• Energy Research

Les observations et les projections pour les régions montagneuses montrent une forte tendance au déplacement vers le haut de leurs biomes dans les conditions climatiques futures. En raison de leur hétérogénéité climatique et topographique, une réponse plus complexe est attendue pour les points chauds de la biodiversité tels que les régions montagneuses tropicales. Cette étude analyse les changements potentiels dans la distribution des biomes dans les Andes tropicales et identifie les zones cibles à conserver. Des modèles de distribution du biome ont été développés à l'aide de régressions logistiques. Ces modèles ont ensuite été couplés à un ensemble de 8 modèles climatiques globaux pour projeter la distribution future des biomes andins et leurs incertitudes. Nous avons analysé les changements projetés dans l'étendue et la plage d'altitude et identifié les régions les plus sujettes au changement. Nos résultats montrent une réponse hétérogène au changement climatique. Bien que les biomes plus humides présentent un déplacement vers le haut des limites supérieure et inférieure comme prévu, la plupart des biomes secs ont tendance à montrer une expansion vers le bas. Bien que des pertes importantes soient prévues pour plusieurs biomes, les projections suggèrent qu'entre 74,8 % et 83,1 % du total actuel des Andes tropicales resteront stables, en fonction du scénario d'émission et de l'horizon temporel. Entre 3,3 % et 7,6 % de la zone d'étude devrait changer, principalement vers une augmentation de la structure verticale. Pour la zone restante (13,1%-17,4%), il n'y a pas de concordance entre les projections du modèle. Ces résultats remettent en question la croyance commune selon laquelle le changement climatique entraînera un déplacement vers le haut des limites du biome dans les régions montagneuses. Au lieu de cela, nos modèles projettent des réponses divergentes, y compris l'expansion de la pente descendante et de vastes zones qui devraient rester stables. Enfin, une partie importante de la zone qui devrait changer est déjà affectée par les changements d'affectation des terres, ce qui a des implications importantes pour la gestion. Ceci, ainsi que l'inclusion d'une analyse complète des incertitudes, aidera à éclairer les stratégies de conservation dans les Andes tropicales et à guider des évaluations similaires pour d'autres montagnes tropicales. Las observaciones y proyecciones para las regiones montañosas muestran una fuerte tendencia al desplazamiento ascendente de sus biomas en condiciones climáticas futuras. Debido a su heterogeneidad climática y topográfica, se espera una respuesta más compleja para los puntos críticos de biodiversidad, como las regiones montañosas tropicales. Este estudio analiza los cambios potenciales en la distribución de los biomas en los Andes Tropicales e identifica áreas objetivo para conservar. Los modelos de distribución de biomas se desarrollaron utilizando regresiones logísticas. Estos modelos se acoplaron a un conjunto de 8 modelos climáticos globales para proyectar la distribución futura de los biomas andinos y sus incertidumbres. Analizamos los cambios proyectados en la extensión y el rango de altitud e identificamos las regiones más propensas a cambiar. Nuestros resultados muestran una respuesta heterogénea al cambio climático. Aunque los biomas más húmedos exhiben un desplazamiento ascendente de los límites superior e inferior como se esperaba, la mayoría de los biomas secos tienden a mostrar una expansión descendente. A pesar de que se proyectan pérdidas importantes para varios biomas, las proyecciones sugieren que entre el 74.8% y el 83.1% del total actual de los Andes Tropicales se mantendrán estables, dependiendo del escenario de emisión y el horizonte temporal. Se proyecta que entre el 3.3% y el 7.6% del área de estudio cambie, principalmente hacia un aumento en la estructura vertical. Para el área restante (13.1%-17.4%), no hay acuerdo entre las proyecciones del modelo. Estos resultados desafían la creencia común de que el cambio climático conducirá a un desplazamiento ascendente de los límites del bioma en las regiones montañosas. En cambio, nuestros modelos proyectan respuestas divergentes, incluida la expansión cuesta abajo y grandes áreas proyectadas para permanecer estables. Por último, una parte significativa del área que se espera que cambie ya está afectada por los cambios en el uso de la tierra, lo que tiene importantes implicaciones para la gestión. Esto, y la inclusión de un análisis exhaustivo de la incertidumbre, ayudarán a informar las estrategias de protección en los Andes Tropicales y a guiar evaluaciones similares para otras montañas tropicales. Observations and projections for mountain regions show a strong tendency towards upslope displacement of their biomes under future climate conditions. Because of their climatic and topographic heterogeneity, a more complex response is expected for biodiversity hotspots such as tropical mountain regions. This study analyzes potential changes in the distribution of biomes in the Tropical Andes and identifies target areas for conservation. Biome distribution models were developed using logistic regressions. These models were then coupled to an ensemble of 8 global climate models to project future distribution of the Andean biomes and their uncertainties. We analysed projected changes in extent and elevational range and identified regions most prone to change. Our results show a heterogeneous response to climate change. Although the wetter biomes exhibit an upslope displacement of both the upper and the lower boundaries as expected, most dry biomes tend to show downslope expansion. Despite important losses being projected for several biomes, projections suggest that between 74.8% and 83.1% of the current total Tropical Andes will remain stable, depending on the emission scenario and time horizon. Between 3.3% and 7.6% of the study area is projected to change, mostly towards an increase in vertical structure. For the remaining area (13.1%-17.4%), there is no agreement between model projections. These results challenge the common believe that climate change will lead to an upslope displacement of biome boundaries in mountain regions. Instead, our models project diverging responses, including downslope expansion and large areas projected to remain stable. Lastly, a significant part of the area expected to change is already affected by land use changes, which has important implications for management. This, and the inclusion of a comprehensive uncertainty analysis, will help to inform conservation strategies in the Tropical Andes, and to guide similar assessments for other tropical mountains. تُظهر الملاحظات والإسقاطات الخاصة بالمناطق الجبلية ميلًا قويًا نحو نزوح المناطق الأحيائية في المنحدرات في ظل الظروف المناخية المستقبلية. بسبب عدم تجانسها المناخي والطبوغرافي، من المتوقع أن تكون هناك استجابة أكثر تعقيدًا للنقاط الساخنة للتنوع البيولوجي مثل المناطق الجبلية الاستوائية. تحلل هذه الدراسة التغيرات المحتملة في توزيع المناطق الأحيائية في جبال الأنديز الاستوائية وتحدد المناطق المستهدفة للحفظ. تم تطوير نماذج توزيع المناطق الحيوية باستخدام الانحدارات اللوجستية. ثم اقترنت هذه النماذج بمجموعة من 8 نماذج مناخية عالمية لإبراز التوزيع المستقبلي للمناطق الأحيائية في الأنديز وشكوكها. قمنا بتحليل التغيرات المتوقعة في المدى ونطاق الارتفاع وحددنا المناطق الأكثر عرضة للتغيير. تظهر نتائجنا استجابة غير متجانسة لتغير المناخ. على الرغم من أن المناطق الأحيائية الرطبة تظهر إزاحة منحدرة لكل من الحدود العلوية والسفلية كما هو متوقع، فإن معظم المناطق الأحيائية الجافة تميل إلى إظهار توسع المنحدر. على الرغم من الخسائر الكبيرة المتوقعة للعديد من المناطق الأحيائية، تشير التوقعات إلى أن ما بين 74.8 ٪ و 83.1 ٪ من إجمالي جبال الأنديز الاستوائية الحالية ستظل مستقرة، اعتمادًا على سيناريو الانبعاثات والأفق الزمني. من المتوقع أن يتغير ما بين 3.3 ٪ و 7.6 ٪ من مساحة الدراسة، ومعظمها نحو زيادة في الهيكل الرأسي. بالنسبة للمنطقة المتبقية (13.1 ٪-17.4 ٪)، لا يوجد اتفاق بين توقعات النموذج. تتحدى هذه النتائج الاعتقاد الشائع بأن تغير المناخ سيؤدي إلى نزوح المنحدرات لحدود المناطق الأحيائية في المناطق الجبلية. بدلاً من ذلك، تتوقع نماذجنا استجابات متباينة، بما في ذلك توسع المنحدرات ومناطق واسعة من المتوقع أن تظل مستقرة. أخيرًا، يتأثر جزء كبير من المنطقة المتوقع تغييرها بالفعل بتغيرات استخدام الأراضي، والتي لها آثار مهمة على الإدارة. سيساعد هذا، بالإضافة إلى تضمين تحليل شامل لعدم اليقين، في توجيه استراتيجيات الحفظ في جبال الأنديز الاستوائية، وتوجيه تقييمات مماثلة للجبال الاستوائية الأخرى.

AbstractNatural patchiness and human fragmentation result in habitats that are not continuously distributed. How spatial configuration of patches in fragmented habitats influences biodiversity remains largely controversial. Here, we propose a framework to extend the species–area relationship (SAR) approach to analyze how changes in habitat configuration affect species richness in fragmented habitats. We use hypothetical communities that are characterized by (1) their tolerance to human activities, (2) the dispersal capability of the individuals of any species, (3) the SAR, and (4) the species turnover among patches. Further, the species turnover is a function of (4a) the predictability of species survival and (4b) the species recolonization odds. In our framework, we identify three extreme communities that encompass the richness of all potential different communities, and thus encapsulate the richness of real communities. We propose a graph to visualize the effect of different patch sizes on species richness, an index to quantify those changes, and a second graph using the index to visualize the effect of distance between patches on species richness. After applying our framework and tools to the Tropical Andes, we found strong differences in the impact of natural vs. human‐driven fragmentation on richness between biomes. When projecting future richness values under climate change scenarios, the largest sources of uncertainty in our richness calculation (>90%) were species turnover among patches and species dispersal for most of the biomes rather than future climate or species tolerance to human activities. Habitat loss consistently decreased the species richness; however, fragmentation per se often increased it. The increment was mostly linked to the species turnover rate among patches. Our framework is a new theoretical tool to study the main patterns that underlie regional richness and therefore can provide new insights to face spatial habitat reconfiguration caused by human activities.

AbstractEutrophication is a widespread environmental change that usually reduces the stabilizing effect of plant diversity on productivity in local communities. Whether this effect is scale dependent remains to be elucidated. Here, we determine the relationship between plant diversity and temporal stability of productivity for 243 plant communities from 42 grasslands across the globe and quantify the effect of chronic fertilization on these relationships. Unfertilized local communities with more plant species exhibit greater asynchronous dynamics among species in response to natural environmental fluctuations, resulting in greater local stability (alpha stability). Moreover, neighborhood communities that have greater spatial variation in plant species composition within sites (higher beta diversity) have greater spatial asynchrony of productivity among communities, resulting in greater stability at the larger scale (gamma stability). Importantly, fertilization consistently weakens the contribution of plant diversity to both of these stabilizing mechanisms, thus diminishing the positive effect of biodiversity on stability at differing spatial scales. Our findings suggest that preserving grassland functional stability requires conservation of plant diversity within and among ecological communities.

SignificancePredicting the effects of anthropogenic nutrient enrichment on plant communities is critical for managing implications for biodiversity and ecosystem services. Plant functional types that fix atmospheric nitrogen (e.g., legumes) may be at particular risk of nutrient-driven global decline, yet global-scale evidence is lacking. Using an experiment in 45 grasslands across six continents, we showed that legume cover, richness, and biomass declined substantially with nitrogen additions. Although legumes benefited from phosphorus, potassium, and other nutrients, these nutrients did not ameliorate nitrogen-induced legume decline. Given global trends in anthropogenic nutrient enrichment, our results indicate the potential for global decline in grassland legumes, with likely consequences for biodiversity, food webs, soil health, and genetic improvement of protein-rich plant species for food production.

Global change is associated with variable shifts in the annual production of aboveground plant biomass, suggesting localized sensitivities with unclear causal origins. Combining remotely sensed normalized difference vegetation index data since the 1980s with contemporary field data from 84 grasslands on 6 continents, we show a widening divergence in site-level biomass ranging from +51% to -34% globally. Biomass generally increased in warmer, wetter and species-rich sites with longer growing seasons and declined in species-poor arid areas. Phenological changes were widespread, revealing substantive transitions in grassland seasonal cycling. Grazing, nitrogen deposition and plant invasion were prevalent in some regions but did not predict overall trends. Grasslands are undergoing sizable changes in production, with implications for food security, biodiversity and carbon storage especially in arid regions where declines are accelerating.

AbstractHuman activities are transforming grassland biomass via changing climate, elemental nutrients, and herbivory. Theory predicts that food-limited herbivores will consume any additional biomass stimulated by nutrient inputs (‘consumer-controlled’). Alternatively, nutrient supply is predicted to increase biomass where herbivores alter community composition or are limited by factors other than food (‘resource-controlled’). Using an experiment replicated in 58 grasslands spanning six continents, we show that nutrient addition and vertebrate herbivore exclusion each caused sustained increases in aboveground live biomass over a decade, but consumer control was weak. However, at sites with high vertebrate grazing intensity or domestic livestock, herbivores consumed the additional fertilization-induced biomass, supporting the consumer-controlled prediction. Herbivores most effectively reduced the additional live biomass at sites with low precipitation or high ambient soil nitrogen. Overall, these experimental results suggest that grassland biomass will outstrip wild herbivore control as human activities increase elemental nutrient supply, with widespread consequences for grazing and fire risk.