ALBERT

Beschreibung: 〈b〉Stochastic downscaling of precipitation in complex orography: a simple method to reproduce a realistic fine-scale climatology〈/b〉〈br〉 Silvia Terzago, Elisa Palazzi, and Jost von Hardenberg〈br〉 Nat. Hazards Earth Syst. Sci., 18, 2825-2840, https://doi.org/10.5194/nhess-18-2825-2018, 2018〈br〉 This study proposes a modification to a stochastic downscaling method for precipitation, RainFARM, to improve the representation of the statistics of the daily precipitation at fine scales (1 km) in mountain areas. This method has been demonstrated in the Alps and it has been found to reconstruct small-scale precipitation distribution. It can be employed in a number of applications, including the analysis of extreme events and their statistics and hydrometeorological hazards.

Beschreibung: 〈b〉High-spatial resolution probability maps of drought duration and magnitude across Spain〈/b〉〈br〉 Fernando Domínguez-Castro, Sergio M. Vicente-Serrano, Miquel Tomás-Burguera, Marina Peña-Gallardo, Santiago Beguería, Ahmed El Kenawy, Yolanda Luna, and Ana Morata〈br〉 Nat. Hazards Earth Syst. Sci. Discuss., https//doi.org/10.5194/nhess-2018-289,2018〈br〉 〈b〉Manuscript under review for NHESS〈/b〉 (discussion: open, 0 comments)〈br〉 We mapped – for the first time – the probability of occurrence of drought over Spain, with the overriding aim of improving current drought assessment, management and mitigation measures and strategies across the region. Spatially, our estimations suggest a higher probability of extreme drought events in southern and central areas of Spain, compared to northern and eastern regions. Nevertheless, there are strong differences between drought indices, as well as among drought timescales.

Beschreibung: 〈b〉Challenges to implementing bottom-up flood risk decision analysis frameworks: how strong are social networks of flooding professionals?〈/b〉〈br〉 James O. Knighton, Osamu Tsuda, Rebecca Elliott, and M. Todd Walter〈br〉 Hydrol. Earth Syst. Sci., 22, 5657-5673, https://doi.org/10.5194/hess-22-5657-2018, 2018〈br〉 Decision-making for flood risk management is often the collective effort of professionals within government, NGOs, private practice, and advocacy groups. Our research investigates differences among flood experts within Tompkins County, New York (USA). We explore how they differ in their perceptions of flooding risk, desired project outcomes, and knowledge. We observe substantial differences among experts, and recommend formally acknowledging these perceptions when engaging in flood management.

Beschreibung: 〈b〉A General Analytical Model for Head Response to Oscillatory Pumping in Unconfined Aquifers: Consider the Effects of Delayed Gravity Drainage and Initial Condition〈/b〉〈br〉 Ching-Sheng Huang, Ya-Hsin Tsai, Hund-Der Yeh, and Tao Yang〈br〉 Hydrol. Earth Syst. Sci. Discuss., https//doi.org/10.5194/hess-2018-482,2018〈br〉 〈b〉Manuscript under review for HESS〈/b〉 (discussion: open, 2 comments)〈br〉 This study develops a new model describing head fluctuation induced by oscillatory pumping test (OPT) in unconfined aquifer with the effects of delayed gravity drainage (DGD) and initial condition regarding the hydraulic head prior to OPT. The DGD reduces to instantaneous gravity drainage when a dimensionless parameter exceeds 500. A pseudo-steady state model excluding initial condition causes a time shift from the actual transient model in predicting simple harmonic motion of head fluctuation.

Beschreibung: 〈b〉Direct or indirect recharge on groundwater in the middle-latitude desert of Otindag, China?〈/b〉〈br〉 Bing-Qi Zhu, Xiao-Zong Ren, and Patrick Rioual〈br〉 Hydrol. Earth Syst. Sci. Discuss., https//doi.org/10.5194/hess-2018-395,2018〈br〉 〈b〉Manuscript under review for HESS〈/b〉 (discussion: open, 0 comments)〈br〉 Although rainfall is scarce in global deserts, the Otindag Desert is abundant of water resources (mainly groundwater). To understand the water origin in this desert, stable and radioactive isotopes and hydrochemistry of natural waters were investigated. The groundwaters in the desert were young but not of meteoric origin, i.e., out of control by the modern and palaeo- direct recharge. The tectonic control, but not the climate control, is essentially responsible for the water origin there.

Beschreibung: 〈b〉Direct or indirect recharge on groundwater in the middle-latitude desert of Otindag, China?〈/b〉〈br〉 Bing-Qi Zhu, Xiao-Zong Ren, and Patrick Rioual〈br〉 Hydrol. Earth Syst. Sci. Discuss., https//doi.org/10.5194/hess-2018-395,2018〈br〉 〈b〉Manuscript under review for HESS〈/b〉 (discussion: open, 0 comments)〈br〉 Although rainfall is scarce in global deserts, the Otindag Desert is abundant of water resources (mainly groundwater). To understand the water origin in this desert, stable and radioactive isotopes and hydrochemistry of natural waters were investigated. The groundwaters in the desert were young but not of meteoric origin, i.e., out of control by the modern and palaeo- direct recharge. The tectonic control, but not the climate control, is essentially responsible for the water origin there.

Beschreibung: 〈b〉Monitoring Groundwater Storage Depletion Using Gravity Recovery and Climate Experiment (GRACE) Data in the Semi-Arid Catchments〈/b〉〈br〉 Nizar Abou Zaki, Ali Torabi Haghighi, Pekka M. Rossi, Mohammad J. Tourian, and Bjørn Klove〈br〉 Hydrol. Earth Syst. Sci. Discuss., https//doi.org/10.5194/hess-2018-471,2018〈br〉 〈b〉Manuscript under review for HESS〈/b〉 (discussion: open, 0 comments)〈br〉 Groundwater is considered a main source of fresh water in semi-arid climatic zones, especially for agricultural usage. This study compares in-situ groundwater volume variation measurements with GRACE derived water mass data. The study concludes the possibility of using GRACE data to monitor groundwater depletion in catchments that lack measured data. GRACE data can here help in drawing general conclusions for integrated water resources management, and sustainable usage of this resources.

Beschreibung: 〈b〉Stochastic hydrogeology's biggest hurdles analyzed and its big blind spot〈/b〉〈br〉 Yoram Rubin, Ching-Fu Chang, Jiancong Chen, Karina Cucchi, Bradley Harken, Falk Heße, and Heather Savoy〈br〉 Hydrol. Earth Syst. Sci., 22, 5675-5695, https://doi.org/10.5194/hess-22-5675-2018, 2018〈br〉 This paper addresses questions related to the adoption of stochastic methods in hydrogeology, looking at factors such as environmental regulations, financial incentives, higher education, and the collective feedback loop involving these factors. We show that stochastic hydrogeology's blind spot is in focusing on risk while ignoring uncertainty, to the detriment of its potential clients. The imbalance between the treatments of risk and uncertainty is shown to be common to multiple disciplines.

Beschreibung: 〈b〉Monitoring Groundwater Storage Depletion Using Gravity Recovery and Climate Experiment (GRACE) Data in the Semi-Arid Catchments〈/b〉〈br〉 Nizar Abou Zaki, Ali Torabi Haghighi, Pekka M. Rossi, Mohammad J. Tourian, and Bjørn Klove〈br〉 Hydrol. Earth Syst. Sci. Discuss., https//doi.org/10.5194/hess-2018-471,2018〈br〉 〈b〉Manuscript under review for HESS〈/b〉 (discussion: open, 0 comments)〈br〉 Groundwater is considered a main source of fresh water in semi-arid climatic zones, especially for agricultural usage. This study compares in-situ groundwater volume variation measurements with GRACE derived water mass data. The study concludes the possibility of using GRACE data to monitor groundwater depletion in catchments that lack measured data. GRACE data can here help in drawing general conclusions for integrated water resources management, and sustainable usage of this resources.

Beschreibung: A knowledge of climatic legacies can improve our understanding of how species might change under altered climates and land uses. Ecological clusters of biological soil crust taxa responded differently to climatic legacies. Rainfall and temperature legacies influenced the current distribution of major ecological clusters of biocrust species. Abstract Predicting the distribution of biocrust species, mosses, lichens and liverworts associated with surface soils is difficult, but climatic legacies (changes in climate over the last 20 k years) can improve our prediction of the distribution of biocrust species. To provide empirical support for this hypothesis, we used a combination of network analyses and structural equation modelling to identify the role of climatic legacies in predicting the distribution of ecological clusters formed by species of mosses, lichens and liverworts using data from 282 large sites distributed across 0.6 million km2 of eastern Australia. Two ecological clusters contained 87% of the 120 moss, lichen and liverwort species. Both clusters contained lichen, moss and liverwort species, but were dominated by different families. Sites where the air temperature increased the most over 20k years (positive temperature legacies) were associated with reductions in the relative abundance of species from the lichen (Peltulaceae and Teloschistaceae) and moss (Bryaceae) families (Cluster A species), greater groundstorey plant cover and lower soil pH. Sites where precipitation has increased over the past 20k years (positive precipitation legacy) were associated with increases in the relative abundance of lichen (Cladoniaceae, Lecideaceae and Thelotremataceae) and moss (Pottiaceae) families (Cluster B species) and lower levels of soil pH. Sites where temperatures have increased the most in the past 20k years suppressed the negative effects of plant cover on Cluster B by reducing plant cover. Increased intensity of grazing suppressed the negative effect of soil pH and the positive effect of soil carbon, on the relative abundance of Cluster B taxa. Finally, increasing temperature and precipitation legacies reduced the negative effect of soil pH on Cluster B. Understanding of the importance of climatic legacies improves our ability to predict how biocrust assemblies might respond to ongoing global environmental change associated with increasing land use intensification, increasing temperature and reduced rainfall.

Beschreibung: 〈b〉Wave run-up prediction and observation in a micro-tidal beach〈/b〉〈br〉 Diana Di Luccio, Guido Benassai, Giorgio Budillon, Luigi Mucerino, Raffaele Montella, and Eugenio Pugliese Carratelli〈br〉 Nat. Hazards Earth Syst. Sci., 18, 2841-2857, https://doi.org/10.5194/nhess-18-2841-2018, 2018〈br〉 Forecasting and hindcasting the action of sea storms on piers, coastal structures and beaches is important to mitigate their effects. To this end, with particular regard to low coasts and beaches, we have configured a computational model chain based partly on open-access models and partly on an ad-hoc-developed numerical calculator to evaluate beach wave run-up levels. The results were validated by a set of specially conceived video-camera-based experiments on a micro-tidal beach.

Beschreibung: 〈b〉Evaluation of soil moisture from CCAM-CABLE simulation, satellite based models estimates and satellite observations: Skukuza and Malopeni flux towers regional case study〈/b〉〈br〉 Floyd Vukosi Khosa, Mohau Jacob Mateyisi, Martina Reynita van Der Merwe, Gregor Timothy Feig, Francois Alwyn Engelbrecht, and Michael John Savage〈br〉 Hydrol. Earth Syst. Sci. Discuss., https//doi.org/10.5194/hess-2018-546,2018〈br〉 〈b〉Manuscript under review for HESS〈/b〉 (discussion: open, 0 comments)〈br〉 The paper evaluates soil moisture outputs from three structurally distinct models against in situ data. Our goal is to find how site and region representative the model outputs are. This is a question of interest as some of the models have a specific regional focus on their inceptions. Much focus is placed on how the models capture the soil moisture signal. We find that there is agreement on seasonal patterns between the models and observations with a tolerable level of model uncertainty.

Beschreibung: 〈b〉Wave run-up prediction and observation in a micro-tidal beach〈/b〉〈br〉 Diana Di Luccio, Guido Benassai, Giorgio Budillon, Luigi Mucerino, Raffaele Montella, and Eugenio Pugliese Carratelli〈br〉 Nat. Hazards Earth Syst. Sci., 18, 2841-2857, https://doi.org/10.5194/nhess-18-2841-2018, 2018〈br〉 Forecasting and hindcasting the action of sea storms on piers, coastal structures and beaches is important to mitigate their effects. To this end, with particular regard to low coasts and beaches, we have configured a computational model chain based partly on open-access models and partly on an ad-hoc-developed numerical calculator to evaluate beach wave run-up levels. The results were validated by a set of specially conceived video-camera-based experiments on a micro-tidal beach.

Beschreibung: 〈b〉Ice cliff contribution to the tongue-wide ablation of Changri Nup Glacier, Nepal, central Himalaya〈/b〉〈br〉 Fanny Brun, Patrick Wagnon, Etienne Berthier, Joseph M. Shea, Walter W. Immerzeel, Philip D. A. Kraaijenbrink, Christian Vincent, Camille Reverchon, Dibas Shrestha, and Yves Arnaud〈br〉 The Cryosphere, 12, 3439-3457, https://doi.org/10.5194/tc-12-3439-2018, 2018〈br〉 On debris-covered glaciers, steep ice cliffs experience dramatically enhanced melt compared with the surrounding debris-covered ice. Using field measurements, UAV data and submetre satellite imagery, we estimate the cliff contribution to 2 years of ablation on a debris-covered tongue in Nepal, carefully taking into account ice dynamics. While they occupy only 7 to 8 % of the tongue surface, ice cliffs contributed to 23 to 24 % of the total tongue ablation.

Beschreibung: 〈b〉HESS Opinions: Incubating deep-learning-powered hydrologic science advances as a community〈/b〉〈br〉 Chaopeng Shen, Eric Laloy, Amin Elshorbagy, Adrian Albert, Jerad Bales, Fi-John Chang, Sangram Ganguly, Kuo-Lin Hsu, Daniel Kifer, Zheng Fang, Kuai Fang, Dongfeng Li, Xiaodong Li, and Wen-Ping Tsai〈br〉 Hydrol. Earth Syst. Sci., 22, 5639-5656, https://doi.org/10.5194/hess-22-5639-2018, 2018〈br〉 Recently, deep learning (DL) has emerged as a revolutionary tool for transforming industries and scientific disciplines. We argue that DL can offer a complementary avenue toward advancing hydrology. New methods are being developed to interpret the knowledge learned by deep networks. We argue that open competitions, integrating DL and process-based models, more data sharing, data collection from citizen scientists, and improved education will be needed to incubate advances in hydrology.

Beschreibung: 〈b〉HESS Opinions: Incubating deep-learning-powered hydrologic science advances as a community〈/b〉〈br〉 Chaopeng Shen, Eric Laloy, Amin Elshorbagy, Adrian Albert, Jerad Bales, Fi-John Chang, Sangram Ganguly, Kuo-Lin Hsu, Daniel Kifer, Zheng Fang, Kuai Fang, Dongfeng Li, Xiaodong Li, and Wen-Ping Tsai〈br〉 Hydrol. Earth Syst. Sci., 22, 5639-5656, https://doi.org/10.5194/hess-22-5639-2018, 2018〈br〉 Recently, deep learning (DL) has emerged as a revolutionary tool for transforming industries and scientific disciplines. We argue that DL can offer a complementary avenue toward advancing hydrology. New methods are being developed to interpret the knowledge learned by deep networks. We argue that open competitions, integrating DL and process-based models, more data sharing, data collection from citizen scientists, and improved education will be needed to incubate advances in hydrology.

Beschreibung: 〈b〉Challenges to implementing bottom-up flood risk decision analysis frameworks: how strong are social networks of flooding professionals?〈/b〉〈br〉 James O. Knighton, Osamu Tsuda, Rebecca Elliott, and M. Todd Walter〈br〉 Hydrol. Earth Syst. Sci., 22, 5657-5673, https://doi.org/10.5194/hess-22-5657-2018, 2018〈br〉 Decision-making for flood risk management is often the collective effort of professionals within government, NGOs, private practice, and advocacy groups. Our research investigates differences among flood experts within Tompkins County, New York (USA). We explore how they differ in their perceptions of flooding risk, desired project outcomes, and knowledge. We observe substantial differences among experts, and recommend formally acknowledging these perceptions when engaging in flood management.

Beschreibung: 〈b〉Hess Opinions: Socio-economic and ecological trade-offs of flood management – benefits of a transdisciplinary approach〈/b〉〈br〉 Karl Auerswald, Peter Moyle, Simon Paul Seibert, and Juergen Geist〈br〉 Hydrol. Earth Syst. Sci. Discuss., https//doi.org/10.5194/hess-2018-544,2018〈br〉 〈b〉Manuscript under review for HESS〈/b〉 (discussion: open, 0 comments)〈br〉 The demand for flood protection often results in the construction of more and bigger levees along rivers. We highlight that such technical solutions often result in undesired socioeconomic and ecological consequences such as increased downstream flooding risk, changes of groundwater levels and a loss of aquatic and terrestrial biodiversity. We propose a transdisciplinary approach of integrated flood management and green infrastructure instead of reliance on technical protection measures.

Beschreibung: 〈b〉Hess Opinions: Socio-economic and ecological trade-offs of flood management – benefits of a transdisciplinary approach〈/b〉〈br〉 Karl Auerswald, Peter Moyle, Simon Paul Seibert, and Juergen Geist〈br〉 Hydrol. Earth Syst. Sci. Discuss., https//doi.org/10.5194/hess-2018-544,2018〈br〉 〈b〉Manuscript under review for HESS〈/b〉 (discussion: open, 0 comments)〈br〉 The demand for flood protection often results in the construction of more and bigger levees along rivers. We highlight that such technical solutions often result in undesired socioeconomic and ecological consequences such as increased downstream flooding risk, changes of groundwater levels and a loss of aquatic and terrestrial biodiversity. We propose a transdisciplinary approach of integrated flood management and green infrastructure instead of reliance on technical protection measures.

Beschreibung: Retraction “Comparison of nitrogen inputs and accumulation in 210Pb‐dated peat cores: Evidence for biological N2‐fixation in Central European peatlands despite decades of atmospheric N pollution” https://doi.org/10.1111/gcb.14505, by Martin Novak, Melanie A. Vile, Jan Curik, Bohuslava Cejkova, Jiri Barta, Marketa Stepanova, Ivana Jackova, Frantisek Buzek, Leona Bohdalkova, Eva Prechova, Frantisek Veselovsky, Marie Adamova, Ivana Valkova and Arnost Komarek. The above article, first published online in Wiley Online Library (wileyonlinelibrary.com) in Global Change Biology, has been retracted by agreement between the authors, the journal Editor‐in‐Chief, Stephen P. Long, and John Wiley & Sons Ltd. Since publication of the above article, it was brought to the attention of the authors that the peat accretion rates violate reasonable ranges of peatland C/N/P stoichiometry, placing the quantitative conclusions of the article in serious error. The authors apologize for any inconvenience the publication of this work may have caused our readers. REFERENCE Novak, M., Vile, M. A., Cejkova, B., Barta, J., Stepanova, M., Jackova, I., Buzek, F., Bohdalkova, L., Prechova, E., Veselovsky, F., Adamova, M., Valkova, I., & Komarek, A. (2018). Comparison of nitrogen inputs and accumulation in 210Pb‐dated peat cores: Evidence for biological N2‐fixation in Central European peatlands despite decades of atmospheric N pollution. Global Change Biology.. https://doi.org/10.1111/gcb.14505

Beschreibung: 〈b〉Estimation of soil erosion considering soil loss tolerance in karst area〈/b〉〈br〉 Yue Cao, Shijie Wang, Xiaoyong Bai, Huiwen Li, Cheng Zeng, Yichao Tian, Fei Chen, Luhua Wu, and Mingming Wang〈br〉 Nat. Hazards Earth Syst. Sci. Discuss., https//doi.org/10.5194/nhess-2018-310,2018〈br〉 〈b〉Manuscript under review for NHESS〈/b〉 (discussion: open, 0 comments)〈br〉 Due to the soil holding capacity is very limited in karst area, it is necessary to consider the allowable loss of soil. Here we took thermodynamic dissolution model of carbonate rocks and the lithological characteristics to estimate soil loss tolerance, then corrected and quantitatively evaluated the soil erosion. We identified the spatial pattern of soil loss tolerance in karst area, found RUSLE overestimated soil erosion in karst area and proposed an idea for evaluating soil erosion in karst.

Beschreibung: 〈b〉Evaluation of soil moisture from CCAM-CABLE simulation, satellite based models estimates and satellite observations: Skukuza and Malopeni flux towers regional case study〈/b〉〈br〉 Floyd Vukosi Khosa, Mohau Jacob Mateyisi, Martina Reynita van Der Merwe, Gregor Timothy Feig, Francois Alwyn Engelbrecht, and Michael John Savage〈br〉 Hydrol. Earth Syst. Sci. Discuss., https//doi.org/10.5194/hess-2018-546,2018〈br〉 〈b〉Manuscript under review for HESS〈/b〉 (discussion: open, 0 comments)〈br〉 The paper evaluates soil moisture outputs from three structurally distinct models against in situ data. Our goal is to find how site and region representative the model outputs are. This is a question of interest as some of the models have a specific regional focus on their inceptions. Much focus is placed on how the models capture the soil moisture signal. We find that there is agreement on seasonal patterns between the models and observations with a tolerable level of model uncertainty.

Beschreibung: 〈b〉InSAR Technique Applied to the Monitoring of the Qinghai-Tibet Railway〈/b〉〈br〉 Qingyun Zhang, Yongsheng Li, Jingfa Zhang, and Yi Luo〈br〉 Nat. Hazards Earth Syst. Sci. Discuss., https//doi.org/10.5194/nhess-2018-287,2018〈br〉 〈b〉Manuscript under review for NHESS〈/b〉 (discussion: open, 0 comments)〈br〉 Before the opening of the railway, the deformation of Qinghai-Tibet Railway was very small and considered stable. After opening, the overall stability of the railway section was good. The main deformation areas are concentrated in the areas where railway lines turn and geological disasters are concentrated. In order to ensure the safety of railway operation, it is necessary to carry out long-term time series observation along the Qinghai-Tibet Railway.

Beschreibung: 〈b〉High-spatial resolution probability maps of drought duration and magnitude across Spain〈/b〉〈br〉 Fernando Domínguez-Castro, Sergio M. Vicente-Serrano, Miquel Tomás-Burguera, Marina Peña-Gallardo, Santiago Beguería, Ahmed El Kenawy, Yolanda Luna, and Ana Morata〈br〉 Nat. Hazards Earth Syst. Sci. Discuss., https//doi.org/10.5194/nhess-2018-289,2018〈br〉 〈b〉Manuscript under review for NHESS〈/b〉 (discussion: open, 0 comments)〈br〉 We mapped – for the first time – the probability of occurrence of drought over Spain, with the overriding aim of improving current drought assessment, management and mitigation measures and strategies across the region. Spatially, our estimations suggest a higher probability of extreme drought events in southern and central areas of Spain, compared to northern and eastern regions. Nevertheless, there are strong differences between drought indices, as well as among drought timescales.

Beschreibung: 〈b〉InSAR Technique Applied to the Monitoring of the Qinghai-Tibet Railway〈/b〉〈br〉 Qingyun Zhang, Yongsheng Li, Jingfa Zhang, and Yi Luo〈br〉 Nat. Hazards Earth Syst. Sci. Discuss., https//doi.org/10.5194/nhess-2018-287,2018〈br〉 〈b〉Manuscript under review for NHESS〈/b〉 (discussion: open, 0 comments)〈br〉 Before the opening of the railway, the deformation of Qinghai-Tibet Railway was very small and considered stable. After opening, the overall stability of the railway section was good. The main deformation areas are concentrated in the areas where railway lines turn and geological disasters are concentrated. In order to ensure the safety of railway operation, it is necessary to carry out long-term time series observation along the Qinghai-Tibet Railway.

Beschreibung: 〈b〉Mapping soil hydraulic properties using random forest based pedotransfer functions and geostatistics〈/b〉〈br〉 Brigitta Tóth, Gábor Szatmári, Katalin Takács, Annamária Laborczi, András Makó, Kálmán Rajkai, and László Pásztor〈br〉 Hydrol. Earth Syst. Sci. Discuss., https//doi.org/10.5194/hess-2018-552,2018〈br〉 〈b〉Manuscript under review for HESS〈/b〉 (discussion: open, 0 comments)〈br〉 This paper analyses differences in performance and spatial patterns between soil hydraulic maps derived with indirect and direct mapping methods. Maps of saturated water content, field capacity and wilting point are interpreted for a 5775 km〈sup〉2〈/sup〉 catchment at 100 m resolution. Advantages and disadvantages of the two methods are discussed. Absolute difference in soil water retention values are less than 0.025 cm〈sup〉3〈/sup〉 cm〈sup〉−3〈/sup〉 between maps derived with indirect and direct methods for 65–86 % of the catchment.

Beschreibung: Variability in sea level rise (SLR) drivers and responses makes it difficult to predict SLR effects across individual wetlands or wetland types and to develop a holistic perspective on regional SLR response. To improve regional predictions, we developed a model based on wetland elevation, or hypsometry, that augments existing SLR assessments by considering multiple spatial scales, addressing data gaps, and accommodating wetland diversity. Our approach can inform restoration and adaptation efforts of SLR vulnerability, improve understanding of the SLR drivers relevant to specific wetlands, and highlight significant data gaps that impede SLR response modeling across spatial scales. Abstract Sea level rise (SLR) threatens coastal wetlands worldwide, yet the fate of individual wetlands will vary based on local topography, wetland morphology, sediment dynamics, hydrologic processes, and plant‐mediated feedbacks. Local variability in these factors makes it difficult to predict SLR effects across wetlands or to develop a holistic regional perspective on SLR response for a diversity of wetland types. To improve regional predictions of SLR impacts to coastal wetlands, we developed a model that addresses the scale‐dependent factors controlling SLR response and accommodates different levels of data availability. The model quantifies SLR‐driven habitat conversion within wetlands across a region by predicting changes in individual wetland hypsometry. This standardized approach can be applied to all wetlands in a region regardless of data availability, making it ideal for modeling SLR response across a range of scales. Our model was applied to 105 wetlands in southern California that spanned a broad range of typology and data availability. Our findings suggest that if wetlands are confined to their current extents, the region will lose 12% of marsh habitats (vegetated marsh and unvegetated flats) with 0.6 m of SLR (projected for 2050) and 48% with 1.7 m of SLR (projected for 2100). Habitat conversion was more drastic in wetlands with larger proportions of marsh habitats relative to subtidal habitats and occurred more rapidly in small lagoons relative to larger sites. Our assessment can inform management of coastal wetland vulnerability, improve understanding of the SLR drivers relevant to individual wetlands, and highlight significant data gaps that impede SLR response modeling across spatial scales. This approach augments regional SLR assessments by considering spatial variability in SLR response drivers, addressing data gaps, and accommodating wetland diversity, which will provide greater insights into regional SLR response that are relevant to coastal management and restoration efforts.

Beschreibung: 〈b〉Stochastic downscaling of precipitation in complex orography: a simple method to reproduce a realistic fine-scale climatology〈/b〉〈br〉 Silvia Terzago, Elisa Palazzi, and Jost von Hardenberg〈br〉 Nat. Hazards Earth Syst. Sci., 18, 2825-2840, https://doi.org/10.5194/nhess-18-2825-2018, 2018〈br〉 This study proposes a modification to a stochastic downscaling method for precipitation, RainFARM, to improve the representation of the statistics of the daily precipitation at fine scales (1 km) in mountain areas. This method has been demonstrated in the Alps and it has been found to reconstruct small-scale precipitation distribution. It can be employed in a number of applications, including the analysis of extreme events and their statistics and hydrometeorological hazards.

Beschreibung: 〈b〉Stochastic hydrogeology's biggest hurdles analyzed and its big blind spot〈/b〉〈br〉 Yoram Rubin, Ching-Fu Chang, Jiancong Chen, Karina Cucchi, Bradley Harken, Falk Heße, and Heather Savoy〈br〉 Hydrol. Earth Syst. Sci., 22, 5675-5695, https://doi.org/10.5194/hess-22-5675-2018, 2018〈br〉 This paper addresses questions related to the adoption of stochastic methods in hydrogeology, looking at factors such as environmental regulations, financial incentives, higher education, and the collective feedback loop involving these factors. We show that stochastic hydrogeology's blind spot is in focusing on risk while ignoring uncertainty, to the detriment of its potential clients. The imbalance between the treatments of risk and uncertainty is shown to be common to multiple disciplines.

Beschreibung: Increasing population and urban sprawl are causing rapid land use change, and the effect this has on soil nutrient cycles and greenhouse gas budgets is unclear. Fluxes of N2O and CH4 were measured from native forest, pasture and turf grass continuously over two years using an automated chamber system. The fertilized turf increased N2O emissions immediately following establishment, though all land uses were a net sink for CH4. Land use change from native forest to turf grass increased non‐CO2 GWP from a net annual GHG sink of −83 CO2‐e ha−1 year−1 to a source of 245 kg CO2‐e ha−1 year−1. Abstract Increasing population densities and urban sprawl are causing rapid land use change from natural and agricultural ecosystems into smaller, urban residential properties. However, there is still great uncertainty about the effect that urbanization will have on biogeochemical C and N cycles and associated greenhouse gas (GHG) budgets. We aimed to evaluate how typical urbanization related land use change in subtropical Australia affects soil GHG exchange (N2O and CH4) and the associated global warming potential (GWP). Fluxes were measured from three land uses: native forest, a long‐term pasture, and a turf grass lawn continuously over two years using a high‐resolution automated chamber system. The fertilized turf grass had the highest N2O emissions, dominated by high fluxes 〉100 g N2O‐N day−1 immediately following establishment though decreased to just 0.6 kg N2O‐N ha−1 in the second year. Only minor fluxes occurred in the forest and pasture, with the high aeration of the sandy topsoil limiting N2O emissions while promoting substantial CH4 uptake. Native forest was consistently the strongest CH4 sink (−2.9 kg CH4‐C ha−1 year−1), while the pasture became a short‐term CH4 source after heavy rainfall when the soil reached saturation. On a two‐year average, land use change from native forest to turf grass increased the non‐CO2 GWP from a net annual GHG sink of −83 CO2‐e ha–1 year−1 to a source of 245 kg CO2‐e ha–1 year−1. This study highlights that urbanization can substantially alter soil GHG exchange by altering plant soil water use and by increasing bulk density and inorganic N availability. However, on well‐drained subtropical soils, the impact of urbanization on inter‐annual non‐CO2 GWP of turf grass was low compared to urbanized ecosystems in temperate climates.

Beschreibung: This study compares measurements of the greenhouse gas cost of an irrigated and nonirrigated corn–soybean–wheat system in the Midwest US. Irrigation significantly increased soil organic carbon storage in the upper 25 cm, but not by enough to make up for the CO2‐equivalent costs of fossil fuel power, soil emissions of nitrous oxide (N2O), and degassing of supersaturated CO2 and N2O from the groundwater. Groundwater degassing of CO2 and N2O are missing components of previous assessments of the GHG cost of groundwater irrigation; together they were 4% of the irrigated system's total emissions. Abstract Groundwater irrigation of cropland is expanding worldwide with poorly known implications for climate change. This study compares experimental measurements of the net global warming impact of a rainfed versus a groundwater‐irrigated corn (maize)–soybean–wheat, no‐till cropping system in the Midwest US, the region that produces the majority of U.S. corn and soybean. Irrigation significantly increased soil organic carbon (C) storage in the upper 25 cm, but not by enough to make up for the CO2‐equivalent (CO2e) costs of fossil fuel power, soil emissions of nitrous oxide (N2O), and degassing of supersaturated CO2 and N2O from the groundwater. A rainfed reference system had a net mitigating effect of −13.9 (±31) g CO2e m−2 year−1, but with irrigation at an average rate for the region, the irrigated system contributed to global warming with net greenhouse gas (GHG) emissions of 27.1 (±32) g CO2e m−2 year−1. Compared to the rainfed system, the irrigated system had 45% more GHG emissions and 7% more C sequestration. The irrigation‐associated increase in soil N2O and fossil fuel emissions contributed 18% and 9%, respectively, to the system's total emissions in an average irrigation year. Groundwater degassing of CO2 and N2O are missing components of previous assessments of the GHG cost of groundwater irrigation; together they were 4% of the irrigated system's total emissions. The irrigated system's net impact normalized by crop yield (GHG intensity) was +0.04 (±0.006) kg CO2e kg−1 yield, close to that of the rainfed system, which was −0.03 (±0.002) kg CO2e kg−1 yield. Thus, the increased crop yield resulting from irrigation can ameliorate overall GHG emissions if intensification by irrigation prevents land conversion emissions elsewhere, although the expansion of irrigation risks depletion of local water resources.

Beschreibung: This study examined the difference of vegetation indices (VIs), evapotranspiration (ET), gross primary production (GPP), and solar‐induced chlorophyll fluorescence (SIF) during 2000–2010 between pure grasslands (PG) and juniper‐encroached grasslands (JEG). The changes of GPP and ET for grasslands with different proportions of juniper encroachment (JWPE) were also assessed. The results suggested mean annual GPP and ET were ~55% and ~45% higher when grasslands were completely converted into juniper forests under contemporary climate during 2000–2010. The enhancement of annual GPP and ET for grasslands with JWPE varied over years in association with the moisture conditions. Abstract Woody plant encroachment (WPE) into grasslands has been occurring globally and may be accelerated by climate change in the future. This land cover change is expected to alter the carbon and water cycles, but it remains uncertain how and to what extent the carbon and water cycles may change with WPE into grasslands under current climate. In this study, we examined the difference of vegetation indices (VIs), evapotranspiration (ET), gross primary production (GPP), and solar‐induced chlorophyll fluorescence (SIF) during 2000–2010 between grasslands and juniper‐encroached grasslands. We also quantitatively assessed the changes of GPP and ET for grasslands with different proportions of juniper encroachment (JWPE). Our results suggested that JWPE increased the GPP, ET, greenness‐related VIs, and SIF of grasslands. Mean annual GPP and ET were, respectively, ~55% and ~45% higher when grasslands were completely converted into juniper forests under contemporary climate during 2000–2010. The enhancement of annual GPP and ET for grasslands with JWPE varied over years ranging from about +20% GPP (~+30% for ET) in the wettest year (2007) to about twice as much GPP (~+55% for ET) in the severe drought year (2006) relative to grasslands without encroachment. Additionally, the differences in GPP and ET showed significant seasonal dynamics. During the peak growing season (May–August), GPP and ET for grasslands with JWPE were ~30% and ~40% higher on average. This analysis provided insights into how and to what degree carbon and water cycles were impacted by JWPE, which is vital to understanding how JWPE and ecological succession will affect the regional and global carbon and water budgets in the future.

Beschreibung: The body size was compared between adults of Polionemobius mikado collected from wide ranges of latitudes in Japan in recent years and those collected four decades ago, and the results showed that the body size had decreased significantly at the middle latitude. The length of the growing season at the middle latitude in recent years was comparable to that at lower latitudes four decades ago, where P. mikado populations were bivoltine. These findings suggested that the latitudinal range suitable for the bivoltine life cycle has expanded northward over the last four decades because of climate warming. Abstract Recent climate warming has affected some life‐history traits of insects, including voltinism and body size. The magnitude of changes in these traits may differ latitudinally within a species because of the differing lengths of season available for growth. The present study aims to estimate the change in voltinism of the lawn ground cricket, Polionemobius mikado (Shiraki) (Orthoptera: Trigonidiidae), over the last four decades by comparing the body size between adults collected from a wide range of latitudes in Japan in recent years (2015–2017) and those collected four decades ago (1969–1976). The body size of adults collected in recent years showed a latitudinal saw‐tooth cline, in the same way as body size did four decades ago, and the cline shifted northward over the last four decades: In 2015–2017, the body size decreased slightly with increasing latitude from 31°N to 36°N, and then increased to 40°N, and again decreased from 40°N to 44°N. Comparison of the body size between recent years and four decades ago revealed that the body size has decreased significantly at the middle latitudes (36–40°N), suggesting that the proportion of smaller bivoltine individuals there has increased over the last four decades. The sum of effective temperatures for postdiapause embryonic development at around 36°N in recent years was comparable to that at 31–35°N four decades ago, at which P. mikado populations were bivoltine. Taken together, these findings suggested that the latitudinal range suitable for the bivoltine life cycle of P. mikado has expanded northward over the last four decades because of climate warming. This is the first report that shows that a decrease in body size can be caused by climate warming via an increase in voltinism.

Beschreibung: Landscape fire is a key but poorly understood component of the global carbon cycle. We undertook an extensive field survey across Australia to measure rates of biomass consumption by fire. We found that in a typical year, fire consumes the equivalent of about 11% of the carbon captured by vegetation across Australia. In the far north, rates of biomass consumption were about 20 times that in the far south. Our results emphasise that fire management to reduce greenhouse gas emissions should focus on fire‐prone tropical savanna landscapes, where the vast majority of fire activity occurs. Abstract Landscape fire is a key but poorly understood component of the global carbon cycle. Predicting biomass consumption by fire at large spatial scales is essential to understanding carbon dynamics and hence how fire management can reduce greenhouse gas emissions and increase ecosystem carbon storage. An Australia‐wide field‐based survey (at 113 locations) across large‐scale macroecological gradients (climate, productivity and fire regimes) enabled estimation of how biomass combustion by surface fire directly affects continental‐scale carbon budgets. In terms of biomass consumption, we found clear trade‐offs between the frequency and severity of surface fires. In temperate southern Australia, characterised by less frequent and more severe fires, biomass consumed per fire was typically very high. In contrast, surface fires in the tropical savannas of northern Australia were very frequent but less severe, with much lower consumption of biomass per fire (about a quarter of that in the far south). When biomass consumption was expressed on an annual basis, biomass consumed was far greater in the tropical savannas (〉20 times that of the far south). This trade‐off is also apparent in the ratio of annual carbon consumption to net primary production (NPP). Across Australia's naturally vegetated land area, annual carbon consumption by surface fire is equivalent to about 11% of NPP, with a sharp contrast between temperate southern Australia (6%) and tropical northern Australia (46%). Our results emphasise that fire management to reduce greenhouse gas emissions should focus on fire prone tropical savanna landscapes, where the vast bulk of biomass consumption occurs globally. In these landscapes, grass biomass is a key driver of frequency, intensity and combustion completeness of surface fires, and management actions that increase grass biomass are likely to lead to increases in greenhouse gas emissions from savanna fires.

Beschreibung: We investigated the bacterial community response to a decade‐long preindustrial‐to‐future CO2 gradient (250–500 ppm) among three contrasting soil types using 16S rRNA gene amplicon sequencing. We found that bacterial communities may be largely unresponsive to indirect effects of CO2 enrichment through plants. Instead, bacterial communities are strongly regulated by edaphic conditions, presumably because soil differences create distinct environmental niches for bacteria. Abstract Rising atmospheric CO2 concentration directly stimulates plant productivity and affects nutrient dynamics in the soil. However, the influence of CO2 enrichment on soil bacterial communities remains elusive, likely due to their complex interactions with a wide range of plant and soil properties. Here, we investigated the bacterial community response to a decade long preindustrial‐to‐future CO2 gradient (250–500 ppm) among three contrasting soil types using 16S rRNA gene amplicon sequencing. In addition, we examined the effect of seasonal variation and plant species composition on bacterial communities. We found that Shannon index (H’) and Faith's phylogenetic diversity (PD) did not change in response to the CO2 gradient (R2 = 0.01, p 〉 0.05). CO2 gradient and season also had a negligible effect on overall community structure, although silty clay soil communities were better structured on a CO2 gradient (p 〈 0.001) among three soils. Similarly, CO2 gradient had no significant effect on the relative abundance of different phyla. However, we observed soil‐specific variation of CO2 effects in a few individual families. For example, the abundance of Pirellulaceae family decreased linearly with CO2 gradient, but only in sandy loam soils. Conversely, the abundance of Micromonosporaceae and Gaillaceae families increased with CO2 gradient in clay soils. Soil water content (SWC) and nutrient properties were the key environmental constraints shaping bacterial community structure, one manifestation of which was a decline in bacterial diversity with increasing SWC. Furthermore, the impact of plant species composition on community structure was secondary to the strong influence of soil properties. Taken together, our findings indicate that bacterial communities may be largely unresponsive to indirect effects of CO2 enrichment through plants. Instead, bacterial communities are strongly regulated by edaphic conditions, presumably because soil differences create distinct environmental niches for bacteria.

Beschreibung: The rapid measurement of trace gas exchanges in coastal plant communities is necessary for establishing their sensitivity to highly dynamic physical controlling factors. We demonstrated and validated automated soil‐flux chamber measurement methods for unattended hourly collection of CO2, CH4, and N2O data including tidally flooded periods. Deployment on an eastern Pacific salt marsh for a lunar month in winter showed that storm surge conditions during the day and night significantly influenced the magnitude and frequency of CO2 and CH4 flux (p 〈 0.001) but did not affect N2O flux. We modeled CO2‐equivalent flux using sustained‐flux global potentials and increased storm surge frequency scenarios, 2020 to 2100. Abstract The physical controlling factors on coastal plant communities are among the most dynamic of known ecosystems, but climate change alters coastal surface and subsurface hydrologic regimes, which makes rapid measurement of greenhouse gas fluxes critical. Greenhouse gas exchange rates in these terrestrial–aquatic ecosystems are highly variable worldwide with climate, soil type, plant community, and weather. Therefore, increasing data collection and availability should be a priority. Here, we demonstrate and validate physical and analytical modifications to automated soil‐flux chamber measurement methods for unattended use in tidally driven wetlands, allowing the high‐frequency capture of storm surge and day/night dynamics. Winter CO2 flux from Sarcocornia perennis marsh to the atmosphere was significantly greater during the day (2.8 mmol m−2 hr−1) than the night (2.2 mmol m−2 hr−1; p 〈 0.001), while CH4 was significantly greater during the night (0.16 μmol m−2 hr−1) than the day (−0.13 μmol m−2 hr−1; p = 0.04). The magnitude of CO2 flux during the day and the frequency of CH4 flux were reduced during a surge (p 〈 0.001). Surge did not significantly affect N2O flux, which without non‐detects was normally distributed around −24.2 nmol m−2 hr−1. Analysis with sustained‐flux global potentials and increased storm surge frequency scenarios, 2020 to 2100, suggested that the marsh in winter remains an atmospheric CO2 source. The modeled results showed an increased flux of CO2 to the atmosphere, while in soil, the uptake of CH4 increased and N2O uptake decreased. We present analytical routines to correctly capture gas flux curves in dynamic overland flooding conditions and to flag data that are below detection limits or from unobserved chamber‐malfunction situations. Storm surge is an important phenomenon globally, but event‐driven, episodic factors can be poorly estimated by infrequent sampling. Wider deployment of this system would permit inclusion of surge events in greenhouse gas estimates.

Beschreibung: Coastal “blue carbon” ecosystems (mangroves, saltmarshes, seagrasses) play an important role in the global carbon cycle but are increasingly impacted by the introduction of invasive species. In a global meta‐analysis of previously published data, we show that introduced plant species increase the amount of carbon stored in blue carbon ecosystems. However, introduced animals and algae reduce blue carbon storage. This study will enable managers and conservationists to make informed decisions with regard to invasions and carbon storage benefits. Abstract Human‐caused shifts in carbon (C) cycling and biotic exchange are defining characteristics of the Anthropocene. In marine systems, saltmarsh, seagrass, and mangrove habitats—collectively known as “blue carbon” and coastal vegetated habitats (CVHs)—are a leading sequester of global C and increasingly impacted by exotic species invasions. There is growing interest in the effect of invasion by a diverse pool of exotic species on C storage and the implications for ecosystem‐based management of these systems. In a global meta‐analysis, we synthesized data from 104 papers that provided 345 comparisons of habitat‐level response (plant and soil C storage) from paired invaded and uninvaded sites. We found an overall net effect of significantly higher C pools in invaded CVHs amounting to 40% (±16%) higher C storage than uninvaded habitat, but effects differed among types of invaders. Elevated C storage was driven by blue C‐forming plant invaders (saltmarsh grasses, seagrasses, and mangrove trees) that intensify biomass per unit area, extend and elevate coastal wetlands, and convert coastal mudflats into C‐rich vegetated habitat. Introduced animal and structurally distinct primary producers had significant negative effects on C pools, driven by herbivory, trampling, and native species displacement. The role of invasion manifested differently among habitat types, with significant C storage increases in saltmarshes, decreases in seagrass, and no significant effect in mangroves. There were also counter‐directional effects by the same species in different systems or locations, which underscores the importance of combining data mining with analyses of mean effect sizes in meta‐analyses. Our study provides a quantitative basis for understanding differential effects of invasion on blue C habitats and will inform conservation strategies that need to balance management decisions involving invasion, C storage, and a range of other marine biodiversity and habitat functions in these coastal systems.

Beschreibung: Housing much of Earth’s carbon and biodiversity, tropical forests are, arguably, our planet’s most important ecosystems. Yet, humanity is destroying tropical primary forests at an alarming rate. Mitigating this is the expansion of secondary forests (SFs). However, SF conservation value is controversial and hotly debated. We show that SFs can accumulate large amounts of carbon and support many forest‐dependent species but that they do not attain the characteristics of undisturbed primary forests (UPFs), even after several decades of succession. As such, SFs are not substitutes for UPFs. Abstract Secondary forests (SFs) regenerating on previously deforested land account for large, expanding areas of tropical forest cover. Given that tropical forests rank among Earth’s most important reservoirs of carbon and biodiversity, SFs play an increasingly pivotal role in the carbon cycle and as potential habitat for forest biota. Nevertheless, their capacity to regain the biotic attributes of undisturbed primary forests (UPFs) remains poorly understood. Here, we provide a comprehensive assessment of SF recovery, using extensive tropical biodiversity, biomass, and environmental datasets. These data, collected in 59 naturally regenerating SFs and 30 co‐located UPFs in the eastern Amazon, cover 〉1,600 large‐ and small‐stemmed plant, bird, and dung beetles species and a suite of forest structure, landscape context, and topoedaphic predictors. After up to 40 years of regeneration, the SFs we surveyed showed a high degree of biodiversity resilience, recovering, on average among taxa, 88% and 85% mean UPF species richness and composition, respectively. Across the first 20 years of succession, the period for which we have accurate SF age data, biomass recovered at 1.2% per year, equivalent to a carbon uptake rate of 2.25 Mg/ha per year, while, on average, species richness and composition recovered at 2.6% and 2.3% per year, respectively. For all taxonomic groups, biomass was strongly associated with SF species distributions. However, other variables describing habitat complexity—canopy cover and understory stem density—were equally important occurrence predictors for most taxa. Species responses to biomass revealed a successional transition at approximately 75 Mg/ha, marking the influx of high‐conservation‐value forest species. Overall, our results show that naturally regenerating SFs can accumulate substantial amounts of carbon and support many forest species. However, given that the surveyed SFs failed to return to a typical UPF state, SFs are not substitutes for UPFs.

Beschreibung: This article examines the projected impacts of cropland expansion on both carbon storage and biodiversity if current trends continue. It focuses on biodiversity hotspots and the Alliance for Zero Extinction (AZE) sites for biodiversity as well as both soil and standing vegetation carbon stocks. Results are compared on both a regional and national level identifying priority areas where impacts on both ecosystem services are likely to be the greatest. Abstract Cropland expansion threatens biodiversity by driving habitat loss and impacts carbon storage through loss of biomass and soil carbon (C). There is a growing concern land‐use change (LUC) to cropland will result in a loss of ecosystem function and various ecosystem services essential for human health and well‐being. This paper examines projections of future cropland expansion from an integrated assessment model IMAGE 3.0 under a “business as usual” scenario and the direct impact on both biodiversity and C storage. By focusing on biodiversity hotspots and Alliance for Zero Extinction (AZE) sites, loss of habitat as well as potential impacts on endangered and critically endangered species are explored. With regards to C storage, the impact on both soil and vegetation standing C stocks are examined. We show that if projected trends are realized, there are likely to be severe consequences for these resources. Substantial loss of habitat in biodiversity hotspots such as Indo‐Burma, and the Philippians is expected as well as 50% of species in AZE sites losing part of their last remaining habitat. An estimated 13.7% of vegetation standing C stocks and 4.6% of soil C stocks are also projected to be lost in areas affected with Brazil and Mexico being identified as priorities in terms of both biodiversity and C losses from cropland expansion. Changes in policy to regulate projected cropland expansion, and increased measures to protect natural resources, are highly likely to be required to prevent these biodiversity and C losses in the future.

Beschreibung: This review analyses present knowledge on plant sensing and signaling mechanisms under conditions of climate change. Plant cells are endowed with environmental and stress sensors and internal signals that can act as potential mechanisms of climate change sensing. However, optimal functioning of existing sensors, optimal integration of additive constraints and signals, or stress memory processes can be hampered by conflicting interferences between climate change‐related factors. Analysis of these contrasted situations emphasizes the need for future research on the diversity and robustness of plant signaling mechanisms under climate change conditions. Abstract Climate change reshapes the physiology and development of organisms through phenotypic plasticity, epigenetic modifications, and genetic adaptation. Under evolutionary pressures of the sessile lifestyle, plants possess efficient systems of phenotypic plasticity and acclimation to environmental conditions. Molecular analysis, especially through omics approaches, of these primary lines of environmental adjustment in the context of climate change has revealed the underlying biochemical and physiological mechanisms, thus characterizing the links between phenotypic plasticity and climate change responses. The efficiency of adaptive plasticity under climate change indeed depends on the realization of such biochemical and physiological mechanisms, but the importance of sensing and signaling mechanisms that can integrate perception of environmental cues and transduction into physiological responses is often overlooked. Recent progress opens the possibility of considering plant phenotypic plasticity and responses to climate change through the perspective of environmental sensing and signaling. This review aims to analyze present knowledge on plant sensing and signaling mechanisms and discuss how their structural and functional characteristics lead to resilience or hypersensitivity under conditions of climate change. Plant cells are endowed with arrays of environmental and stress sensors and with internal signals that act as molecular integrators of the multiple constraints of climate change, thus giving rise to potential mechanisms of climate change sensing. Moreover, mechanisms of stress‐related information propagation lead to stress memory and acquired stress tolerance that could withstand different scenarios of modifications of stress frequency and intensity. However, optimal functioning of existing sensors, optimal integration of additive constraints and signals, or memory processes can be hampered by conflicting interferences between novel combinations and novel changes in intensity and duration of climate change‐related factors. Analysis of these contrasted situations emphasizes the need for future research on the diversity and robustness of plant signaling mechanisms under climate change conditions.

Beschreibung: Glacier retreat is known to threaten the biodiversity of freshwaters worldwide, but little is understood of the effects on algal communities that play key roles in primary production, biogeochemical cycling and the resource base of alpine freshwater food webs. This research investigated the biodiversity of benthic diatom assemblages in rivers of the European Alps to determine their response to reducing catchment glacier cover. Diatom α‐diversity and density increased but β‐diversity was reduced. Six conservation Red‐List taxa may require reclassification as they were found exclusively ≥28% glacier cover and are therefore under threat from ongoing glacier loss. Abstract Climate change poses a considerable threat to the biodiversity of high altitude ecosystems worldwide, including cold‐water river systems that are responding rapidly to a shrinking cryosphere. Most recent research has demonstrated the severe vulnerability of river invertebrates to glacier retreat but effects upon other aquatic groups remain poorly quantified. Using new data sets from the European Alps, we show significant responses to declining glacier cover for diatoms, which play a critical functional role as freshwater primary producers. Specifically, diatom α‐diversity and density in rivers presently fed by glaciers will increase with future deglaciation, yet β‐diversity within and between sites will reduce because declining glacier influence will lower the spatiotemporal variability of glacier cover and its associated habitat heterogeneity. Changes in diatom assemblage composition as glacier cover declined were associated strongly with increasing riverbed stability and water temperature. At the species level, diatoms showed a gradation of responses; for example, Eunotia trinacria, found exclusively at river sites with high (≥52%) catchment glacier cover, may be affected negatively by ice loss. Conversely, seven taxa confined to sites with no glacier cover, including Gomphonema calcareum, stand to benefit. Nineteen (22%) taxa were noted as threatened, endangered, rare or decreasing on the Red List of Algae for Germany, with most at sites ≤26% glacier cover, meaning further ice loss may benefit these diatoms. However, six taxa found only in rivers ≥28% glacier cover may require reclassification of their Red List conservation status, as this habitat is threatened by deglaciation. Our identification of clear links between decreasing glacier cover and river diatom biodiversity suggests there could be significant reorganization of river ecosystems with deglaciation, for example, through alterations to primary production, biogeochemical cycles, and the shifting resource base of alpine freshwater food webs which lack significant allochthonous energy inputs.

Beschreibung: Rapidly increasing temperatures across the Arctic are thawing permafrost soils and changing the way carbon and nutrients are delivered from upland areas to surface waters such as rivers and lakes. Analysis of long‐term data from Arctic Alaska show increases in stream water alkalinity and cation concentrations consistent with signatures of permafrost thaw. Changes are also documented for concentrations of nitrate (+),dissolved organic carbon (−), and total phosphorus (−), as well as δ13C isotope values of aquatic invertebrates (−). These changes show that warming temperatures and thawing permafrost are leading to shifts in the supply of carbon and nutrients to aquatic ecosystems and consequently changing resources that support aquatic food webs. Abstract Rapidly, increasing air temperatures across the Arctic are thawing permafrost and exposing vast quantities of organic carbon, nitrogen, and phosphorus to microbial processing. Shifts in the absolute and relative supplies of these elements will likely alter patterns of ecosystem productivity and change the way carbon and nutrients are delivered from upland areas to surface waters such as rivers and lakes. The ultra‐oligotrophic nature of surface waters across the Arctic renders these ecosystems particularly susceptible to changes in productivity and food web dynamics as permafrost thaw alters terrestrial‐aquatic linkages. The objectives of this study were to evaluate decadal‐scale patterns in surface water chemistry and assess potential implications of changing water chemistry to benthic organic matter and aquatic food webs. Data were collected from the upper Kuparuk River on the North Slope of Alaska by the U.S. National Science Foundation's Long‐Term Ecological Research program during 1978–2014. Analyses of these data show increases in stream water alkalinity and cation concentrations consistent with signatures of permafrost thaw. Changes are also documented for discharge‐corrected nitrate concentrations (+), discharge‐corrected dissolved organic carbon concentrations (−), total phosphorus concentrations (−), and δ13C isotope values of aquatic invertebrate consumers (−). These changes show that warming temperatures and thawing permafrost in the upland environment are leading to shifts in the supply of carbon and nutrients available to surface waters and consequently changing resources that support aquatic food webs. This demonstrates that physical, geochemical, and biological changes associated with warming permafrost are fundamentally altering linkages between upland and aquatic ecosystems in rapidly changing arctic environments.

Beschreibung: We modeled the regional carbon balance of sub‐Arctic tundra over a decade in a region with lakes, wetlands, and uplands using process‐based biogeochemical models. Interannual variability over the decade was relatively small in comparison with variability among the land cover types. Wetlands were hot spots for C cycling in this sub‐Arctic tundra ecosystem. Capturing the relative fraction of uplands versus wetlands was key to determining the net regional C balance at this and other Arctic tundra sites. Abstract Across the Arctic, the net ecosystem carbon (C) balance of tundra ecosystems is highly uncertain due to substantial temporal variability of C fluxes and to landscape heterogeneity. We modeled both carbon dioxide (CO2) and methane (CH4) fluxes for the dominant land cover types in a ~100‐km2 sub‐Arctic tundra region in northeast European Russia for the period of 2006–2015 using process‐based biogeochemical models. Modeled net annual CO2 fluxes ranged from −300 g C m−2 year−1 [net uptake] in a willow fen to 3 g C m−2 year−1 [net source] in dry lichen tundra. Modeled annual CH4 emissions ranged from −0.2 to 22.3 g C m−2 year−1 at a peat plateau site and a willow fen site, respectively. Interannual variability over the decade was relatively small (20%–25%) in comparison with variability among the land cover types (150%). Using high‐resolution land cover classification, the region was a net sink of atmospheric CO2 across most land cover types but a net source of CH4 to the atmosphere due to high emissions from permafrost‐free fens. Using a lower resolution for land cover classification resulted in a 20%–65% underestimation of regional CH4 flux relative to high‐resolution classification and smaller (10%) overestimation of regional CO2 uptake due to the underestimation of wetland area by 60%. The relative fraction of uplands versus wetlands was key to determining the net regional C balance at this and other Arctic tundra sites because wetlands were hot spots for C cycling in Arctic tundra ecosystems.

Beschreibung: Ecological theory illustrates that current null model approaches do not promote mechanistic understanding of community‐ and ecosystem‐level effects of multiple environmental changes. I present an alternative framework that makes a clear distinction between two different kinds of drivers (resource ratio shifts and multiple stressors) and integrates both by incorporating stressor effects into resource uptake theory. Abstract Understanding the joint effect of multiple drivers of environmental change is a key scientific challenge. The dominant approach today is to compare observed joint effects with predictions from various types of null models. Drivers are said to combine synergistically (antagonistically) when their observed joint effect is larger (smaller) than that predicted by the null model. Here, I argue that this approach does not promote understanding of effects on important community‐ and ecosystem‐level variables such as biodiversity and ecosystem function. I use ecological theory to show that different mechanisms can lead to the same deviation from a null model's prediction. Inversely, I show that the same mechanism can lead to different deviations from a null model's prediction. These examples illustrate that it is not possible to make strong mechanistic inferences from null models. Next, I present an alternative framework to study such effects. This framework makes a clear distinction between two different kinds of drivers (resource ratio shifts and multiple stressors) and integrates both by incorporating stressor effects into resource uptake theory. I show that this framework can advance understanding because of three reasons. First, it forces formalization of “multiple stressors,” using factors that describe the number and kind of stressors, their selectivity and dynamic behaviour, and the initial trait diversity and tolerance among species. Second, it produces testable predictions on how these factors affect biodiversity and ecosystem function, alone and in combination with resource ratio shifts. Third, it can fail in informative ways. That is, its assumptions are clear, so that different kinds of deviations between predictions and observed effects can guide new experiments and theory improvement. I conclude that this framework will more effectively progress understanding of global change effects on communities and ecosystems than does the current practice of null model testing.

Beschreibung: Abstract Increasing both crop productivity and the tolerance of crops to abiotic and biotic stresses is a major challenge for global food security in our rapidly changing climate. For the first time, we show how the spatial variation and severity of tropospheric ozone effects on yield compare with effects of other stresses on a global scale, and discuss mitigating actions against the negative effects of ozone. We show that the sensitivity to ozone declines in the order soybean 〉 wheat 〉 maize 〉 rice, with genotypic variation in response being most pronounced for soybean and rice. Based on stomatal uptake, we estimate that ozone (mean of 2010–2012) reduces global yield annually by 12.4%, 7.1%, 4.4% and 6.1% for soybean, wheat, rice and maize, respectively (the “ozone yield gaps”), adding up to 227 Tg of lost yield. Our modelling shows that the highest ozone‐induced production losses for soybean are in North and South America whilst for wheat they are in India and China, for rice in parts of India, Bangladesh, China and Indonesia, and for maize in China and the United States. Crucially, we also show that the same areas are often also at risk of high losses from pests and diseases, heat stress and to a lesser extent aridity and nutrient stress. In a solution‐focussed analysis of these results, we provide a crop ideotype with tolerance of multiple stresses (including ozone) and describe how ozone effects could be included in crop breeding programmes. We also discuss altered crop management approaches that could be applied to reduce ozone impacts in the shorter term. Given the severity of ozone effects on staple food crops in areas of the world that are also challenged by other stresses, we recommend increased attention to the benefits that could be gained from addressing the ozone yield gap.

Beschreibung: Biological responses to multiple stressors are often complex and are not easily generalizable. We used data from 494 European lakes, categorized into eight types to test the generality of the widely hypothesized synergistic effect of temperature and eutrophication on cyanobacterial abundance and the effect of prolonged periods of drought as an additional stressor. The abundance of cyanobacteria was explained by different combinations of stressors in each lake type and the hypothesized synergy was only detected in two lake types, indicating that a one‐size fits‐all approach is not appropriate for effectively managing the future risk of cyanobacterial blooms to climate change. Abstract Blooms of cyanobacteria are a current threat to global water security that is expected to increase in the future because of increasing nutrient enrichment, increasing temperature and extreme precipitation in combination with prolonged drought. However, the responses to multiple stressors, such as those above, are often complex and there is contradictory evidence as to how they may interact. Here we used broad scale data from 494 lakes in central and northern Europe, to assess how cyanobacteria respond to nutrients (phosphorus), temperature and water retention time in different types of lakes. Eight lake types were examined based on factorial combinations of major factors that determine phytoplankton composition and sensitivity to nutrients: alkalinity (low and medium‐high), colour (clear and humic) and mixing intensity (polymictic and stratified). In line with expectations, cyanobacteria increased with temperature and retention time in five of the eight lake types. Temperature effects were greatest in lake types situated at higher latitudes, suggesting that lakes currently not at risk could be affected by warming in the future. However, the sensitivity of cyanobacteria to temperature, retention time and phosphorus varied among lake types highlighting the complex responses of lakes to multiple stressors. For example, in polymictic, medium‐high alkalinity, humic lakes cyanobacteria biovolume was positively explained by retention time and a synergy between TP and temperature, while in polymictic, medium‐high alkalinity, clear lakes only retention time was identified as an explanatory variable. These results show that, although climate change will need to be accounted for when managing the risk of cyanobacteria in lakes, a “one‐size fits‐all” approach is not appropriate. When forecasting the response of cyanobacteria to future environmental change, including changes caused by climate and local management, it will be important to take this differential sensitivity of lakes into account.

Beschreibung: Abstract Climate and land‐use change are the major drivers of global biodiversity loss. Their effects are particularly acute for wide‐ranging consumers, but little is known about how these factors interact to affect the abundance of large carnivores and their herbivore prey. We analyzed population densities of a primary and secondary consumer (mule deer, Odocoileus hemionus, and mountain lion, Puma concolor) across a climatic gradient in western North America by combining satellite‐based maps of plant productivity with estimates of animal abundance and foraging area derived from Global Positioning Systems telemetry data (GPS). Mule deer density exhibited a positive, linear relationship with plant productivity (r2 = 0.58), varying by a factor of 18 across the climate‐vegetation gradient (range: 38–697 individuals/100 km2). Mountain lion home range size decreased in response to increasing primary productivity and consequent changes in the abundance of their herbivore prey (range: 20–450 km2). This pattern resulted in a strong, positive association between plant productivity and mountain lion density (r2 = 0.67). Despite varying densities, the ratio of prey to predator remained constant across the climatic gradient (mean ± SE = 363 ± 29 mule deer/mountain lion), suggesting that the determinacy of the effect of primary productivity on consumer density was conserved across trophic levels. As droughts and longer term climate changes reduce the suitability of marginal habitats, consumer home ranges will expand in order for individuals to meet basic nutritional requirements. These changes portend decreases in the abundance of large‐bodied, wide‐ranging wildlife through climatically driven reductions in carrying capacity, as well as increased human–wildlife interactions stemming from anthropogenic land use and habitat fragmentation.

Beschreibung: The persistence of many species under climate change will depend on our ability to identify and protect areas that facilitate dispersal to newly climatically suitable habitat. We used centrality metrics to identify climate connectivity areas across North America by delineating paths between current climate types and their future analogs that avoided non‐analogous climates. Paths were funneled along north‐south trending passes and valley systems and away from areas of novel and disappearing climates. Climate connectivity areas, where many potential dispersal paths overlap, are distinct from refugia and thus poorly captured by many existing conservation strategies. Abstract As climatic conditions shift in coming decades, persistence of many populations will depend on their ability to colonize habitat newly suitable for their climatic requirements. Opportunities for such range shifts may be limited unless areas that facilitate dispersal under climate change are identified and protected from land uses that impede movement. While many climate adaptation strategies focus on identifying refugia, this study is the first to characterize areas which merit protection for their role in promoting climate connectivity at a continental extent. We identified climate connectivity areas across North America by delineating paths between current climate types and their future analogs that avoided nonanalogous climates, and used centrality metrics to rank the contribution of each location to facilitating dispersal across the landscape. The distribution of connectivity areas was influenced by climatic and topographic factors at multiple spatial scales. Results were robust to uncertainty in the magnitude of future climate change arising from differing emissions scenarios and general circulation models, but sensitive to analysis extent and assumptions concerning dispersal behavior and maximum dispersal distance. Paths were funneled along north‐south trending passes and valley systems and away from areas of novel and disappearing climates. Climate connectivity areas, where many potential dispersal paths overlapped, were distinct from refugia and thus poorly captured by many existing conservation strategies. Existing protected areas with high connectivity values were found in southern Mexico, the southwestern US, and western and arctic Canada and Alaska. Ecoregions within the Isthmus of Tehuantepec, Great Plains, eastern temperate forests, high Arctic, and western Canadian Cordillera hold important climate connectivity areas which merit increased conservation focus due to anthropogenic pressures or current low levels of protection. Our coarse‐filter climate‐type‐based results complement and contextualize species‐specific analyses and add a missing dimension to climate adaptation planning by identifying landscape features which promote connectivity among refugia.

Beschreibung: For aquatic organisms, variation in the ability to tolerate high temperatures and low oxygen levels is likely to influence resilience to climate change. Here, we use populations of killifish to show that naturally occurring variations in upper thermal tolerance and hypoxia tolerance have genetic bases, and that these two traits are not functionally or genetically correlated. This genetic variation provides the material needed for the action of natural selection, but the lack of trait association could limit rapid adaptation to combined stressors. However, this lack of association potentially provides flexibility to fine‐tune adaptive responses to specific local conditions. Abstract The resilience of organisms to climate change through adaptive evolution is dependent on the extent of genetically based variation in key phenotypic traits and the nature of genetic associations between them. For aquatic animals, upper thermal tolerance and hypoxia tolerance are likely to be a important determinants of sensitivity to climate change. To determine the genetic basis of these traits and to detect associations between them, we compared naturally occurring populations of two subspecies of Atlantic killifish, Fundulus heteroclitus, that differ in both thermal and hypoxia tolerance. Multilocus association mapping demonstrated that 47 and 35 single nucleotide polymorphisms (SNPs) explained 43.4% and 51.9% of variation in thermal and hypoxia tolerance, respectively, suggesting that genetic mechanisms underlie a substantial proportion of variation in each trait. However, no explanatory SNPs were shared between traits, and upper thermal tolerance varied approximately linearly with latitude, whereas hypoxia tolerance exhibited a steep phenotypic break across the contact zone between the subspecies. These results suggest that upper thermal tolerance and hypoxia tolerance are neither phenotypically correlated nor genetically associated, and thus that rates of adaptive change in these traits can be independently fine‐tuned by natural selection. This modularity of important traits can underpin the evolvability of organisms to complex future environmental change.

Beschreibung: This letter deals with the critique by Lefevre, McKenzie, and Nilsson (2017, 2018) of the use of Gill‐Oxygen Limitation Theory (GOLT) to explain observed and predict further decreases of the maximum body size of fish under warming.

Beschreibung: Abstract Extracellular enzymes catalyze rate‐limiting steps in soil organic matter decomposition, and their activities (EEAs) play a key role in determining soil respiration (SR). Both EEAs and SR are highly sensitive to temperature, but their responses to climate warming remain poorly understood. Here, we present a meta‐analysis on the response of soil cellulase and ligninase activities and SR to warming, synthesizing data from 56 studies. We found that warming significantly enhanced ligninase activity by 21.4% but had no effect on cellulase activity. Increases in ligninase activity were positively correlated with changes in SR, while no such relationship was found for cellulase. The warming response of ligninase activity was more closely related to the responses of SR than a wide range of environmental and experimental methodological factors. Furthermore, warming effects on ligninase activity increased with experiment duration. These results suggest that soil microorganisms sustain long‐term increases in SR with warming by gradually increasing the degradation of the recalcitrant carbon pool.

Beschreibung: Abstract Restoration and rehabilitation of native vegetation in dryland ecosystems, which encompass over 40% of terrestrial ecosystems, is a common challenge that continues to grow as wildfire and biological invasions transform dryland plant communities. The difficulty in part stems from low and variable precipitation, combined with limited understanding about how weather conditions influence restoration outcomes, and increasing recognition that one‐time seeding approaches can fail if they do not occur during appropriate plant establishment conditions. The sagebrush biome, which once covered over 620,000 km2 of western North America, is a prime example of a pressing dryland restoration challenge for which restoration success has been variable. We analyzed field data on Artemisia tridentata (big sagebrush) restoration collected at 771 plots in 177 wildfire sites across its western range, and used process‐based ecohydrological modeling to identify factors leading to its establishment. Our results indicate big sagebrush occurrence is most strongly associated with relatively cool temperatures and wet soils in the first spring after seeding. In particular, the amount of winter snowpack, but not total precipitation, helped explain the availability of spring soil moisture and restoration success. We also find considerable interannual variability in the probability of sagebrush establishment. Adaptive management strategies that target seeding during cool, wet years or mitigate effects of variability through repeated seeding may improve the likelihood of successful restoration in dryland ecosystems. Given consistent projections of increasing temperatures, declining snowpack, and increasing weather variability throughout midlatitude drylands, weather‐centric adaptive management approaches to restoration will be increasingly important for dryland restoration success.

Beschreibung: In the region around the Dumont d'Urville research station in Antarcica, when sea ice covers approximately 20% of the Adélie penguins’ foraging area, we found that breeding success reaches a peak, and that most diving parameters reach an optimum for similar sea‐ice conditions, suggesting that sea ice affects the reproductive performance of Adélie penguins through its effects on diving activity. Abstract The Southern Ocean is currently experiencing major environmental changes, including in sea‐ice cover. Such changes strongly influence ecosystem structure and functioning and affect the survival and reproduction of predators such as seabirds. These effects are likely mediated by reduced availability of food resources. As such, seabirds are reliable eco‐indicators of environmental conditions in the Antarctic region. Here, based on 9 years of sea‐ice data, we found that the breeding success of Adélie penguins (Pygoscelis adeliae) reaches a peak at intermediate sea‐ice cover (ca. 20%). We further examined the effects of sea‐ice conditions on the foraging activity of penguins, measured at multiple scales from individual dives to foraging trips. Analysis of temporal organisation of dives, including fractal and bout analyses, revealed an increasingly consistent behaviour during years with extensive sea‐ice cover. The relationship between several dive parameters and sea‐ice cover in the foraging area appears to be quadratic. In years of low and high sea‐ice cover, individuals adjusted their diving effort by generally diving deeper, more frequently and by resting at the surface between dives for shorter periods of time than in years with intermediate sea‐ice cover. Our study therefore suggests that sea‐ice cover is likely to affect the reproductive performance of Adélie penguins through its effects on foraging behaviour, as breeding success and most diving parameters share a common optimum. Some years, however, deviated from this general trend, suggesting that other factors (e.g. precipitation during the breeding season) might sometimes become preponderant over the sea‐ice effects on breeding and foraging performance. Our study highlights the value of monitoring fitness parameters and individual behaviour concomitantly over the long‐term to better characterize optimal environmental conditions and potential resilience of wildlife. Such an approach is crucial if we want to anticipate the effects of environmental change on Antarctic penguin populations.

Beschreibung: Abstract Human land use causes major changes in species abundance and composition, yet native and exotic species can exhibit different responses to land use change. Native populations generally decline in human‐impacted habitats while exotic species often benefit. In this study, we assessed the effects of human land use on exotic and native reptile diversity, including functional diversity, which relates to the range of habitat use strategies in biotic communities. We surveyed 114 reptile communities from localities that varied in habitat structure and human impact level on two Caribbean islands, and calculated species richness, overall abundance, and evenness for every plot. Functional diversity indices were calculated using published trait data, which enabled us to detect signs of trait filtering associated with impacted habitats. Our results show that environmental variation among sampling plots was explained by two Principal Component Analysis (PCA) ordination axes related to habitat structure (i.e., forest or nonforest) and human impact level (i.e., addition of man‐made constructions such as roads and buildings). Several diversity indices were significantly correlated with the two PCA axes, but exotic and native species showed opposing responses. Native species reached the highest abundance in forests, while exotic species were absent in this habitat. Human impact was associated with an increase in exotic abundance and species richness, while native species showed no significant associations. Functional diversity was highest in nonforested environments on both islands, and further increased on St. Martin with the establishment of functionally unique exotic species in nonforested habitat. Habitat structure, rather than human impact, proved to be an important agent for environmental filtering of traits, causing divergent functional trait values across forested and nonforested environments. Our results illustrate the importance of considering various elements of land use when studying its impact on species diversity and the establishment and spread of exotic species.

Beschreibung: Abstract Treeline advance has occurred throughout the twentieth century in mountainous regions around the world; however, local variation and temporal lags in responses to climate warming indicate that the upper limits of some treelines are not necessarily in climatic equilibrium. These observations suggest that factors other than climate are constraining tree establishment beyond existing treelines. Using a seed addition experiment, we tested the effects of seed availability, predation and microsite limitation on the establishment of two subalpine tree species (Picea engelmannii and Abies lasiocarpa) across four treelines in the Canadian Rocky Mountains. The effect of vegetation removal on seedling growth was also determined, and microclimate conditions were monitored. Establishment limitations observed in the field were placed in context with the effects of soil properties observed in a parallel experiment. The seed addition experiment revealed reduced establishment with increasing elevation, suggesting that although establishment within the treeline ecotone is at least partially seed limited, other constraints are more important beyond the current treeline. The effects of herbivory and microsite availability significantly reduced seedling establishment but were less influential beyond the treeline. Microclimate monitoring revealed that establishment was negatively related to growing season temperatures and positively related to the duration of winter snow cover, counter to the conventional expectation that establishment is limited by low temperatures. Overall, it appears that seedling establishment beyond treeline is predominantly constrained by a combination of high soil surface temperatures during the growing season, reduced winter snowpack and unfavourable soil properties. Our study supports the assertion that seedling establishment in alpine treeline ecotones is simultaneously limited by various climatic and nonclimatic drivers. Together, these factors may limit future treeline advance in the Canadian Rocky Mountains and should be considered when assessing the potential for treeline advance in alpine systems elsewhere

Beschreibung: Abstract The relationship between levels of dominance and species richness is highly contentious, especially in ant communities. The dominance‐impoverishment rule states that high levels of dominance only occur in species‐poor communities, but there appear to be many cases of high levels of dominance in highly diverse communities. The extent to which dominant species limit local richness through competitive exclusion remains unclear, but such exclusion appears more apparent for non‐native rather than native dominant species. Here we perform the first global analysis of the relationship between behavioral dominance and species richness. We used data from 1,293 local assemblages of ground‐dwelling ants distributed across five continents to document the generality of the dominance‐impoverishment rule, and to identify the biotic and abiotic conditions under which it does and does not apply. We found that the behavioral dominance–diversity relationship varies greatly, and depends on whether dominant species are native or non‐native, whether dominance is considered as occurrence or relative abundance, and on variation in mean annual temperature. There were declines in diversity with increasing dominance in invaded communities, but diversity increased with increasing dominance in native communities. These patterns occur along the global temperature gradient. However, positive and negative relationships are strongest in the hottest sites. We also found that climate regulates the degree of behavioral dominance, but differently from how it shapes species richness. Our findings imply that, despite strong competitive interactions among ants, competitive exclusion is not a major driver of local richness in native ant communities. Although the dominance‐impoverishment rule applies to invaded communities, we propose an alternative dominance‐diversification rule for native communities.

Beschreibung: Abstract In climate change ecology, simplistic research approaches may yield unrealistically simplistic answers to often more complicated problems. In particular, the complexity of vegetation responses to global climate change begs a better understanding of the impacts of concomitant changes in several climatic drivers, how these impacts vary across different climatic contexts, and of the demographic processes underlying population changes. Using a replicated, factorial, whole‐community transplant experiment, we investigated regional variation in demographic responses of plant populations to increased temperature and/or precipitation. Across four perennial forb species and 12 sites, we found strong responses to both temperature and precipitation change. Changes in population growth rates were mainly due to changes in survival and clonality. In three of the four study species, the combined increase in temperature and precipitation reflected nonadditive, antagonistic interactions of the single climatic changes for population growth rate and survival, while the interactions were additive and synergistic for clonality. This disparity affects the persistence of genotypes, but also suggests that the mechanisms behind the responses of the vital rates differ. In addition, survival effects varied systematically with climatic context, with wetter and warmer + wetter transplants showing less positive or more negative responses at warmer sites. The detailed demographic approach yields important mechanistic insights into how concomitant changes in temperature and precipitation affect plants, which makes our results generalizable beyond the four study species. Our comprehensive study design illustrates the power of replicated field experiments in disentangling the complex relationships and patterns that govern climate change impacts across real‐world species and landscapes.

Beschreibung: Abstract Theoretical and eddy covariance studies demonstrate that aerosol‐loading stimulates canopy photosynthesis, but field evidence for the aerosol effect on tree growth is limited. Here, we measured in situ daily stem growth rates of aspen trees under a wide range of aerosol‐loading in China. The results showed that daily stem growth rates were positively correlated with aerosol‐loading, even at exceptionally high aerosol levels. Using structural equation modeling analysis, we showed that variations in stem growth rates can be largely attributed to two environmental variables covarying with aerosol loading: diffuse fraction of radiation and vapor pressure deficit (VPD). Furthermore, we found that these two factors influence stem growth by influencing photosynthesis from different parts of canopy. Using field observations and a mechanistic photosynthesis model, we demonstrate that photosynthetic rates of both sun and shade leaves increased under high aerosol‐loading conditions but for different reasons. For sun leaves, the photosynthetic increase was primarily attributed to the concurrent lower VPD; for shade leaves, the positive aerosol effect was tightly connected with increased diffuse light. Overall, our study provides the first field evidence of increased tree growth under high aerosol loading. We highlight the importance of understanding biophysical mechanisms of aerosol‐meteorology interactions, and incorporating the different pathways of aerosol effects into earth system models to improve the prediction of large‐scale aerosol impacts, and the associated vegetation‐mediated climate feedbacks.

Beschreibung: Abstract While there is a lot of data on interactive effects of eutrophication and warming, to date, we lack data to generate reliable predictions concerning possible effects of nutrient decrease and temperature increase on community composition and functional responses. In recent years, a wide‐ranging trend of nutrient decrease (re‐oligotrophication) was reported for freshwater systems. Small lakes and ponds, in particular, show rapid responses to anthropogenic pressures and became model systems to investigate single as well as synergistic effects of warming and fertilization in situ and in experiments. Therefore, we set up an experiment to investigate the single as well as the interactive effects of nutrient reduction and gradual temperature increase on a natural freshwater phytoplankton community, using an experimental indoor mesocosm setup. Biomass production initially increased with warming but decreased with nutrient depletion. If nutrient supply was constant, biomass increased further, especially under warming conditions. Under low nutrient supply, we found a sharp transition from initially positive effects of warming to negative effects when resources became scarce. Warming reduced phytoplankton richness and evenness, whereas nutrient reduction at ambient temperature had positive effects on diversity. Our results indicate that temperature effects on freshwater systems will be altered by nutrient availability. These interactive effects of energy increase and resource decrease have major impacts on biodiversity and ecosystem function and thus need to be considered in environmental management plans.

Beschreibung: Abstract Interannual variations of photosynthesis in tropical seasonally dry vegetation are one of the dominant drivers to interannual variations of atmospheric CO2 growth rate. Yet, the seasonal differences in the response of photosynthesis to climate variations in these ecosystems remain poorly understood. Here using Normalized Difference Vegetation Index (NDVI), we explored the response of photosynthesis of seasonally dry tropical vegetation to climatic variations in the dry and the wet seasons during the past three decades. We found significant (p 〈 0.01) differences between dry and wet seasons in the interannual response of photosynthesis to temperature (γint) and to precipitation (δint). γint is ~1% °C−1 more negative and δint is ~8% 100 mm−1 more positive in the dry season than in the wet season. Further analyses show that the seasonal difference in γint can be explained by background moisture and temperature conditions. Positive γint occurred in wet season where mean temperature is lower than 27°C and precipitation is at least 60 mm larger than potential evapotranspiration. Two widely used Gross Primary Productivity (GPP) estimates (empirical modeling by machine‐learning algorithm applied to flux tower measurements, and nine process‐based carbon cycle models) were examined for the GPP–climate relationship over wet and dry seasons. The GPP derived from empirical modeling can partly reproduce the divergence of γint, while most process models cannot. The overestimate by process models on negative impacts by warmer temperature during the wet season highlights the shortcomings of current carbon cycle models in representing interactive impacts of temperature and moisture on photosynthesis. Improving representations on soil water uptake, leaf temperature, nitrogen cycling, and soil moisture may help improve modeling skills in reproducing seasonal differences of photosynthesis–climate relationship and thus the projection for impacts of climate change on tropical carbon cycle.

Beschreibung: Abstract The net flux of CO2 exchanged with the atmosphere following grassland‐related land‐use change (LUC) depends on the subsequent temporal dynamics of soil organic carbon (SOC). Yet, the magnitude and timing of these dynamics are still unclear. We compiled a global data set of 836 paired‐sites to quantify temporal SOC changes after grassland‐related LUC. In order to discriminate between SOC losses from the initial ecosystem and gains from the secondary one, the post‐LUC time series of SOC data was combined with satellite‐based net primary production observations as a proxy of carbon input to the soil. Globally, land conversion from either cropland or forest into grassland leads to SOC accumulation; the reverse shows net SOC loss. The SOC response curves vary between different regions. Conversion of cropland to managed grassland results in more SOC accumulation than natural grassland recovery from abandoned cropland. We did not consider the biophysical variables (e.g., climate conditions and soil properties) when fitting the SOC turnover rate into the observation data but analyzed the relationships between the fitted turnover rate and these variables. The SOC turnover rate is significantly correlated with temperature and precipitation (p 〈 0.05), but not with the clay fraction of soils (p 〉 0.05). Comparing our results with predictions from bookkeeping models, we found that bookkeeping models overestimate by 56% of the long‐term (100 years horizon) cumulative SOC emissions for grassland‐related LUC types in tropical and temperate regions since 2000. We also tested the spatial representativeness of our data set and calculated SOC response curves using the representative subset of sites in each region. Our study provides new insight into the impact grassland‐related LUC on the global carbon budget and sheds light on the potential of grassland conservation for climate mitigation.

Beschreibung: Abstract Human and natural systems have adapted to and evolved within historical climatic conditions. Anthropogenic climate change has the potential to alter these conditions such that onset of unprecedented climatic extremes will outpace evolutionary and adaptive capabilities. To assess whether and when future climate extremes exceed their historical windows of variability within impact‐relevant socioeconomic, geopolitical, and ecological domains, we investigate the timing of perceivable changes (time of emergence; TOE) for 18 magnitude‐, frequency‐, and severity‐based extreme temperature (10) and precipitation (8) indices using both multimodel and single‐model multirealization ensembles. Under a high‐emission scenario, we find that the signal of frequency‐ and severity‐based temperature extremes is projected to rise above historical noise earliest in midlatitudes, whereas magnitude‐based temperature extremes emerge first in low and high latitudes. Precipitation extremes demonstrate different emergence patterns, with severity‐based indices first emerging over midlatitudes, and magnitude‐ and frequency‐based indices emerging earliest in low and high latitudes. Applied to impact‐relevant domains, simulated TOE patterns suggest (a) unprecedented consecutive dry day occurrence in 〉50% of 14 terrestrial biomes and 12 marine realms prior to 2100, (b) earlier perceivable changes in climate extremes in countries with lower per capita GDP, and (c) emergence of severe and frequent heat extremes well‐before 2030 for the 590 most populous urban centers. Elucidating extreme‐metric and domain‐type TOE heterogeneities highlights the challenges adaptation planners face in confronting the consequences of elevated twenty‐first century radiative forcing.

Beschreibung: Long term dynamics of hard coral cover, bioconstruction potential, carbonate deposition, and reef accretion were monitored over a 20‐year period on Maldivian coral reefs in order to investigate the effects of high‐temperature anomalies on coral reefs and their recovery potential. Abnormally high temperatures in 1998 and 2016 led to severe coral bleaching and consequent mortality, especially of the primary builders. Renewed carbonate deposition was not documented until 2–3 years after the bleaching, 6–9 years passed until constratal (low relief) growth was achieved, and 14–16 years were required to reach accretion rates high enough to ensure superstratal (high relief) growth. Abstract Global climate change has increased the frequency and intensity of extreme heat anomalies and consequent mass coral bleaching events. Long‐term dynamics of hard coral cover, bioconstruction potential, carbonate deposition, and reef accretion was monitored over a 20‐year period on Maldivian coral reefs in order to investigate the effects of high‐temperature anomalies on coral reef accretion and their recovery potential. Changes experienced by shallow reefs between 1997 and 2017 were evaluated by considering five different bioconstructional guilds and the BioConstruction Potential index (BCP), a proxy for the constructional capacity of reefs. Abnormally high temperatures in 1998 and 2016 led to severe coral bleaching and consequent mortality, especially of the primary builders. Renewed carbonate deposition was not documented until 2–3 years after the bleaching, and 6–9 years passed until constratal (i.e., low relief) growth was achieved. Finally, 14–16 years were required to reach accretion rates high enough to ensure superstratal (i.e., high relief) growth. Coral mortality in the Maldives during the 2016 bleaching event was lower than in 1998, and the initial recovery was faster and occurred via a different trajectory than in 1998. Rising levels of anthropogenic carbon emissions are predicted to accelerate sea level rise and trigger severe coral bleaching events at least twice per decade, a frequency that will (a) prevent coral recovery, (b) nullify reef accretion, and consequently, (c) result in the drowning of Maldivian reefs under the worst climate projections.

Beschreibung: Climate warming and harvesting affect the dynamics of species across the globe through a multitude of mechanisms, including distribution changes of spawning fish. For the Northeast Arctic cod, two major hypotheses have been put forward to explain these changes: climate and harvesting. Here, we evaluate these hypotheses by combining two sources of modern data: economic data from the Norwegian fisheries and genetically determined individual fish sampled at the spawning grounds. Our results indicate that demographic size truncation due to harvesting is currently not the dominating factor in shaping spawning ground distribution, but our results provide support for the climate hypothesis. Abstract Climate warming and harvesting affect the dynamics of species across the globe through a multitude of mechanisms, including distribution changes. In fish, migrations to and distribution on spawning grounds are likely influenced by both climate warming and harvesting. The Northeast Arctic (NEA) cod (Gadus morhua) performs seasonal migrations from its feeding grounds in the Barents Sea to spawning grounds along the Norwegian coast. The distribution of cod between the spawning grounds has historically changed at decadal scales, mainly due to variable use of the northern and southern margins of the spawning area. Based on historical landing records, two major hypotheses have been put forward to explain these changes: climate and harvesting. Climate could affect the distribution through, for example, spatial habitat shifts. Harvesting could affect the distribution through impacting the demographic structure. If demographic structure is important, theory predicts increasing spawner size with migration distance. Here, we evaluate these hypotheses with modern data from a period (2000–2016) of increasing temperature and recovering stock structure. We first analyze economic data from the Norwegian fisheries to investigate geographical differences in size of spawning fish among spawning grounds, as well as interannual differences in mean latitude of spawning in relation to changes in temperature and demographic parameters. Second, we analyze genetically determined fish sampled at the spawning grounds to unambiguously separate between migratory NEA cod and potentially smaller sized coastal cod of local origin. Our results indicate smaller spawners farther away from the feeding grounds, hence not supporting the hypothesis that harvesting is a main driver for the contemporary spawning ground distribution. We find a positive correlation between annual mean spawning latitude and temperature. In conclusion, based on contemporary data, there is more support for climate compared to harvesting in shaping spawning ground distribution in this major fish stock in the North Atlantic Ocean.

Beschreibung: This study harnesses 894,392 digital herbarium records and 1,959 in situ observations to produce the first assessment of the effects of a 25 of climate parameters on the flowering time of 2,468 of angiosperm taxa throughout North using a regression approach—elastic net regularization—that has not previously been used in phenological modeling, but exhibits several advantages over ordinary least squares and stepwise regression. Multivariate models based on herbarium‐derived data and in situ phenological observations had similar predictive capacity. By vetting these models across an unprecedented number of taxa, this work demonstrates a new approach to phenological modeling. Abstract Determining the manner in which plant species shift their flowering times in response to climatic conditions is essential to understanding and forecasting the impacts of climate change on the world's flora. The limited taxonomic diversity and duration of most phenological datasets, however, have impeded a comprehensive, systematic determination of the best predictors of flowering phenology. Additionally, many studies of the relationship between climate conditions and plant phenology have included only a limited set of climate parameters that are often chosen a priori and may therefore overlook those parameters to which plants are most phenologically sensitive. This study harnesses 894,392 digital herbarium records and 1,959 in situ observations to produce the first assessment of the effects of a large number (25) of climate parameters on the flowering time of a very large number (2,468) of angiosperm taxa throughout North America. In addition, we compare the predictive capacity of phenological models constructed from the collection dates of herbarium specimens vs. repeated in situ observations of individual plants using a regression approach—elastic net regularization—that has not previously been used in phenological modeling, but exhibits several advantages over ordinary least squares and stepwise regression. When herbarium‐derived data and in situ phenological observations were used to predict flowering onset, the multivariate models based on each of these data sources had similar predictive capacity (R2 = 0.27). Further, apart from mean maximum temperature (TMAX), the two best predictors of flowering time have not commonly been included in phenological models: the number of frost‐free days (NFFD) and the quantity of precipitation as snow (PAS) in the seasons preceding flowering. By vetting these models across an unprecedented number of taxa, this work demonstrates a new approach to phenological modeling.

Beschreibung: How plant communities and soil microorganisms interact to determine the multifunctionality under climate change is poorly known. We evaluated, using an experimental approach, how simulated climate change (warming and rainfall reduction) and initial plant species richness affect plant functional structure and soil microorganisms. Also, we assessed how all these factors affect, directly and indirectly, soil multifunctionality. Warming selected for the larger and most productive plant species, increasing the average size in the communities and leading to reductions in functional plant diversity. These changes increased the total abundance of bacteria that, in turn, increased that of protists, ultimately promoting soil multifunctionality. Abstract Despite their importance, how plant communities and soil microorganisms interact to determine the capacity of ecosystems to provide multiple functions simultaneously (multifunctionality) under climate change is poorly known. We conducted a common garden experiment using grassland species to evaluate how plant functional structure and soil microbial (bacteria and protists) diversity and abundance regulate soil multifunctionality responses to joint changes in plant species richness (one, three and six species) and simulated climate change (3°C warming and 35% rainfall reduction). The effects of species richness and climate on soil multifunctionality were indirectly driven via changes in plant functional structure and their relationships with the abundance and diversity of soil bacteria and protists. More specifically, warming selected for the larger and most productive plant species, increasing the average size within communities and leading to reductions in functional plant diversity. These changes increased the total abundance of bacteria that, in turn, increased that of protists, ultimately promoting soil multifunctionality. Our work suggests that cascading effects between plant functional traits and the abundance of multitrophic soil organisms largely regulate the response of soil multifunctionality to simulated climate change, and ultimately provides novel experimental insights into the mechanisms underlying the effects of biodiversity and climate change on ecosystem functioning.

Beschreibung: Four patterns of imminent extinction from metacommunities if patches were lost in small‐to‐large size order compared with random placement predictions (gray solid and dashed lines). A 20% area loss comprising only the smallest patches (vertical dashed line) would remove species in over 80% of 163 metacommunities analyzed. Losses were lowest among vertebrates, which predominantly followed threshold (a) and step (c) patterns. Random loss (b) was typical in migratory and highly disturbed metacommunities. The highest proportional loss was predicted for vascular plants and invertebrates due to higher species turnover with these taxa mainly following step (c) or linear (d) patterns. Abstract Under many global‐change scenarios, small habitat patches are the most vulnerable to destruction. For example, smaller ponds are at greater risk in a drying climate and their loss would remove any obligate aquatic individuals present. We asked what proportional loss of species diversity from metacommunities comprised of discrete habitat patches should be expected from attrition (complete loss) of only the smallest patches under such a premise. We analyzed 175 published datasets for different taxonomic groups (vertebrates, invertebrates, and plants) and habitat types (islands, habitat islands, and fragments). We simulated the destruction of only the smallest patches to an approximate 20% of total area (range: 15.2%–24.2%) and analyzed species loss. Mean [± 95% CI] species loss was 12.7% [10.8, 14.6], although 18.3% of datasets lost no species. Four broad patterns of species loss were evident, reflecting underlying differences in minimum area requirements and the degree of species turnover among patches. Regression modeling showed species loss increased with greater species turnover among patches (βSIM) and decreased with greater area scaling of diversity (i.e., larger power‐law island species–area relationship exponents). Losses also increased with greater numbers of single‐patch endemics and with increasing proportions of patches destroyed. After accounting for these predictors, neither taxonomic group nor habitat type increased explained variation in species loss. Attrition of the smallest patches removed species in 〉80% of metacommunities, despite all larger patches and 〉75% of total area remaining intact. At both 10% and 20% area reduction, median species loss across all datasets was around 50% higher than predicted from methods based on the species–area relationship. We conclude that any mechanism of global change that selectively destroys small habitat patches will lead to imminent extinctions in most discrete metacommunities.

Beschreibung: We measured over 3 years the net ecosystem exchange of CO2, methane, and dissolved organic carbon (DOC) at a restored post‐extraction peatland and compared our observations to the C balance of an intact reference peatland that has a long‐term continuous flux record. The restored peatland was an annual sink for CO2, and a source of methane and DOC, resulting in a mean annual net ecosystem uptake of C. Integrating structures to increase water retention, alongside re‐establishing key species, have been effective at re‐establishing the net C sink rate to that of an intact peatland. Abstract Peatlands after drainage and extraction are large sources of carbon (C) to the atmosphere. Restoration, through re‐wetting and revegetation, aims to return the C sink function by re‐establishing conditions similar to that of an undrained peatland. However, the time needed to re‐establish C sequestration is not well constrained due to the lack of multi‐year measurements. We measured over 3 years the net ecosystem exchange of CO2 (NEE), methane (), and dissolved organic carbon (DOC) at a restored post‐extraction peatland (RES) in southeast Canada (restored 14 years prior to the start of the study) and compared our observations to the C balance of an intact reference peatland (REF) that has a long‐term continuous flux record and is in the same climate zone. Small but significant differences in winter respiration driven by temperature were mainly responsible for differences in cumulative NEE between years. Low growing season inter‐annual variability was linked to constancy of the initial spring water table position, controlled by the blocked drainage ditches and the presence of water storage structures (bunds and pools). Half‐hour at RES was small except when Typha latifolia‐invaded drainage ditches were in the tower footprint; this effect at the ecosystem level was small as ditches represent a minor fraction of RES. The restored peatland was an annual sink for CO2 (−90 ± 18 g C m−2 year−1), a source of CH4 (4.4 ± 0.2 g C m−2 year−1), and a source of DOC (6.9 ± 2.2 g C m−2 year−1), resulting in mean net ecosystem uptake of 78 ± 17 g C m−2 year−1. Annual NEE at RES was most similar to wetter, more productive years at REF. Integrating structures to increase water retention, alongside re‐establishing key species, have been effective at re‐establishing the net C sink rate to that of an intact peatland.

Beschreibung: Winter snow exerts little effect on tree growth in drier regions attributed to limited snow accumulation during winter. We further found that there was no compensatory effect of winter snow on the intensifying drought limitation of tree growth across temperate China. Abstract Winter snow is an important driver of tree growth in regions where growing‐season precipitation is limited. However, observational evidence of this influence at larger spatial scales and across diverse bioclimatic regions is lacking. Here, we investigated the interannual effects of winter (here defined as previous October to current February) snow depth on tree growth across temperate China over the period of 1961–2015, using a regional network of tree ring records, in situ daily snow depth observations, and gridded climate data. We report uneven effects of winter snow depth on subsequent growing‐season tree growth across temperate China. There shows little effect on tree growth in drier regions that we attribute mainly to limited snow accumulation during winter. By contrast, winter snow exerts important positive influence on tree growth in stands with high winter snow accumulation (e.g., in parts of cold arid regions). The magnitude of this effect depends on the proportion of winter snow to pre‐growing‐season (previous October to current April) precipitation. We further observed that tree growth in drier regions tends to be increasingly limited by warmer growing‐season temperature and early growing‐season water availability. No compensatory effect of winter snow on the intensifying drought limitation of tree growth was observed across temperate China. Our findings point toward an increase in drought vulnerability of temperate forests in a warming climate.

Beschreibung: Straw return to croplands is widely recommended to increase soil C storage. However, because C and N cycles are tightly coupled, straw return also affects soil reactive N (Nr) losses, but these effects remain uncertain. Therefore, we use the method of meta‐analysis to address this knowledge gap. We found that straw return increased soil C sequestration, but simultaneously increased net Nr losses from global croplands due to greater stimulated NH3 emissions. This result highlights the importance of reasonably managing straw return to soils to limit NH3 emissions without decreasing associated C sequestration potential. Abstract It is widely recommended that crop straw be returned to croplands to maintain or increase soil carbon (C) storage in arable soils. However, because C and nitrogen (N) biogeochemical cycles are closely coupled, straw return may also affect soil reactive N (Nr) losses, but these effects remain uncertain, especially in terms of the interactions between soil C sequestration and Nr losses under straw addition. Here, we conducted a global meta‐analysis using 363 publications to assess the overall effects of straw return on soil Nr losses, C sequestration and crop productivity in agroecosystems. Our results show that on average, compared to mineral N fertilization, straw return with same amount of mineral N fertilizer significantly increased soil organic C (SOC) content (14.9%), crop yield (5.1%), and crop N uptake (10.9%). Moreover, Nr losses in the form of nitrous oxide (N2O) emissions from rice paddies (17.3%), N leaching (8.7%), and runoff (25.6%) were significantly reduced, mainly due to enhanced microbial N immobilization. However, N2O emissions from upland fields (21.5%) and ammonia (NH3) emissions (17.0%) significantly increased following straw return, mainly due to the stimulation of nitrification/denitrification and soil urease activity. The increase in NH3 and N2O emissions was significantly and negatively correlated with straw C/N ratio and soil clay content. Regarding the interactions between C sequestration and Nr losses, the increase in SOC content following straw return was significantly and positively correlated with the decrease in N leaching and runoff. However, at a global scale, straw return increased net Nr losses from both rice and upland fields due to a greater stimulation of NH3 emissions than the reduction in N leaching and runoff. The trade‐offs between increased net Nr losses and soil C sequestration highlight the importance of reasonably managing straw return to soils to limit NH3 emissions without decreasing associated C sequestration potential.

Beschreibung: The satellite record revealed substantial land surface “greening” in the northern hemisphere over recent decades, but process‐based Earth system models (ESMs) poorly reproduce observed spatial patterns of greening. Here, we show strong greening over Europe during the past 15 years. The spatial patterns of vegetation change indicate that woody regrowth following land abandonment is an important driver of land surface greening throughout Europe. The results offer an explanation for the large discrepancies between ESM‐derived and satellite‐derived greening estimates, and thus generate new avenues for improving the ESMs on which we rely for crucial climate forecasts. Abstract The satellite record has revealed substantial land surface “greening” in the northern hemisphere over recent decades. Process‐based Earth system models (ESMs) attribute enhanced vegetation productivity (greening) to CO2 fertilisation. However, the models poorly reproduce observed spatial patterns of greening, suggesting that they ignore crucial processes. Here, we explore whether fine‐scale land cover dynamics, as modified by ecological and land‐use processes, can explain the discrepancy between models and satellite‐based estimates of greening. We used 500 m satellite‐derived Leaf Area Index (LAI) to quantify greening. We focus on semi‐natural vegetation in Europe, and distinguish between conservation areas and unprotected land. Within these ecological and land‐use categories, we then explored the relationships between vegetation change and major climatic gradients. Despite the relatively short time‐series (15 years), we found a strong overall increase in LAI (i.e., greening) across all European semi‐natural vegetation types. The spatial pattern of vegetation change identifies land‐use change, particularly land abandonment, as a major initiator of vegetation change both in‐ and outside of protected areas. The strongest LAI increases were observed in mild climates, consistent with more vigorous woody regrowth after cessation of intensive management in these environments. Surprisingly, rates of vegetation change within protected areas did not differ significantly from unprotected semi‐natural vegetation. Overall, the detected LAI increases are consistent with previous, coarser‐scale, studies. The evidence indicates that woody regrowth following land abandonment is an important driver of land surface greening throughout Europe. The results offer an explanation for the large discrepancies between ESM‐derived and satellite‐derived greening estimates and thus generate new avenues for improving the ESMs on which we rely for crucial climate forecasts.

Beschreibung: Global Change Biology, Volume 25, Issue 1, Page e1-e3, January 2019.

Beschreibung: Trophic amplification of twenty‐first century marine biomass declines is a consistent feature of Earth System Models, across different scenarios of future climate change. An analytical explanation of this trophic amplification can be derived from generic plankton differential equations. Using an ocean biogeochemical model, we show that the inclusion of variable C:N:P phytoplankton stoichiometry can substantially increase the trophic amplification of biomass declines in low latitude regions. Abstract The impact of climate change on the marine food web is highly uncertain. Nonetheless, there is growing consensus that global marine primary production will decline in response to future climate change, largely due to increased stratification reducing the supply of nutrients to the upper ocean. Evidence to date suggests a potential amplification of this response throughout the trophic food web, with more dramatic responses at higher trophic levels. Here we show that trophic amplification of marine biomass declines is a consistent feature of the Coupled Model Intercomparison Project Phase 5 (CMIP5) Earth System Models, across different scenarios of future climate change. Under the business‐as‐usual Representative Concentration Pathway 8.5 (RCP8.5) global mean phytoplankton biomass is projected to decline by 6.1% ± 2.5% over the twenty‐first century, while zooplankton biomass declines by 13.6% ± 3.0%. All models project greater relative declines in zooplankton than phytoplankton, with annual zooplankton biomass anomalies 2.24 ± 1.03 times those of phytoplankton. The low latitude oceans drive the projected trophic amplification of biomass declines, with models exhibiting variable trophic interactions in the mid‐to‐high latitudes and similar relative changes in phytoplankton and zooplankton biomass. Under the assumption that zooplankton biomass is prey limited, an analytical explanation of the trophic amplification that occurs in the low latitudes can be derived from generic plankton differential equations. Using an ocean biogeochemical model, we show that the inclusion of variable C:N:P phytoplankton stoichiometry can substantially increase the trophic amplification of biomass declines in low latitude regions. This additional trophic amplification is driven by enhanced nutrient limitation decreasing phytoplankton N and P content relative to C, hence reducing zooplankton growth efficiency. Given that most current Earth System Models assume that phytoplankton C:N:P stoichiometry is constant, such models are likely to underestimate the extent of negative trophic amplification under projected climate change.

Beschreibung: Changing the timing of migration to breeding grounds in coastal western Alaska can influence the ecosystem process of CO2 exchange. Early and late arrival of birds that graze this system can decrease and increase uptake of CO2, respectively. Removing geese from the system greatly enhances CO2 uptake. Abstract The advancement of spring and the differential ability of organisms to respond to changes in plant phenology may lead to “phenological mismatches” as a result of climate change. One potential for considerable mismatch is between migratory birds and food availability in northern breeding ranges, and these mismatches may have consequences for ecosystem function. We conducted a three‐year experiment to examine the consequences for CO2 exchange of advanced spring green‐up and altered timing of grazing by migratory Pacific black brant in a coastal wetland in western Alaska. Experimental treatments represent the variation in green‐up and timing of peak grazing intensity that currently exists in the system. Delayed grazing resulted in greater net ecosystem exchange (NEE) and gross primary productivity (GPP), while early grazing reduced CO2 uptake with the potential of causing net ecosystem carbon (C) loss in late spring and early summer. Conversely, advancing the growing season only influenced ecosystem respiration (ER), resulting in a small increase in ER with no concomitant impact on GPP or NEE. The experimental treatment that represents the most likely future, with green‐up advancing more rapidly than arrival of migratory geese, results in NEE changing by 1.2 µmol m−2 s−1 toward a greater CO2 sink in spring and summer. Increased sink strength, however, may be mitigated by early arrival of migratory geese, which would reduce CO2 uptake. Importantly, while the direct effect of climate warming on phenology of green‐up has a minimal influence on NEE, the indirect effect of climate warming manifest through changes in the timing of peak grazing can have a significant impact on C balance in northern coastal wetlands. Furthermore, processes influencing the timing of goose migration in the winter range can significantly influence ecosystem function in summer habitats.

Beschreibung: We aimed to isolate effects of earlier snowmelt timing on soil greenhouse gas fluxes in a seasonally snow‐covered forest ecosystem. We found that soil greenhouse gas fluxes were surprisingly resistant to hydrological changes associated with earlier snowmelt and interannual variation in precipitation amount, which suggests that net greenhouse gas emissions will increase from Sierra Nevada soils in the future with earlier snowmelt and a longer snow‐free season. Abstract The release of water during snowmelt orchestrates a variety of important belowground biogeochemical processes in seasonally snow‐covered ecosystems, including the production and consumption of greenhouse gases (GHGs) by soil microorganisms. Snowmelt timing is advancing rapidly in these ecosystems, but there is still a need to isolate the effects of earlier snowmelt on soil GHG fluxes. For an improved mechanistic understanding of the biogeochemical effects of snowmelt timing during the snow‐free period, we manipulated a high‐elevation forest that typically receives over two meters of snowfall but little summer precipitation to influence legacy effects of snowmelt timing. We altered snowmelt rates for two years using black sand to accelerate snowmelt and white fabric to postpone snowmelt, thus creating a two‐ to three‐week disparity in snowmelt timing. Soil microclimate and fluxes of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) were monitored weekly to monthly during the snow‐free period. Microbial abundances were estimated by potential assays near the end of each snow‐free period. Although earlier snowmelt caused soil drying, we found no statistically significant effects (p 〈 0.05) of altered snowmelt timing on fluxes of CO2 or N2O, or soil microbial abundances. Soil CH4 fluxes, however, did respond to snowmelt timing, with 18% lower rates of CH4 uptake in the earlier snowmelt treatment, but only after a dry winter. Cumulative CO2 emission and CH4 uptake were 43% and 88% greater, respectively, after the dry winter. We conclude that soil GHG fluxes can be surprisingly resistant to hydrological changes associated with earlier snowmelt, likely because of persistent moisture and microbial activities in deeper mineral soils. As a result, a drier California in the future may cause seasonally snow‐covered soils in the Sierra Nevada to emit more GHGs, not less.

Beschreibung: Future warming may limit the distribution of many ectomycorrhizal (EM) fungal species that are currently adapted to only cold climates. This could eventually reduce EM fungal biodiversity, which is linked to forest functions through symbiotic associations with trees. Abstract Species with narrow niche breadths are assumed to be more susceptible to environmental changes than those with wide niche breadths. Although information on niche properties is necessary for predicting biological responses to environmental changes, such information is largely missing for soil microbes. In this study, we present the temperature niche positions and breadths of a functionally important group of eukaryotic soil microbes, ectomycorrhizal (EM) fungi. We compiled high‐quality EM fungal sequence data from 26 forested sites in Japan (with mean annual temperatures ranging from 1.6 to 23.6°C) to create temperature niche profiles for each individual fungal species. Nested theory and a newly developed weighted‐randomization null model were applied to 75 fungal operational taxonomic units (OTUs) with high occurrence records to examine potential preferences for certain temperature positions and breadths. Our analyses revealed that (a) many EM fungal OTUs were restricted to habitats with low mean annual temperatures, (b) fungal OTUs observed at colder sites exhibited narrower temperature breadths than expected by chance, (c) the composition of EM fungal OTUs exhibited a nested pattern along the temperature gradient, and (d) EM fungal richness was highest at colder sites, where the greatest degree of overlap in OTU occurrence was observed. These findings imply that future warming may limit the distribution of many EM fungal species that are currently adapted to only cold climates. This could eventually reduce EM fungal biodiversity, which is linked to forest function through symbiotic associations with trees. This study demonstrates the distribution and environmental ranges of various EM fungal species and can contribute to develop species distribution models with the aim of conserving microbes in the face of climate change.

Beschreibung: Plant litter decay in drylands is poorly understood but can have a significant influence on the global C cycle. We found that the decay of Sonoran Desert leaf litter varied considerably among species, but traditional indices of litter quality for microbial degradation failed to predict this variability. While microbial respiration of litter was a strong predictor of decay, it was not correlated with these indices. Rather, respiration rates were strongly correlated with the water‐soluble fraction in litter types. Surprisingly, both this labile fraction as well as respiration rates of litter increased over our 34‐month field experiment, in contrast to traditional views of litter decay in which this fraction declines and limits microbial degradation over time. Moreover, exposure to UV and blue sunlight accelerated this process and was likely responsible for the faster decay of litter in sunlight. The processes driving litter decay appeared to differ appreciably from more mesic systems, and involved strong couplings between abiotic and biotic drivers. Abstract The mechanisms of plant litter decay in drylands are poorly understood, limiting the accuracy of nutrient‐cycling models for these systems. We monitored the decay of 12 leaf litter types on the soil surface of the Sonoran Desert for 34 months and assessed what traits predicted mass loss and how exposure to different wavebands of sunlight influenced mass loss. Mass loss varied considerably among litter types, ranging from 42%–96% after 34 months in full sunlight. Traditional indices of litter quality (e.g., initial C:N or lignin:N ratios) failed to predict differences in mass loss among litter types. The strongest predictor of mass loss was the microbial respiration rate of initial litter, which explained 45%–54% of the variation in loss among litter types. Microbial respiration rates were not correlated with traditional indices of litter quality, but were positively correlated with the water‐soluble fraction in litter and concentrations of dissolved organic C in this fraction. Traditional indices of litter quality failed to predict decay likely because they did a poor job of predicting microbial degradability of litter, not because microbial degradation was a minor driver of decay. In all radiation‐exposure treatments, water‐soluble fractions and respiration rates increased through decay and were several times higher after 34 months than initially. Hence, labile pools and microbial degradability of litter increased through decay in contrast to traditional views that labile pools decline and constrain microbes. Litter exposed to UV or UV through blue radiation wavelengths, lost on average 1.3 times or 1.5 times more mass, respectively, than litter not exposed to these wavebands. The magnitude of this photodegradation was greater in litter types that had higher initial concentrations of hemicellulose and cellulose per unit surface area. Litter exposed to full sun had higher water‐soluble fractions and usually had higher respiration rates, illustrating that sunlight accelerated microbial degradation by increasing labile pools. The processes driving litter decay appeared to differ appreciably from mesic systems and involved strong couplings between abiotic and biotic drivers.

Beschreibung: Using field experiments, we investigated the responses of bats to street lights with different emission spectra. Fast‐flying species are attracted to orange, white and green light, while slower‐flying species are deterred. The threatened lesser horseshoe bat Rhinolophus hipposideros is also deterred by red light, challenging a previously held assumption that red light is safe for bats. Using radio tracking, we demonstrate that the impact of lights on R. hipposideros can be mitigated by controlling light spill along preferred commuting routes. We argue it is essential to preserve dark corridors to mitigate the impacts of light pollution on bats. Abstract The rapid global spread of artificial light at night is causing unprecedented disruption to ecosystems. In otherwise dark environments, street lights restrict the use of major flight routes by some bats, including the threatened lesser horseshoe bat Rhinolophus hipposideros, and may disrupt foraging. Using radio tracking, we examined the response of individual female R. hipposideros to experimental street lights placed on hedgerows used as major flight routes. Hedgerows were illuminated on one side over four nights using lights with different emission spectra, while the opposite side of the hedge was not illuminated. Automated bat detectors were used to examine changes in overall bat activity by R. hipposideros and other bat species present. R. hipposideros activity reduced significantly under all light types, including red light, challenging a previously held assumption that red light is safe for bats. Despite this, R. hipposideros rapidly adapted to the presence of lights by switching their flight paths to the dark side of the hedgerow, enabling them to reach foraging sites without restriction. Red light had no effect on the activity of the other species present. Slow‐flying Myotis spp. avoided orange, white and green light, while more agile Pipistrellus spp. were significantly more active at these light types compared to dark controls, most probably in response to accumulations of insect prey. No effect of any light type was found for Nyctalus or Eptesicus spp. Our findings demonstrate that caution must be used when promoting forms of lighting that are thought to be safe for wildlife before they are tested more widely. We argue that it is essential to preserve dark corridors to mitigate the impacts of artificial light at night on bat activity and movements.

Beschreibung: In this quantitative review, we examine the response of key microbially mediated nitrogen transformation processes (A) to ocean acidification (OA, i.e., elevated CO2/low pH), using meta‐analyses of 49 data sets. Among others, results indicate an increase in marine N2 fixation (green arrow in B, significance level p 〈 .01**)) along with a reduction in nitrification with a medium level of evidence (red arrow in B, significance level p 〈 .01**)). Our results propose alteration of the marine nitrogen cycle, with potential shifts in the relative stocks of reduced (NH4+) and oxidized nitrogen (NO3−) species, arising from the positive response of N2 fixation, and negative response of nitrification to OA. Abstract Ocean acidification (OA), arising from the influx of anthropogenically generated carbon, poses a massive threat to the ocean ecosystems. Our knowledge of the effects of elevated anthropogenic CO2 in marine waters and its effect on the performance of single species, trophic interactions, and ecosystems is increasing rapidly. However, our understanding of the biogeochemical cycling of nutrients such as nitrogen is less advanced and lacks a comprehensive overview of how these processes may change under OA. We conducted a systematic review and meta‐analysis of eight major nitrogen transformation processes incorporating 49 publications to synthesize current scientific understanding of the effect of OA on nitrogen cycling in the future ocean by 2100. The following points were identified by our meta‐analysis: (a) Diazotrophic nitrogen fixation is likely enhanced by 29% ± 4% under OA; (b) species‐ and strain‐specific responses of nitrogen fixers to OA were detectable, which may result in alterations in microbial community composition in the future ocean; (c) nitrification processes were reduced by a factor of 29% ± 10%; (d) declines in nitrification rates were not reflected by nitrifier abundance; and (e) contrasting results in unispecific culture experiments versus natural communities were apparent for nitrogen fixation and denitrification. The net effect of the nitrogen cycle process responses also suggests there may be a shift in the relative nitrogen pools, with excess ammonium originating from CO2‐fertilized diazotrophs. This regenerated inorganic nitrogen may recycle in the upper water column increasing the relative importance of the ammonium‐fueled regenerated production. However, several feedback mechanisms with other chemical cycles, such as oxygen, and interaction with other climate change stressors may counteract these findings. Finally, our review highlights the shortcomings and gaps in current understanding of the potential changes in nitrogen cycling under future climate and emphasizes the need for further ecosystem studies.

Beschreibung: To assess the relative influence of climate and land use to bird distributions of the California Central Valley, we conducted resurveys of sites visited in the early 1900s and analyzed bird occurrence using occupancy models. We found high species turnover, with occupancy increases predominantly by habitat generalists and human adapters. Despite these changes, community‐level occupancy, richness, and diversity remained unexpectedly stable, and were all driven most strongly by water availability relative to temperature, urbanization, or agriculture. Abstract Climate and land‐use changes are thought to be the greatest threats to biodiversity, but few studies have directly measured their simultaneous impacts on species distributions. We used a unique historic resource—early 20th‐century bird surveys conducted by Joseph Grinnell and colleagues—paired with contemporary resurveys a century later to examine changes in bird distributions in California's Central Valley, one of the most intensively modified agricultural zones in the world and a region of heterogeneous climate change. We analyzed species‐ and community‐level occupancy using multispecies occupancy models that explicitly accounted for imperfect detection probability, and developed a novel, simulation‐based method to compare the relative influences of climate and land‐use covariates on site‐level species richness and beta diversity (measured by Jaccard similarity). Surprisingly, we show that mean occupancy, species richness and between‐site similarity have remained remarkably stable over the past century. Stability in community‐level metrics masked substantial changes in species composition; occupancy declines of some species were equally matched by increases in others, predominantly species with generalist or human‐associated habitat preferences. Bird occupancy, richness and diversity within each era were driven most strongly by water availability (precipitation and percent water cover), indicating that both climate and land‐use are important drivers of species distributions. Water availability had much stronger effects than temperature, urbanization and agricultural cover, which are typically thought to drive biodiversity decline.

Beschreibung: Global Change Biology, Volume 24, Issue 10, Page i-ii, October 2018. 〈br/〉

Beschreibung: We report trends in freshwater zooplankton phenology from the Southern Hemisphere for the first time. Analysis of the time series of zooplankton abundance from Lake Chascomús (2005 to 2015) revealed significant delays in phenological metrics of two rotifer species: Brachionus havanaensis and Keratella americana. The timing of the observed shift in B. havanaensis phenology was coincident with a warming trend in lake water temperature during autumn (May). Analysis from six additional lakes and previous experimental results provided further evidence that the lake water warming trend in May was responsible for the delayed decline of B. havanaensis populations in autumn. Abstract The relationship between the timing of recurrent biological events and seasonal climatic patterns (i.e., phenology) is a crucial ecological process. Changes in phenology are increasingly linked to global climate change. However, current evidence of phenological responses to recent climate change is subjected to substantial regional and seasonal biases. Most available evidence on climate‐driven phenological changes comes from Northern Hemisphere (NH) ecosystems and typically involves increases in spring and summer temperatures, which translate into earlier onsets of spring population developments. In the Argentine Pampa region, warming has occurred at a much slower pace than in the NH, and trends are mostly restricted to increases in the minimum temperatures. We used zooplankton abundance data from Lake Chascomús (recorded every two weeks from 2005 to 2015) to evaluate potential changes in phenology. We adopted a sequential screening approach to identify taxa displaying phenological trends and evaluated whether such trends could be associated to observe long‐term changes in water temperature. Two zooplankton species displayed significant later shifts in phenology metrics (end date of Brachionus havanaensis seasonal distribution: 31 day/decade, onset and end dates of Keratella americana seasonal distribution: 59 day/decade and 82 day/decade, respectively). The timing of the observed shift in B. havanaensis phenology was coincident with a warming trend in the May lake water temperature (4.7°C per decade). Analysis of abundance versus temperature patterns from six additional shallow Pampean lakes, and evaluation of previous experimental results, provided further evidence that the lake water warming trend in May was responsible for the delayed decline of B. havanaensis populations in autumn. This study is the first report of freshwater zooplankton phenology changes in the Southern Hemisphere (SH).

Beschreibung: Written Summary:Local‐scale microclimatic conditions in forest understoreys play a key role in shaping the composition, diversity and function of these ecosystems. Yet our ability to capture microclimate at scales relevant for management and conservation remains inherently limited. By combining a network of microclimate sensors with high‐resolution airborne laser scanning data acquired across a land‐use intensity gradient in Borneo, here we characterise how topography and canopy structure shape variation in microclimate in human‐modified tropical landscapes. We estimate that by 2080 forest regeneration could be hampered in large tracts of degraded secondary forest that make up much of Borneo’s lowlands. Abstract Local‐scale microclimatic conditions in forest understoreys play a key role in shaping the composition, diversity and function of these ecosystems. Consequently, understanding what drives variation in forest microclimate is critical to forecasting ecosystem responses to global change, particularly in the tropics where many species already operate close to their thermal limits and rapid land‐use transformation is profoundly altering local environments. Yet our ability to characterize forest microclimate at ecologically meaningful scales remains limited, as understorey conditions cannot be directly measured from outside the canopy. To address this challenge, we established a network of microclimate sensors across a land‐use intensity gradient spanning from old‐growth forests to oil‐palm plantations in Borneo. We then combined these observations with high‐resolution airborne laser scanning data to characterize how topography and canopy structure shape variation in microclimate both locally and across the landscape. In the processes, we generated high‐resolution microclimate surfaces spanning over 350 km2, which we used to explore the potential impacts of habitat degradation on forest regeneration under both current and future climate scenarios. We found that topography and vegetation structure were strong predictors of local microclimate, with elevation and terrain curvature primarily constraining daily mean temperatures and vapour pressure deficit (VPD), whereas canopy height had a clear dampening effect on microclimate extremes. This buffering effect was particularly pronounced on wind‐exposed slopes but tended to saturate once canopy height exceeded 20 m—suggesting that despite intensive logging, secondary forests remain largely thermally buffered. Nonetheless, at a landscape‐scale microclimate was highly heterogeneous, with maximum daily temperatures ranging between 24.2 and 37.2°C and VPD spanning two orders of magnitude. Based on this, we estimate that by the end of the century forest regeneration could be hampered in degraded secondary forests that characterize much of Borneo's lowlands if temperatures continue to rise following projected trends.

Beschreibung: Climate change and associated rises in seawater temperature and acidity are considered key drivers of coral reef degradation. The implementation of effective coral reef management is, however, hampered by contradicting outcomes in empirical research. We therefore applied a suite of meta‐analysis techniques to a dataset of 294 experimental comparisons from 62 publications testing individual and combined effects of elevated temperature and acidification on coral calcification. Effects differed between coral families, life stages, habitats, feeding regimes, climates, and seasons. Our results also demonstrate that climate change needs to be curbed for corals to maintain their capacity to build reefs. Abstract Increased temperature and CO2 levels are considered key drivers of coral reef degradation. However, individual assessments of ecological responses (calcification) to these stressors are often contradicting. To detect underlying drivers of heterogeneity in coral calcification responses, we developed a procedure for the inclusion of stress–effect relationships in ecological meta‐analyses. We applied this technique to a dataset of 294 empirical observations from 62 peer‐reviewed publications testing individual and combined effects of elevated temperature and pCO2 on coral calcification. Our results show an additive interaction between warming and acidification, which reduces coral calcification by 20% when pCO2 levels exceed 700 ppm and temperature increases by 3°C. However, stress levels varied among studies and significantly affected outcomes, with unaffected calcification rates under moderate stresses (pCO2 ≤ 700 ppm, ΔT 〈 3°C). Future coral reef carbon budgets will therefore depend on the magnitude of pCO2 and temperature elevations and, thus, anthropogenic CO2 emissions. Accounting for stress–effect relationships enabled us to identify additional drivers of heterogeneity including coral taxa, life stage, habitat, food availability, climate, and season. These differences can aid reef management identifying refuges and conservation priorities, but without a global effort to reduce CO2 emissions, coral capacity to build reefs will be at risk.

Beschreibung: Observations and process‐based models have both shown that climate warming has resulted in an increase in vegetation greenness on the Tibetan Plateau in recent decades. Using satellite observations and gridded climate data, our analysis documented a substantial mismatch between the elevational shifts of greenness and temperature isolines during a rapid period 2000–2016. This mismatch is probably associated with a lagging response of greenness to temperature change and with the elevational gradient of greenness. The mismatches suggest that there is potentially large micro‐topographical difference in response and acclimation/adaptation of greenness to temperature changes in plants. Abstract Climate warming on the Tibetan Plateau tends to induce an uphill shift of temperature isolines. Observations and process‐based models have both shown that climate warming has resulted in an increase in vegetation greenness on the Tibetan Plateau in recent decades. However, it is unclear whether the uphill shift of temperature isolines has caused greenness isolines to shift upward and whether the two shifts match each other. Our analysis of satellite observed vegetation greenness during the growing season (May–Sep) and gridded climate data for 2000–2016 documented a substantial mismatch between the elevational shifts of greenness and temperature isolines. This mismatch is probably associated with a lagging response of greenness to temperature change and with the elevational gradient of greenness. The lagging response of greenness may be associated with water limitation, resources availability, and acclimation. This lag may weaken carbon sequestration by Tibetan ecosystems, given that greenness is closely related to primary carbon uptake and ecosystem respiration increases exponentially with temperature. We also found that differences in terrain slope angle accounted for large spatial variations in the elevational gradient of greenness and thus the velocity of elevational shifts of greenness isolines and the sensitivity of elevational shifts of greenness isolines to temperature, highlighting the role of terrain effects on the elevational shifts of greenness isolines. The mismatches and the terrain effect found in this study suggest that there is potentially large micro‐topographical difference in response and acclimation/adaptation of greenness to temperature changes in plants. More widespread in situ measurements and fine‐resolution remote sensing observations and fine‐gridded climate data are required to attribute the mismatch to specific environmental drivers and ecological processes such as vertical changes in community structure, plant physiology, and distribution of species.

Beschreibung: We performed a spatially explicit time‐window analysis of the effect of weather on mean spring passage dates at Helgoland (Germany) over a 55‐year period (1960–2014). Although we allowed for a time window of any length at any location, nevertheless incorporating various measures to avoid spurious correlations, time windows at the likely wintering or spring stopover grounds were almost exclusively selected as the best predicting variables, explaining up to 77% of the interannual variability in spring passage. Yet, the response of spring migration phenology to weather at the winter or stopover areas does not fully explain the observed trends. Abstract Over the past decades, spring arrival and passage of most short‐ and medium‐distance migrating birds in the Northern Hemisphere have advanced. Changes in spring temperature at the passage or arrival area have been most frequently shown to be related to these changes in spring migration phenology. In most studies, preliminary assumptions are made on both the spatial location and the specific time frame of the weather influencing spring migration phenology. We performed a spatially explicit time‐window analysis of the effect of weather on mean spring passage dates of nine short‐ and medium‐distance passerines. We analysed data from standardized daily captures at the Helgoland (Germany) constant‐effort site, in combination with gridded daily temperature, precipitation and wind data from the NCEP data set over a 55‐year period (1960–2014), across the whole of West Europe and North Africa. Although we allowed for a time window of any length at any location, nevertheless incorporating various measures to avoid spurious correlations, time windows at the likely wintering or spring stopover grounds were almost exclusively selected as the best predicting variables (96%–100% of identified variables). The weather variables at the wintering and stopover grounds explain up to 77% of the interannual variability in spring passage. Yet, the response of spring migration phenology to weather at the winter or stopover areas does not fully explain the observed trends. Spring migration phenology is, hence, strongly driven by weather at the wintering and stopover grounds, but additional mechanisms are needed to fully explain the advancement of spring migration. Our results also clearly show that previously illustrated correlations, or the lack thereof, between spring migration phenology and weather at the passage or arrival location are due to spatio‐temporal correlations in the weather data. This spatial mismatch might have led to false conclusions, especially the further away the wintering or stopover sites are.

Beschreibung: Compared to black brant, snow geese and white‐fronted geese completed spring migration earlier and derived more of their egg nutrients from Arctic plants (income). Brant derived more of their egg nutrients from endogenous reserves (capital) built during winter and migration. With warmer spring temperatures, brant increased capital investment to eggs to meet costs of earlier reproduction, whereas snow geese and white‐fronted geese invested less capital likely due to improved Arctic foraging. Global warming may adversely impact coastal habitats where brant build reproductive capital, but improve Arctic nutrient availability to snow geese and white‐fronted geese during nesting. Abstract The macronutrients that Arctic herbivores invest in their offspring are derived from endogenous reserves of fat and protein (capital) that females build prior to the period of investment or from foods they consume concurrently with investment (income). The relative contribution from each source can be influenced by temporal and environmental constraints on a female's ability to forage on Arctic breeding areas. Warming temperatures and advancing Arctic phenology may alter those constraints. From 2011 to 2014, we examined relationships among spring temperature, timing of migration and reproduction, and the sources of nutrients females deposited in eggs for three sympatric species of geese that nested in northern Alaska. Compared to lesser snow geese (Anser caerulescens caerulescens) and greater white‐fronted geese (Anser albifrons frontalis), black brant (Branta bernicla nigricans) were more likely to initiate follicle development during migration, resulting in fewer days between their arrival in the Arctic and the onset of incubation and requiring a relatively greater capital investment in eggs. Delaying follicle development until after their arrival in the Arctic provided snow geese and white‐fronted geese an opportunity to forage near their nesting area and to deposit exogenous nutrients in eggs. With warmer spring temperatures, brant invested more capital in eggs, but snow geese invested less capital. Brant likely used capital to meet costs associated with earlier onset of follicle development when phenology was advanced, whereas snow geese used capital to compensate for poor foraging conditions during colder Arctic springs. Global warming is likely to reduce the quality of lower latitude marine habitats where brant acquire endogenous reserves and advancing Arctic phenology may increase their reliance on those reserves during reproduction. Near‐term warming in northern Alaska may improve foraging conditions and favor the reproductive strategies of some herbivores such as snow geese and white‐fronted geese that mainly invest Arctic nutrients in their offspring.

Beschreibung: We show that current optimization and empirical methods to determine stomatal conductance in Earth system models (ESMs) yield similar results and exhibit similar species‐specific sensitivities to environmental variables, including CO2. Failure to account for different stomatal sensitivities across species or vegetation types will lead to significant errors in ESM simulations, particularly for terrestrial water fluxes. The key fitted parameter calibrating optimization or empirical stomatal conductance models to different global vegetation types may be determined from mean annual precipitation, as shown here for the empirical Ball‐Berry slope, overcoming constraints imposed by inflexibilities in current global calibration methods. Abstract Earth system models (ESMs) rely on the calculation of canopy conductance in land surface models (LSMs) to quantify the partitioning of land surface energy, water, and CO2 fluxes. This is achieved by scaling stomatal conductance, gw, determined from physiological models developed for leaves. Traditionally, models for gw have been semi‐empirical, combining physiological functions with empirically determined calibration constants. More recently, optimization theory has been applied to model gw in LSMs under the premise that it has a stronger grounding in physiological theory and might ultimately lead to improved predictive accuracy. However, this premise has not been thoroughly tested. Using original field data from contrasting forest systems, we compare a widely used empirical type and a more recently developed optimization‐type gw model, termed BB and MED, respectively. Overall, we find no difference between the two models when used to simulate gw from photosynthesis data, or leaf gas exchange from a coupled photosynthesis‐conductance model, or gross primary productivity and evapotranspiration for a FLUXNET tower site with the CLM5 community LSM. Field measurements reveal that the key fitted parameters for BB and MED, g1B and g1M, exhibit strong species specificity in magnitude and sensitivity to CO2, and CLM5 simulations reveal that failure to include this sensitivity can result in significant overestimates of evapotranspiration for high‐CO2 scenarios. Further, we show that g1B and g1M can be determined from mean ci/ca (ratio of leaf intercellular to ambient CO2 concentration). Applying this relationship with ci/ca values derived from a leaf δ13C database, we obtain a global distribution of g1B and g1M, and these values correlate significantly with mean annual precipitation. This provides a new methodology for global parameterization of the BB and MED models in LSMs, tied directly to leaf physiology but unconstrained by spatial boundaries separating designated biomes or plant functional types.

Beschreibung: Written Summary: It is important to understand how sun‐sensor geometry affects satellite sun‐induced fluorescence (SIF) in order to take full advantage of these measurements, particularly given their close relationship with gross primary production (GPP). We displayed the bidirectionality of SIF at different viewing zenith angles in the solar principal plane and observed a clear bowl shape of SIF from the backward to forward scattering directions. Therefore, it is important to consider the bidirectionality of SIF when using OCO‐2 SIF data to evaluate the SIF‐GPP relationship.

Beschreibung: Windthrow severity and time since disturbance explain a large portion of observable variations in biomass patterns and functional composition across Central Amazon forests. Biomass stock in windthrown areas is drastically reduced and although rates of biomass increment in recovering vegetation are nearly double those of old‐growth forests, biomass loss due to post‐windthrow mortality is also high and unpredictable. Biomass recovery from windthrows takes up to 40 years and the recovery of the functional composition typical for old‐growth forests dominated by species with high wood densities is likely to take much longer than four decades. Abstract Amazon forests account for ~25% of global land biomass and tropical tree species. In these forests, windthrows (i.e., snapped and uprooted trees) are a major natural disturbance, but the rates and mechanisms of recovery are not known. To provide a predictive framework for understanding the effects of windthrows on forest structure and functional composition (DBH ≥10 cm), we quantified biomass recovery as a function of windthrow severity (i.e., fraction of windthrow tree mortality on Landsat pixels, ranging from 0%–70%) and time since disturbance for terra‐firme forests in the Central Amazon. Forest monitoring allowed insights into the processes and mechanisms driving the net biomass change (i.e., increment minus loss) and shifts in functional composition. Windthrown areas recovering for between 4–27 years had biomass stocks as low as 65.2–91.7 Mg/ha or 23%–38% of those in nearby undisturbed forests (~255.6 Mg/ha, all sites). Even low windthrow severities (4%–20% tree mortality) caused decadal changes in biomass stocks and structure. While rates of biomass increment in recovering vegetation were nearly double (6.3 ± 1.4 Mg ha−1 year−1) those of undisturbed forests (~3.7 Mg ha−1 year−1), biomass loss due to post‐windthrow mortality was high (up to −7.5 ± 8.7 Mg ha−1 year−1, 8.5 years since disturbance) and unpredictable. Consequently, recovery to 90% of “pre‐disturbance” biomass takes up to 40 years. Resprouting trees contributed little to biomass recovery. Instead, light‐demanding, low‐density genera (e.g., Cecropia, Inga, Miconia, Pourouma, Tachigali, and Tapirira) were favored, resulting in substantial post‐windthrow species turnover. Shifts in functional composition demonstrate that windthrows affect the resilience of live tree biomass by favoring soft‐wooded species with shorter life spans that are more vulnerable to future disturbances. As the time required for forests to recover biomass is likely similar to the recurrence interval of windthrows triggering succession, windthrows have the potential to control landscape biomass/carbon dynamics and functional composition in Amazon forests.

Beschreibung: This is important to know what extent are greenhouse gas (GHG) emissions from intensive arable agriculture in China mitigated by sequestration of carbon in soil. We calculated the net GHG balance (kg C‐eq ha−1 year−1) between SOC stock change and emissions of N2O and CH4 and upstream CO2‐eq emissions associated with agronomic management. Despite the soil carbon sink found in Chinese cropland soils, it acted as a net GHG source because the emissions of total GHG are about one order of magnitude larger than the soil carbon sink under current farmers’ practices. Abstract Soil carbon sequestration is being considered as a potential pathway to mitigate climate change. Cropland soils could provide a sink for carbon that can be modified by farming practices; however, they can also act as a source of greenhouse gases (GHG), including not only nitrous oxide (N2O) and methane (CH4), but also the upstream carbon dioxide (CO2) emissions associated with agronomic management. These latter emissions are also sometimes termed “hidden” or “embedded” CO2. In this paper, we estimated the net GHG balance for Chinese cropping systems by considering the balance of soil carbon sequestration, N2O and CH4 emissions, and the upstream CO2 emissions of agronomic management from a life cycle perspective during 2000–2017. Results showed that although soil organic carbon (SOC) increased by 23.2 ± 8.6 Tg C per year, the soil N2O and CH4 emissions plus upstream CO2 emissions arising from agronomic management added 269.5 ± 21.1 Tg C‐eq per year to the atmosphere. These findings demonstrate that Chinese cropping systems are a net source of GHG emissions and that total GHG emissions are about 12 times larger than carbon uptake by soil sequestration. There were large variations between different cropping systems in the net GHG balance ranging from 328 to 7,567 kg C‐eq ha−1 year−1, but all systems act as a net GHG source to the atmosphere. The main sources of total GHG emissions are nitrogen fertilization (emissions during production and application), power use for irrigation, and soil N2O and CH4 emissions. Optimizing agronomic management practices, especially fertilization, irrigation, plastic mulching, and crop residues to reduce total GHG emissions from the whole chain is urgently required in order to develop a low‐carbon future for Chinese crop production.

Beschreibung: Fire frequency and severity are increasing in tundra and boreal regions as climate warms, which can directly affect climate feedbacks by increasing carbon (C) emissions from combustion of the large soil C pool and indirectly via changes in vegetation, permafrost thaw, hydrology, and nutrient availability. We created experimental burns in the Siberian arctic to better understand the direct and indirect effects of changing fire regimes in northern ecosystems. We found that increasing fire severity caused a brief increase in nutrient availability but slowed soil microbial respiration and extracellular enzyme activities. Abstract Fire frequency and severity are increasing in tundra and boreal regions as climate warms, which can directly affect climate feedbacks by increasing carbon (C) emissions from combustion of the large soil C pool and indirectly via changes in vegetation, permafrost thaw, hydrology, and nutrient availability. To better understand the direct and indirect effects of changing fire regimes in northern ecosystems, we examined how differences in soil burn severity (i.e., extent of soil organic matter combustion) affect soil C, nitrogen (N), and phosphorus (P) availability and microbial processes over time. We created experimental burns of three fire severities (low, moderate, and high) in a larch forest in the northeastern Siberian Arctic and analyzed soils at 1, 8 days, and 1 year postfire. Labile dissolved C and N increased with increasing soil burn severity immediately (1 day) postfire by up to an order of magnitude, but declined significantly 1 week later; both variables were comparable or lower than unburned soils by 1 year postfire. Soil burn severity had no effect on P in the organic layer, but P increased with increasing severity in mineral soil horizons. Most extracellular enzyme activities decreased by up to 70% with increasing soil burn severity. Increasing soil burn severity reduced soil respiration 1 year postfire by 50%. However, increasing soil burn severity increased net N mineralization rates 1 year postfire, which were 10‐fold higher in the highest burn severity. While fires of high severity consumed approximately five times more soil C than those of low severity, soil C pools will also be driven by indirect effects of fire on soil processes. Our data suggest that despite an initial increase in labile C and nutrients with soil burn severity, soil respiration and extracellular activities related to the turnover of organic matter were greatly reduced, which may mitigate future C losses following fire.

Beschreibung: Bacteria degraded identical terrestrial organic matter additions differently between two lakes with contrasting water clarity because of differences in their composition and functional genes. These results highlight that ongoing brownification of inland waters can have contrasting outcomes for regional carbon cycling and food web production depending on the chemistry of receiving waters. Abstract Boreal lakes are major components of the global carbon cycle, partly because of sediment‐bound heterotrophic microorganisms that decompose within‐lake and terrestrially derived organic matter (t‐OM). The ability for sediment bacteria to break down and alter t‐OM may depend on environmental characteristics and community composition. However, the connection between these two potential drivers of decomposition is poorly understood. We tested how bacterial activity changed along experimental gradients in the quality and quantity of t‐OM inputs into littoral sediments of two small boreal lakes, a dark and a clear lake, and measured the abundance of operational taxonomic units and functional genes to identify mechanisms underlying bacterial responses. We found that bacterial production (BP) decreased across lakes with aromatic dissolved organic matter (DOM) in sediment pore water, but the process underlying this pattern differed between lakes. Bacteria in the dark lake invested in the energetically costly production of extracellular enzymes as aromatic DOM increased in availability in the sediments. By contrast, bacteria in the clear lake may have lacked the nutrients and/or genetic potential to degrade aromatic DOM and instead mineralized photo‐degraded OM into CO2. The two lakes differed in community composition, with concentrations of dissolved organic carbon and pH differentiating microbial assemblages. Furthermore, functional genes relating to t‐OM degradation were relatively higher in the dark lake. Our results suggest that future changes in t‐OM inputs to lake sediments will have different effects on carbon cycling depending on the potential for photo‐degradation of OM and composition of resident bacterial communities.

Beschreibung: Based on 20 treeline plots along an east–west precipitation gradient in the central Himalayas, this research showed that treelines shifted upward in response to recent climate warming, but their shift rates were mediated by spring precipitation. The drying tendency in association with the recent warming trends observed in the central Himalayas, however, will likely hinder an upslope advancement of alpine treelines and promote downward treeline shifts if moisture availability crosses a critical minimum threshold. Our study highlights the complexity of plant responses to climate and the need to consider multiple climate factors when analyzing treeline dynamics. Abstract Among forest ecosystems, the alpine treeline ecotone can be considered to be a simplified model to study global ecology and climate change. Alpine treelines are expected to shift upwards in response to global warming given that tree recruitment and growth are assumed to be mainly limited by low temperatures. However, little is known whether precipitation and temperature interact to drive long‐term Himalayan treeline dynamics. Tree growth is affected by spring rainfall in the central Himalayan treelines, being good locations for testing if, in addition to temperature, precipitation mediates treeline dynamics. To test this hypothesis, we reconstructed spatiotemporal variations in treeline dynamics in 20 plots located at six alpine treeline sites, dominated by two tree species (birch, fir), and situated along an east–west precipitation gradient in the central Himalayas. Our reconstructions evidenced that treelines shifted upward in response to recent climate warming, but their shift rates were primarily mediated by spring precipitation. The rate of upward shift was higher in the wettest eastern Himalayas, suggesting that its ascent rate was facilitated by spring precipitation. The drying tendency in association with the recent warming trends observed in the central Himalayas, however, will likely hinder an upslope advancement of alpine treelines and promote downward treeline shifts if moisture availability crosses a critical minimum threshold. Our study highlights the complexity of plant responses to climate and the need to consider multiple climate factors when analyzing treeline dynamics.

Beschreibung: Global change will affect ecosystems in ways that are often challenging to predict from short‐term responses alone. To understand the shorter‐ and longer‐term impacts of climate and land use changes on the Tibetan Plateau, we integrated findings from a climate warming and yak grazing experiment with landscape‐level observations in central Tibet. We found that in the short term, warming rapidly drove the ecosystem into a degraded state, regardless of whether livestock were present, while in the longer term, grazing removal will likely exacerbate warming‐driven losses of forage production and carbon storage, thus further reducing Tibet’s ability to provide key ecosystem services. Abstract Alpine meadows on the Tibetan Plateau comprise the largest alpine ecosystem in the world and provide critical ecosystem services, including forage production and carbon sequestration, on which people depend from local to global scales. However, the provision of these services may be threatened by climate warming combined with land use policies that are altering if and how pastoralists can continue to graze livestock, the dominant livelihood practice in this region for millennia. We synthesized findings from a climate warming and yak grazing experiment with landscape‐level observations in central Tibet to gain insight into the trajectories of change that Tibet's alpine meadows will undergo in response to expected changes in climate and land use. We show that within 5 years, experimental warming drove an alpine community with intact, sedge‐dominated turfs into a degraded state. With removal of livestock, consistent with policy intended to reverse degradation, a longer‐term shift to a more shrub‐dominated community will likely occur. Neither degraded nor shrub meadows produce forage or sequester carbon to the same degree as intact meadows, indicating that climate warming and drying will reduce the ability of Tibet’s alpine meadows to provide key ecosystem services, and that livestock reduction policies intended to counteract trajectories of land degradation instead endanger contemporary livelihoods on the Tibetan Plateau.

Beschreibung: Calanus hyperboreus is a key zooplankton species in the Arctic marine food web, but it is unclear if individuals in the central Arctic Ocean are locally produced (scenario 1) or must be supplied through advection from more productive areas because the short growth season prevents individuals from reaching the first overwintering stage, C3 (scenario 2). We show that C. hyperboreus functions as a peripheral population pushing its range limits in the central Arctic, but that plastic life history strategies make the species preadapted to take advantage of improved growth conditions and potentially increase its abundance in the “new” central Arctic. Abstract Life history strategies such as multiyear life cycles, resting stages, and capital breeding allow species to inhabit regions with extreme and fluctuating environmental conditions. One example is the zooplankton species Calanus hyperboreus, whose life history is considered an adaptation to the short and unpredictable growth season in the central Arctic Ocean. This copepod is commonly described as a true Arctic endemic; however, by statistically analyzing compiled observational data, we show that abundances are relatively low and later stages and adults dominate in the central Arctic Ocean basins, indicating expatriation. Combining data analyses with individual‐based modeling and energy requirement estimation, we further demonstrate that while C. hyperboreus can reach higher abundances in areas with greater food availability outside the central Arctic basins, the species’ resilience to environmental fluctuations enables the life cycle to be completed in the central Arctic basins. Specifically, the energy level required to reach the first overwintering stage—a prerequisite for successful local production—is likely met in some—but not all—years. This fine balance between success and failure indicates that C. hyperboreus functions as a peripheral population in the central Arctic basins and its abundance will likely increase in areas with improved growth conditions in response to climate change. By illustrating a key Arctic species’ resilience to extreme and fluctuating environmental conditions, the results of this study have implications for projections of future biogeography and food web dynamics in the Arctic Ocean, a region experiencing rapid warming and sea ice loss.

Beschreibung: Written Summary: Increase in winter precipitation can alleviate strong advancing trends in spring vegetation growth in conjunction with global warming even for temperature‐limited ecosystems. Abstract Understanding the variations in spring vegetation phenology associated with preseason climate conditions can significantly improve our knowledge on ecosystem dynamics and biosphere–atmosphere interactions. Recent studies have shown that wet winters can delay the start date of the vegetation growing season (SOS) in the high latitudes. However, associated underlying mechanisms remain unclear due to the lack of observation sites as well as complex interactions between various climate and ecosystem variables. In this study, the impact of winter precipitation on year‐to‐year variations of the SOS in boreal forests from 1982 to 2005 was investigated. Two experiments were performed using the Community Land Model version 4.5. In the control experiment, observed precipitation was used; in the sensitivity experiment, precipitation in the year 1982 was repeated throughout the period. The SOS in the control experiment shows high temporal correlations with the SOS estimated from the satellite‐retrieved leaf area index, indicating that the land model is capable of simulating realistic response of vegetation to interannual climate variability. The effects of winter precipitation on the SOS are examined by comparing the two model experiments for wet‐ and dry winters. After wet winters, the SOS was delayed by 2.7 days over 70.1% of the boreal forests than after dry winters; this accounts for 42.5% of the interannual variation in the SOS. The SOS delay is related to the decrease in the growing degree‐days (GDD) based on soil temperatures, suggesting that the effects of heat exposure on vegetation growth is strongly modulated by winter precipitation. The GDD decrease is related to both the increase in snowmelt heat flux and reduced absorption of solar radiation, which are proportional to the amount of winter precipitation and the ratio of short plants to tall trees, respectively. Our results provide a physical basis for the winter precipitation–SOS relationship, suggesting that an increase in winter precipitation can alleviate strong advancing trends in spring vegetation growth in conjunction with global warming even for temperature‐limited ecosystems.

Beschreibung: Using long‐term field data of black‐tailed godwits, we modelled the combined effects of increasing spring temperature and declining habitat quality on laying dates and population dynamics. We examined how laying date affected fitness, and consequently population growth rates, and predicted how laying date would change over time. We found selection pressure for earlier laying, yet we predicted only a small advance in laying dates if spring temperatures continue to increase. We show that declining habitat quality amplifies negative effects of climate change: Only in the best‐quality habitats, we predicted no detrimental effects of spring warming on population growth rates. Abstract In seasonal environments, increasing spring temperatures lead many taxa to advance the timing of reproduction. Species that do not may suffer lower fitness. We investigated why black‐tailed godwits (Limosa limosa limosa), a ground‐breeding agricultural grassland shorebird, have not advanced timing of reproduction during the last three decades in the face of climate change and human‐induced habitat degradation. We used data from an 11‐year field study to parameterize an Integral Projection Model to predict how spring temperature and habitat quality simultaneously influence the timing of reproduction and population dynamics. We found apparent selection for earlier laying, but not a correlation between the laying dates of parents and their offspring. Nevertheless, in warmer springs, laying dates of adults show a stronger positive correlation with laying date in previous springs than in cooler ones, and this leads us to predict a slight advance in the timing of reproduction if spring temperatures continue to increase. We also show that only in landscapes with low agricultural activity, the population can continue to act as a source. This study shows how climate change and declining habitat quality may enhance extinction risk.

Beschreibung: Annual variations in daily average and standard error of ecosystem‐scale net ecosystem exchange of methane (NEE) and groundwater level (GWL) between June 1, 2016, and May 31, 2017. The gray‐shaded areas indicate periods when methane emission increased despite GWL declining. Annual methane budget was neutral, ranging from 0.09 to 0.17 g C m−2 year−1. Abstract Data on ecosystem‐scale methane (CH4) fluxes in tropical peatlands are currently lacking in the global CH4 budget. Although the waterlogged Indonesian peatlands contain the largest share of peat carbon in South‐East Asia, ecosystem‐scale CH4 budgets have not yet been reported, although these peatlands have the potential to emit CH4. We observed 1‐year variations in the ecosystem‐scale CH4 flux in an undrained secondary peat swamp forest in central Kalimantan, Indonesia, using the eddy covariance method. We found that the peat swamp forest switched from being a CH4 sink during the dry season (as low as −8.9 mg C m−2 day−1) to a source of CH4 during the wet season (up to 10.7 mg C m−2 day−1), and this was dependent on changes in the groundwater level (GWL). The high GWL during the wet season enhanced the anaerobic CH4 production in the surface layer that had more labile organic matter. However, the CH4 emission also increased when the GWL dropped during dry spells in the wet season. The annual CH4 budget in the studied tropical peat swamp forest (0.09–0.17 g C m−2 year−1) was much lower than that in northern, temperate, and subtropical wetlands. We found that CH4 fluxes had almost no effect on the global warming gas budget of the peat swamp forest, and values were only a few percent less than the CO2 fluxes at the same site. In addition, we conducted anaerobic soil incubation experiments to examine the effect of land‐use change on CH4 production. The results indicated much higher CH4 production potential in undrained forest soil than in drained or drained and burned ex‐forest soils. However, although CH4 production decreased in drained soils relative to undrained soils, conserving pristine peat swamp forests with high GWLs is important to suppress global warming because CO2 emissions increase in drained peatlands.

Beschreibung: We integrate empirical and theoretical approaches to show how feedbacks involving fire, herbivores, and the spatial structure of tree cover explain the resilience of tree cover across climates in the tropics. We find that these feedbacks generate emergent alternative stable states in tree cover with hysteresis across rainfall levels. At lower rainfall levels, a herbivore–tree cover feedback dominates; at higher rainfall levels, a fire–tree cover feedback dominates, which depends strongly on rainfall seasonality. Abstract Fires and herbivores shape tropical vegetation structure, but their effects on the stability of tree cover in different climates remain elusive. Here, we integrate empirical and theoretical approaches to determine the effects of climate on fire‐ and herbivore‐driven forest‐savanna shifts. We analyzed time series of remotely sensed tree cover and fire observations with estimates of herbivore pressure across the tropics to quantify the fire–tree cover and herbivore–tree cover feedbacks along climatic gradients. From these empirical results, we developed a spatially explicit, stochastic fire‐vegetation model that accounts for herbivore pressure. We find emergent alternative stable states in tree cover with hysteresis across rainfall conditions. Whereas the herbivore–tree cover feedback can maintain low tree cover below 1,100 mm mean annual rainfall, the fire–tree cover feedback can maintain low tree cover at higher rainfall levels. Interestingly, the rainfall range where fire‐driven alternative vegetation states can be found depends strongly on rainfall variability. Both higher seasonal and interannual variability in rainfall increase fire frequency, but only seasonality expands the distribution of fire‐maintained savannas into wetter climates. The strength of the fire–tree cover feedback depends on the spatial configuration of tree cover: Landscapes with clustered low tree‐cover areas are more susceptible to cross a tipping point of fire‐driven forest loss than landscapes with scattered deforested patches. Our study shows how feedbacks involving fire, herbivores, and the spatial structure of tree cover explain the resilience of tree cover across climates.