈/sub〉) by 〈em〉c〈/em〉. 9 °C and base water potentials (Ψ〈sub〉b〈/sub〉) by -1.5 MPa. Crop seed lots of 〈em〉Brassica oleracea〈/em〉 had shorter θ〈sub〉H〈/sub〉 for germination and higher values of Ψ〈sub〉b〈/sub〉, but longer θ〈sub〉T〈/sub〉 for germination than their CWR. For the CWRs, the mean monthly precipitation and the precipitation of the predicted month of germination of the seed collection site, was linearly correlated with T〈sub〉b〈/sub〉, θ〈sub〉T〈/sub〉, and Ψ〈sub〉b〈/sub〉. This increases the predictability of identifying valuable brassica germplasm for crop development through regeneration trait screening.〈/p〉 〈p〉In conclusion, the selection of the crop 〈em〉B. oleracea〈/em〉 for fastest germination under irrigated conditions likely limits the capacity of the current genepool to cope with erratic periods of drought predicted in future European climates.〈/p〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0168192318303381-ga1.jpg" width="214" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 264〈/p〉 〈p〉Author(s): Rafael Calama, Mar Conde, Javier de-Dios-García, Guillermo Madrigal, Javier Vázquez-Piqué, Francisco Javier Gordo, Marta Pardos〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Climate, competition and site conditions are the main drivers controlling annual secondary growth in tree species. These factors do no act independently on tree growth, but by means of interactions, resulting in mediated interactive effects. For example, the stress gradient hypothesis postulates alleviated interspecific competition under limiting spatial (site) or temporal (climate) resources. According to this, models predicting annual growth and yield for a given forest should consider these issues in their formulation. In this study, we present a modelling approach based on using data from permanent plots and dendrochronological analysis in order to describe annual tree growth in pure, even-aged stands of 〈em〉Pinus pinea〈/em〉 L. in the Spanish Northern Plateau, a highly limiting environment due to its Mediterranean continental climate. Our method is based on identifying the different sources of variability by means of a multilevel linear mixed model, and thereby identifying the potential covariates explaining observed variability at the different spatiotemporal scales. Our results indicate that site related factors such as site index or dominant height exert a greater influence on annual secondary growth than size-symmetric competition. In addition, we found that the controlling influence of water stress is greater than that of temperatures on tree growth. Furthermore, our results allow evidence to be identified for the stress gradient hypothesis in temporal intraspecific interactions, since trees exposed to a higher degree of competition tend to grow more than expected in dry periods. In contrast, the effect of competition on growth, on average, tends to be aggravated at very poor sites. Finally, our modelling approach allows us to conduct growth and yield simulations under different climate scenarios at different spatial scales, providing results which point to significant decreases in timber and cone production under the more severe scenarios, which can be alleviated through more intensive silviculture.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 265〈/p〉 〈p〉Author(s): Ester Scotto di Perta, Nunzio Fiorentino, Laura Gioia, Elena Cervelli, Salvatore Faugno, Stefania Pindozzi〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉Agriculture is still the main source of NH〈sub〉3〈/sub〉 emissions. Consequently, ammonia reduction and monitoring are included in the strict EU targets. Unfortunately, the main issue with the quantification of NH〈sub〉3〈/sub〉 emissions is that some uncertainties are still related to NH〈sub〉3〈/sub〉 volatilization measurements, mainly because of the absence of a standard measurement technique.〈/p〉 〈p〉This study compares two different methods for measuring NH〈sub〉3〈/sub〉 fluxes: the Integrated Horizontal Flux (IHF) method used with glass tubes and the wind tunnels (WT) with acid traps, in order to provide further insights into quantification of NH〈sub〉3〈/sub〉 emissions. Specifically, three field trials were carried out, using different fertilizers on bare soil: urea, raw manure and liquid separated digestate from Mediterranean buffalo cows (〈em〉Bubalus bubalis〈/em〉 L.).〈/p〉 〈p〉Results show that the same diurnal flux variations for both methods was observed, except for those in urea trials, mainly because of the dynamics of urea volatilization. Generally, WT underestimated ammonia emissions, especially during the first six hours of experimentation, since the fixed air speed inside the tunnel is lower than the outside wind speed at the same height. Cumulative ammonia volatilization measured with WT differs from those measured with IHF by 32% (urea), 43% (raw manure) and 46% (liquid separated digestate), respectively. Moreover, WT estimations seemed to be affected by a short exposition time of the acid traps, demonstrating a poor correlation of IHF and WT method within 2–3 h. Indeed, linear correlation between two methods was improved to R〈sup〉2〈/sup〉 = 0.92, by increasing the minimum samplers exposition time up to 3 h.〈/p〉 〈/div〉

Description: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 265〈/p〉 〈p〉Author(s): Galo Carrillo-Rojas, Brenner Silva, Rütger Rollenbeck, Rolando Célleri, Jörg Bendix〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Atmospheric carbon (CO〈sub〉2〈/sub〉) exchange, evapotranspiration (ET) processes, and their interactions with climatic drivers across tropical alpine grasslands are poorly understood. This lack of understanding is particularly evident for the páramo, the highest vegetated frontier in the northern Andes, the main source of water for inter-Andean cities, and a large carbon storage area. Studies of CO〈sub〉2〈/sub〉 and ET fluxes via the standard Eddy Covariance (EC) technique have never been applied to this region, limiting the understanding of diurnal / nocturnal exchanges and budget estimations. In this paper, we report the first EC analysis conducted on the Andean páramo (3765 m a.s.l.); this analysis measured CO〈sub〉2〈/sub〉, ET, and micrometeorological variables over two years (2016–2018) to understand their interactions with climatic / biophysical controls. The páramo was found to be a source of CO〈sub〉2〈/sub〉 and exhibited a net positive exchange (mean = +99 ± 30 gC m〈sup〉−2〈/sup〉 per year). The light-responses of net CO〈sub〉2〈/sub〉 exchange and the primary productivity were correlated and model-parameterized. Evapotranspiration was 635 ± 9 mm per year (51% of the annual rainfall total), and we obtained crop coefficients for the dominant vegetation (Tussock grass) based on reference-ET models FAO56 and ASCE-ERWI (0.90 and 0.78, respectively). We also compared our results to those from other high-altitude (alpine) and high-latitude grasslands (tundra). Finally, we demonstrate that our measurement period is representative of the páramo’s longer-term climate dynamics. Our investigation contributes to the body of knowledge on the land surface-atmosphere processes of the tropical Andes and supports decision-making about ecosystem services management and the preservation of this vulnerable biome.〈/p〉〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0168192318303526-ga1.jpg" width="499" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 265〈/p〉 〈p〉Author(s): S. Kutikoff, X. Lin, S. Evett, P. Gowda, J. Moorhead, G. Marek, P. Colaizzi, R. Aiken, D. Brauer〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉High quality estimates of evapotranspiration (ET) are needed for water-limited agriculture where irrigation is necessary to efficiently grow crops. Eddy covariance (EC) systems are observational tools used to measure water and heat fluxes, but a tendency to underestimate fluxes causes a lack of surface energy balance closure. Surface energy budgets are useful for verifying ET estimates, especially in advective conditions that affect energy partitioning. Here, we explored the effect of heat storage and advective conditions on surface energy balance closure for the 2014 and 2015 growing seasons in Bushland, Texas. Storage components were estimated near the center of an irrigated sorghum field using an array of soil and surface layer measurements. A comparison of EC estimated turbulent fluxes and available energy consisting of net radiation, soil heat flux, and storage was used to identify advective conditions and assess surface energy balance closure. Our results indicated daytime mean heat storage of approximately 40 W m〈sup〉−2〈/sup〉 with a diurnal pattern featuring a midday peak that exceeded the evening minimum in magnitude, mostly reflective of soil heat storage but also affected by air, water, and biomass heat storage during the morning hours and photosynthesis storage during midday hours. Daytime advective conditions were associated with higher heat storage frequently under stable atmospheric conditions. The surface energy balance was more closed in 2014 than 2015; the 2014 energy balance exhibited a hysteretic pattern with a surplus of turbulent energy in the afternoon, whereas systematic underestimation was common in 2015. This finding is related to a larger proportion of data in 2014 being advective, characterized by a lower Bowen ratio and greater ET, particularly during the late afternoon. Regardless of advection classification, heat storage was demonstrated to be important for daytime energy balance in this irrigated cropland.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 264〈/p〉 〈p〉Author(s): Simon Madec, Xiuliang Jin, Hao Lu, Benoit De Solan, Shouyang Liu, Florent Duyme, Emmanuelle Heritier, Frédéric Baret〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Wheat ear density estimation is an appealing trait for plant breeders. Current manual counting is tedious and inefficient. In this study we investigated the potential of convolutional neural networks (CNNs) to provide accurate ear density using nadir high spatial resolution RGB images. Two different approaches were investigated, either using the Faster-RCNN state-of-the-art object detector or with the TasselNet local count regression network. Both approaches performed very well (rRMSE≈6%) when applied over the same conditions as those prevailing for the calibration of the models. However, Faster-RCNN was more robust when applied to a dataset acquired at a later stage with ears and background showing a different aspect because of the higher maturity of the plants. Optimal spatial resolution for Faster-RCNN was around 0.3 mm allowing to acquire RGB images from a UAV platform for high-throughput phenotyping of large experiments. Comparison of the estimated ear density with in-situ manual counting shows reasonable agreement considering the relatively small sampling area used for both methods. Faster-RCNN and in-situ counting had high and similar heritability (H²≈85%), demonstrating that ear density derived from high resolution RGB imagery could replace the traditional counting method.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 265〈/p〉 〈p〉Author(s): Xiuliang Yuan, Jie Bai, Longhui Li, Alishir Kurban, Philippe De Maeyer〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Drip irrigation under plastic mulch is a common agricultural practice for oasis agroecosystems in the extensive arid regions of northwest China, and it is widely used to improve agricultural production by suppressing soil evaporation. The widespread application of plastic mulch has also obviously altered land characteristics and the partitioning of vapor and energy between the surface and the atmosphere. However, these physical processes, to date, are poorly incorporated into land surface models. In this study, an irrigation scheme and a plastic mulch module were incorporated into the Common Land Model (CoLM) to examine their influences on vapor (evapotranspiration) and energy fluxes, and the evapotranspiration observations were used to evaluate the model performance of irrigation effects. A sensitivity analysis indicates significant sensitivity relative to both the amount and timing of irrigation on vapor and energy fluxes. In addition, our results show that the revised CoLM with an irrigation module produced a better simulation of evapotranspiration than the default CoLM. However, large uncertainties still exist that fluctuation in simulated evapotranspiration is substantial, without considering the impact of plastic mulch. Incorporating the mulch module improved the CoLM performance for both vapor and energy fluxes. Plastic mulch reduced net radiation, sensible and latent heat fluxes. It aslo suppressed ground heat fluxes at daytime but improved ground heat fluxes at nighttime. Our results indicate that the agricultural practice, drip irrigation under plastic mulch, should be implemented into CoLM and other land surface models for studying vapor and energy fluxes in oasis agroecosystems or other similar agricultural ecosystems.〈/p〉〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0168192318303824-ga1.jpg" width="225" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volumes 266–267〈/p〉 〈p〉Author(s): Carla Leite, Vanda Oliveira, Alexandra Lauw, Helena Pereira〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Climate scenarios in the Mediterranean region predicts raising temperatures and more frequent and extreme drought conditions. Cork oak is a Mediterranean species with a large distribution in Portugal from which cork is extracted in a sustainable way and mainly used as the raw material for cork stoppers and insulating materials. To study the response of cork oak to drought and the effect of phellogen age on that response we examined cork growth from a 30-year chronology of trees from 12 sites in the main Portuguese cork oak production area. For the first time in cork, a components resilience study was performed. The research confirmed that drought reduces cork growth and provided extra knowledge on the responses of cork oak to drought: more severe droughts correspond to higher decrease of cork growth and more trees affected but to greater recovery performance. Moreover, cork oak is very tolerant and resilient to extreme droughts. Nevertheless, there are other factors that affect cork growth during and after drought, namely site, tree and the age of the phellogen. In fact, in the first 2 years and in the last 2 years of the production cycle the effects of drought on growth are more pronounced than in the middle of the cycle. The age of the phellogen is significant in the recovery, resistance and resilience but not in the relative resilience. The most noticeable differences occurred in the recovery for phellogen under 3 years (17% lower than that for phellogen with 3 to 6 years of age). Moreover, under drought conditions, there is a strong evidence that forest managers should enlarge debarking rotations, namely if drought occurs in the first 2 years of the production cycle and/or establish new cork oak stands in more humid areas, namely, in higher latitudes than the actual species distribution area.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 265〈/p〉 〈p〉Author(s): Thomas Laemmel, Manuel Mohr, Bernard Longdoz, Helmer Schack-Kirchner, Friederike Lang, Dirk Schindler, Martin Maier〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Molecular diffusion is commonly assumed as main physical process of gas transport in soils. However, non-diffusive gas transport processes like the so-called pressure-pumping effect can affect soil gas transport significantly. The pressure-pumping effect has only been detected indirectly and the underlying mechanisms remain unclear. Using a novel 〈em〉in situ〈/em〉 method the soil gas transport at a conifer forest site was monitored over a seven-week period. Airflow and air pressure were simultaneously measured above and below the forest canopy and air pressure was also measured in the soil. During episodes of high above-canopy wind speed, the effective soil gas diffusivity temporarily increased due to pressure-pumping. The enhancement of the gas transport rate in the topsoil reached up to 30%. We found that the best meteorological proxy explaining this effect was related to air pressure fluctuations measured at soil surface and not the mean wind speed directly above ground. While sub-canopy wind speeds continuously decreased from the bottom of the tree crown to the soil surface, amplitudes of the air pressure fluctuations were nearly constant in the whole sub-canopy profile and in the soil. We hypothesize that the air pressure fluctuations responsible for pressure-pumping are related to characteristics of above-canopy airflow rather than to airflow directly above the soil surface.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volumes 266–267〈/p〉 〈p〉Author(s): J. Kevin Hiers, Christina L. Stauhammer, Joseph J. O’Brien, Henry L. Gholz, Timothy A. Martin, John Hom, Gregory Starr〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Fine dead fuel moisture has a major influence on wildland fire behavior yet the dynamics driving water exchange of fuel particles in forested environments remain poorly understood. Most fire behavior models rely on simple, stand-level fuel moisture estimates, ignoring potentially important variation occurring within fuelbeds that could influence fire behavior. This is especially true in surface fire regimes where variation in fine-scale fuel properties drive fire behavior and subsequent fire effects. Saw palmetto [〈em〉Serenoa repens〈/em〉 (Bartr.) Small] dominated fuelbeds in the pine forests of the southeastern United States have high within stand variation in one of the most fire prone habitats in the world. Pine needles and palmetto fronds dominate the biomass of fine dead fuel types that produce extreme fire behavior. To assess predictors of fine dead fuel moisture, we analyzed fuel moisture dynamics of these two fine dead fuel types over a two-year period in conjunction with under- and overstory forest meteorological data. Using multiple models and time lag analysis of within-stand moisture dynamics, the results indicate that saw palmetto and pine dramatically differ in drying regimes, primarily resulting from different responses to cumulative rainfall, net radiation, and antecedent atmospheric moisture content. Despite being responsive to changes in relative humidity, saw palmetto was significantly dryer than pine under nearly all meteorological conditions, and it was capable of maintaining extremely low fuel moisture despite high relative humidity or rainfall. Our results point to the need to capture additional drivers of microclimatic variation to aid fire managers in accurately predicting within-stand fuel moisture and subsequent fire behavior. Improving the scientific community’s understanding of variation in complex fuel beds is critical for effectively managing risk in fire prone ecosystems.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 265〈/p〉 〈p〉Author(s): Mahmuda Islam, Mizanur Rahman, Achim Bräuning〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Trees can adjust their hydraulic architecture by adjusting vessel size and frequency in response to stressful environmental condition. Little is known about the long term adjustment of tropical moist forest trees to changing environment. Here we develop the standard chronologies of seven vessel features and radial growth of two ecologically contrasting South Asian moist forest trees, 〈em〉Toona ciliata〈/em〉 M. Roem. and 〈em〉Lagerstroemia speciosa〈/em〉 (L.) Pers. and evaluate their hydraulic response to short term climate variability and long term climate variations. Measurements of vessel variables were performed on digital microscopic images. Standard dendrochronological procedure were applied to develop vessel and ring-width chronologies. Relationships among the chronologies and their interaction with climate variables were assessed by Principal Component Analysis (PCA), bootstrap correlations and moving correlations. Pre-monsoon temperature negatively influenced ring-width (RW) and positively influenced vessel density (VD) in 〈em〉T. ciliata〈/em〉. Mean vessel area (MVA) was negatively related with prior year monsoon temperature. In 〈em〉L. speciosa〈/em〉, previous year temperatures and precipitation showed strong correlations with vessel features and radial growth in the following growing season, probably due to carbon carry over effects. Current year October precipitation was positively related with MVA in both species. Differences in functional traits might have caused the observed variation in hydraulic strategies between the two study species. Our analyses suggest that cellular dendrochronology can be used to understand the long-term hydraulic responses of functionally different moist forest trees to climatic changes which is relevant for forest management under changing climate conditions.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 265〈/p〉 〈p〉Author(s): Guangjian Yan, Ronghai Hu, Jinghui Luo, Marie Weiss, Hailan Jiang, Xihan Mu, Donghui Xie, Wuming Zhang〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Leaf area index (LAI) is a key parameter of vegetation structure in the fields of agriculture, forestry, and ecology. Optical indirect methods based on the Beer-Lambert law are widely adopted in numerous fields given their high efficiency and feasibility for LAI estimation. These methods have undergone considerable progress in the past decades, thereby making them operational in ground-based LAI measurement and even in airborne estimation. However, several challenges remain, given the requirement of increasing accuracy and new applications. Clumping effect correction attained significant progress for continuous canopies with non-randomly disturbed leaves while non-continuous canopies are rarely studied. Convenient and operational measurement of leaf angle distribution and woody components is lacked. Accurate and comprehensive validations are still very difficult due to the limitations of direct measurement. The introduction of active laser scanning technology is a driving force for addressing several challenges, but its three-dimensional information has not been fully explored and utilized. In order to update the general knowledge and identify the possible error source, this study comprehensively reviews the temporal development, theoretical framework, and issues of indirect LAI measurement, followed by current methods, instruments, and platforms. Latest methods and instruments are introduced and compared to traditional ones. Current challenges, recent advances, and future perspectives are discussed to provide recommendations for further research.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 265〈/p〉 〈p〉Author(s): Paulo R.L. Bittencourt, Fernanda de V. Barros, Cleiton B. Eller, Caroline S. Müller, Rafael S. Oliveira〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Fog is a frequent phenomenon in tropical montane cloud forests (TMCFs). These ecosystems are important to the water supply of adjacent lowland regions which is largely determined by the effect of fog on TCMF evapotranspiration rates and hydrological balance. Understanding fog regimes at fine-grained temporal resolution is key to predict plant functioning and effects of climatic changes in TMCFs, especially on key hydrological services that these forests provide. Here, we combine a suite of micrometeorological and hydrological sensors with a visibilimeter, a reliable sensor of fog occurrence, to gather fine-grained information on fog frequency, duration and timing and its contribution to water inputs, light availability and microclimatic variability in a Brazilian TMCF. Despite occurring on 64% of days, fog was highly variable at daily and seasonal scales, occurring mostly at night and during the rainy season. Approximately 1200 liters of fog were intercepted per tree per year (259 mm or 10.7% of total net precipitation). Fog also increased net precipitation provided by concomitant fog-rain events. Monthly net precipitation to precipitation ratio, a measure of how much water arrives at the soil and how much evaporates or is intercepted by the canopy, was 0.96 - much higher than the 0.72 typical of lowland rainforest, due to the additional fog water input on TMCF. Cloudiness, and not fog, dominated light availability and inter-day microclimatic variability (air temperature and vapor pressure deficit). High fog regime variability indicates that understanding TMCFs functioning requires integration of plant function with fine-grained data of fog and cloud occurrence. We discuss possible consequences of our results to TMCFs plant functioning.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 265〈/p〉 〈p〉Author(s): Prakash K. Jha, Panos Athanasiadis, Silvio Gualdi, Antonio Trabucco, Valentina Mereu, Vakhtang Shelia, Gerrit Hoogenboom〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Skillful seasonal climate predictions paired with a dynamic crop model can assist agricultural management and help farmers minimize risk. For crop yield predictions, the skill in generating realistic distributions of weather for the crop growing season matters more than the skill of forecasting the mean seasonal climate itself. In this regard, the ensemble of daily fields of the Seasonal Prediction Systems (SPSs) output could be a potential alternative to other methods that are available to generate daily weather from the monthly or seasonal mean forecasts. However, the SPSs are not expected to forecast individual weather events at a given grid point (deterministic forecast), but if the statistics of the predicted weather are correct, an ensemble of yield predictions using individual realizations of the ensemble seasonal forecast may produce a more skillful yield forecast. So far, the potential of this new approach has not been tested. The goal of this study was to determine the potential applicability of using daily data from SPSs to predict rice yield through a case study of Nepal’s Terai. The study used 28 years (1983–2010) daily hindcasts of the coupled forecast system model version 2 (CFSv2) SPS into a Cropping System Model (CSM)-CERES-Rice. The hindcasts of the CFSv2, initialized at different lead times, were used in various ways to simulate rice yield, which were then compared to the reference yield and to the simulated yield using climatology alone to examine the predictive skill at different lead times. The results from this study indicate that unlike the typical ensemble averaging approach commonly used in seasonal climate forecasting, averaging the simulated yield using individual member does not guarantee better yield prediction. Further analyses should be made, including alternative downscaling methods as well as a similar analysis for an area where quality meteorological and agricultural data are available and where the seasonal forecasts exhibit better skill.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 265〈/p〉 〈p〉Author(s): Zoubair Rafi, Olivier Merlin, Valérie Le Dantec, Saïd Khabba, Patrick Mordelet, Salah Er-Raki, Abdelhakim Amazirh, Luis Olivera-Guerra, Bouchra Ait Hssaine, Vincent Simonneaux, Jamal Ezzahar, Francesc Ferrer〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉A precise estimate of the evapotranspiration (ET) partitioning is fundamental for determining the crop water needs and optimizing irrigation management. The plant transpiration (T) is generally considered to be the most desirable component, while reducing the soil evaporation (E) could be one of the most important water-saving actions in semi-arid agricultural regions. Given the lack of reference method to estimate the E/T partitioning of wheat crop, this study inter-compares four different methods based on eddy covariance, sap flow and lysimetry measurements and FAO modeling. The objectives are: i) to quantify the systematic and random uncertainty in E and T observations, ii) to evaluate the partitioning ratio (T/ET) at the daily/field scale and iii) to assess the performance of the FAO model over two drip irrigated wheat fields. Results indicate that despite the small surface sensed by mini-lysimeters, the partitioning ratio is evaluated more precisely (19% relative error) with lysimetry than with the other systems (any combination of eddy covariance, lysimetry and sap flow measurements). Moreover, stem-scale T measurements from sap flow sensors are subject to representativeness issues at the field scale, and to systematic errors during water-stress and senescence periods. The lysimeter-derived partitioning ratio increases from about 0.50 to 0.85 during the growth stage and rapidly drops towards 0 during senescence. Its dynamics is found to be significantly correlated (R〉0.7) with the 5-cm soil moisture. By comparing FAO simulations with observations, it is found that the FAO method overestimates T and underestimates E, while keeping satisfying ET estimates for drip irrigated wheat. This study suggests that different independent measurement techniques should be implemented to both quantify and reduce uncertainties in the T/ET ratio, and that accurate observations are still needed to improve the modeling of E/T components.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 265〈/p〉 〈p〉Author(s): Xuezhi Tan, Shu Chen, Thian Yew Gan, Bingjun Liu, Xiaohong Chen〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉On May 2016 an extreme large wildfire affected Fort McMurray of Canada, leading to the largest wildfire evacuation and the costliest natural disaster in Canadian history. This wildfire was caused by extremely warm and dry weather conditions in spring. Here we investigate thermodynamic and dynamic (atmospheric circulation) conditions, and teleconnections conducive to extreme wildfire climate of western Canada since 1871. Results show that the extreme wildfire was very likely an outcome of anthropogenic effects that increase the occurrence of a persistent upper ridge associated with a warm and dry weather over western Canada. Changes in dynamic conditions decreased temperature and increased precipitation, while changes in thermodynamic conditions increased temperature and decreased precipitation. Thus the observed increase in temperature and decrease in precipitation on 26 April–15 May over western Canada were caused by changes in thermodynamic conditions. Although the Pacific North American (PNA) pattern was teleconnected with the occurrence of certain synoptic circulation patterns over western Canada, changes in the occurrence of the synoptic circulation pattern associated with the extreme wildfire cannot be explained by increased occurrences of the positive phase of PNA. The El Niño-Southern Oscillation and the Pacific Decadal Oscillation have not been found to have contributed to wildfire weather in western Canada. The spring warming and drying trends since 1871 over western Canada cannot be attributed to changes in common teleconnections.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 265〈/p〉 〈p〉Author(s): Tao Yan, Tiantian Qu, Huanhuan Song, Zhenzhong Sun, Hui Zeng, Shushi Peng〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Soil respiration (Rs) is generally partitioned into autotrophic respiration (by roots and mycorrhizae) and heterotrophic respiration (by decomposers). Boreal and temperate forests are widely associated with ectomycorrhizal (EM) fungi, which play a critical role in belowground carbon dynamics. However, the magnitude and factors controlling EM fungal respiration (Rem) have not been well studied in field experiments. In this study, we quantified Rem using the micro-pore mesh method in three 〈em〉Larix principis-rupprechtii〈/em〉 plantations of different ages (i.e., 11-, 20-, and 45-year-old, representing sapling, young, and mature stands, respectively) during the growing seasons from 2014 to 2016 in North China. The results showed clear seasonality of Rem, with an initial increase in spring (May and June), peak in summer (July and August), and decrease in autumn (September and October). Rem represented 37, 47 and 39% of rhizosphere respiration in the sapling, young, and mature stands, respectively, with an average of 41% across the three stands, indicating that a significant portion of rhizosphere respiration originated from EM fungi in larch plantations. Rem was positively correlated with soil temperature and the annual fine root increment, but negatively correlated with soil moisture when values exceeded 0.055 cm〈sup〉3〈/sup〉 cm〈sup〉–3〈/sup〉. Stand age had no significant effects on Rem, but Rem and the contribution of Rem to Rs in summer in the sapling stand was significantly higher than values in the young and mature stands. These results may be due to the higher values of soil temperature and annual fine root increment and lower soil inorganic nitrogen in the sapling stand relative to the other two stands. Overall, our results emphasize the importance of partitioning and quantifying EM fungal respiration to improve our understanding and predictions of belowground carbon dynamics under global climate change.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 265〈/p〉 〈p〉Author(s): Dirk Schindler, Manuel Mohr〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The response of four Scots pine trees to wind excitation was measured and analyzed. We investigated whether wind-induced tree sway in the fundamental mode is affected and enhanced by resonance effects between cyclic wind loading and oscillatory tree response. By combining results from wavelet analysis and analysis of phase-amplitude coupling, we demonstrate that the response in the fundamental mode is an indirect reaction of the trees to displacement from their rest position mainly caused by large organized turbulent structures in the canopy airflow, such as sweeps and ejections. In particular, sweeps caused large tree displacement. It is suggested that sway in the fundamental mode mainly results indirectly from the trees’ elastic energy that is stored in the stem and roots because of wind-induced compression and tension, and the damping that returns them to their rest position. Since no direct excitation of sway in the fundamental mode was found, it is concluded that there is no resonant response of the studied Scots pine trees to wind excitation.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 265〈/p〉 〈p〉Author(s): Kshitij Parajuli, Scott B. Jones, David G. Tarboton, Gerald N. Flerchinger, Lawrence E. Hipps, L. Niel Allen, Mark S. Seyfried〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Quantification of evapotranspiration (ET) is crucial for understanding the water balance and for efficient water resources planning. Agricultural settings have received most attention regarding ET measurements while less knowledge is available for actual ET (ET〈sub〉A〈/sub〉) in natural ecosystems, many of which have soils containing significant amounts of stones. This study is focused on modelling ET〈sub〉A〈/sub〉 from stony soil, particularly in montane ecosystems where we estimate the contribution of stone content on water retention properties in soil. We employed a numerical model (HYDRUS-1D) to simulate ET〈sub〉A〈/sub〉 in natural settings in northern Utah and southern Idaho during the 2015 and 2016 growing seasons based on meteorological and soil moisture measurements at a range of depths. We simulated ET〈sub〉A〈/sub〉 under three different scenarios, considering soil with (i) no stones, (ii) highly porous stones, and (iii) negligibly porous stones. The simulation results showed significant overestimation of ET〈sub〉A〈/sub〉 when neglecting stones in comparison to ET〈sub〉A〈/sub〉 measured by eddy covariance. ET〈sub〉A〈/sub〉 estimates with negligibly porous stones were lower for all cases due to the decrease in soil water storage compared with estimates made considering highly porous stones. Assumptions of highly porous or negligibly porous stones led to reductions in simulated ET〈sub〉A〈/sub〉 of between 10% and 30%, respectively, compared with no stones. These results reveal the important role played by soil stones, which can impact the water balance by altering available soil moisture and thus ET〈sub〉A〈/sub〉 in montane ecosystems.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 265〈/p〉 〈p〉Author(s): Upasana Bhuyan-Erhardt, Tobias M. Erhardt, Gregor Laaha, Christian Zang, Juraj Parajka, Annette Menzel〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Aiming for refined drought characterization, the validation of targeted drought indices is of vital importance. In this study, we compared the performance of established drought indices – the SPI (Standardized Precipitation Index) and the SPEI (Standardized Precipitation Evapotranspiration Index) – with standardized drought indices using a recently developed, vine copula based method for the computation of multivariate drought indices (here addressed as VCI). For our validation study, we used several environmental drought indicators: monthly streamflow anomalies and streamflow drought events from a network of 332 catchments across Europe, as well as gross primary production (GPP) and net ecosystem exchange (NEE) for Germany. The novel multivariate VC-Indices can combine two or more user-selected, drought relevant variables to model different drought types, depending on the user-application. Validation with streamflow data showed that the maximum probability of drought detection values for SPEI, SPI and VCI was observed for 12.0%, 25.9% and 62.0% of the catchments, and the minimum false alarm rate values for SPEI, SPI and VCI was observed for 20.5%, 33.4% and 46.1% of the catchments, respectively. Validation with carbon flux data showed that the average R〈sup〉2〈/sup〉 values of a pixel-wise linear regression for the growing season for the period 1980 to 2010 between SPEI, SPI and VCI with NEE were 0.26, 0.07 and 0.37, respectively. Similarly, the average R〈sup〉2〈/sup〉 values for SPEI, SPI and VCI with GPP were 0.03, 0.04 and 0.14, respectively. Our results emphasize using the VCI as an additional source of information in order to allow better understanding of drought characterization.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 265〈/p〉 〈p〉Author(s): Giovanni Pastore, Brian Tobin, Maarten Nieuwenhuis〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉Losses of carbon (C) and nitrogen (N) from the decomposition of woody debris in harvested forest ecosystems is of interest in national C accounting, regional water quality assessment as well as for managing long-term localised forest fertility. The main commercial forest type in Ireland is Sitka spruce dominated plantations and the woody debris from harvesting is routinely gathered into windrows in reforested stands. This study examined woody decomposition losses via two pathways namely respiration to the atmosphere and rainwater leaching to soil water. A chronosequence of forest stands was sampled, ranging in age (of the harvest debris) from three to fifteen years.〈/p〉 〈p〉Respiratory C loss from windrows was found to be 11.5 t C ha〈sup〉−1〈/sup〉 year〈sup〉−1〈/sup〉 three years after reforestation. This rate had dropped by 29% to 8.1 t C ha〈sup〉−1〈/sup〉 yr〈sup〉−1〈/sup〉 twelve years later. There was a strong seasonal trend in this efflux and the main driver of this variation was soil temperature, however moisture content and drying/rewetting cycles also played a role. Leached losses of C followed a similar trend to respired losses, but their rate was consistently less than 1% of respiration. Total dissolved N fluxes in woody debris leachate followed a different pattern, where more was retained by the system than lost. Thus, windrowed woody debris acted as a nutrient reservoir for N but as a steady source of C.〈/p〉 〈/div〉

Description: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 265〈/p〉 〈p〉Author(s): Pradeep Wagle, Prasanna H. Gowda, Brian K. Northup〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉A thorough investigation of annual dynamics of carbon dioxide (CO〈sub〉2〈/sub〉) fluxes with respect to major controlling factors and harvest management is lacking for rainfed alfalfa (〈em〉Medicago sativa〈/em〉 L.), a high quality perennial legume forage. To address this knowledge gap, this study reports two years (April 2016 - March 2018) of eddy covariance measurements of CO〈sub〉2〈/sub〉 fluxes over a rainfed alfalfa field in central Oklahoma, USA. Alfalfa yields were strongly regulated by amount and timing of rainfall. As a result, cumulative dry forage yield was ∼7.5 t ha〈sup〉−1〈/sup〉 (four harvests) in 2016 (dry year) and ∼10 t ha〈sup〉−1〈/sup〉 (five harvests) in 2017 (wet year). An optimum air temperature (T〈sub〉a〈/sub〉) and vapor pressure deficit (VPD) for net ecosystem CO〈sub〉2〈/sub〉 exchange (NEE) was approximately 25 °C and 2.2 kPa, respectively. The response of gross primary production (GPP) to photosynthetically active radiation (PAR) varied with growth stage of alfalfa and climatic conditions (i.e., dry or normal/wet periods). Daily (8-day averages) NEE and gross primary production (GPP) reached -8.17 and 16.69 g C m〈sup〉-2〈/sup〉 d〈sup〉−1〈/sup〉, respectively. Magnitudes of GPP (GPP〈sub〉MOD〈/sub〉) derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) were 〈 50% of tower-derived GPP, most likely due to a smaller value (0.15 g C mol〈sup〉−1〈/sup〉 PAR) for light use efficiency in the GPP〈sub〉MOD〈/sub〉 algorithm. The observed 8-day composite ecosystem light use efficiency (ELUE) was up to 0.36 g C mol〈sup〉−1〈/sup〉 PAR in this study. The rainfed alfalfa field with 4–5 hay harvests per year showed large carbon uptake potential (e.g., cumulative NEE of -454 g C m〈sup〉-2〈/sup〉 in 2017) at an annual scale. The GPP and ELUE showed a strong correspondence with MODIS-derived vegetation indices, indicating the potential of applying satellite remote sensing to upscale site-level observations of CO〈sub〉2〈/sub〉 fluxes for alfalfa to larger spatial scales.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 265〈/p〉 〈p〉Author(s): Roberto Tognetti, Bruno Lasserre, Mirko Di Febbraro, Marco Marchetti〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Due to the recent spread of forest die-off worldwide, concerns arise about the relative influence of specific climate parameters on tree growth decline in semi-arid environments, such as the Mediterranean mountain forests. As temperatures increase, drought may reduce tree productivity and survival across these forest ecosystems. Drought-induced tree growth decline can be interpreted as an early-warning signal of forest vulnerability. Here, we modeled the relationship between tree-ring width index (RWI) of beech populations in mountain forests of south-central Italy and the standardized precipitation evapotranspiration index (SPEI) derived from local weather stations. The aim of the research was to propose a procedure to determine the tipping point of drought severity triggering tree decline in beech forests. We focused on the cumulative water balance over the previous 〈em〉1〈/em〉 month, which was particularly appropriate in relationship with the soil water conditions of these Mediterranean mountains. Under drier conditions, the correlation between RWI and SPEI was stronger, soil water supply (early fall of current year) and atmospheric evaporative demand (late spring of current year) being the dominant factors limiting tree growth of southern beech populations.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 265〈/p〉 〈p〉Author(s): D.P. Billesbach, S.W. Chan, D.R. Cook, D. Papale, R. Bracho-Garrillo, J. Verfallie, R. Vargas, S.C Biraud〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉In late 2015 and early 2016, work done by the AmeriFlux Management Project Technical Team (amerilfux.lbl.gov) helped to uncover an issue with Gill WindMaster and WindMaster Pro sonic anemometers used by many researchers for eddy covariance flux measurements. Gill has addressed this issue and has since sent out a notice that the vertical wind speed component (a critical piece of all eddy covariance fluxes) was being erroneously computed and reported. The problem (known as the “w-boost” bug) resulted in positive (upward) wind speeds being under-reported by 16.6% and negative (downward) wind speeds being under-reported by 28.9%. This has the potential to cause similar under estimates in fluxes derived from measurements using these instruments. Additionally, the bug affects corrections for angle of attack as derived by Nakai and Shimoyama, rendering them invalid. While the manufacturer has offered a firmware upgrade for existing instruments that will fix this issue, many existing data sets have been affected by it and are currently in use by the scientific community.〈/p〉 〈p〉To address the issue of affected data, currently in use, we analyzed multi-year and short-term data sets from a variety of ecosystems to assess methods of correcting existing flux data. We found that simple multiplicative correction factors (∼1.18) may be used to remove most of the “w-boost” bias from fluxes in existing data sets that do not include angle of attack corrections.〈/p〉 〈/div〉

Description: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 265〈/p〉 〈p〉Author(s): Zhongsheng Cao, Xia Yao, Hongyan Liu, Bing Liu, Tao Cheng, Yongchao Tian, Weixing Cao, Yan Zhu〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉With the changing of the climate, the detection of heat stress as early as possible has become increasingly important for wheat (〈em〉Triticum aestivum〈/em〉 L.) production. Previous studies have demonstrated that photosynthetic parameters can serve as indicators of the stress conditions, and vegetation indices (VIs) provide the ability to non-destructively monitor photosynthetic parameters. However, it remains unclear whether VIs can be used to detect heat stress in a similar manner as the photosynthetic parameters. In addition, the optimal VIs for indicating heat stress and detecting the stress status are also currently unknown. In the present study, a heat stress experiment was designed with four temperature levels [T1, 17 °C/27 °C (T〈sub〉min〈/sub〉/T〈sub〉max〈/sub〉), T2 (25 °C/35 °C), T3 (29 °C/39 °C), and T4 (33 °C/43 °C)] and three treatment durations [three days (D1), six days (D2) and nine days (D3)]. Three photosynthetic parameters [leaf chlorophyll content (LCC), net photosynthesis rate (〈em〉P〈/em〉〈sub〉n〈/sub〉), and maximum efficiency of photosystem II (〈em〉F〈/em〉〈sub〉v〈/sub〉/〈em〉F〈/em〉〈sub〉m〈/sub〉)] and 17 published VIs were selected to compare their sensitivity and assess their feasibility for detecting heat stress. The results showed that 〈em〉F〈/em〉〈sub〉v〈/sub〉/〈em〉F〈/em〉〈sub〉m〈/sub〉 was the most sensitive photosynthetic parameter to heat stress and had the ability to indicate the start and end of heat stress at the slight level or the early stage. The chlorophyll index-red edge (CI〈sub〉red-edge〈/sub〉), normalized difference red edge index (NDRE) and photochemical reflectance index (PRI) were sensitive to heat stress owing to their close relationships with photosynthetic parameters. Among these three VIs, PRI displayed the highest sensitivity. Nevertheless, the sensitivity of PRI was less than that of 〈em〉F〈/em〉〈sub〉v〈/sub〉/〈em〉F〈/em〉〈sub〉m〈/sub〉, and it failed to detect the beginning and end of heat stress lasting for three days. The ability of PRI to detect heat stress became similar to that of 〈em〉F〈/em〉〈sub〉v〈/sub〉/〈em〉F〈/em〉〈sub〉m〈/sub〉 when the duration of heat stress was increased to seven days. In conclusion, 〈em〉F〈/em〉〈sub〉v〈/sub〉/〈em〉F〈/em〉〈sub〉m〈/sub〉 is the optimum indicator for detecting early-stage heat stress, in which only the photosynthetic functions change. In contrast, PRI, a non-destructive indicator, works well to indicate relatively late-stage heat stress, in which the chemical and physical characteristics of leaves (e.g., chlorophyll content) are affected.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 265〈/p〉 〈p〉Author(s): T. Jackson, A. Shenkin, A. Wellpott, K. Calders, N. Origo, M. Disney, A. Burt, P. Raumonen, B. Gardiner, M. Herold, T. Fourcaud, Y. Malhi〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉Wind damage is an important driver of forest structure and dynamics, but it is poorly understood in natural broadleaf forests. This paper presents a new approach in the study of wind damage: combining terrestrial laser scanning (TLS) data and finite element analysis. Recent advances in tree reconstruction from TLS data allowed us to accurately represent the 3D geometry of a tree in a mechanical simulation, without the need for arduous manual mapping or simplifying assumptions about tree shape. We used this simulation to predict the mechanical strains produced on the trunks of 21 trees in Wytham Woods, UK, and validated it using strain data measured on these same trees.〈/p〉 〈p〉For a subset of five trees near the anemometer, the model predicted a five-minute time-series of strain with a mean cross-correlation coefficient of 0.71, when forced by the locally measured wind speed data. Additionally, the maximum strain associated with a 5 ms〈sup〉−1〈/sup〉 or 15 ms〈sup〉-1〈/sup〉 wind speed was well predicted by the model (N = 17, R〈sup〉2〈/sup〉 = 0.81 and R〈sup〉2〈/sup〉 = 0.79, respectively). We also predicted the critical wind speed at which the trees will break from both the field data and models and find a good overall agreement (N = 17, R〈sup〉2〈/sup〉 = 0.40). Finally, the model predicted the correct trend in the fundamental frequencies of the trees (N = 20, R〈sup〉2〈/sup〉 = 0.38) although there was a systematic underprediction, possibly due to the simplified treatment of material properties in the model. The current approach relies on local wind data, so must be combined with wind flow modelling to be applicable at the landscape-scale or over complex terrain. This approach is applicable at the plot level and could also be applied to open-grown trees, such as in cities or parks.〈/p〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0168192318303605-ga1.jpg" width="466" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volumes 266–267〈/p〉 〈p〉Author(s): Fernando Coelho Eugenio, Alexandre Rosa dos Santos, Beatriz Duguy Pedra, José Eduardo Macedo Pezzopane, Reginaldo Gonçalves Mafia, Edmilson Bitti Loureiro, Lima Deleon Martins, Nathália Suemi Saito〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Wildfires are the result of a complex interaction between climate, vegetation, topography and socioeconomic factors (BEDIA et al., 2012). The present study aims at analyzing how the relations between the meteorological and physical variables of the terrain correlate with the parameters of occurrence of wildfires in areas of planted forests in Brazil. The analysis of the wildfire regime in the study area was divided into three important aspects: temporal, spatial and causal. There are two periods of wildfire occurrence in the studied area, and for the first season, subzone 1 is from December to March; for the subzone 2 is from January to March; and, for subzone 3, is in the months of January and February. The second season, for all subzones, is between the months of August and October. Most climatic variables, isolated, do not present a direct relation with the occurrence of wildfires for both subzones, excepting some variables in some subzones. Considering both subzones, approximately 80% of the fires analyzed correspond to areas smaller than 4 ha.〈/p〉〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0168192318304076-ga1.jpg" width="354" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volumes 266–267〈/p〉 〈p〉Author(s): C.L. Pinheiro, L.M.G. Rosa, A.R. Falqueto〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Overgrazed grasslands of Southern Brazil are responsible in part for the degradation, low productivity and loss of biodiversity of the grassland ecosystems submitted to such management. 〈em〉Axonopus affinis〈/em〉 Chase, the carpet grass, is a dominant creeping grass species in overgrazed grasslands. The species readily spreads, is highly tolerant of frequent defoliation and to trampling. In any natural environment, different light intensity regimes vary considerably along the day. Such phenomenon requires a high level of plasticity, resistance, and resilience from plants. Within this context, the aim of this study was to describe the mechanisms of photochemical activity in 〈em〉Axonopus affinis〈/em〉 (Poaceae) in response to natural variations in daylight. Here we report hysteresis related functional behavior in overgrazed grasslands. This study was conducted in grassland vegetation within an experimental overgrazed area from the Embrapa Pecuária Sul, Bagé/Rio Grande do Sul, Brazil (austral spring 2014). By means of preferential sampling, homogeneous areas with a 90% dominance of 〈em〉Axonopus affinis〈/em〉 Chase were selected. In the present study 60 sample units were analyzed (young leaves, non-damaged and fully expanded). Photochemical variables and OJIP curves were sampled in two distinct conditions along one day, under light intensities labeled as: 1 – high photosynthetic photon flux density (HI), when under full sunlight; and 2 - low photosynthetic photon flux density (LI), when under cloudy days. It was possible to quantify and identify the alternative stable states of 〈em〉A. affinis〈/em〉 in response to light resource availability, expanding the interpretation of the multivariate analysis (triangular trajectory) and therefore, contributing to univariate metrics (bimodal trajectory). In this study, HI produced hysteretic behavior while LI of dynamic photoinhibition in 〈em〉A. affinis〈/em〉. The ΔF/F〈sub〉m′〈/sub〉 variable was the most important mechanism to explain the plasticity of 〈em〉A. affinis〈/em〉 in HI and LI (R〈sup〉2〈/sup〉 〉 0.98 in function of the PCoA coordinates). However, the non-photochemical quenching activity was responsible for the stability in the OJIP curve. Therefore, 〈em〉A. affinis〈/em〉 presented photochemical mechanisms that contribute to the occupation and dominance of overgrazed grasslands with different light regimes.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volumes 266–267〈/p〉 〈p〉Author(s): Kerou Zhang, Qiuan Zhu, Jinxun Liu, Meng Wang, Xiaolu Zhou, Mingxu Li, Kefeng Wang, Juhua Ding, Changhui Peng〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉A process-based dynamic ecosystem model of TRIPLEX-GHG was used to estimate the spatial and temporal patterns of N〈sub〉2〈/sub〉O fluxes from global forest and grassland ecosystems under the effects of global warming and elevated CO〈sub〉2〈/sub〉 concentrations. From 1992 to 2015, the estimated average N〈sub〉2〈/sub〉O emissions from forests and grasslands were 3.62 ± 0.16 Tg N yr〈sup〉−1〈/sup〉 and 1.40 ± 0.03 Tg N yr〈sup〉−1〈/sup〉, respectively. Tropical regions made large contributions (83.9% for forests and 74% for grasslands) to the total N〈sub〉2〈/sub〉O budgets, which were due to the larger N〈sub〉2〈/sub〉O flux values and large natural forest and grassland areas. The regional variations in N〈sub〉2〈/sub〉O emissions mainly resulted from the differences in the spatial distributions of climate characteristics, especially the precipitation patterns. In addition, anomalous years when N〈sub〉2〈/sub〉O emissions were relatively low/high were mainly due to the changes in climate patterns, which may have been induced by El Niño/La Niña events with different strengths and frequencies. Soil N〈sub〉2〈/sub〉O emissions from forests showed a positive effect on the atmospheric N〈sub〉2〈/sub〉O concentrations during June to November (R〈sup〉2〈/sup〉: 0.14˜0.28), while those from grasslands showed a positive effect during the growing seasons (R〈sup〉2〈/sup〉: 0.17˜0.28). Although natural N〈sub〉2〈/sub〉O sources (forests and grasslands in this study) showed slightly increasing trends, with 9.9 Gg N increment per year for forests and 2.1 Gg N increment per year for grasslands, they were not the main contributors to the elevated N〈sub〉2〈/sub〉O concentrations.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 264〈/p〉 〈p〉Author(s): Yandong Wang, Xiaoli Liu, Guangxin Ren, Gaihe Yang, Yongzhong Feng〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Knowledge about drought variability in the main potato producing areas can provide a scientific basis for management of potato crops. In this study, the variations and patterns of drought in the potato growing period (GP), seedling stage (SS), tuber-growth stage (TS), and mature stage (MS) identified by the Standardized Precipitation Evapotranspiration Index (SPEI) were investigated in the north single cropping zone (NSCZ) in China for the period of 1960–2016 based on the empirical orthogonal function analysis, Mann–Kendall statistical test, Mann–Kendall test, Sen’s slope, Hurst exponent, and continuous wavelet transform. Additionally, grey theory was used to study the relationship between drought and potato production. The results of the study follow: 1) The spatiotemporal patterns of drought of the two leading patterns were identified. 2) Since the 1970s, the NSCZ has become drier in the GP and MS, has become wetter in the TS, but has always remained in an unstable state of alternating wet and dry conditions in the SS. 3) The changes in dryness/wetness conditions include significant periodic oscillation features. 4) The future drought trend is generally consistent with the current state. In addition, it is worth noting that the NSCZ as a whole will become drier in the MS. 5) The drought of SS and TS had a relatively large negative effect on potato production, whereas that of MS had a relatively small positive effect. Because the NSCZ is within the marginal region of the Asian monsoon and the agro-pastoral ecotone, it is an ecologically fragile region. Therefore, under the background of global climate change, studying changes in dryness/wetness conditions has important implications for the ecological security and potato production of the region.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 265〈/p〉 〈p〉Author(s): Bo Zhao, Jing Cao, Yan Geng, Xiuhai Zhao, Klaus von Gadow〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Understanding the responses of soil respiration (Rs) to thinning is essential to evaluate the effects of management practices on carbon cycling in plantation forest ecosystems. However, how Rs and its components (autotrophic, Ra and heterotrophic respiration, Rh) vary with thinning intensity and the underlying mechanisms are not well understood. In the present study we monitored Rs, Ra and Rh over five growing seasons using a trenching method in a 〈em〉Pinus tabuliformis〈/em〉 plantation subjected to four thinning treatments (no thinning, CK; light thinning, LT; moderate thinning, MT and heavy thinning, HT). On average, LT and MT significantly increased Rs by 13% and 17%, respectively, compared with the CK. These increments of Rs were ascribed to the enhanced Ra in LT and MT plots, because light and moderate thinning promoted root growth and productivity (higher fine root biomass). However, HT did not result in a further increase in Ra, suggesting that increases in the activity of remaining trees and understory plants did not compensate for the reduced photosynthesis and the amount of respiring tree roots by extensive tree-cut. In contrast to Ra, variation in Rh was unrelated to thinning, partly due to the stable forest floor mass (non-living organic materials such as litter and fine woody debris) and microbial biomass carbon content (MBC) between thinned and control plots. The temperature sensitivity (Q〈sub〉10〈/sub〉) of Ra and Rh ranged from 1.40 to 3.07 and 2.34–3.42, respectively. The highest Q〈sub〉10〈/sub〉 of Ra was observed in MT while that of Rh occurred in LT. Soil moisture was significantly correlated with Rh but a poor predictor for Ra. Our findings demonstrated that Ra and Rh responded to thinning intensity independently of each other. The intensity of management and plant-mediated biological processes are of particular importance in evaluating the impacts of forest management on C sequestration potential in plantation forests.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 265〈/p〉 〈p〉Author(s): Huiying Fan, Zhaowu Yu, Gaoyuan Yang, Tsz Yiu Liu, Tsz Ying Liu, Carmem Huang Hung, Henrik Vejre〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Urban areas typically experience higher temperatures compared to surrounding rural areas that is known as the urban heat island effect (UHI). Urban greenery is capable of mitigating the UHI by creating microclimates that are lower in temperature than their surroundings, which are known as urban cooling islands (UCI). Previous studies have proved the effectiveness of UCI from different perspectives. However, a specific optimal level of landscape patch size at a regional scale that can be implemented by urban planners has not been identified. In this study, we estimated the optimal patch size in seven selected hot-humid Asian cities with the help of Google Cloud Computing, Python Programming, as well as spatial and statistical analysis. A two-tier (two optimal patch sizes) distribution of the threshold value of efficiency (TVoE) of urban trees in this region was found. Eight landscape-level indexes were used to explore the variance of TVoE. The percentage of landscape (PLAND), edge density (ED), mean landscape shape index (Shape_MN), mean fractal dimension (FRAC_MN), largest patch index (LPI), and mean Euclidian nearest-neighbor distance (ENN_MN) were found to have no significant correlation with TVoE. While the average normalized difference vegetation index (NDVI_MN) and average background temperature (BGT_MN) were found to be highly associated with the variance in TVoE. Further, a concept model that can simulate the effects of NDVI_MN and BGT_MN was also proposed. These findings extend the understanding of the UCI effect of urban trees as well as providing a basis for scientific climate adaption planning in this region.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 265〈/p〉 〈p〉Author(s): Ziqiang Liu, Xinxiao Yu, Guodong Jia〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Extreme drought and precipitation are expected to occur more frequently due to climate change, which may influence the water uptake patterns by vegetation in the rocky mountainous area of northern China. In this work, dual stable isotopes were used to detect the water sources of mixed forest of coniferous and broad-leaved tree species and their response of leaf water potential under differently sized precipitation events (no rain: 0.0 mm; light rain: 9.8 mm; moderate rain: 21.8 mm; large rain: 31.6 mm and rainstorm: 51.2 mm). The results showed that 〈em〉Platycladus orientalis〈/em〉 and 〈em〉Quercus variabilis〈/em〉 had different water use strategies and opposite responses to precipitation. On dry (no rain) days, 〈em〉P. orientalis〈/em〉 and 〈em〉Q. variabilis〈/em〉 predominantly obtained water from natural springs (43.3% and 36.2%, respectively) and deep soil layer (32.8% and 31.3%, respectively), while 〈em〉Q. variabilis〈/em〉 also used water from shallow soil layer (23.4%). Following the rainfall events, the 〈em〉P. orientalis〈/em〉 with dense and shallow fine root system absorbed more water from the soil surface layers (23.1–33.5%) and precipitation (15.2–30.7%). The pre-dawn water potential (ψ〈sub〉pd〈/sub〉) and the midday water potential (ψ〈sub〉md〈/sub〉) of 〈em〉P. orientalis〈/em〉 increased with the amount of rainfall, revealing a sensitive response to precipitation. On the other hand, 〈em〉Q. variabilis〈/em〉 mostly took up water from natural springs (32.3–36.7%) and deep soil layer (33.8–37.1 %) after the rainfall events through its well-developed taproot system. The 〈em〉ψ〈/em〉〈sub〉pd〈/sub〉 and 〈em〉ψ〈/em〉〈sub〉md〈/sub〉 of 〈em〉Q. variabilis〈/em〉 had no significant variation between no rain and light rain events, though they increased significantly for large rainfall and rainstorm events with 〉 60 cm of soil water recharge provided by the precipitation. The study provides more insights into reforestation and water management in the region of northern China.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 265〈/p〉 〈p〉Author(s): Ayumi Kotani, Atsushi Saito, Alexander V. Kononov, Roman E. Petrov, Trofim C. Maximov, Yoshihiro Iijima, Takeshi Ohta〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉This study investigated the CO〈sub〉2〈/sub〉 exchange over a 10-year period (2005–2014) inside and above a larch-dominant forest in the central Lena river basin, eastern Siberia. A wet-soil condition, such as that found in the active layer (seasonally thawed soil layer of upper permafrost), containing unusually high soil water close to saturation and partial surface waterlogging, was prolonged during the warm season of 2005–2009. In later years, the soil layer closer to the ground surface became dry (∼10% volumetric water content), although the deeper part remained relatively wet (∼30%). We quantitatively compared the whole forest and the understory CO〈sub〉2〈/sub〉 exchanges to detect the separate effects of excessive soil waters on the overstory and understory vegetation. The conventional light and temperature response functions for half-hourly CO〈sub〉2〈/sub〉 fluxes, that is, the net ecosystem exchange of daytime and night-time, respectively, were applicable to the understory observations. Comparison of the fitting parameters of the light response function at two levels revealed a smaller maximum net ecosystem exchange (NEE) under light saturation with a steep response under weak light conditions for the understory. The CO〈sub〉2〈/sub〉 exchanges at the understory increased from the wet-soil period to the drying soil period by 46% (1.3 g C m〈sup〉−2〈/sup〉 d〈sup〉−1〈/sup〉) of gross primary production (GPP) and 29% (1.2 g C m〈sup〉−2〈/sup〉 d〈sup〉−1〈/sup〉) of ecosystem respiration (ER), while no trend was found in the ecosystem scale fluxes. These increases were due to an increasing understory biomass, changes in plentiful light and soil water in the inside-canopy environments, and enhanced turbulent mixing. The decline in the larch contribution could be compensated for by the understory growth and the remaining wetness of the active layer, which indicated that the interactions between the larch and the understory supported the stability of carbon cycles in this forest ecosystem.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 265〈/p〉 〈p〉Author(s): Xi Li, Pierre Gentine, Changjie Lin, Sha Zhou, Zan Sun, Yi Zheng, Jie Liu, Chunmiao Zheng〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Separating evapotranspiration (〈em〉ET〈/em〉) into evaporation (〈em〉E〈/em〉) and transpiration (〈em〉T〈/em〉) is challenging but key for a better understanding and prediction of the hydrological cycle and plant water use. In this study, flux data at 30 routine eddy-covariance sites were used to develop a new and simple method for 〈em〉ET〈/em〉 partitioning based on the separation of soil and canopy conductances, with the main assumption that the latter is proportional to gross primary productivity (GPP). The result of 〈em〉T:ET〈/em〉 across different plant functional types (PFTs) was consistent with recent modeling or empirical results. The mean annual 〈em〉T:ET〈/em〉 was highest for evergreen needleleaf forests (0.75 ± 0.17), followed by croplands (0.62 ± 0.16) and grasslands (0.56 ± 0.15). The leaf area index (LAI) was shown to explain only small (20%) variations of mean annual 〈em〉T:ET〈/em〉 across sites. However, at each site, the correlation of 〈em〉T:ET〈/em〉 with LAI was strong at the seasonal scale, where 〈em〉T:ET〈/em〉 increased nonlinearly with LAI. The results did not show significant relationship of 〈em〉T:ET〈/em〉 with long-term mean precipitation across sites at multiyear timescales. However, the partitioned soil evaporation after each precipitation pulse is consistent with three-stage soil evaporation theory. This 〈em〉ET〈/em〉 partitioning method is an objective assessment as it is mainly data-driven. The procedure to apply this method is also simple so it can be readily applied to global flux tower networks at different temporal and spatial scales, enabling continuous estimation of 〈em〉T:ET〈/em〉 to monitor ecosystem dynamics and hydrological responses to environmental change.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 265〈/p〉 〈p〉Author(s): A. Klosterhalfen, A.F. Moene, M. Schmidt, T.M. Scanlon, H. Vereecken, A. Graf〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉Scanlon and Sahu (2008) and Scanlon and Kustas (2010) proposed a source partitioning method (SK10 in the following) to estimate contributions of transpiration, evaporation, photosynthesis, and respiration to H〈sub〉2〈/sub〉O and CO〈sub〉2〈/sub〉 fluxes obtained by the eddy covariance method. High frequency eddy covariance raw data time series are needed, and the source partitioning is estimated based on separate application of the flux-variance similarity theory to stomatal and non-stomatal components of the regarded fluxes, as well as on additional assumptions on leaf-level water use efficiency (WUE).〈/p〉 〈p〉We applied SK10 to data from two test sites (forest and cropland) and analyzed partitioning results depending on various ways to estimate WUE from available data. Also, we conducted large eddy simulations (LES), simulating the turbulent transport of H〈sub〉2〈/sub〉O and CO〈sub〉2〈/sub〉 for contrasting vertical distributions of the canopy sinks/sources, as well as for varying relative magnitudes of soil sources and canopy sinks/sources. SK10 was applied to the synthetic high frequency data generated by LES and the effects of canopy type, measurement height, given sink-source-distributions, and input of varying WUEs were tested regarding the partitioning performance. SK10 requires that the correlation coefficient between stomatal and non-stomatal scalar fluctuations is determined by the ratio of the transfer efficiencies of these scalar components, an assumption (transfer assumption in the following) that could be tested with the generated LES data.〈/p〉 〈p〉The partitioning results of the field sites yielded satisfactory flux fractions, when fair-weather conditions (no precipitation) and a high productive state of the vegetation were present. Further, partitioning performance with regard to soil fluxes increased with crop maturity. Results also showed relatively large dependencies on WUE, where the partitioning factors (median) changed by around -57% and +36%. Measurements of outgoing longwave radiation used for the estimation of foliage temperature and WUE could slightly increase the plausibility of the partitioning results in comparison to soil respiration measurements by decreasing the partitioning factor by up to 42%. The LES-based analysis revealed that for a satisfying performance of SK10, a certain degree of decorrelation of the H〈sub〉2〈/sub〉O and CO〈sub〉2〈/sub〉 fluctuations (here, |〈em〉ρ〈sub〉q’c’〈/sub〉〈/em〉| 〈 0.975) was needed. This decorrelation is enhanced by a clear separation between soil sources and canopy sinks/sources, and for observations within the roughness sublayer. The expected dependence of the partitioning results on the WUE input could be observed. However, due to violation of the abovementioned transfer assumption, the known true input WUE did not yield the known true input partitioning. This could only be achieved after introducing correction factors for the transfer assumption, which were known however only in the special case of the LES experiments.〈/p〉 〈/div〉

Description: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 265〈/p〉 〈p〉Author(s): Lars Dietrich, Ansgar Kahmen〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Decreasing amounts of precipitation and more frequent dry periods will challenge temperate European forests in the future. During such dry periods, short drought-intermitting rainfall events might be the only renewing water source for trees. We investigated the effects of short drought-intermitting rainfall events on the water relations of mature individuals of six different tree species in a near-natural temperate forest during the exceptionally dry summer of 2015. We found the trees to strongly respond to short drought-intermitting rainfall events: maximum daily sap flow recovered already at precipitation amounts of 1.5 mm by up to 20%, and tree water deficit (TWD) and midday shoot water potential (Ψ〈sub〉midday〈/sub〉) improved by up to 60% from rainfall amounts of 〉4.5 mm. We speculate that a mix of foliar and root water uptake as well as relaxation of canopy VPD and thus stomatal water control lead to the observed recoveries. Hydraulic conductivity was found to partly explain the differences in TWD recovery among species. Duration of the rainfall-facilitated recovery of tree water relations was on average 3 days in the coniferous species and 〈em〉Q. petraea〈/em〉 but distinctly longer in 〈em〉C. betulus〈/em〉 and 〈em〉F. sylvatica〈/em〉 for which it reached 9 days. These results show that drought-intermitting short rainfall events strongly facilitate the relaxation of water stress in temperate tree species during drought events and possibly contribute as such to the ability of temperate trees to withstand longer periods of drought.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 264〈/p〉 〈p〉Author(s): Weiwei Li, Qianlai Zhuang, Wei Wu, Xiaoxia Wen, Juan Han, Yuncheng Liao〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Ridge–furrow mulching system (RFMS) is widely used in arid and semi–arid areas, but its effect on soil respiration (R〈sub〉s〈/sub〉) and its components, including heterotrophic (R〈sub〉h〈/sub〉) and autotrophic respiration (R〈sub〉a〈/sub〉) are still poorly understood. In this study, CO〈sub〉2〈/sub〉 flux from the soil of furrows and ridges was measured across different RFMS practices (i.e., three different ridge/furrow ratios) and conventional flat planting (CK). A trenching method was used to estimate the contribution of R〈sub〉h〈/sub〉 to R〈sub〉s〈/sub〉. Compared with CK, RFMS significantly increased soil temperature of the ridge, promoted soil moisture of the furrow, and enhanced microbial diversity at the early crop growth stage, resulting in increased R〈sub〉s〈/sub〉 and its components. The ridge soils exhibited much higher R〈sub〉s〈/sub〉 (3.43 μmol m〈sup〉–2〈/sup〉 s〈sup〉–1〈/sup〉) than the furrow soils (2.98 μmol m〈sup〉–2〈/sup〉 s〈sup〉–1〈/sup〉) under all three RFMS practices. The contribution ratios of R〈sub〉h〈/sub〉 to R〈sub〉s〈/sub〉 across the different practices ranged from 50.4% to 59.6%. Soil temperature rather than soil moisture explained the seasonal variation of R〈sub〉s〈/sub〉 and its components for both CK and RFMS. Nonetheless, high R〈sub〉s〈/sub〉 and R〈sub〉h〈/sub〉 values in RFMS did not induce a decline of soil organic carbon during the two–year experimental period. Improved root growth in RFMS practices may provide more exudates to the soil, thus offsetting soil carbon decomposition. Compared with CK, RFMS with ridge/furrow ratios of 40:70 cm, 55:55 cm, and 70:40 cm, significantly increased soil CO〈sub〉2〈/sub〉 emissions by 10.6%, 19.6%, and 20.4%, respectively, while increasing maize yield by 26.1%, 36.4%, and 50.3%, respectively. Carbon emission efficiency (CEE) was significantly higher in RFMS than in CK in both years. This study suggests that, due to its high CEE, RFMS with a ridge/furrow ratio of 70:40 cm could be a highly promising strategy for sustaining crop productivity while minimizing environmental impacts.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 264〈/p〉 〈p〉Author(s): Marcos Rodrigues, José Carlos González-Hidalgo, Dhais Peña-Angulo, Adrián Jiménez-Ruano〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉In this paper we present a detailed spatial assessment of the association between atmospheric synoptic conditions (the weather types, WT) and fires on the Spanish mainland. The WT approach allows the continuum of atmospheric fields to be compressed into a few comprehensive patterns, providing meaningful information on the movement of air masses, wind direction and, ultimately, wind speed. We analyzed a total of 291,547 individual fires from the official Spanish Fire database (1974–2014) and corresponding daily WT patterns on the Iberian Peninsula from the daily NCEP/NCAR Reanalysis database, 1951–2015. Underlying spatial patterns of association among fire and weather types were explored by means of self-organizing maps (SOM) coupled to hierarchical clustering.〈/p〉 〈p〉Our analyses have detected that fires tend to occur and become largermore likely under certain atmospheric conditions suggesting that specific weather patterns can promote or boost fire events. From a pyrogeographical point of view, the contribution of WTs to wildfires on the Spanish mainland seems to be highly diverse, and displays several temporal and spatial patterns. The northwest region responds mostly to eastern flows during summer and southern during winter. Fires in the northern Mediterranean coast are promoted by northerly flows while in southern regions fires are linked to C or SE extreme heat episodes during summer. Overall, fires activity usually increases in the lee ward of mountain ranges depending on the prevalent flow from WTs, and thus related to adiabatic heating of the air flow.〈/p〉 〈/div〉

Description: 〈p〉Publication date: 15 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 264〈/p〉 〈p〉Author(s): Daniel L. Warner, Mario Guevara, Shreeram Inamdar, Rodrigo Vargas〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Upscaling soil-atmosphere greenhouse gas (GHG) fluxes across complex landscapes is a major challenge for environmental scientists and land managers. This study employs a quantile-based digital soil mapping approach for estimating the spatially continuous distributions (2 m spatial resolution) and uncertainties of seasonal mean mid-day soil CO〈sub〉2〈/sub〉 and CH〈sub〉4〈/sub〉 fluxes. This framework was parameterized using manual chamber measurements collected over two years within a temperate forested headwater watershed. Model accuracy was highest for early (r〈sup〉2〈/sup〉 = 0.61) and late summer (r〈sup〉2〈/sup〉 = 0.64) for CO〈sub〉2〈/sub〉 and CH〈sub〉4〈/sub〉 fluxes. Model uncertainty was generally lower for predicted CO〈sub〉2〈/sub〉 fluxes than CH〈sub〉4〈/sub〉 fluxes. Within the study area, predicted seasonal mean CO〈sub〉2〈/sub〉 fluxes ranged from 0.17 to 0.58 μmol m〈sup〉−2〈/sup〉 s〈sup〉−1〈/sup〉 in winter, and 1.4 to 5.1 μmol m〈sup〉−2〈/sup〉 s〈sup〉−1〈/sup〉 in early summer. Predicted CH〈sub〉4〈/sub〉 fluxes across the study area ranged from −0.52 to 0.02 nmol m〈sup〉−2〈/sup〉 s〈sup〉−1〈/sup〉 in winter, and −2.1 to 0.61 nmol m〈sup〉−2〈/sup〉 s〈sup〉−1〈/sup〉 in early and late summer. The models estimated a per hectare net GHG potential ranging from 0.44 to 4.7 kg CO〈sub〉2〈/sub〉 eq. hr〈sup〉−1〈/sup〉 in winter and early summer, with an estimated 0.4 to 1.5% of emissions offset by CH〈sub〉4〈/sub〉 uptake. Flux predictions fell within ranges reported in other temperate forest systems. Soil CO〈sub〉2〈/sub〉 fluxes were more sensitive to seasonal temperature changes than CH〈sub〉4〈/sub〉 fluxes, with significant temperature relationships for soil CO〈sub〉2〈/sub〉 emissions and CH〈sub〉4〈/sub〉 uptake in pixels with high slope angles. In contrast, soil CH〈sub〉4〈/sub〉 fluxes from flat low-lying areas near the stream network within the watershed were significantly correlated to seasonal precipitation. This study identified key challenges for modeling high spatial resolution soil CO〈sub〉2〈/sub〉 and CH〈sub〉4〈/sub〉 fluxes, and suggests a larger spatial heterogeneity and complexity of underlying processes that govern CH〈sub〉4〈/sub〉 fluxes.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 264〈/p〉 〈p〉Author(s): Xiaojing Chu, Guangxuan Han, Qinghui Xing, Jianyang Xia, Baoyu Sun, Xinge Li, Junbao Yu, Dejun Li, Weimin Song〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Changes in the timing and magnitude of precipitation is a threat to agricultural productivity and farmland carbon stocks. However, the relationship between inter-annual variations in precipitation and net ecosystem CO〈sub〉2〈/sub〉 exchange (NEE) remains to be clarified, particularly when combined with water-salt transport in reclaimed coastal wetland. Here, based on the eddy-covariance technique, we investigated the interannual variation in carbon dioxide exchange and its control mechanism over a reclaimed coastal wetland of the Yellow River Delta from 2010 to 2014. The coastal wetland functioned as a strong sink for atmospheric CO〈sub〉2〈/sub〉, with the annual NEE of −229, −175, −142, −92 and −80 g C m〈sup〉−2〈/sup〉 in the 5 years from 2010 to 2014, respectively. Surprisingly, we find that large annual variation in net ecosystem exchange (NEE) can be predicted accurately using plant biomass. Plant biomass was driven by soil water content (SWC), with about 48%–80% seasonal variation of biomass attributed to SWC. During the early growing stage, high SWC accompanied with low salinity promoted plant biomass and NEE. While high SWC accompanied with increased waterlogged stress inhibited plant biomass and NEE during the middle growing stage. The same results were also observed in a field manipulation experiment over a nearby natural coastal wetland. Our study indicated that extreme climate accompanied with extreme drought and flooding may decrease carbon sequestration capacity of the reclaimed coastal wetland due to the increase in salinity.〈/p〉〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0168192318303083-ga1.jpg" width="228" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 264〈/p〉 〈p〉Author(s): Andrew J. Nelson, Nebila Lichiheb, Sotiria Koloutsou-Vakakis, Mark J. Rood, Mark Heuer, LaToya Myles, Eva Joo, Jesse Miller, Carl Bernacchi〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Studies of NH〈sub〉3〈/sub〉 flux over agricultural ecosystems in the USA are limited by low temporal resolution (typically hours or days) and sparse spatial coverage, with no studies over corn in the Midwest USA. We report on NH〈sub〉3〈/sub〉 flux measurements over a corn canopy in Central Illinois, USA, using the relaxed eddy accumulation (REA) and flux gradient (FG) methods, providing measurements at 4 h and 0.5 h intervals, respectively. The REA and FG systems were operated for the duration of the 2014 corn-growing season. Flux-footprint analysis was used to select data from both systems, resulting in 82 concurrent measurements. Mean NH〈sub〉3〈/sub〉 flux of concurrent measurements was 205 ± 300 ng m〈sup〉−2〈/sup〉 s〈sup〉−1〈/sup〉 from REA and 110 ± 256 ng m〈sup〉−2〈/sup〉 s〈sup〉−1〈/sup〉 from FG for all concurrent samples. Results from both methods were not significantly different at a 95% confidence level for all concurrent measurements. The FG system resolved NH〈sub〉3〈/sub〉 emission peaks at 0.5 h averaging time that were otherwise un-observed with 4 h REA averaging. Two early-season peak emission periods were identified (DOY 130-132 and 140-143), where the timing and intensity of such emissions were attributed to a combination of urease inhibitor, applied as a field-management decision, and localized soil temperature and precipitation. Given the dependence of NH〈sub〉3〈/sub〉 fluxes on multiple parameters, this study further highlights the need for increased spatial coverage and high temporal resolution (〈em〉e.g.,〈/em〉 〈1 h) of measurements to better understand the impact of agricultural NH〈sub〉3〈/sub〉 emissions on air quality and the global nitrogen cycle. Such measurements are also needed for evaluation of models describing surface-atmosphere exchange of NH〈sub〉3〈/sub〉.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 264〈/p〉 〈p〉Author(s): Tongtiegang Zhao, Quan J. Wang, Andrew Schepen, Morwenna Griffiths〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Long-range forecasts of climatic variables are generated by climate centres around the world using global climate models (GCMs). This paper investigates ensemble forecasting of reference crop evapotranspiration (ETo) based on GCM outputs. The Penman-Monteith formula is used to calculate raw forecasts of ETo from GCM forecasts of solar radiation, temperature, wind speed, and vapor pressure. The Bayesian joint probability (BJP) modelling approach is applied to post-process raw monthly forecasts, separately for different lead times (month 1, 2 and 3 ahead). The Schaake shuffle is then employed to link the ensemble members of post-processed forecasts for all lead times to give a temporal structure. Forecasts of seasonal ETo total are obtained by aggregating the monthly forecasts. For comparison purposes, seasonal forecasts are also derived directly by post-processing raw seasonal forecasts without going through the monthly steps. Three case studies are presented for post-processing forecasts from the Australian Community Climate and Earth System Simulator-Seasonal (ACCESS-S1). Both raw forecasts and observations of monthly and seasonal ETo are found to be reasonably normally distributed. The post-processed forecasts of monthly and seasonal ETo are skilful in reference to climatology forecasts and statistically reliable in ensemble spread. The indirect and direct ways of generating forecasts of seasonal ETo total show similar skill and reliability, demonstrating the effectiveness of the Schaake shuffle. In this paper, the proposed post-processing method is evaluated through leave-one-out cross validation. The method can be easily adapted for post-processing raw GCM forecasts in real-time to produce ensemble forecasts of monthly and seasonal ETo.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 264〈/p〉 〈p〉Author(s): Nan Di, Ye Wang, Brent Clothier, Yang Liu, Liming Jia, Benye Xi, Haixiang Shi〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In order to improve water management in 〈em〉Populus tomentosa〈/em〉 plantations, the variation in the FAO-56 parameters of the basal crop coefficient (〈em〉K〈/em〉〈sub〉cb〈/sub〉) and soil evaporation (〈em〉E〈/em〉〈sub〉s〈/sub〉) in mature 〈em〉P〈/em〉. 〈em〉tomentosa〈/em〉 plantations under different soil water availability treatments were investigated over two growing seasons. Empirical models for predicting 〈em〉E〈/em〉〈sub〉s〈/sub〉 in well-watered drip irrigated stands were constructed and validated. Changes in the relationship between 〈em〉K〈/em〉〈sub〉cb〈/sub〉 and leaf area index (LAI) during the growing seasons and differing soil water availabilities, were also studied. The 〈em〉K〈/em〉〈sub〉cb〈/sub〉 in all treatments increased rapidly to its maximum in about mid-May, and then decreased and remained relatively constant until late August or September. The 〈em〉K〈/em〉〈sub〉cb〈/sub〉 increased sharply with increasing LAI, but plateaued when the LAI reached a critical value. With increasing stand age, the limit of 〈em〉K〈/em〉〈sub〉cb〈/sub〉 of all treatments increased, while the critical values of the LAI declined markedly. In contrast, these two values declined with decreasing soil water availability, but the difference in 〈em〉K〈/em〉〈sub〉cb〈/sub〉 limit could disappear with increasing stand age. Distinct spatial heterogeneity in 〈em〉E〈/em〉〈sub〉s〈/sub〉 appeared only from April to June, during which the 〈em〉E〈/em〉〈sub〉s〈/sub〉 from the wet soil zone accounted for 66% of the total 〈em〉E〈/em〉〈sub〉s〈/sub〉 on average. Among the five empirical models, the L〈sub〉-ww〈/sub〉 (constructed model based on LAI data during the “well-watered” period) and LT〈sub〉-ww〈/sub〉 (constructed model based on data of LAI multiplied by soil temperature at 20 cm depth during the “well-watered” period) models had the lowest 〈em〉E〈/em〉〈sub〉s〈/sub〉 prediction errors (RMSE of 0.25 and 0.20 mm d〈sup〉−1〈/sup〉), and the highest modelling efficiency (0.49 and 0.63) and index of agreement (0.84 and 0.88) for the “whole year” and “well-watered” periods, respectively. In conclusion, for predicting stand transpiration more accurately using a crop coefficient model, the quantitative relationship between LAI and 〈em〉K〈/em〉〈sub〉cb〈/sub〉 needs to be adjusted for stand age and soil water availability. Spatial heterogeneity in 〈em〉E〈/em〉〈sub〉s〈/sub〉 should be considered when estimating 〈em〉E〈/em〉〈sub〉s〈/sub〉 in drip irrigated plantations of 〈em〉P. tomentosa〈/em〉 and other tree species.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 264〈/p〉 〈p〉Author(s): Anne-Frédérique Gendron St-Marseille, Gaétan Bourgeois, Jacques Brodeur, Benjamin Mimee〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Climate change will undoubtedly impact air and soil temperature in the future. For agriculture, climate warming could be beneficial by opening new lands to profitable crops at higher latitudes. In Canada, soybean production has had a spectacular growth over the last five years with an increase of 27% in the acreage devoted to its cultivation. However, the anticipated climatic changes, coupled with global trading intensification could also favor the introduction and establishment of invasive alien soybean pests. For example, the soybean cyst nematode (SCN) has recently been discovered in the province of Québec, Canada and its presence raised several questions on its reproductive potential, spatial distribution and possible impacts on long term soybean cultivation. To investigate the consequences of climate warming on soybean and SCN development and distribution, and their interactions, two phenology models have been developed and used with the Representative Concentration Pathways (RCP) 4.5 and 8.5, associated with climate change scenarios. These pathways describe two possible future climates based on the level of greenhouse gases concentration in air. Using temperature optimum for soybean maturity group I, our results showed that soybean could be cultivated over all cropland of Québec by the 2050 horizon (2041–2070). Based on phenology models, SCN can currently complete from one to three generations in the different regions of Québec. In the future, the nematode could produce up to four or five generations in an optimistic (RCP 4.5) or pessimistic (RCP 8.5) scenario, respectively. Climate warming will promote the expansion of soybean production to northern areas and expected conditions will be more favourable to SCN development. Accordingly, we should develop more soybean lines with an early maturity and containing other sources of resistance than PI88788 to reduce its reproduction capacity under a more favourable climate in the future.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 264〈/p〉 〈p〉Author(s): Jongmin Kim, Youngryel Ryu, Chongya Jiang, Yorum Hwang〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Continuous monitoring of vegetation indices (VIs) the fraction of absorbed photosynthetically active radiation (fPAR) and leaf area index (LAI) through satellite remote sensing has advanced our understanding of biosphere–atmosphere interactions. Substantial efforts have been put into monitoring individual variables in the field, but options to concurrently monitor VIs, fPAR, and LAI in-situ have been lacking. In this paper, we present the Smart Surface Sensing System (4S), which automatically collects, transfers and processes VIs, fPAR and LAI data streams. The 4S consists of a microcomputer, controller and camera, a multi-spectral spectrometer built in with a light-emitting diode (LED) and an internet connection. Lab testing and field observations in a rice paddy site that experiences wet summer monsoon seasons confirmed the linear response of 4S to light intensities in the blue, green, red and near-infrared spectral channels, with wide ranging temperatures and humidity having only a minor impact on 4S throughout the growing season. Applied over an entire rice growing season (day of year [DOY] 120 - 248), VIs and fPAR from 4S were linearly related to corresponding VIs from a reference spectrometer (R〈sup〉2〈/sup〉 = 0.98; NDVI, R〈sup〉2〈/sup〉 = 0.96; EVI) and the LAI-2200 instrument (R〈sup〉2〈/sup〉 = 0.76), respectively. Integration of gap fraction-based LAI from LED sensors and a green index from the micro-camera allowed tracking of the seasonality of green LAI. The continuous and diverse nature of 4S observations highlights its potential for evaluating satellite remote sensing products. We believe that 4S will be useful for the expansion of ecological sensing networks across multiple spatial and temporal scales.〈/p〉〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0168192318303095-ga1.jpg" width="199" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 264〈/p〉 〈p〉Author(s): Birgitta Putzenlechner, Philip Marzahn, Ralf Kiese, Ralf Ludwig, Arturo Sanchez-Azofeifa〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉The estimation of the Fraction of Absorbed Active Radiation (FAPAR) and its uncertainties is key for understanding global carbon balances. This work investigates the variability and associated uncertainties of in-situ two-flux FAPAR observations attributed to changes in phenological and meteorological conditions. Specifically, we assessed influences of illumination conditions with solar zenith angle and the ratio of diffuse-to-total incident radiation, wind speed, leaf color and snow coverage on the variability of two-flux FAPAR. We assumed FAPAR acquired under diffuse light conditions to be closest to “true” FAPAR as it is not influenced by the solar zenith angle. To reveal the uncertainty of the two-flux FAPAR measurements, we investigated the difference (Δ〈sub〉two-flux〈/sub〉) between FAPAR acquired under diffuse light conditions and two-flux FAPAR acquired during a certain environmental condition (e.g. large solar zenith angle). A positive (negative) value obtained from this difference was interpreted as an indication for an underestimation (overestimation) of “true” FAPAR by the two-flux FAPAR estimate, as found in previously investigations with canopy radiative transfer models (RTM).〈/p〉 〈p〉Therefore, permanent PAR measurements were carried out 2015–2017 in a sub-alpine, spruce-dominated forest in Southern Germany using a Wireless Sensor Network (WSN). FAPAR observations exhibited considerable seasonal variability (0.89 to 0.99 ± 0.03) despite the dominance of evergreen spruces. The in-situ observations confirm significant overestimation of FAPAR by up to 0.06 under solar zenith angles above 60° and by up to 0.05 during the presence of colored autumn leaves, similarly to the results obtained from previous studies with canopy RTMs. Additionally, our results indicate an effect of wind speed which we consider crucial at sites where high wind speeds occur more frequently. Overall, this study shows the potential of permanent WSN monitoring activities to ensure multi-year FAPAR observations with associated uncertainty information that are demanded to validate satellite-derived FAPAR products in forest ecosystems.〈/p〉 〈/div〉

Description: 〈p〉Publication date: 15 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 264〈/p〉 〈p〉Author(s): Martin Krůček, Jan Trochta, Miloš Cibulka, Kamil Král〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉There are many indications that for a true understanding of aboveground canopy competition, the concept of symmetric trees is oversimplified and unsatisfactory; in spite of that, this concept is still commonly used in forest ecology research. In this study we analyzed and quantified the effect of tree/crown asymmetry on crown-to-crown interactions and canopy light availability with respect to tree size and species.〈/p〉 〈p〉Geometric crown models were used to represent the concept of symmetric trees, while data from terrestrial laser scanning were employed to constitute real crown shapes, positions and mutual crown-to-crown interactions. We developed an original approach for measuring three-dimensional crown asymmetry, separating the effect of positional crown shift and local crown plasticity, and analyzed their effect in aboveground competition for space and light.〈/p〉 〈p〉In comparison with reality, the models neglecting tree asymmetry were only poor predictors of trees mutually competing for space. Geometric models taking the positional crown shift into account were good predictors of ‘space competitors’ for Norway spruce, but were still insufficient for European beech. This is because for spruce crown shifting seems to be the major neighbor avoidance strategy, while beech in addition exhibited high local crown shape plasticity. Additionally, of the two species beech showed overall greater crown plasticity, which (in contrast to spruce) decreased only slowly with increasing tree size.〈/p〉 〈p〉Importantly, the concept of symmetric trees significantly underestimates the potential canopy light availability (and thus overestimates canopy competition for light), because asymmetric and the plastic ‘puzzle-like’ arrangement of real tree crowns is more effective than assumed symmetric organization. This most likely inserts a systematic bias into stand growth simulators that are based on the concept of symmetric trees.〈/p〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0168192318303113-ga1.jpg" width="498" alt="Graphical abstract for this article" title=""〉〈/figure〉〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 263〈/p〉 〈p〉Author(s): J.H.N. Palma, R.M. Cardoso, P.M.M. Soares, T.S. Oliveira, M. Tomé〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉Forest management decisions often rely on forest growth process based models. These models require climate data at a time-scale and a time-frame that is frequently not available in the area of interest. With the purpose of evaluating the use of modelled climate as a replacement for observational data, we compared the performance (efficiency, precision and bias) of a forest growth process based model (3-PG) when the inputs of the observational climate data were replaced by modelled climate data. Based on previous research, we focused on two promising regional climate models: 1) the Regional Atmospheric Climate Model (RACMO) and 2) the Weather Research and Forecast Modelling System and Program (WRF).〈/p〉 〈p〉Results suggest that when using simulated climate data there are minor losses of performance in the forest growth model predictions with a general growth overestimation, with RACMO providing the best results. A deeper analysis suggests that improving the temperature accuracy of the model will reduce the overestimation of the predictions.〈/p〉 〈p〉The use of simulated climate data with RACMO and WRF is therefore recommended when observed climate is scarce or inexistent. The use of these datasets can certainly widen the usage of forest growth process based models, improving the support for decision-making in forest management, especially when considering climate change, one of the cornerstones for which modelled climate is developed.〈/p〉 〈/div〉

Description: 〈p〉Publication date: 15 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 264〈/p〉 〈p〉Author(s): Samuel Eze, Sheila M. Palmer, Pippa J. Chapman〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Hoffmann et al. suspected a likely overestimation of carbon (C) sink reported in our paper (Eze et al., 2018) entitled “Upland grasslands in Northern England were atmospheric carbon sinks regardless of management regime”. They attributed this to potential sources of error associated with the estimation of C fluxes from closed-chamber measurements. We have explained why we think that the C sink reported in our paper was not overestimated as suspected by Hoffmann et al. However, we acknowledge the potential for error due to unavoidable operational and data limitations.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 263〈/p〉 〈p〉Author(s): Pierre-Erik Isabelle, Daniel F. Nadeau, Marie-Hélène Asselin, Richard Harvey, Keith N. Musselman, Alain N. Rousseau, François Anctil〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Forest canopies act as permeable barriers between the atmosphere and the ground, reflecting and absorbing solar radiation. In the boreal forest, the large number of gaps and heterogeneities further complicates these processes. Several studies have adequately measured and modeled the transmittance of solar radiation through forest canopies in western North America and Scandinavia, but few have addressed those of Eastern North America. Furthermore, most of these studies have assessed the effects of solar radiation transmittance on snowpack energetics, but few have focused on the hydrological impacts during the growing season. This paper addresses this knowledge gap with precise measurements of sub-canopy solar radiation in a juvenile balsam fir forest located in the Montmorency Forest, Quebec, Canada. Twenty (20) sub-canopy stations were deployed in a 200 m by 150 m gridded box around a flux tower measuring above canopy radiation and eddy covariance fluxes during late summer and early fall 2016. Results show that the heterogeneous forest has substantial spatial variability of transmittance, with site-specific seasonal averages ranging between 0.07 and 0.69. Canopy gaps of size relative to tree height (〈em〉H〈/em〉) between 0.1〈em〉H〈/em〉 and 〈em〉H〈/em〉 had a temporal influence on solar radiation transmittance in canopy gaps at the sub-daily scale, but do not influence seasonal trends. This is attributed to very frequent cloudiness at the site, which renders the solar radiation mostly diffuse. As a result, a Beer-Lambert extinction law proved adequate at modeling site-specific or spatially averaged transmittance on a seasonal basis. We complement the observations by modeling canopy and soil moisture balances at 20 sites using the Canadian Land Surface Scheme (CLASS). The modeling results exhibit the following trend: a thicker (thinner) vegetation leads to more (less) evapotranspiration, because there is more (less) evaporation of intercepted precipitation and more (less) transpiration, but less (more) ground evaporation. During drier periods, the latter leads to wetter soil conditions for the thicker vegetation. These modeling results of sensitivity to vegetation density, while informative, still need to be confirmed with observations.〈/p〉〈/div〉

Description: 〈p〉Publication date: 15 December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 263〈/p〉 〈p〉Author(s): 〈/p〉

Description: 〈p〉Publication date: 15 December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Agricultural and Forest Meteorology, Volume 263〈/p〉 〈p〉Author(s): Yiming Chen, Wuming Zhang, Ronghai Hu, Jianbo Qi, Jie Shao, Dan Li, Peng Wan, Chen Qiao, Aojie Shen, Guangjian Yan〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Terrestrial Laser Scanning (TLS) is an active technology that can acquire the finest characteristics of canopy structure and plays an increasing role in estimating Leaf Area Index (LAI) in forest canopies. However, 3D information is not directly used in conventional TLS-based methods using the gap fraction theory. In addition, quantifying clumping effect within canopies is still a difficult task. In this paper, we presented a method to reduce clumping effect and estimate LAI using TLS data. Our recently proposed path length distribution model was applied to TLS data. Instead of converting 3D points to 2D image, the path length distribution can be extracted using the TLS-recorded 3D data and the crown models built with the alpha shapes algorithm. Two simulated scenes and one actual forest plot were utilized for validation. The results of the proposed method agree well with both the true LAI (in the simulated scenes) and the extracted PAI by the digital hemispherical photography (in the actual plot). This LAI estimation method using TLS and the path length distribution model provides a novel way for ground-based LAI measurements and shows its great potential.〈/p〉〈/div〉