ALBERT

Description: It has been argued that scale is the central problem in ecology ( Levin, 1992 ). Studies on carbon cycles and global climate change, the current major themes in modern ecology, require the interfacing of phenomena that occur on different scales of space, time, and ecological organization. For several decades, tremendous efforts have been made to reveal the general patterns of, and the mechanisms for the global carbon cycles. However, many uncertainties remain, particularly on local to regional scales. To reduce these uncertainties, regional collaborations across the board of nations are required.

Description: Aims Boreal forest is the largest and contains the most soil carbon among global terrestrial biomes. Soil respiration during the prolonged winter period may play an important role in the carbon cycles in boreal forests. This study aims to explore the characteristics of winter soil respiration in the boreal forest and to show how it is regulated by environmental factors, such as soil temperature, soil moisture and snowpack. Methods Soil respiration in an old-growth larch forest ( Larix gmelinii Ruppr.) in Northeast China was intensively measured during the winter soil-freezing process in 2011 using an automated soil CO 2 flux system. The effects of soil temperature, soil moisture and thin snowpack on soil respiration and its temperature sensitivity were investigated. Important Findings Total soil respiration and heterotrophic respiration both showed a declining trend during the observation period, and no significant difference was found between soil respiration and heterotrophic respiration until the snowpack exceeded 20cm. Soil respiration was exponentially correlated with soil temperature and its temperature sensitivity (Q 10 value) for the entire measurement duration was 10.5. Snow depth and soil moisture both showed positive effects on the temperature sensitivity of soil respiration. Based on the change in the Q 10 value, we proposed a ‘freeze–thaw critical point’ hypothesis, which states that the Q 10 value above freeze–thaw critical point is much higher than that below it (16.0 vs . 3.5), and this was probably regulated by the abrupt change in soil water availability during the soil-freezing process. Our findings suggest interactive effects of multiple environmental factors on winter soil respiration and recommend adopting the freeze–thaw critical point to model soil respiration in a changing winter climate.

Description: Aims Clear-cutting is a common forest management practice, especially in subtropical China. However, the potential ecological consequences of clear-cutting remain unclear. In particular, the effect of clear-cutting on soil processes, such as the carbon cycle, has not been quantified in subtropical forests. Here, we investigated the response of soil respiration (Rs) to clear-cutting during a 12-month period in a subtropical forest in eastern China. Methods We randomly selected four clear-cut (CC) plots and four corresponding undisturbed forest (UF) plots. Measurements of Rs were made at monthly time points and were combined with continuous climatic measurements in both CC and UF. Daily Rs was estimated by interpolating data with an exponential model dependent on soil temperature. Daily Rs was cumulated to annual Rs estimates. Important Findings In the first year after clear-cutting, annual estimates of Rs in CC (508±23g C m –2 yr –1 ) showed no significant difference to UF plots (480±12g C m –2 yr –1 ). During the summer, soil temperatures were usually higher, whereas the soil volumetric water content was lower in CC than in UF plots. The long-term effects of clear-cutting on Rs are not significant, although there might be effects during the first several months after clear-cutting. Compared with previous work, this pattern was more pronounced in our subtropical forest than in the temperate and boreal forests that have been studied by others. With aboveground residuals off-site after clear-cutting, our results indicate that the stimulation of increasing root debris, as well as environmental changes, will not lead to a significant increase in Rs. In addition, long-term Rs will not show a significant decrease from the termination of root respiration, and this observation might be because of the influence of fast-growing vegetation after clear-cutting in situ .

Description: Aims Understanding carbon (C) and nitrogen (N) dynamics and their dependence on the stand density of an even-aged, mature forest provides knowledge that is important for forest management. This study investigated the differences in ecosystem total C and N storage and flux between a low-density stand (LD) and a high-density stand (HD) and examined the effects of stand density on aboveground net primary productivity (ANPP), total belowground C allocation (TBCA) and net ecosystem production (NEP) in a naturally regenerated, 65- to 75-year-old Pinus densiflora S. et Z. forest. Methods LD (450 trees ha –1 ) and HD (842 trees ha –1 ) were established in an even-aged, mature P. densiflora forest in September 2006. The forest had been naturally regenerated following harvesting, and the stand density was naturally maintained without any artificial management such as thinning. The diameter at breast height (DBH ≥ 5.0cm) of all live stems within the stands was measured yearly from 2007 to 2011. To compare C and N storage and fluxes in LD and HD, C and N pools in aboveground and belowground biomass, the forest floor, coarse woody debris (CWD) and soil; soil CO 2 efflux ( R S ); autotrophic respiration ( R A ); litter production; and soil N availability were measured. Further, ANPP, TBCA and NEP were estimated from plot-based measurement data. Important Findings Ecosystem C (Mg C ha –1 ) and N (Mg N ha –1 ) storage was, respectively, 173.0±7.3 (mean ± SE) and 4.69±0.30 for LD and 162±11.8 and 4.08±0.18 for HD. There were no significant differences in C and N storage in the ecosystem components, except for soils, between the two stands. In contrast, there were significant differences in aboveground ANPP and TBCA between the two stands ( P 〈 0.05). Litterfall, biomass increment and R S were major C flux components with values of, respectively, 3.89, 3.74 and 9.07 Mg C ha –1 year –1 in LD and 3.15, 2.94 and 7.06 Mg C ha –1 year –1 in HD. Biometric-based NEP (Mg C ha –1 year –1 ) was 4.18 in LD and 5.50 in HD. Although the even-aged, mature P. densiflora forest had similar C and N allocation patterns, it showed different C and N dynamics depending on stand density. The results of the current study will be useful for elucidating the effects of stand density on C and N storage and fluxes, which are important issues in managing natural mature forest ecosystems.

Description: Aims Tropical forest plays a key role in global C cycle; however, there are few studies on the C budget in the tropical rainforests in Asia. This study aims to (i) reveal the seasonal patterns of total soil respiration ( R T ), litter respiration ( R L ) and soil respiration without surface organic litter ( R NL ) in the primary and secondary Asian tropical mountain rainforests and (ii) quantify the effects of soil temperature, soil moisture and substrate availability on soil respiration. Methods The seasonal dynamics of soil CO 2 efflux was measured by an automatic chamber system (Li-8100), within the primary and secondary tropical mountain rainforests located at the Jianfengling National Reserve in Hainan Island, China. The litter removal treatment was used to assess the contribution of litter to belowground CO 2 production. Important Findings The annual R T was higher in the primary forest (16.73±0.87 Mg C ha –1 ) than in the secondary forest (15.10±0.26 Mg C ha –1 ). The rates of R T , R NL and R L were all significantly higher in the hot and wet season (May–October) than those in the cool and dry season (November–April). Soil temperature at 5cm depth could explain 55–61% of the seasonal variation in R T , and the temperature sensitivity index ( Q 10 ) ranked by R L ( Q 10 = 3.39) 〉 R T (2.17) 〉 R NL (1.76) in the primary forest and by R L (4.31) 〉 R T (1.86) 〉 R NL (1.58) in the secondary forest. The contribution of R L to R T was 22–23%, while litter input and R T had 1 month time lag. In addition, the seasonal variation of R T was mainly determined by soil temperature and substrate availability. Our findings suggested that global warming and increased substrate availability are likely to cause considerable losses of soil C in the tropical forests.

Description: Aims Understanding of the ecophysiological dynamics of forest canopy photosynthesis and its spatial and temporal scaling is crucial for revealing ecological response to climate change. Combined observations and analyses of plant ecophysiology and optical remote sensing would enable us to achieve these studies. In order to examine the utility of spectral vegetation indices (VIs) for assessing ecosystem-level photosynthesis, we investigated the relationships between canopy-scale photosynthetic productivity and canopy spectral reflectance over seasons for 5 years in a cool, temperate deciduous broadleaf forest at ‘Takayama’ super site in central Japan. Methods Daily photosynthetic capacity was assessed by in situ canopy leaf area index (LAI), (LAI x V cmax [single-leaf photosynthetic capacity]), and the daily maximum rate of gross primary production (GPP max ) was estimated by an ecosystem carbon cycle model. We examined five VIs: normalized difference vegetation index (NDVI), enhanced vegetation index (EVI), green–red vegetation index (GRVI), chlorophyll index (CI) and canopy chlorophyll index (CCI), which were obtained by the in situ measurements of canopy spectral reflectance. Important Findings Our in situ observation of leaf and canopy characteristics, which were analyzed by an ecosystem carbon cycling model, revealed that their phenological changes are responsible for seasonal and interannual variations in canopy photosynthesis. Significant correlations were found between the five VIs and canopy photosynthetic capacity over the seasons and years; four of the VIs showed hysteresis-type relationships and only CCI showed rather linear relationship. Among the VIs examined, we applied EVI–GPP max relationship to EVI data obtained by Moderate Resolution Imaging Spectroradiometer to estimate the temporal and spatial variation in GPP max over central Japan. Our findings would improve the accuracy of satellite-based estimate of forest photosynthetic productivity in fine spatial and temporal resolutions, which are necessary for detecting any response of terrestrial ecosystem to meteorological fluctuations.

Description: Aims This study aimed to develop radial growth models and to predict the potential spatial distribution of Pinus densiflora (Japanese red pine) and Quercus spp. (Oaks) in South Korea, considering topographic and climatic factors. Methods We used a dataset of diameter at breast height and radial growth estimates of individual trees, topographic and climatic factors in systematic sample plots distributed over the whole of South Korea. On the basis that radial growth is attributed primarily to tree age, we developed a radial growth model employing tree age as an explanatory variable. We estimated standard growth (SG), defined as radial growth of the tree at age 30, to eliminate the influence of tree age on radial growth. In addition, SG estimates including the Topographic Wetness Index, temperature and precipitation were calculated by the Generalized Additive Model. Important Findings As a result of variogram analysis of SG, we found spatial autocorrelation between SG, topographic and climatic factors. Incremental temperature had negative impacts on radial growth of P. densiflora and positive impacts on that of Quercus spp. Precipitation was associated with positive effects on both tree species. Based on the model, we found that radial growth of P. densiflora would be more vulnerable than that of Quercus spp. to climatic factors. Through simulation with the radial growth model, it was predicted that P. densiflora stands would be gradually replaced with Quercus spp. stands in eastern coastal and southern regions of South Korea in the future. The models developed in this study will be helpful for understanding the impact of climatic factors on tree growth and for predicting changes in distribution of P. densiflora and Quercus spp. due to climate change in South Korea.

Description: Aims Vast grasslands on the Tibetan Plateau are almost all under livestock grazing. It is unclear, however, what is the role that the grazing will play in carbon cycle of the grassland under future climate warming. We found in our previous study that experimental warming can shift the optimum temperature of saturated photosynthetic rate into higher temperature in alpine plants. In this study, we proposed and tested the hypothesis that livestock grazing would alter the warming effect on photosynthetic and respiration through changing physical environments of grassland plants. Methods Experimental warming was carried by using an infrared heating system to increase the air temperature by 1.2 and 1.7°C during the day and night, respectively. The warming and ambient temperature treatments were crossed over to the two grazing treatments, grazing and un-grazed treatments, respectively. To assess the effects of grazing and warming, we examined photosynthesis, dark respiration, maximum rates of the photosynthetic electron transport ( J max ), RuBP carboxylation ( V cmax ) and temperature sensitivity of respiration Q 10 in Gentiana straminea , an alpine species widely distributed on the Tibetan grassland. Leaf morphological and chemical properties were also examined to understand the physiological responses. Important findings 1) Light-saturated photosynthetic rate ( A max ) of G. straminea showed similar temperature optimum at around 16°C in plants from all experimental conditions. Experimental warming increased A max at all measuring temperatures from 10 to 25°C, but the positive effect of the warming occurred only in plants grown under the un-grazed conditions. Under the same measuring temperature, A max was significantly higher in plants from the grazed than the un-grazed condition. 2) There was significant crossing effect of warming and grazing on the temperature sensitivity ( Q 10 ) of leaf dark respiration. Under the un-grazed condition, plants from the warming treatment showed lower respiration rate but similar Q 10 in comparison with plants from the ambient temperature treatment. However, under the grazed condition Q 10 was significantly lower in plants from the warming than the ambient treatment. 3) The results indicate that livestock grazing can alter the warming effects on leaf photosynthesis and temperature sensitivity of leaf dark respiration through changing physical environment of the grassland plants. The study suggests for the first time that grazing effects should be taken into account in predicting global warming effects on photosynthesis and respiration of plants in those grasslands with livestock grazing.

Description: Aims (i) To explore variations in nutrient resorption of woody plants and their relationship with nutrient limitation and (ii) to identify the factors that control these variations in forests of eastern China. Methods We measured nitrogen (N) and phosphorus (P) concentrations in both green and senesced leaves of 172 woody species at 10 forest sites across eastern China. We compared the nutrient resorption proficiency (NuRP) and efficiency (NuRE) of N and P in plant leaves for different functional groups; we further investigated the latitudinal and altitudinal variations in NuRP and NuRE and the impacts of climate, soil and plant types on leaf nutrient resorptions. Important Findings On average, the leaf N resorption proficiency (NRP) and P resorption proficiency (PRP) of woody plants in eastern China were 11.1mg g – 1 and 0.65 mg g – 1 , respectively; and the corresponding N resorption efficiency (NRE) and P resorption efficiency (PRE) were 49.1% and 51.0%, respectively. Angiosperms have higher NRP (are less proficient) values and lower NRE and PRE values than gymnosperms, but there are no significant differences in NRP, PRP and PRE values between species with different leaf habits (evergreen vs. deciduous angiosperms). Trees have higher NRE and PRE than shrubs. Significant geographical patterns of plant nutrient resorption exist in forests of eastern China. In general, NRP and PRE decrease and PRP and NRE increase with increasing latitude/altitude for all woody species and for the different plant groups. Plant functional groups show more controls than environmental factors (climate and soil) on the N resorption traits (NRP and NRE), while site-related variables present more controls than plant types on PRP and PRE. NRP increases and PRP and NRE decrease significantly with increasing temperature and precipitation for the overall plants and for most groups, except that significant PRE–climate relationship holds for only evergreen angiosperms. Leaf nutrient resorption did not show consistent responses in relation to soil total N and P stoichiometry, probably because the resorption process is regulated by the relative costs of drawing nutrients from soil versus from senescing leaves. These results support our hypothesis that plants growing in P-limited habitats (low latitudes/altitudes or areas with high precipitation/temperature) should have lower PRP and higher PRE, compared with their counterparts in relatively N-limited places (high latitudes/altitudes or areas with low precipitation/temperature). Our findings can improve the understanding of variations in N and P resorption and their responses to global change, and thus facilitate to incorporate these nutrient resorption processes into future biogeochemical models.

Description: Anthropogenic nitrogen (N) emissions to atmosphere have increased dramatically in China since 1980s, and this increase has aroused great concerns on its ecological impacts on terrestrial ecosystems. Previous studies have showed that terrestrial ecosystems in China are acting as a large carbon (C) sink, but its potential in the future remains largely uncertain. So far little work on the impacts of the N deposition on C sequestration in China’s terrestrial ecosystems has been assessed at a national scale. Aiming to assess and predict how ecological processes especially the C cycling respond to the increasing N deposition in China’s forests, recently researchers from Peking University and their partners have established a manipulation experimental network on the ecological effects of the N deposition: Nutrient Enrichment Experiments in China’s Forests Project (NEECF). The NEECF comprises 10 experiments at 7 sites located from north to south China, covering major zonal forest vegetation in eastern China from boreal forest in Greater Khingan Mountains to tropical forests in Hainan Island. This paper introduces the framework of the NEECF project and its potential policy implications.

Description: Aims Root and heterotrophic respiration may respond differently to environmental variability, but little evidence is available from large-scale observations. Here we aimed to examine variations of root and heterotrophic respiration across broad geographic, climatic, soil and biotic gradients. Methods We conducted a synthesis of 59 field measurements on root and heterotrophic respiration across China’s forests. Important Findings Root and heterotrophic respiration varied differently with forest types, of which evergreen broadleaf forest was significantly different from those in other forest types on heterotrophic respiration but without statistically significant differences on root respiration. The results also indicated that root and heterotrophic respiration exhibited similar trends along gradients of precipitation, soil organic carbon and satellite-indicated vegetation growth. However, they exhibited different relationships with temperature: root respiration exhibited bimodal patterns along the temperature gradient, while heterotrophic respiration increased monotonically with temperature. Moreover, they showed different relationships with MOD17 GPP, with increasing trend observed for root respiration whereas insignificant change for heterotrophic respiration. In addition, root and heterotrophic respiration exhibited different changes along the age sequence, with insignificant change for root respiration and decreasing trend for heterotrophic respiration. Overall, these results suggest that root and heterotrophic respiration may respond differently to environmental variability. Our findings could advance our understanding on the different environmental controls of root and heterotrophic respiration and also improve our ability to predict soil CO 2 flux under a changing environment.

Description: Aim Due to the important role of lianas in the functioning of forest ecosystem, knowledge of the factors that affect them are important in the management of forests. Currently, there are conflicting reports on the response of liana communities to disturbance, calling for more research in the area. The present study was carried out to investigate the response of liana diversity and structure to human disturbance within two major forests in the Penang National Park, Malaysia. The study also looked at the implication of the findings for conservation. Methods A total of 15 40 x 40-m 2 (or 40-m x 40-m) plots each were randomly located across a range of habitats in a primary forest and disturbed secondary forest. Trees with diameter at breast height ≥10 cm were examined for lianas with diameter ≥2 cm. Both lianas and trees were enumerated and compared between the two forests. Diversity and structural variables of lianas were compared between the two forests using the t -test analysis. Tree abundance was also compared between the two forests with t -test, while linear regression analysis was run to determine the effects of tree abundance on liana abundance. Important Findings A total of 46 liana species belonging to 27 genera and 15 families were identified in the study. Human disturbance significantly reduced liana species richness and species diversity in the secondary forest. Liana abundance remained the same in both forests whereas liana basal area was significantly higher in the primary forest. Twiners and hook climbers were significantly more abundant in the primary and secondary forest, respectively. Large diameter lianas were more abundant in the primary forest compared with the secondary forest. The diameter distribution of most families in the primary forest followed the inverted J-shaped curve whereas only a few of the families in the secondary forest did so. Tree abundance was significantly higher in the primary forest. The abundance of lianas significantly depended on tree abundance in all the forests. The study has provided evidence of negative effects of human disturbance on liana diversity and structure that does not auger well for biodiversity in the forest. In view of the critical role of lianas in maintaining biodiversity in the forest ecosystem, lianas in the national park should be protected from further exploitation.

Description: Aims The present study aims (i) to examine if recently reported interspecific shoot-level biomass allocational trade-offs, i.e. isometric trade-offs between leaf mass (LM) and stem mass (SM) and between leaf size and leaf number, hold intraspecifically and (ii) to explore whether those scaling relationships are independent of shoot type (i.e. long vs. short shoots). Methods In order to address our questions, we used Fagus sylvatica saplings growing under a broad light range that were sampled in the Western Carpathians Mountains (Slovakia). Important Findings We found that: (i) intraspecific shoot-level biomass allocational trade-offs differ from those reported interspecifically and that (ii) long and short shoots differ in biomass allocation scaling coefficients. Allometric relationships with slopes statistically smaller than 1.0 or higher than –1.0, were found between SM and LM and between mean leafing intensity and individual leaf mass, respectively, in long shoots. In contrast, isometric scaling was found in short shoots. This suggests that leaf mass in short shoots is unaffected by shoot stem mass, in contrast to long shoots. Short shoots also had a larger fraction of biomass allocated to leaves. Beech shoots, as has been observed in other shoot dimorphic species, are specialized, with short shoots specializing in carbon gain and long shoots in space acquisition. A greater shift in LM than in SM among species during speciation shifting from allometric intraspecific relationships to an isometric interspecific scaling relationship between those traits could explain the discrepancies between the outputs of the present intraspecific study and others similar studies. This study draws attention to the importance of considering shoot types in future studies dealing with allocation rules in species with dimorphic shoots.

Description: Aims To determine if an experimentally applied anomalous weather year could have effects on species composition and community structure that would carry over into the following year. Methods We conducted a field experiment applying two levels of temperature (ambient and +4°C) and two levels of precipitation (ambient and doubled) and followed cover of plant species during the treatment year and one post-treatment year. Data analysis included ordination analysis, examination of species frequency distributions and comparison of cover of functional groups and individual species. Important Findings A drought during the summer and fall of the treatment year resulted in significant differences in community structure between the 2 years. C 3 and winter annual species were depressed in the spring of the second year following the dry autumn. Species richness and legume cover increased in the second, wetter, year. Treatments caused no overall differences in community structure but did alter the dominance hierarchy of species among treatments as well as years. Warming decreased relative cover of winter annuals and early spring-flowering species but increased other annuals. Warming and double precipitation together increased cover of C 4 perennial graminoids. In particular, the warming and precipitation treatments both increased the abundance of Andropogon gerardii , not individually altering the dominance hierarchy but together nearly doubling the relative cover of A.gerardii , making it the most abundant species in the combined treatment, while the cover of Bromus arvensis , the former dominant, decreased by 25%. The following year, Andropogon relative cover increased further in the former warmed plots, becoming dominant in both the formerly warmed and warmed plus double precipitation treatments. The year following treatments also saw an increase in relative cover of summer-blooming species in the formerly warmed plots and differences among the former treatments in species richness of functional groups. If the effects of one anomalous year on plant abundance can carry over into the following year, several warm years could have a significant impact on plant community structure.

Description: Aims In recent years, coastal mangroves have been frequently affected by large disturbances (cyclones, hurricanes, flooding and tsunamis) and post-disturbance vegetation is often dominated by small stature mangrove, mangrove-associate and non-mangrove species potentially affecting ecosystem functioning. Knowledge on the processes of mangrove vegetation development and recovery (succession) following normal and large disturbances will benefit practitioners in designing robust ecosystem management/restoration plans. Here we propose a conceptual model of disturbance-mediated succession in mangroves. Methods Based on field observations and species’ life history traits, we develop conceptual models of mangrove succession under normal disturbance regime and recently experienced increased frequency of large disturbances. We evaluate our conceptual models by conducting a scenario testing experiment. Important Findings We suggest two predominant processes affecting mangrove succession after disturbance: propagule limitation due to damage of seed producing mature trees and dispersal barrier resulting from biological invasion associated with large disturbance. We argue that large disturbances affect mature trees more than the small-stature non-tree (shrubs, herbs and climbers) species creating a larger propagule shortage for mangrove tree species than non-tree species. Secondly, large disturbances facilitate invasion of free-floating aquatics, which may interfere with the flow-facilitated propagule dispersal and seedling establishment of mangrove species. In a scenario testing experiment, we have shown that similar levels of disturbance impact vegetation development and recovery differently depending on the presence or absence of invasive species. We conclude that since biological invasion is one of the major drivers of post-disturbance mangrove succession, the dimension of biological invasion should be included in prediction, management and restoration of mangrove forests.

Description: Aims In view of the growing interest in modelling the potential spread of invasive species, prediction of plant invasiveness on the basis of native range size holds considerable promise. Our objective was to use a simple model to evaluate whether a wider native range predisposes plant species to become invasive in non-native regions and to easily identify potential invaders on this basis. The Kashmir Himalayan alien flora, of which a large proportion is native to Europe, was used to test this model. Methods The Kashmir Himalayan alien flora comprises 436 species of vascular plants at different stages of invasion. We focussed on plant species at two critical invasion stages ( sensu Colautti and MacIsaac 2004 ), i.e. Stage II (species that are just at the earliest phase of introduction) and Stage V (species that are widespread and dominant in the invaded region and are thus considered invasive). We used the territorial distribution in Europe (number of countries) as a surrogate for the native range size of plants of European origin. Important Findings Using a subset of 88 species, for which information on the native European range was available, we showed that a large proportion (68%) of Stage II species growing in the Kashmir Valley had a relatively restricted European range (present in ≤20 countries); on the other hand, 77% of Stage V species had an extensive native range (present in 〉20 countries). We consequently hypothesized that 14 Kashmir Himalayan Stage II species of European origin that are distributed in 〉20 European countries are at risk of becoming future invaders in Kashmir. On the other hand, those Kashmir Himalayan Stage II species of European origin distributed in ≤20 European countries are less likely to become invasive. Although this analysis is quite simple, the data suggest that a wider native range is a good predictor of plant invasiveness and could be used as a simple and low-cost early warning tool in predicting potential invasive species.

Description: Aims Vegetation type is important in determining variations in soil carbon (C) efflux under grassland managements. This study was conducted to examine the effects of mowing and nitrogen (N) addition on soil respiration and their dependences upon vegetation types in an oldfield grassland of northern China. Methods Soil respiration, temperature, moisture and aboveground net primary productivity (ANPP) and belowground net primary productivity (BNPP) were examined in response to mowing and N addition among the three patches dominated by different species (named as grass, forb and mixed patches, respectively) in the growing seasons (May–October) from 2006 to 2008. Important Findings Across the 3 years, soil respiration in the grass patch was greater than those in the forb and mixed patches, which could have been ascribed to the higher soil moisture (SM) in the grass patch. Mowing had no impact on soil respiration due to unaltered SM and plant growth. Soil respiration was stimulated by 6.53% under N addition, and the enhancement was statistically significant in 2006 but not in 2007 or 2008 because of the limited water availability in the later 2 years. There were no interactive effects between mowing and N addition on soil respiration. Soil respiration showed positive dependence upon SM, ANPP and BNPP across plots. The results suggest that soil water availability and plant growth could be the primary factors in controlling the temporal and spatial variations in soil respiration and its response to different treatments. Our observations indicate that grassland managements (i.e. mowing for hay once a year) may have little influence on soil respiration of the oldfield grassland in northern China.

Description: Aims Numerous studies have showed that the balance between negative and positive plant–plant interactions shifted along environmental gradients. But little is known how the positive or negative plant–plant interactions varied with temporal fluctuating habitat conditions and plant ontogenetic phases. Methods In a 2-year experiment, the four perennial grasses ( Kobresia humilis , Stipa aliena , Elymus nutans and Saussurea superba ) were grown under four interaction treatments (no root or shoot interaction, only shoot interaction, only root interaction, root and shoot interaction). Intensity of above- and belowground interactions is proposed to vary with the fluctuation of seasonal climatic conditions and soil available nutrients. Here we report measurements of above- and belowground interactions during entire growing season. Correlation between plant interaction intensity and seasonal soil available N as well as habitat climate conditions was also performed. Important findings Our experiment found that root interactions had negative effect on plant growth for the four species during growing season. However, both negative and positive shoot interactions occurred among the four species. Despite there being shoot facilitative effect for E. nutans and S. superba , the full interaction was negative, suggested that root interaction take more important role on plant growth than that of shoot interaction. The interaction between root and shoot effect varied as a function of species identity and growth phases. The weak correlation of plant interaction intensity to habitat environmental factors suggested that plant ontogenetic characteristics may be primary factors causing temporal variation in plant interaction.

Description: Aims Ecosystem carbon models often require accurate net ecosystem exchange of CO 2 (NEE) light-response parameters, which can be derived from the Michaelis–Menten equation. These parameters include maximum net ecosystem exchange (NEE max ), apparent quantum use efficiency ( α ) and daytime ecosystem respiration rate ( R e ). However, little is known about the effects of land conversion between steppe and cropland on these parameters, especially in semi-arid regions. To understand how these parameters vary in responses to biotic and abiotic factors under land conversions, seasonal variation of light-response parameters were evaluated for a steppe and a cropland of Inner Mongolia, China, during three consecutive years (2006–08) with different precipitation amounts. Methods NEE was measured over a steppe and a cropland in Duolun, Inner Mongolia, China, using the eddy covariance technique, and NEE light-response parameters (NEE max , α and R e ) were derived using the Michaelis–Menten model. Biophysical regulations of these parameters were evaluated using a stepwise regression analysis. Important Findings The maximum absolute values of NEE max occurred in the meteorological regimes of 15°C ≤ T a 〈 25°C, vapor pressure deficit (VPD) 〈 1 KPa and 0.21 m 3 m – 3 ≤ volumetric soil water content at 10 cm (SWC) 〈 0.28 m 3 m – 3 for both the steppe and the cropland ecosystems. The variations of α and R e showed no regular variation pattern in different T air , VPD and SWC regimes. Under the same regime of T air , VPD and SWC, the cropland had higher absolute values of NEE max than the steppe. Canopy conductance and leaf area index (LAI) were dominant drivers for variations in NEE light-response parameters of the steppe and the cropland. The seasonal variation of NEE light-response parameters followed the variation of LAI for two ecosystems. The peak values of all light-response parameters for the steppe and the cropland occurred from July to August. The values of NEE light-response parameters (NEE max , α and R e ) were lower in the driest year (2007). Seasonally averaged NEE light-response parameters for the cropland surpassed those for the steppe. Land conversion from steppe to cropland enhanced NEE light-response parameters during the plant growing period. These results will have significant implications for improving the models on regional NEE variation under climate change and land-use change scenarios.

Description: Aims Road effects from maintenance and traffic have the potential to alter plant communities, but the exact relationships between these effects and changes in plant community composition have not often been studied in diverse environments. To determine the direction and level of community composition changes in saline environment due to road effects, we conducted a study along roads of different ages and in nearby non-road (i.e. natural) areas in the Yellow River Delta, China. Additionally, to potentially elucidate the mechanisms underlying the changes in the richness and composition of plant communities along roads, we evaluated physiochemical changes in soil of roadside and non-road areas. Methods Floristic and environmental data were collected along roadside of different ages and nearby non-road areas. To evaluate plant communities at each site, six 2 m x 2 m quadrats were placed at 3-m intervals along roads and six quadrats were arranged randomly in non-road areas. To determine the difference in plant community composition between roadside and non-road areas, we measured species richness and the abundance of each species, examined species turnover and floristic dissimilarity between the two areas and positioned plant species and sites in an abstract multivariate space. Plant community (species richness, percentage of halophytes) and soil physicochemical properties (pH, salinity, moisture content, bulk density, nitrate and ammonium nitrogen concentration) were compared between roadside and non-road areas (young roadside vs. corresponding non-road areas, old roadside vs. corresponding non-road areas) by using t -tests. Classification and ordination techniques were used to examine the relationship between vegetation and related environmental variables in both roadside and non-road areas. Important Findings For both the young and old roadside areas, species richness in roadside areas was significantly higher than in non-road areas and high floristic dissimilarity values indicated that roadside and non-road areas differed greatly in community composition. In both the young and old roadside areas, the plant communities in roadside areas had lower percentages of halophytes than non-road communities. Correspondence analysis and two-way indicator species analysis showed that halophytes dominated in the non-road areas, while a number of typical non-salt-tolerant species dominated in the roadside areas. Compared to non-road areas, activities associated with roads significantly decreased soil moisture, bulk density and salinity and increased soil pH and nitrate content. Forward selection for the environmental variables in canonical correspondence analysis showed that soil salinity was the most important factor related to the variation of species composition between roadside and non-road areas. Our study demonstrates that road effects have a significant impact on the associated vegetation and soil, and these changes are consistent across roads of different ages in our system.

Description: Aims Australian alpine ecosystems currently experience high precipitation in the snow-free season, but they are predicted to experience drier conditions under climate change. We observed high mortality of the dominant alpine grasses following drought in 2007. Our aims were as follows: to test the involvement of plant-available water (PAW) and other environmental variables in grass mortality in the field; to detect possible species differences in drought response and to link soil moisture to precipitation using soil properties and climate data. Methods The dominant tussock grasses of the Australian alpine zone, Poa hothamensis var. hothamensis N.G. Walsh, P oa hiemata Vickery and P oa phillipsiana Vickery (Poaceae), all exhibited mortality following drought in the Bogong High Plains, Victoria, Australia in 2007. PAW was calculated using soil water potential measurements, and past drought occurrence was modelled using climate data. We then tested the effects of PAW and soil depth on grass survival both at a large spatial scale spanning the elevational range of the alpine zone and at a smaller scale. Poa hothamensis and P. phillipsiana were compared in a common-garden experiment to test drought tolerance. Important Findings Poa hothamensis survival was predicted by dry-season PAW at the small spatial scale; at the large scale, soil depth and elevation were more important predictors of P. hothamensis survival, but dry-season PAW predicted P. hiemata survival. Common-garden experiments supported field observations that P. hothamensis is more drought-sensitive than is P. phillipsiana . We also present a simple polynomial relationship between rainfall and field soil moisture, which predicts that the alpine soils dry below wilting point several times a year. We suggest the timing of long rain-free periods may be more important than their duration.

Description: Aims Forest growth and recruitment and their relationships to climate are complex. The aims of our study are (i) to examine the patterns in tree radial growth and recruitment along an altitudinal gradient in Mt. Everest region and (ii) to identify the climatic factors that are responsible to the observed patterns in tree growth and recruitment. Methods Four plots, each 30 x 60 m in size, were established from the lower to upper limits of the eastern Himalayan fir forest in Dingjie County of the Mt. Everest Nature Reserve, China. Dendrochronological techniques were applied to obtain information about the radial growth and age of the trees in the plots. Correlation analysis was used to identify the relationships between radial growth and recruitment of trees and climatic variables, i.e. monthly mean temperature and Palmer Drought Severity Index (PDSI). The population age structure was analyzed to investigate the recruitment history. Important Findings The timberline plot was characterized by significant tree recruitments in the recent three decades and sporadic recruitments in earlier periods. The other three plots showed recruitment pulses during 1880–1910 in Plot 3 700 m, during 1870–80 and 1920–30 in Plot 3 520 m and during 1900–40 in Plot 3 410 m. The recruitment of fir trees in the timberline was sensitive to summer (June–September) temperatures, but it was mainly controlled by episodic disturbances in lower altitudes. Fir radial growth in the upper two plots was positively correlated with previous winter and current August temperature. Fir radial growth at the two lower plots was positively correlated with PDSI from previous September to current September.

Description: Aims Possible shifts in the phenotypic performance along invasive plants’ spreading route are rarely examined due to the discontinuous and incomplete records of exotic species. As the invasion history of common ragweed ( Ambrosia artemisiifolia L.) is well documented in Hungary, its residence time is known for each location. By sampling a sequence of older to more recently established populations, we aimed to determine (i) whether there are phenotypic divergences along the historical spreading route of A.artemisiifolia ; (ii) which traits are under selection during the invasion process and (iii) the extent of maternal effects on the individual's performance. Methods We used a hierarchical sampling design to collect seeds from 64 individuals belonging to eight sites in four residence time categories (seven populations along the historical spreading route of ragweed in Hungary and one recently invaded site in Romania). We selected four large and four small individual plants in each population to control for maternal effects. The offspring were reared in a common garden located in Romania. Five vegetative phenotypic traits were measured at the end of the experiments and used in the subsequent analysis (plant height, basal diameter, number of secondary axes, length of the longest secondary axis and biomass). To summarize the variation of these highly correlated traits, principal component analysis was performed first and then the important components were used in linear mixed effect models. Important Findings The residence time categories were significantly distinguished by the first component, which compresses the variation of all five measured traits. The measures gradually decrease from populations with the longest residence time (introduced more than 65 years ago) towards the most recently established populations (established less than 30 years ago). These differences might reflect the invasion history of the populations: the longer the residence time the higher the chance to develop relevant traits beneficial in invasion process. The size of the mother plant significantly influenced not only the seed mass (inversely) but also the adult performance of its offspring (directly).

Description: Aims Although stem CO 2 efflux is critical to ecosystem carbon and energy balance and its feedback to future climate change, little information is available on stem CO 2 efflux and its responses to temperature, especially in subtropical China. This study aims to (i) evaluate the temporal and spatial variations of stem CO 2 efflux of three species, including oak ( Quercus acutissima Carr.), masson pine ( Pinus massoniana Lamb.) and loblolly pine ( Pinus taeda Linn.) in subtropical China and (ii) analyze the temperature sensitivity of stem CO 2 efflux in the three species based on 2-year field measurements. Methods We measured stem CO 2 efflux and stem temperature (at 3 cm depth) of the three species using the horizontally oriented soil chamber technique from September 2008 to August 2010. We also conducted a 24-h measurement to examine the diurnal variation of stem CO 2 efflux in three consecutive days in April 2009. Important findings The temporal dynamics of stem CO 2 efflux followed the change of the stem temperature in a 3-cm depth with a bell-shaped curve in the three species. Stem temperature explained 77–85% of the seasonal variations of stem CO 2 efflux over the entire study period in the three species. The temperature sensitivity ( Q 10 ) of stem CO 2 efflux was obviously different among the three species with higher Q 10 value found in oak (2.24) and lower values in the coniferous species (1.76 and 1.63). Our results also showed that the Q 10 values of stem CO 2 efflux in all the three species were lower in the growing season than that in the non-growing season, indicating that the growth and maintenance respiration had different temperature responses. Moreover, we found that the temperature-normalized stem CO 2 efflux ( R 10 ) changed greatly between the growing and non-growing seasons in oak and masson pine, but not in loblolly pine. Additionally, we also found that in the non-growing season, the principal factor responsible for the spatial variation of stem CO 2 efflux among the 15 sampling trees was sapwood volume, whereas in the growing season, stem CO 2 efflux was closely related to annual dry-matter production in the three subtropical species.

Description: Aims Combining field data analysis and modeling, this study investigates factors influencing the diurnal boundary layer (BL) development in boreal forest. Methods Field data analysis used both air sounding and surface flux measurements collected during the Boreal Ecosystem–Atmosphere Study field campaigns in central Canada. Model study applied a non-local transilient turbulence theory (TTT) to simulate the impact of the heterogeneous boundary conditions together with initial conditions on the BL development at the Candle Lake and Thompson release sites over boreal forests. Boundary conditions were characterized by the integrated surface flux measurements from different forest stands. The lake effect was included in constructing the surface fluxes at Candle Lake release site. Important Findings Analyses of serial upper air sounding data and tower flux data indicate strong linear impacts of surface sensible heat forcing on the diurnal BL development above boreal forests. The regression slopes on the relationship between the BL development and the surface fluxes reflect the influences of initial boundary conditions to the BL developments. Both the modeled and the measured diurnal BLs show that lakes reduce sensible heat flux, leading to a shallower boundary in Candle Lake than in Thompson. Comparison of the model results and field measurements on the BL profiles indicates that the TTT model has the capability to simulate the BL development above boreal forests for sunny, rainfall or cloudy days. This study demonstrates the importance of lake on surface fluxes and BL development. The modeling effort shows the potential to couple the transilient theory with a land surface process model to study land surface and atmosphere interaction in boreal forest.

Description: Aims Preserving and restoring Tamarix ramosissima is urgently required in the Tarim Basin, Northwest China. Using species distribution models to predict the biogeographical distribution of species is regularly used in conservation and other management activities. However, the uncertainty in the data and models inevitably reduces their prediction power. The major purpose of this study is to assess the impacts of predictor variables and species distribution models on simulating T. ramosissima distribution, to explore the relationships between predictor variables and species distribution models and to model the potential distribution of T. ramosissima in this basin. Methods Three models—the generalized linear model (GLM), classification and regression tree (CART) and Random Forests—were selected and were processed on the BIOMOD platform. The presence/absence data of T. ramosissima in the Tarim Basin, which were calculated from vegetation maps, were used as response variables. Climate, soil and digital elevation model (DEM) data variables were divided into four datasets and then used as predictors. The four datasets were (i) climate variables, (ii) soil, climate and DEM variables, (iii) principal component analysis (PCA)-based climate variables and (iv) PCA-based soil, climate and DEM variables. Important Findings The results indicate that predictive variables for species distribution models should be chosen carefully, because too many predictors can reduce the prediction power. The effectiveness of using PCA to reduce the correlation among predictors and enhance the modelling power depends on the chosen predictor variables and models. Our results implied that it is better to reduce the correlating predictors before model processing. The Random Forests model was more precise than the GLM and CART models. The best model for T. ramosissima was the Random Forests model with climate predictors alone. Soil variables considered in this study could not significantly improve the model’s prediction accuracy for T. ramosissima . The potential distribution area of T. ramosissima in the Tarim Basin is ~3.57 x 10 4 km 2 , which has the potential to mitigate global warming and produce bioenergy through restoring T. ramosissima in the Tarim Basin.

Description: Aims In eroded lands of the French Southern Alps, burial of early established seedlings under marly sediment weakens the effect of vegetation on soil stabilization and sediment trapping. Therefore, this protective role is largely dependent on species' resistance to burial, and the understanding of species' tolerance to this environmental disturbance is highly valuable for basic knowledge on plant succession and for ecological restoration purposes. Methods The response of five woody species with contrasting ecological requirements and natural habitats—three tree species, Pinus nigra , Robinia pseudoacacia and Acer campestre , and two shrubs, Ononis fruticosa and Hippophae rhamnoides —to experimental burial under marly sediment was studied. Seedlings were exposed to three burial levels: no burial (control), partial burial (50% of seedling height) and complete burial (100% of seedling height). Burial tolerance was evaluated based on seedling survival, height and biomass. Biomass allocation to shoots and roots and soluble sugar and starch contents in roots and stems were measured to identify plant traits that determine species response to burial. Important Findings All species survived partial burial but only A. campestre seedlings emerged from complete burial. Tree species were more tolerant to burial and buried plants showed no significant differences with control. The two shrubs were found less tolerant and buried plants showed slower growth than controls. The results showed that species response was not related to initial soluble and starch content in roots and stems, but instead to biomass allocation pattern flexibility.

Description: Aims Better understanding of microbial compositional and physiological acclimation mechanisms is critical for predicting terrestrial ecosystem responses to global change. The aim is to assess variations in soil microbial communities under future scenarios of changing precipitation and N deposition in a semiarid grassland of northern China. Methods In order to explicitly estimate microbial responses, a field experiment with water and N addition was established in April 2005 and continuously conducted for 4 years. Specifically, soil microbial community composition and microbial C utilization potential were determined by phospholipid fatty acid (PLFA) and community-level physiological profiles, respectively. Important Findings Water addition had no effects on the PLFA concentrations of gram-positive (GP) and negative bacteria (GN), total bacteria and fungi. However, N addition caused significant reductions in the PLFA concentrations of GP, GN, total bacteria and fungi and thus decreased total PLFA of microbial communities. Moreover, there were interactive effects of water and N addition on GN/GP and the ratio of fungal to bacterial PLFA (F/B). In addition, synergistic effects were found between water and nitrogen in affecting microbial C utilization potentials, which implies that microbial C utilization potentials tend to be enhanced when both N and water availability are sufficient. Overall, the microbial responses to water and N addition support our hypothesis that water and N addition may be combined together to affect microbial communities in the semiarid grassland.

Description: Aims Nighttime sap flow of trees may indicate transpiration and/or recharge of stem water storage at night. This paper deals with the water use of Acacia mangium at night in the hilly lands of subtropical South China. Our primary goal was to reveal and understand the nature of nighttime sap flow and its functional significance. Methods Granier’s thermal dissipation method was used to determine the nighttime sap flux of A. mangium . Gas exchange system was used to estimate nighttime leaf transpiration and stomatal conductance of studied trees. Important Findings Nighttime sap flow was substantial and showed seasonal variation similar to the patterns of daytime sap flow in A. mangium . Mean nighttime sap flow was higher in the less precipitation year of 2004 (1122.4 mm) than in the more precipitation year of 2005 (1342.5 mm) since more daytime transpiration and low soil water availability in the relatively dry 2004 can be the cause of more nighttime sap flow. Although vapor pressure deficit and air temperature were significantly correlated with nighttime sap flow, they could only explain a small fraction of the variance in nighttime sap flow. The total accumulated water loss ( E L ) by transpiration of canopy leaves was only ~2.6–8.5% of the total nighttime sap flow ( E t ) during the nights of July 17–18 and 18–19, 2006. Therefore, it is likely that the nighttime sap flow was mainly used for refilling water in the trunk. The stem diameter at breast height, basal area and sapwood area explained much more variance of nighttime water recharge than environmental factors and other tree form features, such as tree height, stem length below the branch, and canopy size. The contribution of nighttime water recharge to the total transpiration ranged from 14.7 to 30.3% depending on different DBH class and was considerably higher in the dry season compared to the wet season.

Description: Aims Our aim was to study how diversity and dominance of plant species and plant functional types (PFTs) change and covary across three dune fixation stages in the Chinese steppe zone. Methods In the Chinese steppe zone, we measured coverage, mean height and density of each plant species in three types of dunes (mobile, semi-fixed and fixed dunes) in four sites (Mu Us, Otindag, Hulunbeir and Horqin). Plant species were grouped into 24 PFTs according to their lifespan, photosynthetic pathway, reproductive mode and life form. Dominance of each plant species and PFT were determined, and species diversity and PFT diversity were quantified using Shannon–Wiener index. Important Findings PFT diversity was positively related to plant species diversity in each dune stage, but PFT diversity increased more with increasing plant species diversity in the mobile and semi-fixed dunes than in the fixed dunes. Dune fixation stage explained 87.2% of the variation in plant species diversity and 84.8% of the variation in PFT diversity. Dominant species and PFTs differed among the three dune fixation stages; the more fixed the dunes were, the more perennial, shrubby, clonal and C 3 species co-dominated. Specifically, in mobile dunes annual C 4 non-clonal herbs were the most dominant, and in semi-fixed and fixed dunes perennial C 3 clonal shrubs were most dominant.

Description: Aims Many observations concerning biological and ecological differentiation between narrow endemic and widespread congeneric plant species suggest that narrow endemic species are constrained to colonize marginal habitats because of a low tolerance to competition. Despite this topic being an important issue both for understanding evolutionary processes leading to endemism and for conservation purposes, few studies have been performed to compare competitive abilities between endemic and widespread species. Here, we present two independent experiments performed under controlled conditions using two different pairs of endemic and widespread congeneric species: Centaurea corymbosa / Centaurea maculosa and Arenaria provincialis / Arenaria serpyllifolia , both endemic species occurring in rocky calcareous habitats . Methods Mature seeds of C. corymbosa and C. maculosa were sown in pots containing ramets of the common grass, Brachypodium retusum . Pots were sorted in three treatments according to grass cover (low, intermediate and high). A control treatment (without competition) was also used. Germination, seedling survival and rosette growth were followed. For the comparisons between A. provincialis and A. serpyllifolia , seeds from natural populations were first sown without a competitor. One week after germination, healthy seedlings were transplanted in pots without Brachypodium seedling (control) or containing two Brachypodium seedlings (low competition) or four seedlings (high competition). We checked the number of capsules per individual, and we harvested the biomass after capsule maturation. Important Findings Despite differences in the protocol design, results are congruent, and in both cases, endemic species are highly affected by the presence of a competitor, as are the widespread species, although we did not detect any differences between species for response to competition. The results are discussed in relation to processes leading to endemism, suggesting that the specialist model is more likely for both the study species. The present study also contributes to guidelines for the conservation of rare species in relation to landscape modification in the Mediterranean area.

Description: Aims The dispersal of pollen and seeds is spatially restricted and may vary among plant populations because of varying biotic interactions, population histories or abiotic conditions. Because gene dispersal is spatially restricted, it will eventually result in the development of spatial genetic structure (SGS), which in turn can allow insights into gene dispersal processes. Here, we assessed the effect of habitat characteristics like population density and community structure on small-scale SGS and estimate historical gene dispersal at different spatial scales. Methods In a set of 12 populations of the subtropical understory shrub Ardisia crenata , we assessed genetic variation at 7 microsatellite loci within and among populations. We investigated small-scale genetic structure with spatial genetic autocorrelation statistics and heterogeneity tests and estimated gene dispersal distances based on population differentiation and on within-population SGS. SGS was related to habitat characteristics by multiple regression. Important Findings The populations showed high genetic diversity ( H e = 0.64) within populations and rather strong genetic differentiation ( $${{F}^{\prime }}_{\hbox{ ST }}$$ = 0.208) among populations, following an isolation-by-distance pattern, which suggests that populations are in gene flow–drift equilibrium. Significant SGS was present within populations (mean Sp = 0.027). Population density and species diversity had a joint effect on SGS with low population density and high species diversity leading to stronger small-scale SGS. Estimates of historical gene dispersal from between-population differentiation and from within-population SGS resulted in similar values between 4.8 and 22.9 m. The results indicate that local-ranged pollen dispersal and inefficient long-distance seed dispersal, both affected by population density and species diversity, contributed to the genetic population structure of the species. We suggest that SGS in shrubs is more similar to that of herbs than to trees and that in communities with high species diversity gene flow is more restricted than at low species diversity. This may represent a process that retards the development of a positive species diversity–genetic diversity relationship.

Description: Aims With the continuing increase in the impact of human activities on ecosystems, ecologists are increasingly interested in understanding the effects of high temperature on litter decomposition since litter decomposition and the accompanying release of nutrients and carbon dioxide are key processes in ecosystem nutrient cycling and carbon flux. This study was conducted to evaluate the temperature sensitivity of forest litter decomposition and soil enzymes during litter decomposition in subtropical forest in China. Methods Two dominant litter types were chosen from Zijin Mountain in China: Quercus acutissima leaves from a broadleaf forest (BF) and Pinus massoniana needles from a coniferous forest (CF). The litter samples were incubated in soil microcosms at ambient control temperature (20°C) and 10°C warmer. During a 5-month incubation, chemical composition of litter samples, litter mass losses, and related soil enzyme activities were determined. Important Findings Three main results were found: (i) high temperature accelerated decomposition rates of both litter types, and the temperature sensitivities of litter decomposition for BF leaves and that for CF needles are equivalent basically, (ii) high temperature enhanced soil enzyme activities in the two forest types, and the temperature sensitivities of polyphenol oxidase were significantly higher than those of the other soil enzymes and (iii) the temperature sensitivities of nitrate reductase were significantly higher in the CF soil than in the BF soil, while there was no significant difference in the temperature sensitivities of the other soil enzymes between BF and CF. As a long-term consequence, the high-temperature-induced acceleration of litter decomposition rates in these subtropical forests may cause carbon stored belowground to be transferred in the atmosphere, which may alter the balance between carbon uptake and release, and then alter the global carbon cycle in the coming decades.

Description: Aims and Methods Mostly due to land use changes, European heathlands have become increasingly rare. In addition, the increasing amount of atmospheric nitrogen deposition has resulted in an encroachment of grasses and a loss in species diversity. Despite many investigations, information about the precise environmental parameters that determine the development and maintenance of heathland vegetation is still insufficient. In order to determine the environmental factors that control heath succession and grass encroachment, and to develop appropriate management schemes, we studied the influence of several soil and microclimate parameters on species composition and vegetation characteristics in five successional stages in a coastal heathland on the island of Hiddensee, north-east Germany, where the encroachment of Carex arenaria has become a major problem. Important Findings We recorded the highest plant species richness in grey dune and birch forest plots, while the encroachment of C. arenaria let to a significant decline in plant species richness. The most important environmental factors influencing species richness and distribution of single species were microclimate, soil moisture, soil pH and the C/N ratio. While many studies reported the importance of differences in nutrient availability, we found no significant correlations between soil nutrient availability and vegetation pattern. Environmental conditions in dense C. arenaria stands, especially soil properties (e.g. soil pH), showed great differences in comparison to the other successional stages. However, no correlations between the encroachment of C. arenaria and single environmental factors were found. Our results show that not only soil nutrients are important abiotic factors in heaths but that also microclimate and soil moisture play an important role and that many factors are involved in heath succession and in the promotion of grass encroachment. Management plans for the conservation and restoration of heathlands should therefore focus on the specific site conditions and should take several abiotic and biotic factors into account.

Description: Aims The assembly of plant communities is a complex process which combines impacts from the species pool, dispersal and propagule pressure, niche requirements of colonizing species and the niche structure of the community. Recent theory development has incorporated all these aspects, e.g. in ‘stochastic niche theory’. We investigated recruitment into a species-rich grassland community, using an experimental approach where we manipulated the trait composition of the community and examined the success of colonizing species entering with various propagule pressure. Specifically, we examined two predictions: (i) colonization success increases with increasing difference between traits of the colonizing species and the trait profile of the community and (ii) colonization success increases with increasing propagule pressure. Methods The examined communities were species-rich semi-natural grasslands located in southern Sweden. After a careful documentation of the composition of the plant communities at the experimental sites, we manipulated the trait profile of species-rich grassland plots based on the plant functional trait specific leaf area (SLA), which is correlated with several key life history functions. In addition to SLA, seed mass was also used to describe the trait profile of grassland plots. Seeds of 12 plant species from the regional species pool, varying in SLA and seed mass, were sown into plots using four different levels of propagule pressure. Recruitment was examined after 1 year. We also planted juvenile ‘plug plants’ of the same species which allowed us to examine survivorship and growth beyond the seedling stage. Important Findings Overall we found very limited evidence for relationships between the traits of the colonizing species and the trait profile of the community and for recruitment after sowing these relationships were contrary to the prediction. Survival of plug plants after two seasons of growth was high irrespective of the trait profile of the community, but growth of plug plants was affected by the trait profile of the surrounding community. For four of the species there was a positive effect of increased propagule pressure on colonization. The results suggest that species assembly in species-rich grasslands is not strongly dependent on the niche structure of the community. However, the finding that colonization of only a third of the species responded positively to increased propagule pressure indicates that there might be niche-related effects that were not captured by our treatments. Overall, our results indicate that the factors determining colonization in this community are species specific. Some species are able to colonize irrespective of niche relationships, provided that the propagule pressure is sufficiently high to overcome stochastic mortality after seed arrival. For other species, however, we cannot exclude that niche assembly occurred, but we failed to identify the relevant niche factor.

Description: Aims The spatial segregation hypothesis and the low-frequency hypothesis are two important proposed mechanisms that delay or prevent competitive exclusion in ecosystems. Because tree species interact with their neighbors, the importance of these potential processes can be investigated by analyzing the spatial structures of tree species. Methods The distribution of the adults of 27 common tree species in a fully mapped 5-ha subtropical forest plot in Baishanzu, eastern China, was analyzed to investigate the community-level intra- and interspecific spatial association patterns. We first tested for the overall spatial pattern in the 5- to 40-m neighborhoods and classified first-order bivariate associations with a diametric scheme based on Ripley’s K and nearest-neighbor statistic ( G -function). Then heterogeneous Poisson null models were used to distinguish second-order interactions from overall spatial associations (including first-order effects). Finally, we analyzed correlations between the existence of species interactions and some attributes of the species involved. Important Findings Partial overlap and segregation increased with scale, whereas mixing decreased. Nearly 70% of the species pairs occurred less than expected at random, and only 3.4% of the species pairs were well mixed; 11.0% of all species pairs showed significant small-scale interactions, which was a greater frequency than expected by chance if species are abundant or prefer the same habitat, but less frequent than expected if species are highly aggregated. This suggests that both spatial segregation and low frequency of species facilitate species coexistence by reducing the opportunity that trees of two species encounter each other. The study also revealed that positive interactions were more prevalent than negative interactions in the forest, which indicates that positive interactions may have important effects on forest species assemblies.

Description: Aims Rhamnus lycioides L. subsp. Oleoides (Rhamnaceae) is a perennial shrub native to the Mediterranean Basin distributed along an altitudinal gradient, from sea level up to 1 000 m a.s.l. The specific goals of our study were (i) to compare plant morphology between two contrasting populations, (ii) to determine the reproductive system of R. lycioides , quantifying the relative importance of insects and wind as pollen vectors, (iii) to test if pollen limitation differs between populations, (iv) to study the main factors influencing fruit set and (v) to compare plant reproductive performance (mass allocation to flowers, fruits and seeds) between the two habitats. Methods In the present study, we examined plant morphology and the reproductive performance of R. lycioides L. in contrasting environments in two populations located at the extremes of its altitudinal range in the island of Mallorca (Balearic Islands, Western Mediterranean Basin) along a 3-year period. Plant morphology, the relative importance of insects and wind as pollen vectors, the pollen limitation to seed production and the plant reproductive performance (mass allocation to flowers, fruits and seeds) were determined. Important Findings Rhamnus lycioides individuals showed a higher plant surface/plant height ratio at the mountain than at the coast. This species appeared to be ambophilous despite its inconspicuous flowers, although the relative importance of wind as a pollination vector was higher at the mountain than at the coastal site. Fruit set was much higher at the mountain, where pollen appeared to be a limiting factor. By contrast, fruit set was not limited by pollen availability at the coastal population, where resource (water and nutrients) limitation seemed to be more determining. Flower size was greater at the coast, in contrast to fresh fruit weight that was higher at the mountain. Despite the relatively few differences between sites in precipitation patterns along the study period, water availability appeared to be the key factor explaining not only fruit set but also the reproductive performance of this species in the study populations.

Description: Aims A decrease in species diversity after fertilization is a common phenomenon in grasslands; however, the mechanism causing it remains highly controversial. The light competition hypothesis to explain loss of diversity has received much attention. The aim of the present paper was to test this hypothesis. Methods Fertilization was used to control above- and belowground resources simultaneously, while shade was used to control aboveground resource in an alpine meadow on the Tibetan Plateau. Univariate general linear models was used to estimate the effects of fertilization and shade on above- and belowground vegetation characteristics, including photosynthetically active radiation (PAR) in the understory, aboveground biomass, belowground biomass, R:S ratio, species richness and Simpson's diversity index. Important findings PAR was similar in the understory of shaded and fertilized plots, but only fertilization reduced species richness and diversity, suggesting that light competition alone could not explain diversity loss after fertilization. The root biomass and R:S ratio had a significant increase in shaded plots, but the richness and diversity did not change, suggesting that root competition alone also could not explain diversity loss after fertilization in this community. Our results illustrated that the root–shoot competition interactions, investigated from a functional groups perspective, should be the most reasonable explanation leading to the diversity loss due to fertilization.

Description: Aims Recent theories indicate that N is more in demand for plant growth than P; therefore, N concentration and N : C and N : P ratios are predicted to be positively correlated with relative growth rate (RGR) in plants under nutrient-enriched conditions. This prediction was tested in this study. Methods We examined the whole-plant concentrations of C, N and P and RGR, as well as the relationship between RGR and the concentrations and the ratios of N : C, P : C and N : P, for different harvest stages (the days after seed germination) of the seedlings of seven shrub species and four herbaceous species grown in N and P non-limiting conditions. The relationships among plant size, nutrient concentrations and ratios were subsequently determined. Important Findings RGR was positively correlated with N concentration and the ratios of N : P and N : C when the data were pooled for all species and for each shrub species, but not for individual herbaceous species. However, the relationship between RGR and P concentration and P : C was not significantly correlated for either shrubs or herbs. The variation of N among harvest stages and species was much greater than that of P, and the variation in N : P ratio was determined primarily by changes in N concentration. The shrub species differed from the herbaceous species in their N and P concentrations, nutrient ratios and in intraspecific relationships between RGR and nutrient ratios. These differences possibly reflect differences in the capacity for P storage and biomass allocation patterns. In general, our data support recent theoretical predictions regarding the relationship between RGR and C : N : P stoichiometry, but they also show that species with different life forms differ in the relationships among RGR and C : N : P stoichimetries.

Description: Aims Accurate forecast of ecosystem states is critical for improving natural resource management and climate change mitigation. Assimilating observed data into models is an effective way to reduce uncertainties in ecological forecasting. However, influences of measurement errors on parameter estimation and forecasted state changes have not been carefully examined. This study analyzed the parameter identifiability of a process-based ecosystem carbon cycle model, the sensitivity of parameter estimates and model forecasts to the magnitudes of measurement errors and the information contributions of the assimilated data to model forecasts with a data assimilation approach. Methods We applied a Markov Chain Monte Carlo method to assimilate eight biometric data sets into the Terrestrial ECOsystem model. The data were the observations of foliage biomass, wood biomass, fine root biomass, microbial biomass, litter fall, litter, soil carbon and soil respiration, collected at the Duke Forest free-air CO 2 enrichment facilities from 1996 to 2005. Three levels of measurement errors were assigned to these data sets by halving and doubling their original standard deviations. Important Findings Results showed that only less than half of the 30 parameters could be constrained, though the observations were extensive and the model was relatively simple. Higher measurement errors led to higher uncertainties in parameters estimates and forecasted carbon (C) pool sizes. The long-term predictions of the slow turnover pools were affected less by the measurement errors than those of fast turnover pools. Assimilated data contributed less information for the pools with long residence times in long-term forecasts. These results indicate the residence times of C pools played a key role in regulating propagation of errors from measurements to model forecasts in a data assimilation system. Improving the estimation of parameters of slow turnover C pools is the key to better forecast long-term ecosystem C dynamics.

Description: Aims Since 2000, the environmental flow controls project has been implemented in the lower Heihe River Basin, a typical arid inland river basin in northwest China, to restore the deteriorated ecological environment in this region. The aim of this study was to explore the impacts of groundwater fluctuations on vegetation dynamics. Our results can be used as a reference for water resources planning and management to maintain proper environmental flows in arid areas. Methods The location (by Global Positioning System) and depth of the monitoring wells, as well as groundwater table depth and salinity were measured in situ at each site from July to August 2009. Based on the measurements of the groundwater table depth and salinity following the implementation of environmental flow controls project (EFCP) in the lower Heihe River Basin, the groundwater fluctuations during the period from 2001 to 2009 were analyzed. Descriptive statistics and Pearson's correlation were used to analyze the relationship between vegetation changes and groundwater table fluctuations. Additionally, the spatial distributions of the groundwater table depth and salinity were interpolated using the simple kriging method. Trend analysis was applied to the time series of integrated Moderate Resolution Imaging Spectroradiometer normalized difference vegetation index data to identify interannual vegetation dynamics. The relationship between vegetation status and groundwater environment was investigated at different spatial scales by analyzing and comparing the time series and trends. Important Findings (i) The groundwater table and salinity increased significantly in most of the study area with spatial heterogeneity. On average, the groundwater table rose ~0.5 and 1.5 m in the upper and lower Ejina Basin, respectively, and the groundwater salinity increased across the study area by 0–4%. (ii) A notable correlation between the vegetation status and the groundwater table was revealed when the groundwater table depth fluctuated between 1.8 and 3.5 m, whereas the vegetation did not show an obvious response to groundwater table changes when the groundwater table depth was more than 5–6 m. (iii) Vegetation restoration mainly occurred in riparian areas within 500–1 000 m of from natural rivers, where the groundwater table depth varied from 2 to 4 m, and salinity was 〈5%, whereas vegetation degradation appeared at some locations where groundwater environment had deteriorated.

Description: Aims Beech ( Fagus sylvatica L.) is an important species in natural and managed forests in Europe. This drought-sensitive species dominates even-aged stands as well more natural stands composed of a mixture of tree species, age and size classes. This study evaluates the extent that heterogeneity in spacing and tree diameter affect the seasonal availability and use of water. Methods Two stands were evaluated: (i) a heterogeneous forest remnant (NAT) with trees up to ~300 years old, a mean top height of 28.4 m and a total of 733 stems ha –1 with stem diameters averaging 18 cm and (ii) an even-aged 80-year old stand (MAN), with a height of 25 m, and a total of 283 stems ha –1 with diameters averaging 38 cm. Stem sap flow, J s (g m –2 s –1 ), was continuously measured in 12 (MAN) and 13 (NAT) trees using 20-mm long heat dissipation sensors. Individual tree measures of sap flow were correlated using non-linear statistical methods with air vapour pressure deficit ( D , hPa) and global radiation ( R g , J m –2 day –1 ), along with constraints imposed by reductions in soil water content (SWC). SWC was measured as volumetric % using time domain reflectometry. Important Findings The daily integrated J s ( J s-sum ) for trees growing in the evenly spaced MAN stand and trees in canopy and closed forest positions in NAT stand decreased as the availability of soil moisture was reduced. In the heterogeneous NAT stand, SWC in a recently formed canopy gap remained high throughout the vegetation period. Based on regression models, the predicted relative decrease in J s-sum for dry relative to moist soil water conditions in the closed forest (at mean daily D = 10 hPa) was 7–11% for trees near the gap and 39–42% for trees in the closed forest. In MAN, the reduction in J s -sum was 29% in dry relative to moist conditions. J s -sum in the outer 20 mm of the xylem in NAT was lower than that in MAN and the rate of decline in J s with xylem depth was less in NAT than in MAN. In MAN, J s -sum in deep and outer xylem was negatively affected at low soil moisture availability; in NAT, this was the case for only the outer xylem indicating that deep roots could be important in supplying water at times of low soil moisture in the upper soil.

Description: Aims Evapotranspiration (ET) is a key component of water balance and is closely linked to ecosystem productivity. In arid regions, large proportion of precipitation (PPT) is returned to the atmosphere through ET, with only a small amount available to plants. Our objective was to examine the variability in ET–soil water relationship based on a set of ecosystems that are representative for semi-arid Inner Mongolia and its main land use practices. Methods This study used Eddy covariance (EC) data of water vapor (i.e. ET, mm), PPT (mm), soil volumetric water content (VWC, %), root biomass density and soil properties from three paired sites in semi-arid Inner Mongolia: cropland (Cropland-D) versus undisturbed grassland (Steppe-D), grazed grassland (Grazed Steppe-X) versus fenced grassland (Fenced Steppe-X) and poplar plantation (Poplar-K) versus undisturbed shrubland (Shrubland-K). The paired sites experienced similar climate conditions and were equipped with the same monitoring systems. Important Findings The ET/PPT ratio was significantly lower at Cropland-D and Grazed Steppe-X in comparison to the undisturbed grasslands, Steppe-D and Fenced Steppe-X. These differences are in part explained by the lower VWC in the upper soil layers associated with compaction of surface soil in heavily grazed and fallow fields. In contrast, the ET/PPT ratio was much higher at the poplar plantation compared to the undisturbed shrubland because poplar roots tap groundwater. The VWC of different soil layers responded differently to rainfall events across the six study sites. Except for Poplar-K, ET was significantly constrained by VWC at the other five sites, although the correlation coefficients varied among soil layers. The relative contribution of soil water to ET correlated with the density of root biomass in the soil ( R 2 = 0.67, P 〈 0.01). The soil water storage in the upper 50 cm of soil contributed 59, 43, 64 and 23% of total water loss as ET at Steppe-D, Cropland-D, Shrubland-K and Poplar-K, respectively. Our across-site analysis indicates that the site level of soil water for ET differs between land use and land cover type due to altered root distribution and/or soil physical properties. As a result, we recommend that ecosystem models designed to predict the response of a wide variety of vegetation to climatic variation in arid regions include more detail in defining soil layers and interactions between evaporation, infiltration and root distribution patterns.

Description: Aims The field of ecohydrology is providing new theoretical frameworks and methodological approaches for understanding the complex interactions and feedbacks between vegetation and hydrologic flows at multiple scales. Here we review some of the major scientific and technological advances in ecohydrology as related to understanding the mechanisms by which plant–water relations influence water fluxes at ecosystem, watershed and landscape scales. Important Findings We identify several cross-cutting themes related to the role of plant–water relations in the ecohydrological literature, including the contrasting dynamics of water-limited and water-abundant ecosystems, transferring information about water fluxes across scales, understanding spatiotemporal heterogeneity and complexity, ecohydrological triggers associated with threshold behavior and shifts between alternative stable states and the need for long-term data sets at multiple scales. We then show how these themes are embedded within three key research areas where improved understanding of the linkages between plant–water relations and the hydrologic cycle have led to important advances in the field of ecohydrology: upscaling water fluxes from the leaf to the watershed and landscape, effects of plant–soil interactions on soil moisture dynamics and controls exerted by plant water use patterns and mechanisms on streamflow regime. In particular, we highlight several pressing environmental challenges facing society today where ecohydrology can contribute to the scientific knowledge for developing sound management and policy solutions. We conclude by identifying key challenges and opportunities for advancing contributions of plant–water relations research to ecohydrology in the future.

Description: Aims In recent years, there has been an increased interest in examining changes in forest systems in response to drought, flooding, hurricanes and climate change. In the southern United States, forested wetlands are of special interest because of the extent of these forests. Coastal plain forested wetlands are among the most vulnerable to these climatic impacts. One of the problems in developing management practices for these coastal areas is the difficulty in adequately describing productivity relations and predicting how the structure and function of these communities might be affected by natural or anthropogenic disturbances. Community response to environmental change often occurs over a period of years, and the majority of reported studies are for 1–3 years in duration. This study documents long-term changes (10 years) in structure, composition and growth along a catena of high water table forested sites of an ancient beach ridge landscape in coastal South Carolina. Methods Aboveground net primary production (ANPP) of trees was monitored from 2000 to 2009 on three sites within a longleaf pine-swamp blackgum forest system on the southern end of the Waccamaw Neck area of Georgetown County, SC. Permanent study plots (20 x 25 m) were established across a moisture gradient (Dry, Intermediate, and Wet). Water levels were continuously monitored, litterfall was measured monthly and growth of trees ≥10 cm diameter at breast height was monitored on an annual basis. Annual litterfall and tree production values were summed to provide estimates of ANPP. Important Findings The study site was under severe drought conditions July 2001 through late summer 2002 and again in 2007. Diameter growth was affected in all three sites, but with different patterns. It seems that diameter growth in the Wet site was more sensitive to drought conditions in 2001–02 and 2007 than either Dry or Intermediate sites. While droughts did not seem to have a significant impact on litterfall in the Wet site, litterfall in the Intermediate site was more sensitive to the drought than either Dry or Wet sites. ANPP was significantly lower in both Intermediate and Wet sites in 2001 at ≤602 g/m 2 . Highest ANPP (〉1 000 g/m 2 ) occurred in the Intermediate and Wet sites in 2003 following a return to more normal water levels at the end of the drought. Maximum tree production occurred on the Wet site in 2003 (657 g/m 2 ), which exceeded total ANPP of any site in 2001. In the Dry site, ANPP remained relatively consistent throughout the study when compared to Wet and Intermediate sites. While litterfall estimates are well defined with 3–5 years of data, data collection is continuing to assess impact of drought on stem growth across the gradient, which is still not clear with 10 years of data.

Description: Aims To explore whether the trade-off between seed and vegetative reproductive modes is flexible in environments with different amounts of available resources to maintain optimal behaviors. Methods A transition matrix model was established to determine the optimal trade-off between seed and vegetative reproduction in resources–variable habitats. Important Findings The model predicts that plants allocate more resources to seed reproduction when available resources are scarce. With increasing resources, more vegetative propagules are produced. However, if resources keep increasing to a harmful level, plants would switch to seeds again.

Description: Aims Leymus chinensis is an original dominant plant in the Songnen grassland, and it has great value for restoration of severely degraded land. However, seeds are dormant, and low germination percentage is a problem for restoring L.chinensis grassland. The mechanism of seed dormancy is not been well understood. The primary aims of the present study were to investigate the dormancy mechanism of L.chinensis seeds (caryopses) with reference to the role of embryo-covering layers, endogenous hormones and temperature. Methods Changes in concentration of the endogenous hormones GA 3 , indoleacetic acid (IAA), zeatin riboside (ZR) and abscisic acid (ABA) in L.chinensis seeds from anthesis to maturity were measured by the enzyme-linked immunosorbent assay method. Germination at different stages of maturity were tested at 16/28°C, 5/28°C and 5/35°C for intact seeds with glumes (control), intact seeds with glumes removed (naked-whole seeds) and intact seeds with glumes and one-half of the endosperm removed (naked-half seeds). Important Findings Of the four endogenous hormones monitored, only the concentration of ZR differed significantly between the beginning and the end of seed development (increased); the GA 3 /ABA ratio also did not differ. Rank of germination percentage of control at the three temperature regimens was 5/28°C 〉 16/28°C 〉 5/35°C. Germination percentage of the naked-half seeds reached 100% under the three temperature regimens. We concluded that dormancy of L.chinensis seeds is not mainly controlled by endogenous hormones. Germination temperature, mechanical resistance of glumes and inhibition of endosperm are the main factors controlling dormancy and germination of L.chinensis seeds.

Description: Aims Oxygation refers to irrigation of crops with aerated water, through air injection using the venturi principle or the supply of hydrogen peroxide in the root zone, both using subsurface drip irrigation (SDI) system. Oxygation improves water use efficiency (WUE), producing more yield and, and therefore, optimizes the use of drip and SDI. But the efficiency of oxygation is quite possibly dependent on a number of factors. The primary objective of this study was, therefore, to quantify the effects of oxygation, emitter depths and soil type on crop root zone oxygen content, soil respiration, plant physiological response, biomass yield, quality and WUE of three crop species. Methods This study investigated the potential of oxygation to enhance soil respiration, plant growth, yield and water use efficiencies (WUE) of cotton and wheat in experiments in enclosed heavy-duty concrete troughs (tubs) and pineapple and cotton in field experiments. Experimental treatments in tubs for wheat included comparisons between two soil types (vertisol and ferrosol) and superimposed were two oxygation methods (Mazzei air injector and Seair Diffusion System) compared to a control, and for cotton, emitters at two depths using Mazzei air injectors were compared to a control. The field experiments compared Mazzei air injectors and a control for cotton in Emerald and pineapple in Yeppoon, both in central Queensland, Australia. Important findings In all experiments, soil oxygen content and soil respiration markedly increased in response to the oxygation treatments. The O 2 concentration in the crop root zone increased by 2.4–32.6%, for oxygation compared to control at the same depth. The soil respiration increased by 42–100%. The number of wheat ears, leaf dry weight and total dry matter were significantly greater in Mazzei and Seair oxygation compared to the control. Fresh biomass of wheat increased by 11 and 8%, and dry weight of wheat increased by 8 and 3% in Mazzei and Seair oxygation treatments compared to the control, respectively. Likewise, the irrigation water use efficiency increased with oxygation compared to the control in wheat. The yield, WUE and number of other physiological parameters in wheat were enhanced in vertisol compared to ferrosol. The seed cotton yield in the tub experiment increased with oxygation by 14%, and significant differences for fresh biomass, dry matter and yield were also noted between oxygation and the control in the field. Lint yield and WUE both increased by 7% using Mazzei in the cotton field trial during 2008–09. There were significant effects of oxygation on pineapple fresh biomass, and dry matter weight, industry yield and a number of quality parameters were significantly improved. The total fruit yield and marketable increased by 17 and 4% and marketable WUE increased by 3% using Mazzei. Our data suggest that the benefits of oxygation are notable not only for dicotyledonous cotton but also for monocotyledonous wheat and pineapple representing different rooting morphologies and CO 2 fixation pathways.

Description: Aims The Amazon basin plays an important role in the global carbon budget. Interannual climate variability associated with El Niño can affect the Amazon ecosystem carbon balance. In recent years, studies have suggested that there are two different types of El Ninos: eastern-Pacific (EP) El Niño and central-Pacific (CP) El Niño. The impacts of two types of El Niño on the Amazon climate and Amazon ecosystem are analyzed in the study. Methods A composite method has been applied to highlight the common features for the EP- and CP-El Niño events using observational data, IPCC-AR4 model output. Potential impacts of the two different types of El Niño on ecosystem carbon sequestration over the Amazon have been investigated using a process-based biogeochemical model, the Biome–BioGeochemical Cycles model (Biome–BGC). Important Findings Below-normal rainfall is observed year round in northern, central and eastern Amazonia during EP-El Niño years. During CP-El Niño years, negative rainfall anomalies are observed in most of the Amazon during the austral summer wet season, while there is average or above-average precipitation in other seasons. EP- and CP-El Niño events produce strikingly different precipitation anomaly pattern in the tropical and subtropical Andes during the austral fall season: wetter conditions prevail during EP-El Niño years and drier conditions during CP-El Niño years. Temperatures are above-average year round throughout tropical South America during EP-El Niño events, especially during austral summer. During CP-El Niño events, average or slightly above-average temperatures prevail in the tropics, but these temperatures are less extreme than EP year's temperature except in austral fall. These precipitation and temperature anomalies influence ecosystem productivity and carbon sequestration throughout the Amazon. Using the Biome–BGC model, we find that net ecosystem production (NEP) in the EP-El Niño years is below average, in agreement with most previous studies; such results indicate that the Amazon region acts as a net carbon source to the atmosphere during EP-El Niño years. In the CP-El Niño years, NEP does not differ significantly from its climatological value, suggesting that the Amazon forest remains a carbon sink for the atmosphere. Thus, even if CP-El Niño events increase in frequency or amplitude under global warming climate as predicted in some Global Climate Models, the Amazon rainforest may remain a carbon sink to the atmosphere during El Niño years in the near future.

Description: Aims In this study, we examined the effects of Solidago altissima (hereafter Solidago ) and two species in the genus Verbesina , Verbesina virginica and Verbesina occidentalis (hereafter Verbesina ), on the structure of an old-field plant community and establishment by an invasive plant species, Lespedeza cuneata (hereafter Lespedeza ). Methods We removed Solidago , Verbesina and both Solidago and Verbesina from 4-m 2 plots in an intact old-field community during two growing seasons. We then quantified the effects of these removals on richness, evenness, diversity and composition of the subdominant plant community. We also measured the total aboveground biomass and the aboveground biomass of the subdominant community. To assess how these removals affected establishment by Lespedeza , we planted 20 seeds in each plot and tracked seedling emergence and survival for one growing season. Important Findings Subdominant community evenness and Shannon diversity were higher in plots from which Solidago and Verbesina were removed relative to control plots. However, there were no effects of dominant species removal on species richness or composition of the subdominant community. Total aboveground biomass was not affected by dominant species removal, suggesting that the community of subdominant species exhibited compensation. In fact, subdominant community biomass was greater when Solidago , but not Verbesina , was removed. Light availability was also greater in plots where Solidago was removed relative to control plots throughout the growing season. In addition, removal of dominant species, in particular Solidago , indirectly reduced the emergence, but not survival, of Lespedeza seedlings by directly promoting subdominant community biomass. Taken together, our results suggest that dominant old-field plant species affect subdominant community structure and indirectly promote establishment by Lespedeza .

Description: Aims Salt stress resulting from soil salinization is one of the driving forces of the land degradation throughout the world. The modern Yellow River delta is one of the most saline areas in China. Phytoremediation can be an effective way to restore the salinized ecosystems, which requires selecting appropriate plant species. This study explored the germination responses of common plant species from contrasting habitats in the Yellow River delta to varying salinity, offering experimental information for ecosystem restoration in the Yellow River delta. Methods In this study, 15 common plant species from the Yellow River delta were divided into two groups (high-salinity and low-salinity groups) by their natural habitats using Canonical Correlation Analysis. Seeds of each species were treated with five salinity levels (0, 5, 10, 20 and 30 ppt), using a randomized complete block design, and germinated seeds were counted and removed daily for 28 days to calculate the final germination proportion and mean time to germination. The germination responses of seeds to salinity treatments were compared between the two groups. Important Findings In relation to salinity, seed germination behavior of the test species was closely related to the salinity level of the habitats over which they were distributed. Species from the habitats with higher salinity had generally higher final germination proportion but shorter mean time to germination than those from the habitats with lower salinity in all of five salinity treatments used. The final germination proportion and mean time to germination of low-salinity group species were more sensitive to salinity than those of high-salinity group species. Selecting the species with high final germination proportion and short mean time to germination is important for restoration of salinized land.

Description: Aims We used a 10-year field experiment that consisted of mowing and fertilizer treatments to evaluate the role of niche limitation in seedling establishment of species from different functional groups and of varying local abundance in an old field undergoing succession. Methods Seedlings of nine different species were planted into a successional field subjected to mowing and fertilizer treatments for 10 years that resulted in different plant communities and resource availability. Species representative of the factorial combination of three functional groups (C 4 grasses, C 3 grasses and legumes) and three abundance categories (abundant, present, or absent in the old field) were planted in four treatments resulting from the factorial combination of annual spring mowing (mowed and unmowed) and fertilizer application (annually fertilized and unfertilized). Survivorship, relative growth rate (RGR) and biomass were measured to determine the role of niche limitation on recruitment and growth. Important Findings Mowing increased the establishment success of seedlings. Fertilization had little influence on seedling performance and survivorship. C 3 grasses had the highest survivorship, while C 4 grasses and legumes had equivalent RGRs, but higher than C 3 grasses. By contrast, survivorship of legumes was unrelated to mowing or fertilizer, suggesting that establishment of this functional group was dependent on other, unmeasured conditions or processes. Species already present, but at low abundance, performed better than locally abundant or absent species. Propagule limitation may restrict the arrival of a species. However, recruitment and establishment was subject to niche limitation, which varied among species, functional groups and whether a species is already resident at the site and its abundance. Thus, species interactions restrict establishment during old-field succession, supporting the niche limitation hypothesis.

Description: Aims In the mid- and high-latitude regions, three quarters of the land surface is covered by boreal conifer forests, and snow lasts for 6–8 months of the year. Correctly modeling surface energy balance and snowmelt at mid- and high-latitudes has a significant influence on climate and hydrological processes. However, the heterogeneous and clumped forest structure exerts important control over the radiative energy at the forest floor, which results in large variations of underneath snow cover and snowmelt rate. The goal of this study is to investigate the impact of hierarchically clumped vegetation structure in boreal forest on snowmelt and exchanges of energy and water. Methods We used a simple Clumped Canopy Scheme (CCS) for canopy radiation transfer to characterize the impact of the clumped forest structure on net radiation at the snow surface underneath forests. The CCS was integrated with the Variable Infiltration Capacity macroscale hydrological model (herein referred to as VIC-CCS) to characterize the impact of clumped vegetation structure on surface energy balance and snowmelt during the snow season. A twin simulation, VIC-CCS and the standard VIC model, was performed to isolate the impact of CCS on the energy and water fluxes and snowmelt rates. The simulation results were compared to in situ measurements at four different forest stands: old aspen forest in the Southern Study Area (SOA), black spruce forests in the Southern and Northern Study Areas (SOBS and NOBS) and fen wetland in the Northern Study Area (NFEN) within the Boreal Ecosystem–Atmosphere Study (BOREAS) region in central Canada during 1994 to1996. Important Findings Simulations showed that the implementation of CCS has reduced incoming long-wave radiation at the underlying snow surface and, thereby, lowered the snowmelt rate. Comparison against ground observations of net radiation and surface flux rates showed a reasonable agreement while demonstrating implementation of CCS can markedly improve model surface energy budget and energy inputs computation for snowmelt. The modeled snowmelt matches reasonably well with observations with root mean square error (RMSE) ranging from 16.51 to 19.81 mm using VIC-CCS versus 29.86 to 32.61 mm for VIC only in the four forest sites. The improvement is the most significant for the deciduous forest (old aspen) site, reducing RMSE by16 mm. This study demonstrates that taking into account the effect of the clumped forest structure in land surface parameterization schemes is critical for snowmelt prediction in the boreal regions.

Description: Aims Nursery and forest operations require that frost hardiness results be produced faster than can be provided by controlled freezing tests. There is a great challenge to develop a rapid method for predicting frost hardiness that might not necessitate controlled freezing tests. The aim of this study was to examine the assessment of the frost hardiness of shoots and needles of Pinus bungeana by electrical impedance spectroscopy (EIS) with and without controlled exposure to freezing. Methods The frost hardiness of current-year shoots and needles of P. bungeana in an 8-year-old provenance field trial was measured at Shisanlin Nursery in Beijing, China, from September 2006 to January 2007 by means of EIS and conventional electrolyte leakage (EL). In the same plants, but without controlled freezing test, were monitored the EIS parameters in current-year shoots and needles. Important Findings The results showed that (i) after controlled freezing tests, the frost hardiness estimated by EIS parameters (extracellular resistance, r e , and membrane time constant, m ) was significantly correlated with the frost hardiness assessed by EL method ( r = 0.95) and (ii) for the samples not exposed to controlled freezing treatment, the relaxation time 1 for shoots and β for needles had greater correlations with the frost hardiness estimated by EL after controlled freezing tests relative to the other parameters ( r = –0.90 for shoots and r = 0.84 for needles, respectively). The parameters r e of shoots and needles and m of needles might be applied for measuring frost hardiness of samples after exposed to controlled freezing tests. The frost hardiness results can be obtained within 48 h. The parameters 1 of shoots and β of needles could be used for estimating the frost hardiness of samples without using a controlled freezing test. The frost hardiness results can be obtained within 24 h.

Description: Aims With a few exceptions, most well-known field biodiversity experiments on ecosystem functioning have been conducted in plant communities (especially grasslands) in which different numbers of species are planted as treatments. In these experiments, investigators have either kept the total seed weight or seed number constant across treatment plots. However, although in some cases attempts have been made to randomly choose species for planting from a designated species pool, the issue of possible ‘hidden treatments’ remains unsolved. Particularly, the total and relative abundance among species and across treatments could still affect the results. This study aims to determine whether treatments related to planted seed abundance and seed size may contribute to observed productivity. Methods We re-analyzed data from four biodiversity experiments based on a common seeding design (i.e. diversity treatments). Important Findings We show that diversity (richness) treatments usually involve a hidden treatment related to the planted seeds (i.e. weight, number and seed size) that ultimately affect plant density. Thus, the un-intended hidden treatment of seeding more seeds on more diverse plots contributes to the productivity to some degree. Such derivative but often neglected hidden treatments are important for further improvement of experimental design and have significant implications in ecological restoration.

Description: Aims According to traditional theory, superior competitive ability in plants generally requires relatively large plant body size. Yet even within the most crowded vegetation, most resident species are relatively small; species size distributions are right-skewed at virtually every scale. We examine a potential explanation for this paradox: small species coexist with and outnumber large species because they have greater ‘reproductive economy’, i.e. they are better equipped—and hence more likely—to produce offspring despite severe size suppression from intense competition. Methods Randomly placed plots within old-field vegetation were surveyed across the growing season. Within each plot, the largest (MAX) and smallest (MIN) reproductive individuals of each resident species were collected for above-ground dry mass measurement. We tested three hypotheses: (i) smaller resident species (with smaller MAX size) have generally smaller reproductive threshold sizes; (ii) smaller resident species have greater ‘reproductive economy’, i.e. a smaller MIN relative to MAX reproductive plant size; and (iii) MIN size predicts plot occupancy (species abundance within the community) better than MAX size. Important Findings The results supported the first and third, but not the second hypothesis. However, we could not reject the hypothesis that smaller species have greater reproductive economy, as it was not possible to record data for the largest potential plant size for each species—since even the largest (MAX) plants collected from our sampled plots were subjected to competition from neighbours under these natural field conditions. Importantly, contrary to conventional competition theory, more successful species (in terms of greater plot occupancy) had smaller minimum not larger (or smaller) maximum reproductive sizes. These results suggest that a small reproductive threshold size, commonly associated with relatively small potential body size, is generally more effective in transmitting genes into future generations when selection from neighbourhood crowding/competition is intense—at least within natural old-field vegetation. Accordingly, we propose a simple conceptual model that represents the basis for a fundamental paradigm shift in the predicted selection effects of crowding/competition on plant body size evolution.

Description: Aims Changing climate and land use patterns make it increasingly important that the hydrology of catchments and ecosystems can be reliably characterized. The aim of this paper is to identify the biophysical factors that determine the rates of water vapor loss from different types of vegetation, and to seek, from an array of currently available satellite-borne sensors, those that might be used to initialize and drive landscape-level hydrologic models. Important Findings Spatial variation in the mean heights, crowd widths, and leaf area indices (LAI) of plant communities are important structural variables that affect the hydrology of landscapes. Canopy stomatal conductance ( G ) imposes physiological limitation on transpiration by vegetation. The maximum value of G ( G max ) is closely linked to canopy photosynthetic capacity, which can be estimated via remote sensing of foliar chlorophyll or nitrogen contents. G can be modeled as a nonlinear multipliable function of: (i) leaf–air vapor pressure deficit, (ii) water potential gradient between soil and leaves, (iii) photosynthetically active radiation absorbed by the canopy, (iv) plant nutrition, (v) temperature and (vi) the CO 2 concentration of the air. Periodic surveys with Light Detection and Ranging (LiDAR) and interferometric RADAR, along with high-resolution spectral coverage in the visible, near-infrared, and thermal infrared bands, provide, along with meteorological data gathered from weather satellites, the kind of information required to model seasonal and interannual variation in transpiration and evaporation from landscapes with diverse and dynamic vegetation.

Description: Aims The Miyun Reservoir is the most important drinking water source for Beijing—the capital of China with a population of more than 16 million. Since the 1980s, the inflow to the reservoir has been decreasing, which seriously threatens the security of water use in Beijing. Our goal was to analyze the impact of land use and cover change (LUCC) on run-off yield in the upstream of the Miyun Reservoir. Methods In this study, the Soil andWater Assessment Tool (SWAT) was used to simulate the impacts of LUCC on the run-off yield in the Bai River catchment—upstream of the Miyun Reservoir basin in northern China. The investigation was conducted using two 6-year historical streamflow records: from 1986 to 1991 and from 2000 to 2005. A split sample procedure was used for model calibration and validation. The data from 1986 to 1988 and from 2000 to 2002 were used for calibration, while those from 1989 to 1991 and from 2003 to 2005 for validation. The SWAT calibration was based on monthly measured discharge at Zhangjiafen station at the catchment outlet from Bai River catchment. Additionally, the influence of LUCC on the surface run-off was distinguished from that of climate change on the surface runoff through SWAT scenarios modeling, the two-way analysis of variance (ANOVA), and the rainfall–run-off double-mass analysis in the Bai River catchment. Important Findings We found that the SWAT model could be used successfully to accurately simulate run-off yield and different LUCC patterns affecting water quantity in this catchment. During calibraion for the two periods the simulated monthly run-off satisfactorily matched the observed values, with the Nash–Sutcliffe coefficient 〉0.9 and 0.7 and a coefficient of determination of 0.9 and 0.65 at the outlet station (Zhangjiafen station), while during validation for the two periods the obtained values were 0.85, 0.65 and 0.9, 0.65, respectively. During the period of 1986–91, both the SWAT scenarios modeling and the analysis of the two-way ANOVA method showed that LUCC and climate change had some impact on run-off, and the impact of climate change was more significant than that of LUCC. Compared with the period during 1986–91, the run-off yield in the period during 2000–05 significantly decreased. The obtained results from the rainfall–run-off double-mass analysis indicate that since 1998 LUCC has had an increasing influence on the run-off, while the response of the run-off to rainfall has been decreasing. Since 1998, the LUCC has been a major driving force for run-off change in Bai River catchment.

Description: Aims Food-deceptive pollination, in which plants do not offer any food reward to their pollinators, is common within the Orchidaceae. As food-deceptive orchids are poorer competitors for pollinator visitation than rewarding orchids, their occurrence in a given habitat may be more constrained than that of rewarding orchids. In particular, the success of deceptive orchids strongly relies on several biotic factors such as interactions with co-flowering rewarding species and pollinators, which may vary with altitude and over time. Our study compares generalized food-deceptive (i.e. excluding sexually deceptive) and rewarding orchids to test whether (i) deceptive orchids flower earlier compared to their rewarding counterparts and whether (ii) the relative occurrence of deceptive orchids decreases with increasing altitude. Methods To compare the flowering phenology of rewarding and deceptive orchids, we analysed data compiled from the literature at the species level over the occidental Palaearctic area. Since flowering phenology can be constrained by the latitudinal distribution of the species and by their phylogenetic relationships, we accounted for these factors in our analysis. To compare the altitudinal distribution of rewarding and deceptive orchids, we used field observations made over the entire Swiss territory and over two Swiss mountain ranges. Important Findings We found that deceptive orchid species start flowering earlier than rewarding orchids do, which is in accordance with the hypotheses of exploitation of naive pollinators and/or avoidance of competition with rewarding co-occurring species. Also, the relative frequency of deceptive orchids decreases with altitude, suggesting that deception may be less profitable at high compared to low altitude.

Description: Aims Within a habitat of multiple plant species, increased resource availabilities and altered species abundances following disturbances create opportunities for exotic species to successfully establish and subsequently naturalize into its non-native environment. Such post-disturbance changes in abiotic and biotic environments may also promote a naturalized exotic species (or invading species) to become invasive through rapid colonization of the habitat sites by reducing the extent and size of resident plant species. By combining species life history traits with that of the disturbance-induced changes in habitat characteristics, we aimed to determine those interacting factors and associated mechanism allowing an exotic invasion to start off. Methods We used a modified version of the classic competition–colonization (CC) model which was formulated first by Hastings (1980) and studied later by Tilman (1994) to explain spatial coexistence of multiple species. Within this model framework, recruitment-limited spatial competition has explicitly been linked with interspecific resource competition without altering the basic assumptions and structure of the original CC model. Important findings The model results showed that at a constant rate of resource supply, invading species can stably coexist with native species via trade-offs between species competitive ability and colonizing ability. On the other hand, the model predicted that with a fluctuating resource condition, invading species can successfully invade a habitat following continuous reductions in the size and extent of native species. Whether or not invading species holds competitive superiority over the native species for limiting resource, we showed that there exists a range of variation in available resource that allows an exotic invasion to start off in post-disturbance habitat. The associated disturbance-induced mechanism promoting invading species to become invasive has been identified. It states that occurrences of disturbances such as fire or clear-cutting influence variation in resource availability, and in addition open up many vacant microsites; given these disturbance-induced changes, invading species with a higher rate of propagule production and with a higher survival rate of adults particularly in low-resource condition recruits microsites at faster rate relative to native competitor species, and with a given range of variation in resource availabilities, it maintains continued expansions following reductions in size and extent of native species. Moreover, we identified those interacting factors and their specific roles that drive this mechanism. These factors include propagule supply, variable resource level and vacant microsite availability. Increased availability of vacant microsites following disturbances creates an opportunity for rapid colonization. Given this opportunity, higher number of propagules supplied by the invading species enhances the rate of colonization success, whereas the resource variation within a range of given thresholds maintains enhanced colonization rate of the invading species while it depresses native competitor species. Owing to the each factor's invasion regulatory ability, controlling one or all of them may have strong negative impact on the occurrence of exotic invasion.

Description: Aims We investigated the impact of salinity on seed germination, chlorophyll content, chloroplast structure and photosynthesis of the green embryos in desiccated seeds of the xerophyte Haloxylon persicum , xero-halophyte Haloxylon ammodendron and euhalophyte Suaeda physophora. Methods Seeds of H. persicum , H. ammodendron and S. physophora were collected from natural environment in Fukang, Xinjiang province. Pretreatment with 700 mM NaCl was carried out to stimulate the natural ‘seed priming’; we analyzed the joint effect of salinity and different species on germination physiology and cotyledonal structure and photosynthetic function changes during germination and recovery stage. Important Findings We found that seeds did not suffer ion toxicity for the two halophytes H. ammodendron and S. physophora , as evidenced by the high final germination after ungerminated seeds pretreated with 700 mM NaCl were transferred to distilled water, but the final germination of the xerophyte H. persicum was significantly lower than that of control. The Na + concentration in embryos increased under salinity for all species, while K + concentration decreased by salinity only for H. persicum and H. ammodendron , i.e. the concentration of K + in embryos of H. persicum and H. ammodendron decreased by 36% and 46%, respectively. For all species, whether dry intact seeds or cotyledons of dry seeds imbibed in deionized water and NaCl solution, had high chlorophyll content. Treatment with NaCl also caused chloroplast thylakoids to swell and chlorophyll content to decrease in seeds of H. persicum , but no significant change was observed in the more salt-tolerant species S. physophora and H. ammodendron . Fluorescence measurement showed that 700 mM NaCl decreased the Fv/Fm ratio of cotyledons in seeds for all species, especially for H. persicum and H. ammodendron . Photosynthetic oxygen releasing was detected from the seeds that were moistened with distilled water and 700 mM NaCl for 6 or 24 h and from the seeds that were initially moistened with 700 mM NaCl in darkness for 10 days, then transferred to distilled water for another 6 and 24 h. The results indicated that the chlorophyll in cotyledon of desiccated seed had photosynthetic function in early germination stage, even under high-saline condition. In addition, the photosynthesis of chlorophyll in the embryonic cotyledons of desiccated seeds during germination was similar to that in leaves of young seedlings for all species. In conclusion, the chloroplasts of the two halophytes were more salt resistant compared with the xerophyte H. persicum . The photosynthetic function of chlorophyll in cotyledons of mature seeds may be ecologically important for seedling development in early stage for plants growing in extremely saline or arid environments.

Description: Aims Adaptive evolution along geographic gradients of climatic conditions is suggested to facilitate the spread of invasive plant species, leading to clinal variation among populations in the introduced range. We investigated whether adaptation to climate is also involved in the invasive spread of an ornamental shrub, Buddleja davidii , across western and central Europe. Methods We combined a common garden experiment, replicated in three climatically different central European regions, with reciprocal transplantation to quantify genetic differentiation in growth and reproductive traits of 20 invasive B. davidii populations. Additionally, we compared compensatory regrowth among populations after clipping of stems to simulate mechanical damage. Important Findings Our results do not provide evidence for clinal variation among invasive B. davidii populations: populations responded similarly to the different environments, and trait values were not correlated to climatic conditions or geographic coordinates of their home sites. Moreover, we did not detect differences in the compensatory ability of populations. We suppose that the invasive spread of B. davidii has been facilitated by phenotypic plasticity rather than by adaptation to climate and that continent-wide shuffling of cultivars due to horticultural trade may have limited local adaptation so far.

Description: Aims Legumes and non-legumes usually differ in using soil water and nutrients. Both water and nutrients are scarce in the semi-arid Mu Us Sandland where legume and/or non-legume shrubs coexist/dominate. Here, we addressed the responses of legume versus non-legume shrubs to different soil water and nutrient conditions. Methods We conducted an experiment in which a legume ( Hedysarum laeve ) and a non-legume ( Artemisia ordosica ) were used, both of which are dominant species in the Mu Us Sandland. Seedlings of these two species were subjected to three water levels (45.0, 67.5 and 90.0 ml every 3 days) and three nutrient treatments (0, 0.1% and 0.2% nutrient solution every week) during the experiment. Important Findings Interactions between water and nutrients on total biomass, root weight ratio and rain use efficiency (RUE) were detected in A. ordosica but not in H. laeve , suggesting that water effects on A. ordosica but not on H. laeve are dependent on soil nutrients. Nutrient addition alleviated drought stress and increased RUE in A. ordosica . The interspecific differences in response to soil water and nutrients may be linked to the ability of plants to fix nitrogen. In addition, under low-soil water or nutrient conditions, H. laeve produced more biomass than A. ordosica , and the opposite was the case under high-soil resources. The relationship between relative growth rate (RGR) and RUE [or nutrient use efficiency (NUE)] varied with two species. RGR of A. ordosica was positively correlated with both RUE and NUE while RGR of H. laeve was negatively correlated with NUE. The different responses may be linked to the trade-off between high-growth rate and low-resource use efficiency.

Description: Aims Mangrove species are classified as true mangroves and mangrove associates. However, as for some fringe species found mainly on the landward transitional zones of mangroves, no consensus among scientists could be reached in favor of this classification and much debate arises. We hypothesized that true mangroves differ from mangrove associates physiologically and ecologically in their ability to survive in mangrove environment. Methods To test this hypothesis, leaf structural traits and osmotic properties were used to describe variation in 33 mangrove species (17 true mangroves, 6 mangrove associates and 10 controversial species). Important Findings Specific leaf area (SLA) of true mangroves as well as leaf nitrogen concentration on a leaf mass (Nmass) were lower than that of mangrove associates; leaf succulence was, in general, twice as high in true mangroves compared to mangrove associates; true mangroves accumulated 8–9 times more Na and Cl than mangrove associates and the former had K/Na ratios 〈0.5, but the latter had K/Na ratios 〉0.5. These results indicated that true mangroves differed reliably from mangrove associates in leaf traits and osmotic properties. True mangroves are true halophytes and mangrove associates are glycophytes with certain salt tolerance. Combining distribution pattern information, the 10 controversial species were reclassified.

Description: Aims In nature, plant communities are affected simultaneously by a variety of functionally dissimilar organisms both above and below the ground. However, there is a gap of knowledge on interactive effects of functionally dissimilar organisms on plant communities that is needed to be filled to better understand and predict the general impact of biotic factors on plant communities. Methods We conducted a full-factorial mesocosm study to investigate the individual and combined impacts of above- and belowground functionally dissimilar organisms on a grassland plant community. We studied the effects of aboveground herbivores ( Helix aspersa , Gastropoda), arbuscular mycorrhizal fungi (AMF; Glomus spp., Glomeromycota) and endogeic earthworms ( Aporrectodea spp., Lumbricidae) on the diversity, structure and productivity of an experimental grassland plant community and each other. Important Findings Aboveground herbivory by snails decreased, AMF increased and earthworms had no effects on the diversity of the grassland plant community, while their combined effects were additive. The biomass of the plant community was negatively affected by snails and AMF, while no effects of earthworms or interaction effects were found. The plant species were differently affected by snails and AMF. No effects of the above- and belowground organisms on each other’s performance were detected. Since the effects of the functionally dissimilar organisms on the grassland plant community were mainly independent, the results indicate that their combined effects may be predicted by knowing the individual effects, at least under the conditions used in the present mesocosm study.

Description: Aims Symbiotic relationships between fungal endophytes and grass species are known to increase stress resistance in the grass host; however, there is little evidence to suggest that the positive effects occur early in the grass life cycle. In this study, we explored the effects of the endophyte Epichloë festucae on the growth and survival of Festuca eskia seedlings under drought and frequent cutting stress. Methods Festuca eskia seedlings were collected from the western part of the plant repartition area in a non-symbiotic population located in a mesic and heavily grazed site (W-NS) and from the eastern part in a symbiotic population from a xeric and lightly grazed site (E-S). The E-S population was experimentally freed from its endophyte (E-F). Two greenhouse experiments were conducted to compare growth and survival between the three seedling types under drought stress and frequent cutting. In the first experiment, 126 seedlings per seedling type ( n = 378) were grown for 6 weeks under non-limiting conditions before the cessation of watering. After 3 weeks without irrigation, full irrigation was restored for 10 days to measure the survival rate. Leaf length, leaf elongation rate and survival rate were assessed per population. In the second experiment, 156 seedlings per seedling type ( n = 468) were grown under non-limiting conditions. All seedlings were cut to 3 cm high, twice a week, during the first month of growth. Leaf elongation and tillering were monitored on 52 seedlings per seedling type. For each type, seedling survival rate was determined by the number of plants alive after 10 days of regrowth, without cutting. Important Findings The drought experiment revealed a phenotypic differentiation to drought in 30 F. eskia populations, suggesting adaptive differentiation: the eastern seedlings showed the highest survival rate. A trade-off between growth and survival was highlighted: the highest drought survival rate was associated with the lowest leaf elongation rate under non-limiting water conditions. Endophyte presence in the eastern population increased seedling drought survival. In contrast, cutting survival rate was similar between W-NS and E-S because the presence of the endophyte increased seedling survival to frequent cutting. However, this positive effect came with a cost: the endophyte reduced seedling tillering rate.

Description: Aims Selection of tree species with a high capacity to assimilate N and efficiently utilize N resources would facilitate the success of initial tree seedling establishment in infertile soils. The preference for N forms was tested using three pine species ( Pinus densata , Pinus tabuliformis and Pinus yunnanensis ). Pinus densata is a natural diploid hybrid between P. tabuliformis and P. yunnanensis . Methods Seedlings of three pine species were supplied with nitrate-N, ammonium-N (at two different pH regimes) or combined ammonium and nitrate as a nitrogen source in perlite culture in a controlled environment. Important Findings Seedlings of P. densata had higher total biomass and net photosynthesis when supplied with nitrate-N and ammonium nitrate than with ammonium-N. In parental species, total biomass and net photosynthesis for P. yunnanensis seedlings was higher in ammonium-N than in nitrate-N, whereas the other parental species P. tabuliformis had the highest total biomass among species for all treatments except ammonium with CaCO 3 . Most morphological traits in P. densata seedlings were intermediate between its two parental species. However, N-use efficiency and photosynthetic N-use efficiency of P. densata significantly exceeded both parents when supplied with nitrate-N and ammonium nitrate. The results suggested that the diploid hybrid tree species P. densata has a preference for nitrate and is not well adapted to ammonium-N as a sole nitrogen source regardless of the growth medium pH. Based on changes in environmental conditions, such as predicted future temperature increases in high altitude areas associated with climate change, P. densata is likely to be increasingly competitive and have wide adaptation in high altitude regions.

Description: Aims Halophila ovalis is a dioecious seagrass with a wide geographical and water depth range. The objective of this study was to understand its plasticity in clonal characteristics and biomass and also its allocation between above- and belowground in seagrass beds at different water depths. Methods Four monospecific H. ovalis beds, Shabei, Xialongwei, Beimu and Yingluo, which have different water depths at maximum tide level (MTL) but otherwise similar environmental conditions, were studied. We measured main clonal characteristics, i.e. horizontal internodal length, branching angle, shoot height, leaf length and width, and rhizome diameter. Above- and belowground biomasses of H. ovalis were also estimated using a harvest method. Important Findings We found no significant differences in coverage, leaf pair density or number of stem nodes per square meter between the four study sites. However , horizontal internodal length, leaf length, width, rhizome diameter and shoot height all increased significantly with the increases in water depth from 2- to 9-m MTL and decreased when the water depths were greater than 9-m MTL. No significant difference in above- or belowground biomass between the seagrass beds was found. However, the ratio of above- to belowground biomass was significantly higher in the shallowest site compared to the other three seagrass beds, indicating that more biomass was stored belowground in deeper water. The results demonstrated plastic responses in clonal characteristics and biomass allocation in H. ovalis across the water depth gradient.

Description: Aims Biological soil crusts (BSCs) can affect soil properties including water dynamics and cycling of soil carbon and nitrogen in dryland ecosystems. Previous research has mostly focused on effects of BSCs on soil water distribution or carbon and nitrogen fixation in the surface soil layer. Thus, little is known about effects of BSCs on properties throughout the soil profile. In the current study, we assessed the effects of BSCs on the distribution of soil water content (SW), soil organic carbon content (SOC) and soil total nitrogen content (STN) throughout the soil profile as well as the influence of water conditions on the effects of BSCs. Methods In a field investigation in Mu Us Sandland, North China, soil samples were taken from plots with and without BSCs on 13 and 28 September 2006, respectively. On the two sampling dates, average soil gravimetric water content was 3.83% (±1.29%) and 5.08% (±0.89%), respectively, which were regarded as low and high water conditions. Soil samples were collected every 5 cm to a depth of 60 cm, and SW, SOC and STN were measured in the laboratory. Important Findings (i) BSCs affected profile distribution of SW, SOC and STN. In addition, water conditions within the plots significantly modified BSCs’ effects on the profile distribution of SW, but marginally affected the effects on SOC and STN. (ii) Under high water conditions, SW in the surface soil layer (0–10 cm) was higher in soils with BSCs compared to those without BSCs, while the opposite was true in the deep soil layer (30–55 cm). (iii) Under low water conditions, SW was lower with BSCs compared with no BSCs in near-surface (5–20 cm) and deep (25–40 cm) soil layers. (iv) BSCs affected SOC and STN only in the surface soil layer (0–5 cm) and were modified by plot water conditions.

Description: Aims Land use management affects plant carbon (C) supply and soil environments and hence alters soil nitrogen (N) dynamics, with consequent feedbacks to terrestrial ecosystem productivity. The objective of this study was to better identify mechanisms by which land-use management (clipping and shading) regulates soil N in a tallgrass prairie, OK, USA. Methods We conducted 1-year clipping and shading experiment to investigate the effects of changes in land-use management (soil microclimates, plant C substrate supply and microbial activity) on soil inorganic N ( $${\hbox{ NH }}_{4}^{+}-\hbox{ N }$$ and $${\hbox{ NO }}_{3}^{-}-\hbox{ N }$$ ), net N mineralization and nitrification in a tallgrass prairie. Important Findings Land-use management through clipping and/or shading significantly increased annual mean inorganic N, possibly due to lowered plant N uptake and decreased microbial N immobilization into biomass growth. Shading significantly increased annual mean mineralization rates ( P 〈 0.05). Clipping slightly decreased annual mean N nitrification rates whereas shading significantly increased annual mean N nitrification rates. Soil microclimate significantly explained 36% of the variation in $${\hbox{ NO }}_{3}^{-}-\hbox{ N }$$ concentrations ( P = 0.004). However, soil respiration, a predictor of plant C substrate supply and microbial activity, was negatively correlated with $${\hbox{ NH }}_{4}^{+}-\hbox{ N }$$ concentrations ( P = 0.0009), net N mineralization ( P = 0.0037) and nitrification rates ( P = 0.0028) across treatments. Our results suggest that change in C substrate supply and microbial activity under clipping and/or shading is a critical control on $${\hbox{ NH }}_{4}^{+}-\hbox{ N }$$ , net N mineralization and nitrification rates, whereas clipping and shading-induced soil microclimate change can be important for $${\hbox{ NO }}_{3}^{-}-\hbox{ N }$$ variation in the tallgrass prairie.

Description: Aims Nothapodytes nimmoniana (Family Icacinaceae) is a deciduous tree species distributed in Asia facing severe population decline. Wood chips from the tree are a source of camptothecin, a globally sought-after alkaloid with cancer-treating properties, and are harvested unsustainably in natural forests. We studied the pollination ecology of the species and asked if there are constraints in pollination and fruiting success in its natural populations. We also discuss the potential effects of wood extraction on pollinators and reproductive success in the population. Methods The study was carried out during the flowering season in two populations with varying exploitation levels, both located in the Protected Area Network in the Western Ghats of Karnataka State. We assessed floral resource availability and measured pollinator diversity and activity in the canopy from the perspective of the biology of the species. We quantified pollinator abundance and percent fruit set as a function of population density. Important Findings Flowers belong to the fly pollination syndrome and are open to visits by generalists such as Apis dorsata and Trigona iridipennis . Fruiting success did not vary between exploited and unexploited sites, but there was a significant difference in pollinator assemblage. In a lean male flowering year, fruit set was low, suggesting pollen limitation in the population. No fruiting was recorded in the second year at the site where trees were felled soon after the flowering period. We argue that when male floral resources are altered in exploited populations, pollinators of generalist nature may show a shift in foraging pattern. Also, generalist plants may be as susceptible to pollination loss as are specialist plants. The need for outcrossing in the species would probably exacerbate this vulnerability.

Description: Aims Estimation of gross primary production (GPP) from remote sensing data is an important approach to study regional or global carbon cycle. However, for a given algorithm, it usually has its limitation on applications to a wide range of vegetation types and/or under diverse environmental conditions. This study was conducted to compare the performance of two remote sensing GPP algorithms, the MODIS GPP and the vegetation photosynthesis model (VPM), in a semiarid temperate grassland ecosystem. Methods The study was conducted at a typical grassland site in Ujimuqin of Inner Mongolia, North China, over 2 years in 2006 and 2007. Environmental controls on GPP measured by the eddy covariance (EC) technique at the study site were first investigated with path analysis of meteorological and soil moisture data at a daily and 8-day time steps. The estimates of GPP derived from the MODIS GPP and the VPM with site-specific inputs were then compared with the values of EC measurements as ground truthing at the site. Site-specific max (α) was estimated by using rectangular hyperbola function based on the 7-day flux data at 30-min intervals over the peak period of the growing season (May to September). Important Findings Between the two remote sensing GPP algorithms and various estimates of the fraction of absorbed photosynthetic active radiation (FPAR), the VPM based on FPAR derived from the enhanced vegetation index (EVI) works the best in predicting GPP against the ground truthing of EC GPP. A path analysis indicates that the EC GPP in this semiarid temperate grassland ecosystem is controlled predominantly by both soil water and temperature. The site water condition is slightly better simulated by the moisture multiplier in the VPM than in the MODIS GPP algorithm, which is a most probable explanation for a better performance of the VPM than MODIS GPP algorithm in this semiarid grassland ecosystem.

Description: Aims Plants are able to influence their growing environment by changing biotic and abiotic soil conditions. These soil conditions in turn can influence plant growth conditions, which is called plant–soil feedback. Plant–soil feedback is known to be operative in a wide variety of ecosystems ranging from temperate grasslands to tropical rain forests. However, little is known about how it operates in arid environments. We examined the role of plant–soil feedbacks on tree seedling growth in relation to water availability as occurring in arid ecosystems along the west coast of South America. Methods In a two-phased greenhouse experiment, we compared plant–soil feedback effects under three water levels (no water, 10% gravimetric moisture and 15% gravimetric moisture). We used sterilized soil inoculated with soil collected from northwest Peru ( Prosopis pallida forests) and from two sites in north-central Chile ( Prosopis chilensis forest and scrublands without P. chilensis ). Important Findings Plant–soil feedbacks differed between plant species and soil origins, but water availability did not influence the feedback effects. Plant–soil feedbacks differed in direction and strength in the three soil origins studied. Plant–soil feedbacks of plants grown in Peruvian forest soil were negative for leaf biomass and positive for root length. In contrast, feedbacks were neutral for plants growing in Chilean scrubland soil and positive for leaf biomass for those growing in Chilean forest soil. Our results show that under arid conditions, effects of plant–soil feedback depend upon context. Moreover, the results suggest that plant–soil feedback can influence trade-offs between root growth and leaf biomass investment and as such that feedback interactions between plants and soil biota can make plants either more tolerant or vulnerable to droughts. Based on dissecting plant–soil feedbacks into aboveground and belowground tissue responses, we conclude that plant–soil feedback can enhance plant colonization in some arid ecosystems by promoting root growth.

Description: Aims Spatial processes and environmental control are the two distinct, yet not mutually exclusive forces of community structuring, but the relative importance of these factors is controversial due to the species-specific dispersal ability, sensitivity towards environmental variables, organism's abundance and the effect of spatial scale. In the present paper, we explored spatial versus environmental control in shaping community composition (i.e. β-diversity) and species turnover (i.e. change of β-diversity) at an alpine meadow along a slope aspect gradient on the Qinghai–Tibetan Plateau at different spatial scales of sampling (quadrats and plots), by taking account of seed dispersal mode and abundance. Methods We examined the relative importance of spatial processes and environmental factors using all species and four additional subsets of selected species. Moreover, we attempted to explore the effect of scale (quadrat refers to scale of ~0.3 m and plot of ~8 m) on their counter balance. The data were analyzed both by variation partitioning and multiple regressions on distance matrices. The spatial structure was modelled using Moran's eigenvector maps (MEM). Important Findings Both spatial processes and environmental factors were important determinants of the community composition and species turnover. The community composition in the alpine meadow was controlled by spatially structured environment (17.6%), space independent of environment (18.0%) and a negligible effect of environment independent of space (4.4%) at the scale of quadrats. These three components contributed 21.8, 9.9 and 13.9%, respectively, at the scale of plots. The balance between the forces at different spatial scales drove community structures along the slope aspect gradient. The importance of environmental factors on β-diversity at alpine meadow increased with scale while that of spatial processes decreased or kept steady, depending on dispersal mode and abundance of species comprising the subset. But the ‘pure’ effect of spatial processes on species turnover increased with scale while that of environmental factors decreased. This discrepancy highlights that β-diversity and species turnover were determined jointly by spatial processes and environmental factors. We also found that the relative roles of these processes vary with spatial scale. These results underline the importance of considering species-specific dispersal ability and abundance of species comprising the communities and the appropriate spatial scale in understanding the mechanisms of community assembly.

Description: Aims Despite the current interest in services provided by ecosystems and the role of biodiversity, the relationship among human attitudes, biodiversity and ecosystem services has hardly been investigated. Moreover, few studies have examined attitudes toward nature in cross-cultural comparisons. This study investigates the attitudes of Chinese and Swiss people, both environmental experts and laypersons, toward forest biodiversity and ecosystem services. Methods Overall, 640 people in China and Switzerland were interviewed with the help of a standardized questionnaire. In each country, the study population was equally divided into an urban (80 city dwellers and 80 environmental science students) and a rural (80 forest visitors and 80 farmers) study group. The 15-minute interviews took place in the cities of Beijing and Zurich and in the rural forested areas of Dujiangyan, Sichuan Province and Lake Sempach, canton Lucerne. Attitudes toward forest biodiversity were investigated with the help of color photographs that depicted both monocultures and species-rich forests typical for China and Switzerland. Attitudes toward ecosystem services were investigated with the help of 13 statements on provisioning, regulating, cultural and supporting services of forests. Important Findings On average, Chinese participants showed no strong preferences for biodiversity, whereas the Swiss clearly preferred species-rich forests over monocultures. However, Chinese environmental science students did prefer species-rich forests and attributed to them a higher conservation value because of their higher biodiversity. Although there were no strong preferences for Chinese versus Swiss forests, all participants correctly answered that Chinese forests are more species rich in terms of plants and animals and thus found them less boring and more interesting, but also less managed, than Swiss forests. All participants highly valued the ecosystem services provided by forests; especially the regulating and supporting ones. Environmental science students and farmers placed more importance on the provisioning services, whereas city dwellers and forest visitors emphasized more on the regulating services. The disjuncture between the high ecological quality of species-rich forests and their low attractiveness to Chinese study participants points to a potential conflict between conservation policies and the public’s preferences. A better communication of ecosystem services provided by forest biodiversity to the public might change these preferences in favor of ecological quality, as already observed among Chinese environmental science students.

Description: Aims Terrestrial net primary production (NPP), the balance of gross primary production (GPP) and autotrophic respiration (AR), is a critical measure of carbon sequestration capacity for the Earth’s land surface. The aim of this study was to understand the spatio-temporal variability of NPP associated with GPP and AR in the Yangtze River Basin (YRB), China, from 2000 to 2009 during which the basin warmed significantly. Methods We first derived AR and carbon-use efficiency (CUE) from the improved Moderate Resolution Imaging Spectroradiometer GPP/NPP products (MOD17) and then conducted spatial analysis to quantify how NPP relates to GPP, AR and their relationship with key observed climate variables (temperature, precipitation and sunshine percentage) in the YRB during 2000–2009. Important Findings The spatial pattern of NPP in the YRB was predominantly determined by GPP and further modified by AR. Higher GPP and relatively low AR made the southern Jinshajiang sub-basin the most productive area in NPP in the YRB. A large portion of the YRB experienced a warmer and drier climate trend in the growing season during 2000–2009. In the upper reaches of the basin, possessing a relatively low temperature base, increases in temperature led to greater increases in GPP than those in AR, resulting in greater increased NPP. However, in the middle and lower reaches of the basin where the base temperature is relatively high, increases in temperature led to greater increases in AR than those in GPP, leading to decreases in NPP. Overall, 86.7% of the vegetated area showed a consistent GPP and NPP trend through time with 71.3% of the vegetated area having a positive trend both in GPP and NPP, and the remaining 13.3% of vegetated areas showed an opposite trend in GPP and NPP, with positive GPP and negative NPP trajectories dominating (10.1% of vegetated area) the trend. Although climate warming generally had positive effects on vegetation growth in most areas of the basin, areas with increased NPP (74.5%) were less extensive than those with increased GPP (81.4%) due to the wider increase in AR (82.2%). During the study period, increases in AR offset 62% of the total increased GPP, leading to a substantial decline of CUE, particularly in the warmer lower altitude regions in the southeast. Our work reveals the diverse responses of NPP associated with GPP and AR as the climate warms and generally suggests that NPP in the middle and lower sub-basins in the YRB is more sensitive to future climate warming. These findings enhance our understanding of terrestrial ecosystem carbon dynamics in response to global warming and provide a scientific basis for managing ecosystem productivity in the YRB, China.

Description: Aims Understanding the response of farmland weed community assembly to fertilization is important for designing better nutrient management strategies in integrated farmland ecological systems. Many studies have focused on weed characteristics, mainly crop–weed competition responses to fertilization or weed communities alone. However, weed community assembly in association with crop growth is poorly understood in the agroecosystems, but is important for the determination of integrated weed management. Biodiversity promotes ecosystem productivity in the grassland, but whether it applies to the agroecosystems is unclear. Based on an 11-year field experiment, the cumulative effects of different fertilization patterns on the floristic composition and species diversity of farmland weed communities along with wheat growth in a winter wheat–soybean rotation were investigated. Methods The field trial included five fertilization patterns with different combinations of N, P and K fertilizers. Species composition and diversity of weed communities, aboveground plant biomass and nutrient accumulation of weeds and winter wheat, light penetration to the ground surface and wheat yield were measured at each plot in 2009 and 2010. Multivariate analysis, regression and analysis of variance were used to analyze the responses of these parameters to the different fertilization treatments. Important Findings Four dominant weeds ( Galium aparine L., Veronica persica Poir., Vicia sativa L. and Geranium carolinianum L.) accounted for ~90% of the total weed density in the 2 years of experimental duration. The residual weed community assembly was influenced primarily by topsoil available nutrients in the order P 〉 N 〉 K. Competition for nutrients and solar radiation between crops and weeds was the main indirect effect of fertilization on the changes in weed community composition and species diversity. The indices of species diversity (species richness, Shannon–Wiener, Pielou and Simpson indices) showed significant linear relationships with wheat yield. The balanced fertilization treatment was more efficient at inhibiting the potential growth of weeds because of solar radiation being intercepted by wheat. These results support the conclusion that wheat yield is favored by balanced fertilization, whereas the weed community is favored by PK fertilization in terms of density and diversity. However, the negative effects on wheat yield may be compromised by simultaneous positive effects of weed communities in the fertilization treatments, for instance, the NP and NK treatments, which are intermediate in terms of increasing wheat production and to a level maintaining a diverse community.

Description: Aims We explored the decomposition rates of single- and mixed-species litter, the litter-mixing effect and the effect of component litters in a mixture on decomposition. Methods In a litter bag experiment, shoot litters from two dominant grasses ( Leymus chinensis and Stipa baicalensis ) and one legume ( Melissitus ruthenica ) were decomposed separately and as a mixture from May 2010 to September 2011 in the Hulun Buir meadow steppe of Inner Mongolia, China. We separated the litter mixture into its individual component litters (i.e. the different single-species litters) and analyzed the changes in litter mass remaining and litter nitrogen (N) remaining during single- and mixed-species litter decomposition. Important Findings (i) Litter mixing had significant positive effects on litter decomposition. The litter-mixing effect was strongest for the mixture of S. baicalensis and L. chinensis litters, followed by the mixture of S. baicalensis and M. ruthenica litters. (ii) Single-species component litters decomposed faster in the mixtures than separately (positive effect), but these effects were not significant for legume species M. ruthenica litter. Relative to single-species litter decomposition, the decomposition rates of the two grass ( S. baicalensis and L. chinensis ) litters significantly increased when they were mixed with each other or with M. ruthenica litter. (iii) For each species litter type, the percentage of litter N remaining during decomposition ( N R ) differed between the single-species litter and mixed litter treatments. The N R of S. baicalensis litter was higher when it was decomposed in the mixture than in isolation. However, the N R of L. chinensis litter was lowest in its mixture with M. ruthenica among the treatments. Regardless of its decomposition in the mixture or in isolation, the N R of M. ruthenica litter varied little among treatments. There was a significant positive relationship between the N R and percentage of initial litter mass remaining in both the single litter and mixed litter treatments. These results suggest that N transfer may happen among component litters in mixture and further affect the decomposition.

Description: Aims Forest disturbance from extreme weather events due to climate change could increase the contribution of fresh green leaves to the litter layer of soil and subsequently alter the composition and activity of the soil microbial properties and soil carbon cycling. The objective of this study was to compare the effect of naturally fallen litter and fresh leaves on the soil microbial community composition and their activities. Methods Fresh leaves and normal fallen litter were collected from four tree species ( Pinus elliottii , Schima superba , Acacia mangium , A. auriculaeformis ) in subtropical China and mixed with soil. Soil microbial community composition was determined using PLFAs, and its activity was quantified by soil respiration. During a 12-month period, the decomposition rate of litter was measured bimonthly using a litterbag method. Soil microbial samples were collected after 6 and 12 months. Soil respiration was measured monthly. Important Findings We found that fresh leaves decomposed faster than their conspecific fallen litter. Although total microbial biomass and bacterial biomass were similar among treatments, soil fungal biomass was higher in fresh leaf than fallen litter treatments, resulting in greater values of the Fungal phospholipid fatty acids (PLFAs)/Bacterial PLFAs ratio. Fungal PLFA values were greater for Schima superba than the other species. The effect of litter type on soil respiration was species-dependent. Specifically, fallen litter released 35% more CO 2 than fresh leaves of the conifer P. elliottii . The opposite pattern was observed in the broadleaf species whose fresh leaf treatments emitted 17%–32% more CO 2 than fallen litter. Given future predictions that global climate change will cause more disturbances to forests, these results indicate that conifer and broadleaf forests in subtropical China may respond differently to increased fresh litter inputs, with net soil microbial respiration decreasing in conifer forests and increasing in broadleaf forests.

Description: Aims The Mongolian Altai is an old settlement area, which is populated by pastoral nomads since 2000–3000 years. Forests in this region (at ca. 2300 m a.s.l.) are highly fragmented and border on steppe and alpine grasslands, which are used for mobile livestock husbandry. The climate in Central Asia is warming to levels clearly above the global average, which affects the vegetation. Furthermore, the transition from planned to market economy and the decollectivization of livestock 20 years ago has strongly changed land use practices in Mongolia, especially resulting in an increase in recent logging activities. We were interested in the question how climate warming and selective logging influence the annual stem growth and the stand structure. Methods The impact of climate and land use by the pastoral nomads on the annual stem increment of more than 1800 trees of Siberian larch ( Larix sibirica ) was analyzed. Different groups of trees with divergent growth trends depending on the social position and stand history were identified by non-metric multidimensional scaling and analysis of similarities. Long-term trends in the annual stem increment were analyzed by establishing separate regional growth curves for trees of different age classes. Important Findings Instrumental climate data substantiate an increase of temperature by 2.1°C since 1940 at constant precipitation. Trees benefit from the increased temperatures. Climate–response analysis revealed that radial stem increment was promoted by the temperature in early summer, but also high precipitation in spring and in the year before tree-ring formation. Forest dynamics is also strongly influenced by anthropogenic activities. In addition to the natural forest dynamics, logging resulted in divergent growth trends within given age classes and habitats (forest interior and forest edge); overall, 22 groups of trees with different characteristics in the annual radial stem increment were identified. A tree-ring series-based reconstruction of logging intensity since 1935 suggests that moderate selective logging occurred throughout the study period. However, selective logging was strongly intensified after 1990 as the result of the breakdown of the Communist regime in Mongolia and the transition from centrally planned to market economy. Because tree stump densities showed that the ratio of felled to live trees was 2:1 in the interior or even 0.9:1 at the edges of the forests and most logging occurred during the past 20 years, it must be concluded that the forests of the Mongolian Altai are presently exploited far beyond the level of sustainability. A close correlation of the ratio of felled to live trees with the density of summer camps of pastoral nomads in the vicinity suggests that trees are primarily felled by the local population.

Description: Aims Species aggregation is commonly seen in plant communities and may increase diversity by causing intraspecific competition to exceed interspecific competition. One potential source of this spatial aggregation is seed dispersal but it is unclear to what extent aggregated seed distributions affect plant diversity in real communities. Using a field experiment, I tested whether uniform or aggregated seed arrival alters community structure and whether these effects vary with sowing density. Methods The experiment consisted of two spatial seeding treatments (uniform and aggregated) that were fully crossed with three seed density treatments. Sixty, 3 x 4-m plots were arrayed in a low-diversity grassland located in Kansas, USA. Each plot was divided into forty-eight, 0.5 x 0.5-m patches. For aggregated seeding treatments, each of the 15 species was sown into three randomly selected patches within the plot (3 x 15 = 45). To create a uniform species arrival but control for the seed addition method, all 15 species were sown into 45 individual patches (with three patches remaining unsown) within each plot. Seed mass for each species was held constant at the plot scale between uniform or aggregated treatments within a given level of the sowing density treatment. After two growing seasons, plant density was quantified for all sown species in 15 randomly selected patches from each plot. Important Findings I found evidence for shifts in community structure in response to the different spatial seeding patterns. The evenness of added species was higher under aggregated than uniform sowing patterns. There was no detectable effect of aggregated seed sowing on species richness at 3.75 m 2 scale. However, when species richness was extrapolated to larger scales (11.25 m 2 ), aggregated sowing was predicted to have greater richness than uniform sowing. Effects of seed aggregation on community structure were apparent only at moderate to high sowing rates, yet the latter are within the range of measured seed dispersal in similar grasslands. Additionally, as sowing density increased, seed mass became an increasingly effective predictor of relative abundances for added species, but only under uniform sowing patterns supporting the idea that aggregated dispersal may buffer weaker (smaller seeded) species from competition during colonization. This is the first experiment to show that aggregated seed dispersal patterns can increase at least some components of plant diversity in undisturbed grasslands and suggests that previous seed dispersal experiments, which utilize uniform seed sowing, may underestimate the potential effect of dispersal on plant community structure.

Description: Aims In plants, resource allocation to growth and reproduction may depart from trade-off expectations if (i) investment in growth and reproduction relies on different resource pools, (ii) allocation to reproduction is dependent upon reaching some growth threshold or (iii) reproduction is developmentally linked to growth, both functions relying on the same resource pool. We examined the effects of enhanced resource level on patterns of resource allocation to growth and reproduction in holm oak ( Quercus ilex sbsp. ballota ), a Mediterranean evergreen tree. Methods In the experimental year (2003), we manipulated the amount of soil nutrients in autumn (to increase nutrient uptake during shoot elongation in the following spring) and soil water in summer (to increase water uptake during acorn growth). Indicators of growth and male and female reproduction were estimated in the pre-experimental (2002), experimental (2003) and post-experimental (2004) years. Important Findings Fertilized trees produced significantly longer shoots, but the number of female flowers per shoot was not affected by treatments. The production of male catkins was also enhanced by fertilization. Irrigation did not affect the production of female flowers or abortion rates. Growth and female reproduction showed no consistent relationship in untreated trees, but resource addition elicited a growth-female reproduction trade-off in the experimental year. The sign of this significant relationship changed in the post-experimental year, indicating the existence of lagged effects of resource manipulation on acorn production. Overall, patterns of allocation to growth and reproduction varied as a function of sex, resource availability and year, a result consistent with extreme allocational plasticity in holm oak.

Description: Aims Within-community variation accounts for a remarkable proportion of the variation in leaf functional traits. Plant height may be used to explain within-community variances of leaf traits because different microenvironments, especially light intensity, may occur at different heights. This study determines whether or not leaf nitrogen (N) and phosphorus (P) contents as well as leaf mass per area (LMA) are interspecifically correlated with the adult height of forest woody species. We also discuss these relationships with respect to community structure and functions of the ecosystem. Methods A total of 136 dicotyledonous woody species from 6 natural forests (3 evergreen and 3 deciduous ones) in East China (18°44'–45°25'N, 108°50'–128°05'E) were investigated. For each of the 157 species–site combinations, 6 traits were measured: plant adult height relative to the forest canopy ( H R ), leaf N and P contents per unit area ( N area and P area ), N and P contents per unit dry mass ( N mass and P mass ) and LMA. The total variances of each leaf trait across sites were partitioned in a hierarchical manner. The relationships between leaf traits and H R within forest communities were then analyzed using both standardized major axis regression and Felsenstein’s phylogenetic independent contrasts. Relationships between evergreen and deciduous forests were compared by linear mixed models. Important Findings H R is a robust predictor of leaf N area , P area and LMA, explaining 36.7, 39.4 and 12.0% of their total variations across forests, respectively. Leaf N area , P area and LMA increased with H R in all of the studied forests, with slopes that were steeper in evergreen forests than in deciduous ones. Leaf N mass and P mass showed no significant relationship with H R generally. The increase in leaf N area , P area and LMA with H R across species is assumed to maximize community photosynthesis and may favor species with larger H R .

Description: Aims Studies integrating phylogenetic history and large-scale community assembly are few, and many questions remain unanswered. Here, we use a global coastal dune plant data set to uncover the important factors in community assembly across scales from the local filtering processes to the global long-term diversification and dispersal dynamics. Coastal dune plant communities occur worldwide under a wide range of climatic and geologic conditions as well as in all biogeographic regions. However, global patterns in the phylogenetic composition of coastal dune plant communities have not previously been studied. Methods The data set comprised vegetation data from 18463 plots in New Zealand, South Africa, South America, North America and Europe. The phylogenetic tree comprised 2241 plant species from 149 families. We calculated phylogenetic clustering (Net Relatedness Index, NRI, and Nearest Taxon Index, NTI) of regional dune floras to estimate the amount of in situ diversification relative to the global dune species pool and evaluated the relative importance of land and climate barriers for these diversification patterns by geographic analyses of phylogenetic similarity. We then tested whether dune plant communities exhibit similar patterns of phylogenetic structure within regions. Finally, we calculated NRI for local communities relative to the regional species pool and tested for an association with functional traits (plant height and seed mass) thought to vary along sea–inland gradients. Important Findings Regional species pools were phylogenetically clustered relative to the global pool, indicating regional diversification. NTI showed stronger clustering than NRI pointing to the importance of especially recent diversifications within regions. The species pools grouped phylogenetically into two clusters on either side of the tropics suggesting greater dispersal rates within hemispheres than between hemispheres. Local NRI plot values confirmed that most communities were also phylogenetically clustered within regions. NRI values decreased with increasing plant height and seed mass, indicating greater phylogenetic clustering in communities with short maximum height and good dispersers prone to wind and tidal disturbance as well as salt spray, consistent with environmental filtering along sea–inland gradients. Height and seed mass both showed significant phylogenetic signal, and NRI tended to correlate negatively with both at the plot level. Low NRI plots tended to represent coastal scrub and forest, whereas high NRI plots tended to represent herb-dominated vegetation. We conclude that regional diversification processes play a role in dune plant community assembly, with convergence in local phylogenetic community structure and local variation in community structure probably reflecting consistent coastal-inland gradients. Our study contributes to a better understanding of the globally distributed dynamic coastal ecosystems and the structuring factors working on dune plant communities across spatial scales and regions.

Description: Aims Recent mechanistic explanations for community assembly focus on the debates surrounding niche-based deterministic and dispersal-based stochastic models. This body of work has emphasized the importance of both habitat filtering and dispersal limitation, and many of these works have utilized the assumption of species spatial independence to simplify the complexity of the spatial modeling in natural communities when given dispersal limitation and/or habitat filtering. One potential drawback of this simplification is that it does not consider species interactions and how they may influence the spatial distribution of species, phylogenetic and functional diversity. Here, we assess the validity of the assumption of species spatial independence using data from a subtropical forest plot in southeastern China. Methods We use the four most commonly employed spatial statistical models—the homogeneous Poisson process representing pure random effect, the heterogeneous Poisson process for the effect of habitat heterogeneity, the homogenous Thomas process for sole dispersal limitation and the heterogeneous Thomas process for joint effect of habitat heterogeneity and dispersal limitation—to investigate the contribution of different mechanisms in shaping the species, phylogenetic and functional structures of communities. Important Findings Our evidence from species, phylogenetic and functional diversity demonstrates that the habitat filtering and/or dispersal-based models perform well and the assumption of species spatial independence is relatively valid at larger scales (50 x 50 m). Conversely, at local scales (10 x 10 and 20 x 20 m), the models often fail to predict the species, phylogenetic and functional diversity, suggesting that the assumption of species spatial independence is invalid and that biotic interactions are increasingly important at these spatial scales.

Description: Aims Understanding what drives the variation in species composition and diversity among local communities can provide insights into the mechanisms of community assembly. Because ecological traits are often thought to be phylogenetically conserved, there should be patterns in phylogenetic structure and phylogenetic diversity in local communities along ecological gradients. We investigate potential patterns in angiosperm assemblages along an elevational gradient with a steep ecological gradient in Changbaishan, China. Methods We used 13 angiosperm assemblages in forest plots (32 x 32 m) distributed along an elevational gradient from 720 to 1900 m above sea level. We used Faith’s phylogenetic diversity metric to quantify the phylogenetic alpha diversity of each forest plot, used the net relatedness index to quantify the degree of phylogenetic relatedness among angiosperm species within each forest plot and used a phylogenetic dissimilarity index to quantify phylogenetic beta diversity among forest plots. We related the measures of phylogenetic structure and phylogenetic diversity to environmental (climatic and edaphic) factors. Important Findings Our study showed that angiosperm assemblages tended to be more phylogenetically clustered at higher elevations in Changbaishan. This finding is consistent with the prediction of the phylogenetic niche conservatism hypothesis, which highlights the role of niche constraints in governing the phylogenetic structure of assemblages. Our study also showed that woody assemblages differ from herbaceous assemblages in several major aspects. First, phylogenetic clustering dominated in woody assemblages, whereas phylogenetic overdispersion dominated in herbaceous assemblages; second, patterns in phylogenetic relatedness along the elevational and temperature gradients of Changbaishan were stronger for woody assemblages than for herbaceous assemblages; third, environmental variables explained much more variations in phylogenetic relatedness, phylogenetic alpha diversity and phylogenetic beta diversity for woody assemblages than for herbaceous assemblages.

Description: Aims The last decade has seen many plant ecologists integrating phylogenetic analysis into ecology to explain patterns of species co-occurrence and compositional similarity across assemblages. Despite the advances in this area, there are still some challenges that need to be addressed. One challenge is that most of the phylogenetic studies of plant assemblages have focused only on a small proportion of all of the vascular plants that co-occur (e.g. woody plants), while much of the remaining co-occurring flora has been ignored. Methods Here we introduce an analytical approach that we term phylofloristics that analyzes the compositional similarity of floras in relation to spatial and environmental gradients to understand their assembly. As an illustration, we assembled a large phylogenetic tree for the flora of the Lesser Antilles and evaluated the patterns of floristic and phylofloristic similarity among the island-specific floras. We analyzed the relationship of these similarities with spatial and environmental distance and compared the results for non-endemic and endemic lineages. Important Findings The results show a major influence of environmental heterogeneity on the assembly of island floras and far less evidence for the importance of dispersal limitation of lineages and species. This study highlights the importance of incorporating broader taxonomic sampling to improve our understanding of assembly processes in ecology. We expect future phylofloristic studies will improve the approach we have taken by generating more refined phylogenetic trees and by incorporating phylogeographic information.

Description: Aims Environmental gradients are drivers of species diversity; however, we know relatively little about the evolutionary processes underlying these relationships. A potentially powerful approach to studying diversity gradients is to quantify the phylogenetic structure within and between assemblages arrayed along broad spatial and environmental gradients. Here, we evaluate the phylogenetic structure of plant assemblages along an environmental gradient with the expectation that the habitat specialization of entire lineages is an important evolutionary pattern influencing the structure of tree communities along environmental gradients. Methods We evaluated the effect of several environmental variables on the phylogenetic structure of plant assemblages in 145 plots distributed in northwestern South America that cover a broad environmental gradient. The phylogenetic alpha diversity was quantified for each plot and the phylogenetic beta diversity between each pair of plots was also quantified. Both the alpha and beta diversity measures were then related to spatial and environmental gradients in the study system. Important Findings We found that gradients in temperature and potential evapotranspiration have a strong relationship with the phylogenetic alpha diversity in our study system, with phylogenetic overdispersion in low temperatures and phylogenetic clustering at higher temperatures. Further, the phylogenetic beta diversity between two plots increases with an increasing difference in temperature, whereas annual precipitation was not a significant predictor of community phylogenetic turnover. We also found that the phylogenetic structure of the plots in our study system was related to the degree of seasonal flooding and seasonality in precipitation. In particular, more stressful environments such as dry forests and flooded forests showed phylogenetic clustering. Finally, in contrast with previous studies, we find that phylogenetic beta diversity was not strongly related to the spatial distance separating two forest plots, which may be the result of the importance of the three independent mountain ranges in our study system, which generate a high degree of environmental variation over very short distances. In conclusion, we found that environmental gradients are important drivers of both phylogenetic alpha and phylogenetic beta diversities in these forests over spatial distance.

Description: Aims To examine if and how species and phylogenetic diversity change in relation to disturbance, we conducted a review of ecological literature by testing the consistency of the relationship between phylogenetic diversity and disturbance and compared taxonomic groups, type of disturbance and ecosystem/habitat context. We provide a case study of the phylogenetic diversity–disturbance relationship in angiosperm plant communities of a boreal forest region, compared with types of natural and anthropogenic disturbances and plant growth forms. Methods Using a large-scale sampling plot network along a complete (0–100%) anthropogenic disturbance gradient in the boreal biome, we compared the changes of angiosperm plant community structure and composition across plots. We estimated natural disturbance with historical records of major fires. We then calculated phylogenetic diversity indexes and determined species richness in order to compare linear and polynomial trends along disturbance gradients. We also compared the changes of community structure for different types of anthropogenic disturbances and examined how the relationships between species and phylogenetic diversity and disturbance regimes vary among three different life forms (i.e. forbs, graminoids and woody plants). Important Findings Phylogenetic diversity was inconsistently related to disturbance in previous studies, regardless of taxon, disturbance type or ecosystem context. In the understudied boreal ecosystem, angiosperm plant communities varied greatly in species richness and phylogenetic diversity along anthropogenic disturbance gradients and among different disturbance types. In general, a quadratic curve described the relationship between species richness and anthropogenic disturbance, with the highest richness at intermediate anthropogenic disturbance levels. However, phylogenetic diversity was not related to disturbance in any consistent manner and species richness was not correlated with phylogenetic diversity. Phylogenetic relatedness was also inconsistent across plant growth forms and different anthropogenic disturbance types. Unlike the inconsistent patterns observed for anthropogenic disturbance, community assembly among localities varying in time since natural disturbance exhibited a distinct signature of phylogenetic relatedness, although those trends varied among plant growth forms.

Description: Aims The coastal Brazilian rainforest on white-sand (restinga) ranks among the most fragmented forest types in the tropics, owing to both the patchy distribution of sandy soils and widespread coastal development activities. Here we study the environmental and evolutionary determinants of a forest tree assemblage at a single restinga forest in Southeastern Brazil. We also explore the ability of competing hypotheses to explain the maintenance of species diversity in this forest type, which includes contrasting extremes of edaphic conditions associated with flooding stress. Methods The study was conducted in a white-sand forest permanent plot of 10.24 ha on the coastal plain of Southeastern Brazil. This plot was divided into 256 quadrats of 20 x 20 m, which were classified into two main edaphic habitats (flooded and drained). Trees with a diameter ≥1cm at breast height were identified. We assembled DNA sequence data for each of the 116 morphospecies recognized using two chloroplast markers ( rbcL and matK ). A phylogenetic tree was obtained using the maximum likelihood method, and a phylogenetic distance matrix was produced from an ultrametric tree. We analyzed similarity in floristic composition and structure between habitats and related them to cross-plot distances using permutation procedures. Null model torus shift simulations were performed to obtain a statistical significance level for habitat association for each species. The phylogenetic structure for the two habitats and for each 20 x 20 m quadrat was calculated using the mean phylogenetic distance weighted by species abundance and checked for significance using the standardized effect size generated by 5000 randomizations of phylogenetic tip labels. Important Findings Our results indicate that partitioning among edaphic habitats is important for explaining species distributions and coexistence in restinga forests. Species distributions within the plot were found to be non-random: there was greater floristic similarity within than between habitats, and 〉40% of the more abundant species were positively or negatively associated with at least one habitat. Patterns of habitat association were not independent of phylogenetic relatedness: the community was overdispersed with respect to space and habitat type. Closely related species tended to occur in different habitats, while neighboring trees tended to belong to more distantly related species. We conclude that habitat specialization is important for the coexistence of species in restinga forests and that habitat heterogeneity is therefore an essential factor in explaining the maintenance of diversity of this unique but fragile and threatened type of forest.

Description: Aims The relationship between biodiversity and ecological stability is a long-standing issue in ecology. Current diversity–stability studies, which have largely focused on species diversity, often report an increase in the stability of aggregate community properties with increasing species diversity. Few studies have examined the linkage between phylogenetic diversity, another important dimension of biodiversity, and stability. By taking species evolutionary history into account, phylogenetic diversity may better capture the diversity of traits and niches of species in a community than species diversity and better relate to temporal stability. In this study, we investigated whether phylogenetic diversity could affect temporal stability of community biomass independent of species diversity. Methods We performed an experiment in laboratory microcosms with a pool of 12 bacterivorous ciliated protist species. To eliminate the possibility of species diversity effects confounding with phylogenetic diversity effects, we assembled communities that had the same number of species but varied in the level of phylogenetic diversity. Weekly disturbance, in the form of short-term temperature shock, was imposed on each microcosm and species abundances were monitored over time. We examined the relationship between temporal stability of community biomass and phylogenetic diversity and evaluated the role of several stabilizing mechanisms for explaining the influence of phylogenetic diversity on temporal stability. Important Findings Our results showed that increasing phylogenetic diversity promoted temporal stability of community biomass. Both total community biomass and summed variances showed a U-shaped relationship with phylogenetic diversity, driven by the presence of large, competitively superior species that attained large biomass and high temporal variation in their biomass in both low and high phylogenetic diversity communities. Communities without these species showed patterns consistent with the reduced strength of competition and increasingly asynchronous species responses to environmental changes under higher phylogenetic diversity, two mechanisms that can drive positive diversity–stability relationships. These results support the utility of species phylogenetic knowledge for predicting ecosystem functions and their stability.

Description: Aims While using phylogenetic and functional approaches to test the mechanisms of community assembly, functional traits often act as the proxy of niches. However, there is little detailed knowledge regarding the correlation between functional traits of tree species and their niches in local communities. We suggest that the co-varying correlation between functional traits and niches should be the premise for using phylogenetic and functional approaches to test mechanisms of community assembly. Using functional traits, phylogenetic and environmental data, this study aims to answer the questions: (i) within local communities, do functional traits of co-occurring species co-vary with their environmental niches at the species level? and (ii) what is the key ecological process underlying community assembly in Xishuangbanna and Ailaoshan forest dynamic plots (FDPs)? Methods We measured seven functional traits of 229 and 36 common species in Xishuangbanna and Ailaoshan FDPs in tropical and subtropical China, respectively. We also quantified the environmental niches for these species based on conditional probability. We then analyzed the correlations between functional traits and environmental niches using phylogenetic independent contrasts. After examining phylogenetic signals of functional traits using Pagel’s , we quantified the phylogenetic and functional dispersion along environmental gradients within local tree communities. Important Findings For target species, functional traits do co-vary with environmental niches at the species level in both of the FDPs, supporting that functional traits can be used as a proxy for local-scale environmental niches. Functional traits show significant phylogenetic signals in both of the FDPs. We found that the phylogenetic and functional dispersion were significantly clustered along topographical gradients in the Ailaoshan FDP but overdispersion in the Xishuangbanna FDP. These patterns of phylogenetic and functional dispersion suggest that environmental filtering plays a key role in structuring local tree assemblages in Ailaoshan FDP, while competition exclusion plays a key role in Xishuangbanna FDP.

Description: Aims Theory predicts that the success of introduced species is related to the diversity of native species through trait-based processes. Abiotic site characteristics may also affect a site’s susceptibility to invasion. We quantified resident plant species richness, phylogenetic diversity and several abiotic site characteristics for 24 oak forests in Minnesota, USA, to assess their impact on the abundance of a widespread, introduced terrestrial plant species, common buckthorn ( Rhamnus cathartica L.). Specifically, we asked (1) whether resident species richness and phylogenetic diversity affected the abundance of R. cathartica and (2) what site characteristics explained the overall abundance of R. cathartica . Methods Our survey included 24 oak-dominated stands in Minnesota’s deciduous forests. In each stand, we identified all species in 16 plots. We also measured a series of environmental site characteristics, including canopy openness (a proxy for light availability), percent bare soil, soil pH, percent sand, an index of propagule availability, duff layer thickness (a proxy for earthworm activity), an index of insolation and slope. For all species present in at least one site, we estimated a community phylogeny. We combined all site-level characteristics, including phylogenetic diversity of the resident plant species, in a multiple regression model to examine site level drivers of community invasibility. Important Findings Results indicate that sites with higher overall plant phylogenetic diversity harbor less R. cathartica , even though native species richness was not significantly related to R. cathartica abundance. Regression analyses indicated that, in addition to resident species phylogenetic diversity, the most important predictors of R. cathartica abundance were canopy openness and the amount of bare soil, both positively related to the abundance of the invader. By combining the effects of abiotic site characteristics and resident species phylogenetic diversity in a model that predicted the abundance of R. cathartica , we were able to simultaneously account for a wide range of factors that might influence invasibility. Overall, our results suggest that management strategies aimed at reducing disturbances that lead to increased bare soil and light levels may be more successful if they also maximize phylogenetic diversity of the resident plant community.

Description: Aims Australia is among one of the world’s wealthiest nations; yet, its relatively small human population (22.5 million) has been responsible for extensive deforestation and forest degradation since European settlement in the late 18th century. Despite most (~75%) of Australia’s 7.6 million-km 2 area being covered in inhospitable deserts or arid lands generally unsuitable to forest growth, the coastal periphery has witnessed a rapid decline in forest cover and quality, especially over the last 60 years. Here I document the rates of forest loss and degradation in Australia based on a thorough review of existing literature and unpublished data. Important Findings Overall, Australia has lost nearly 40% of its forests, but much of the remaining native vegetation is highly fragmented. As European colonists expanded in the late 18th and the early 19th centuries, deforestation occurred mainly on the most fertile soils nearest to the coast. In the 1950s, southwestern Western Australia was largely cleared for wheat production, subsequently leading to its designation as a Global Biodiversity Hotspot given its high number of endemic plant species and rapid clearing rates. Since the 1970s, the greatest rates of forest clearance have been in southeastern Queensland and northern New South Wales, although Victoria is the most cleared state. Today, degradation is occurring in the largely forested tropical north due to rapidly expanding invasive weed species and altered fire regimes. Without clear policies to regenerate degraded forests and protect existing tracts at a massive scale, Australia stands to lose a large proportion of its remaining endemic biodiversity. The most important implications of the degree to which Australian forests have disappeared or been degraded are that management must emphasize the maintenance of existing primary forest patches, as well as focus on the regeneration of matrix areas between fragments to increase native habitat area, connectivity and ecosystem functions.

Description: Aim Site occupancy probabilities of target species are commonly used in various ecological studies, e.g. to monitor current status and trends in biodiversity. Detection error introduces bias in the estimators of site occupancy. Existing methods for estimating occupancy probability in the presence of detection error use replicate surveys. These methods assume population closure, i.e. the site occupancy status remains constant across surveys, and independence between surveys. We present an approach for estimating site occupancy probability in the presence of detection error that requires only a single survey and does not require assumption of population closure or independence. In place of the closure assumption, this method requires covariates that affect detection and occupancy. Methods Penalized maximum-likelihood method was used to estimate the parameters. Estimability of the parameters was checked using data cloning. Parametric boostrapping method was used for computing confidence intervals. Important Findings The single-survey approach facilitates analysis of historical datasets where replicate surveys are unavailable, situations where replicate surveys are expensive to conduct and when the assumptions of closure or independence are not met. This method saves significant amounts of time, energy and money in ecological surveys without sacrificing statistical validity. Further, we show that occupancy and habitat suitability are not synonymous and suggest a method to estimate habitat suitability using single-survey data.

Description: Aims Fits of species-abundance distributions to empirical data are increasingly used to evaluate models of diversity maintenance and community structure and to infer properties of communities, such as species richness. Two distributions predicted by several models are the Poisson lognormal (PLN) and the negative binomial (NB) distribution; however, at least three different ways to parameterize the PLN have been proposed, which differ in whether unobserved species contribute to the likelihood and in whether the likelihood is conditional upon the total number of individuals in the sample. Each of these has an analogue for the NB. Here, we propose a new formulation of the PLN and NB that includes the number of unobserved species as one of the estimated parameters. We investigate the performance of parameter estimates obtained from this reformulation, as well as the existing alternatives, for drawing inferences about the shape of species abundance distributions and estimation of species richness. Methods We simulate the random sampling of a fixed number of individuals from lognormal and gamma community relative abundance distributions, using a previously developed ‘individual-based’ bootstrap algorithm. We use a range of sample sizes, community species richness levels and shape parameters for the species abundance distributions that span much of the realistic range for empirical data, generating 1 000 simulated data sets for each parameter combination. We then fit each of the alternative likelihoods to each of the simulated data sets, and we assess the bias, sampling variance and estimation error for each method. Important Findings Parameter estimates behave reasonably well for most parameter values, exhibiting modest levels of median error. However, for the NB, median error becomes extremely large as the NB approaches either of two limiting cases. For both the NB and PLN, 〉90% of the variation in the error in model parameters across parameter sets is explained by three quantities that corresponded to the proportion of species not observed in the sample, the expected number of species observed in the sample and the discrepancy between the true NB or PLN distribution and a Poisson distribution with the same mean. There are relatively few systematic differences between the four alternative likelihoods. In particular, failing to condition the likelihood on the total sample sizes does not appear to systematically increase the bias in parameter estimates. Indeed, overall, the classical likelihood performs slightly better than the alternatives. However, our reparameterized likelihood, for which species richness is a fitted parameter, has important advantages over existing approaches for estimating species richness from fitted species-abundance models.

Description: Aims In ecology and conservation biology, the number of species counted in a biodiversity study is a key metric but is usually a biased underestimate of total species richness because many rare species are not detected. Moreover, comparing species richness among sites or samples is a statistical challenge because the observed number of species is sensitive to the number of individuals counted or the area sampled. For individual-based data, we treat a single, empirical sample of species abundances from an investigator-defined species assemblage or community as a reference point for two estimation objectives under two sampling models: estimating the expected number of species (and its unconditional variance) in a random sample of (i) a smaller number of individuals (multinomial model) or a smaller area sampled (Poisson model) and (ii) a larger number of individuals or a larger area sampled. For sample-based incidence (presence–absence) data, under a Bernoulli product model, we treat a single set of species incidence frequencies as the reference point to estimate richness for smaller and larger numbers of sampling units. Methods The first objective is a problem in interpolation that we address with classical rarefaction (multinomial model) and Coleman rarefaction (Poisson model) for individual-based data and with sample-based rarefaction (Bernoulli product model) for incidence frequencies. The second is a problem in extrapolation that we address with sampling-theoretic predictors for the number of species in a larger sample (multinomial model), a larger area (Poisson model) or a larger number of sampling units (Bernoulli product model), based on an estimate of asymptotic species richness. Although published methods exist for many of these objectives, we bring them together here with some new estimators under a unified statistical and notational framework. This novel integration of mathematically distinct approaches allowed us to link interpolated (rarefaction) curves and extrapolated curves to plot a unified species accumulation curve for empirical examples. We provide new, unconditional variance estimators for classical, individual-based rarefaction and for Coleman rarefaction, long missing from the toolkit of biodiversity measurement. We illustrate these methods with datasets for tropical beetles, tropical trees and tropical ants. Important Findings Surprisingly, for all datasets we examined, the interpolation (rarefaction) curve and the extrapolation curve meet smoothly at the reference sample, yielding a single curve. Moreover, curves representing 95% confidence intervals for interpolated and extrapolated richness estimates also meet smoothly, allowing rigorous statistical comparison of samples not only for rarefaction but also for extrapolated richness values. The confidence intervals widen as the extrapolation moves further beyond the reference sample, but the method gives reasonable results for extrapolations up to about double or triple the original abundance or area of the reference sample. We found that the multinomial and Poisson models produced indistinguishable results, in units of estimated species, for all estimators and datasets. For sample-based abundance data, which allows the comparison of all three models, the Bernoulli product model generally yields lower richness estimates for rarefied data than either the multinomial or the Poisson models because of the ubiquity of non-random spatial distributions in nature.