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Le changement d'utilisation des terres/de couverture est la principale cause de dégradation des écosystèmes terrestres. Cependant, ses impacts seront exacerbés en raison du changement climatique et de la croissance démographique, entraînant une expansion agricole en raison de la demande accrue de denrées alimentaires et de la baisse des rendements agricoles dans certaines zones tropicales. Les stratégies internationales visant à atténuer les impacts du changement climatique et du changement du couvert terrestre sont difficiles dans les régions en développement. Cette étude vise à évaluer des alternatives pour minimiser les impacts de ces menaces dans le cadre de trajectoires socio-économiques, dans l'une des régions les plus biologiquement riches du Guatemala et du Mexique. Cette étude est située dans le bassin versant d'Usumacinta, une région transfrontalière qui partage une histoire commune, avec des propriétés biophysiques et des contraintes économiques similaires qui ont conduit à d'importants changements dans l'utilisation/la couverture des terres. Pour comprendre les impacts sur la déforestation et les émissions de carbone des différentes pratiques de gestion des terres, nous avons développé trois scénarios (1) : le statu quo (BAU), (2) un scénario de réduction des émissions visant à réduire la déforestation et la dégradation (REDD+) et (3) zéro déforestation à partir de 2030 sur la base des engagements internationaux. Nos résultats suggèrent que d'ici 2050, la couverture terrestre naturelle pourrait réduire de 22,3 et 12,2% son étendue dans les scénarios BAU et REDD +, respectivement par rapport à 2012. Cependant, le scénario zéro déforestation montre que d'ici 2050, il serait possible d'éviter de perdre 22,4 % du bassin versant boisé (1,7 million d'hectares) et d'en récupérer 5,9 % (0,4 million d'hectares). En termes de séquestration du carbone, les projets REDD + peuvent réduire les pertes de carbone dans la végétation naturelle, mais une politique de zéro déforestation peut doubler la séquestration du carbone produite par les projets REDD + uniquement. Cette étude montre que pour réduire les pressions sur les écosystèmes, en particulier dans les régions fortement marginalisées avec des migrations importantes, il est nécessaire de mettre en œuvre des politiques transfrontalières de gestion des terres qui intègrent également des stratégies de réduction de la pauvreté. El cambio en el uso/cobertura de la tierra es la principal causa de la degradación de los ecosistemas terrestres. Sin embargo, sus impactos se exacerbarán debido al cambio climático y al crecimiento de la población, impulsando la expansión agrícola debido a una mayor demanda de alimentos y menores rendimientos agrícolas en algunas áreas tropicales. Las estrategias internacionales destinadas a mitigar los impactos del cambio climático y el cambio en la cobertura del uso de la tierra son un desafío en las regiones en desarrollo. Este estudio tiene como objetivo evaluar alternativas para minimizar los impactos de estas amenazas bajo trayectorias socioeconómicas, en una de las regiones biológicamente más ricas de Guatemala y México. Este estudio se encuentra en la cuenca de Usumacinta, una región transfronteriza que comparte una historia común, con propiedades biofísicas y limitaciones económicas similares que han llevado a grandes cambios en el uso/cobertura de la tierra. Para comprender los impactos en la deforestación y las emisiones de carbono de las diferentes prácticas de gestión de la tierra, desarrollamos tres escenarios (1): negocios como siempre (BAU), (2) un escenario de reducción de emisiones destinado a reducir la deforestación y la degradación (REDD+) y (3) cero deforestación a partir de 2030 en función de los compromisos internacionales. Nuestros resultados sugieren que para 2050, la cobertura natural de la tierra podría reducir el 22.3 y el 12.2% de su extensión bajo los escenarios BAU y REDD +, respectivamente, en comparación con 2012. Sin embargo, el escenario de deforestación cero muestra que para 2050, sería posible evitar la pérdida del 22,4% de la cuenca forestal (1,7 millones de ha) y recuperar el 5,9% (0,4 millones de hectáreas) de la misma. En términos de secuestro de carbono, los proyectos REDD + pueden reducir las pérdidas de carbono en la vegetación natural, pero una política de deforestación cero puede duplicar el secuestro de carbono producido solo por los proyectos REDD +. Este estudio muestra que para reducir las presiones sobre los ecosistemas, particularmente en regiones altamente marginadas con una migración significativa, es necesario implementar políticas transfronterizas de gestión de la tierra que también integren estrategias de alivio de la pobreza. Land-use/cover change is the major cause of terrestrial ecosystem degradation. However, its impacts will be exacerbated due to climate change and population growth, driving agricultural expansion because of higher demand of food and lower agricultural yields in some tropical areas. International strategies aimed to mitigate impacts of climate change and land use-cover change are challenging in developing regions. This study aims to evaluate alternatives to minimize the impacts of these threats under socioeconomic trajectories, in one of the biologically richest regions in Guatemala and Mexico. This study is located at the Usumacinta watershed, a transboundary region that shares a common history, with similar biophysical properties and economic constraints which have led to large land use/cover changes. To understand the impacts on deforestation and carbon emissions of different land-management practices, we developed three scenarios (1): business as usual (BAU), (2) a reducing emissions scenario aimed to reduce deforestation and degradation (REDD+), and (3) zero-deforestation from 2030 onwards based on the international commitments. Our results suggest that by 2050, natural land cover might reduce 22.3 and 12.2% of its extent under the BAU and REDD + scenarios, respectively in comparison with 2012. However, the zero-deforestation scenario shows that by 2050, it would be possible to avoid losing 22.4% of the forested watershed (1.7 million ha) and recover 5.9% (0.4 million hectares) of it. In terms of carbon sequestration, REDD + projects can reduce the carbon losses in natural vegetation, but a zero-deforestation policy can double the carbon sequestration produced by REDD + projects only. This study shows that to reduce the pressures on ecosystems, particularly in regions highly marginalized with significant migration, it is necessary to implement transboundary land-management policies that also integrate poverty alleviation strategies. استخدام الأراضي/تغيير الغطاء هو السبب الرئيسي لتدهور النظام الإيكولوجي الأرضي. ومع ذلك، ستتفاقم آثاره بسبب تغير المناخ والنمو السكاني، مما يؤدي إلى التوسع الزراعي بسبب ارتفاع الطلب على الغذاء وانخفاض الغلة الزراعية في بعض المناطق الاستوائية. تشكل الاستراتيجيات الدولية الرامية إلى التخفيف من آثار تغير المناخ وتغير استخدام الأراضي تحدياً في المناطق النامية. تهدف هذه الدراسة إلى تقييم البدائل لتقليل آثار هذه التهديدات في إطار المسارات الاجتماعية والاقتصادية، في واحدة من أغنى المناطق بيولوجيًا في غواتيمالا والمكسيك. تقع هذه الدراسة في مستجمع مياه أوسوماسينتا، وهي منطقة عابرة للحدود تشترك في تاريخ مشترك، مع خصائص فيزيائية حيوية مماثلة وقيود اقتصادية أدت إلى تغييرات كبيرة في استخدام الأراضي/تغطيتها. لفهم تأثيرات ممارسات إدارة الأراضي المختلفة على إزالة الغابات وانبعاثات الكربون، وضعنا ثلاثة سيناريوهات (1): العمل كالمعتاد (BAU)، (2) سيناريو خفض الانبعاثات الذي يهدف إلى الحد من إزالة الغابات وتدهورها (REDD+)، و (3) إزالة الغابات الصفرية اعتبارًا من عام 2030 فصاعدًا بناءً على الالتزامات الدولية. تشير نتائجنا إلى أنه بحلول عام 2050، قد يقلل الغطاء الأرضي الطبيعي بنسبة 22.3 و 12.2 ٪ من مداه في إطار سيناريو العمل الاعتيادي وسيناريو خفض الانبعاثات الناجمة عن إزالة الغابات وتدهورها في البلدان النامية، على التوالي مقارنة بعام 2012. ومع ذلك، يُظهر سيناريو إزالة الغابات الصفرية أنه بحلول عام 2050، سيكون من الممكن تجنب فقدان 22.4 ٪ من مستجمعات المياه الحرجية (1.7 مليون هكتار) واستعادة 5.9 ٪ (0.4 مليون هكتار) منها. من حيث عزل الكربون، يمكن لمشاريع خفض الانبعاثات الناجمة عن إزالة الغابات وتدهورها في البلدان النامية أن تقلل من خسائر الكربون في الغطاء النباتي الطبيعي، ولكن سياسة إزالة الغابات الصفرية يمكن أن تضاعف عزل الكربون الناتج عن مشاريع خفض الانبعاثات الناجمة عن إزالة الغابات وتدهورها في البلدان النامية فقط. تُظهر هذه الدراسة أنه للحد من الضغوط على النظم الإيكولوجية، لا سيما في المناطق المهمشة للغاية مع الهجرة الكبيرة، من الضروري تنفيذ سياسات إدارة الأراضي العابرة للحدود التي تدمج أيضًا استراتيجيات التخفيف من حدة الفقر.

Significance Although the response of the Plant Kingdom to climate change is acknowledged as one of the fundamental feedback mechanisms of environmental changes on the Earth, until now, the response of plant species to in situ climate warming has been described at the level of a few fixed plant functional types (i.e. grasses, forbs, shrubs etc.). This approach is very coarse and inflexible. Here, we show that plant functional traits (i.e., plant features) can be used as predictors of vegetation response to climate warming. This finding enlarges possibilities for forecasting ecosystem responses to climate change.

Abstract An assessment of the human impact on the global water cycle requires estimating the volume of water withdrawn for irrigated agriculture. A key parameter in this calculation is the irrigation efficiency, which corrects for the fraction of water lost between irrigation withdrawals and the crop due to management, distribution or conveyance losses. Here we show that the irrigation efficiency used in global irrigation models is flawed for it overlooks key ambiguities in partial efficiencies, irrigation technologies, the definition of ‘large-scale’ irrigated areas or managerial factors. Once accounted for, these uncertainties can make irrigation withdrawal estimates fluctuate by more than one order of magnitude at the country level. Such variability is larger and leads to more extreme values than that caused by the uncertainties related with climate change. Our results highlight the need to embrace deep uncertainties in irrigation efficiency to prevent the design of shortsighted policies at the river basin-water-agricultural interface.

Abstract A central challenge of today's ecological research is predicting how ecosystems will develop under future global change. Accurate predictions are complicated by (a) simultaneous effects of different drivers, such as climate change, nitrogen deposition and management changes; and (b) legacy effects from previous land use. We tested whether herb layer biodiversity (i.e. richness, Shannon diversity and evenness) and functional (i.e. herb cover, specific leaf area [SLA] and plant height) responses to environmental change drivers depended on land‐use history. We used resurvey data from 192 plots across nineteen European temperate forest regions, with large spatial variability in environmental change factors. We tested for interactions between land‐use history, distinguishing ancient and recent (i.e. post‐agricultural) forests and four drivers: temperature, nitrogen deposition, and aridity at the regional scale and light dynamics at the plot‐scale. Land‐use history significantly modulated global change effects on the functional signature of the herb layer (i.e. cover, SLA and plant height). Light availability was the main environmental driver of change interacting with land‐use history. We found greater herb cover and plant height decreases and SLA increases with decreasing light availability in ancient than in recent forests. Furthermore, we found greater decreases in herb cover with increased nitrogen deposition in ancient forests, whereas warming had the strongest decreasing effect on the herb cover in recent forests. Interactive effects between land‐use history and global change on biodiversity were not found, but species evenness increased more in ancient than in recent forests. Synthesis. Our results demonstrate that land‐use history should not be overlooked when predicting forest herb layer responses to global change. Moreover, we found that herb layer composition in semi‐natural deciduous forests is mainly controlled by local canopy characteristics, regulating light levels at the forest floor, and much less by environmental changes at the regional scale (here: warming, nitrogen deposition and aridity). The observed disconnect between biodiversity and functional herb layer responses to environmental changes demonstrates the importance of assessing both types of responses to increase our understanding of the possible impact of global change on the herb layer.

AbstractLarge‐scale bioenergy plays a key role in climate change mitigation scenarios, but its efficacy is uncertain. This study aims to quantify that uncertainty by contrasting the results of three different types of models under the same mitigation scenario (RCP2.6‐SSP2), consistent with a 2°C temperature target. This analysis focuses on a single bioenergy feedstock, Miscanthus × giganteus, and contrasts projections for its yields and environmental effects from an integrated assessment model (IMAGE), a land surface and dynamic global vegetation model tailored to Miscanthus bioenergy (JULES) and a bioenergy crop model (MiscanFor). Under the present climate, JULES, IMAGE and MiscanFor capture the observed magnitude and variability in Miscanthus yields across Europe; yet in the tropics JULES and IMAGE predict high yields, whereas MiscanFor predicts widespread drought‐related diebacks. 2040–2049 projections show there is a rapid scale up of over 200 Mha bioenergy cropping area in the tropics. Resulting biomass yield ranges from 12 (MiscanFor) to 39 (JULES) Gt dry matter over that decade. Change in soil carbon ranges from +0.7 Pg C (MiscanFor) to −2.8 Pg C (JULES), depending on preceding land cover and soil carbon.2090–99 projections show large‐scale biomass energy with carbon capture and storage (BECCS) is projected in Europe. The models agree that <2°C global warming will increase yields in the higher latitudes, but drought stress in the Mediterranean region could produce low yields (MiscanFor), and significant losses of soil carbon (JULES and IMAGE). These results highlight the uncertainty in rapidly scaling‐up biomass energy supply, especially in dry tropical climates and in regions where future climate change could result in drier conditions. This has important policy implications—because prominently used scenarios to limit warming to ‘well below 2°C’ (including the one explored here) depend upon its effectiveness.

Land use is central to addressing sustainability issues, including biodiversity conservation, climate change, food security, poverty alleviation, and sustainable energy. In this paper, we synthesize knowledge accumulated in land system science, the integrated study of terrestrial social-ecological systems, into 10 hard truths that have strong, general, empirical support. These facts help to explain the challenges of achieving sustainability in land use and thus also point toward solutions. The 10 facts are as follows: 1) Meanings and values of land are socially constructed and contested; 2) land systems exhibit complex behaviors with abrupt, hard-to-predict changes; 3) irreversible changes and path dependence are common features of land systems; 4) some land uses have a small footprint but very large impacts; 5) drivers and impacts of land-use change are globally interconnected and spill over to distant locations; 6) humanity lives on a used planet where all land provides benefits to societies; 7) land-use change usually entails trade-offs between different benefits—"win–wins" are thus rare; 8) land tenure and land-use claims are often unclear, overlapping, and contested; 9) the benefits and burdens from land are unequally distributed; and 10) land users have multiple, sometimes conflicting, ideas of what social and environmental justice entails. The facts have implications for governance, but do not provide fixed answers. Instead they constitute a set of core principles which can guide scientists, policy makers, and practitioners toward meeting sustainability challenges in land use.