• Energy Research

Earth harbours an extraordinary plant phenotypic diversity1 that is at risk from ongoing global changes2,3. However, it remains unknown how increasing aridity and livestock grazing pressure-two major drivers of global change4-6-shape the trait covariation that underlies plant phenotypic diversity1,7. Here we assessed how covariation among 20 chemical and morphological traits responds to aridity and grazing pressure within global drylands. Our analysis involved 133,769 trait measurements spanning 1,347 observations of 301 perennial plant species surveyed across 326 plots from 6 continents. Crossing an aridity threshold of approximately 0.7 (close to the transition between semi-arid and arid zones) led to an unexpected 88% increase in trait diversity. This threshold appeared in the presence of grazers, and moved toward lower aridity levels with increasing grazing pressure. Moreover, 57% of observed trait diversity occurred only in the most arid and grazed drylands, highlighting the phenotypic uniqueness of these extreme environments. Our work indicates that drylands act as a global reservoir of plant phenotypic diversity and challenge the pervasive view that harsh environmental conditions reduce plant trait diversity8-10. They also highlight that many alternative strategies may enable plants to cope with increases in environmental stress induced by climate change and land-use intensification.

Earth harbours an extraordinary plant phenotypic diversity1 that is at risk from ongoing global changes2,3. However, it remains unknown how increasing aridity and livestock grazing pressure-two major drivers of global change4-6-shape the trait covariation that underlies plant phenotypic diversity1,7. Here we assessed how covariation among 20 chemical and morphological traits responds to aridity and grazing pressure within global drylands. Our analysis involved 133,769 trait measurements spanning 1,347 observations of 301 perennial plant species surveyed across 326 plots from 6 continents. Crossing an aridity threshold of approximately 0.7 (close to the transition between semi-arid and arid zones) led to an unexpected 88% increase in trait diversity. This threshold appeared in the presence of grazers, and moved toward lower aridity levels with increasing grazing pressure. Moreover, 57% of observed trait diversity occurred only in the most arid and grazed drylands, highlighting the phenotypic uniqueness of these extreme environments. Our work indicates that drylands act as a global reservoir of plant phenotypic diversity and challenge the pervasive view that harsh environmental conditions reduce plant trait diversity8-10. They also highlight that many alternative strategies may enable plants to cope with increases in environmental stress induced by climate change and land-use intensification.

AbstractAimGeographical, climatic and soil factors are major drivers of plant beta diversity, but their importance for dryland plant communities is poorly known. The aim of this study was to: (1) characterize patterns of beta diversity in global drylands; (2) detect common environmental drivers of beta diversity; and (3) test for thresholds in environmental conditions driving potential shifts in plant species composition.LocationGlobal.MethodsBeta diversity was quantified in 224 dryland plant communities from 22 geographical regions on all continents except Antarctica using four complementary measures: the percentage of singletons (species occurring at only one site); Whittaker's beta diversity, β(W); a directional beta diversity metric based on the correlation in species occurrences among spatially contiguous sites, β(R2); and a multivariate abundance‐based metric, β(MV). We used linear modelling to quantify the relationships between these metrics of beta diversity and geographical, climatic and soil variables.ResultsSoil fertility and variability in temperature and rainfall, and to a lesser extent latitude, were the most important environmental predictors of beta diversity. Metrics related to species identity [percentage of singletons and β(W)] were most sensitive to soil fertility, whereas those metrics related to environmental gradients and abundance [(β(R2) and β(MV)] were more associated with climate variability. Interactions among soil variables, climatic factors and plant cover were not important determinants of beta diversity. Sites receiving less than 178 mm of annual rainfall differed sharply in species composition from more mesic sites (> 200 mm).Main conclusionsSoil fertility and variability in temperature and rainfall are the most important environmental predictors of variation in plant beta diversity in global drylands. Our results suggest that those sites annually receiving c. 178 mm of rainfall will be especially sensitive to future climate changes. These findings may help to define appropriate conservation strategies for mitigating effects of climate change on dryland vegetation.

AbstractAimGeographical, climatic and soil factors are major drivers of plant beta diversity, but their importance for dryland plant communities is poorly known. The aim of this study was to: (1) characterize patterns of beta diversity in global drylands; (2) detect common environmental drivers of beta diversity; and (3) test for thresholds in environmental conditions driving potential shifts in plant species composition.LocationGlobal.MethodsBeta diversity was quantified in 224 dryland plant communities from 22 geographical regions on all continents except Antarctica using four complementary measures: the percentage of singletons (species occurring at only one site); Whittaker's beta diversity, β(W); a directional beta diversity metric based on the correlation in species occurrences among spatially contiguous sites, β(R2); and a multivariate abundance‐based metric, β(MV). We used linear modelling to quantify the relationships between these metrics of beta diversity and geographical, climatic and soil variables.ResultsSoil fertility and variability in temperature and rainfall, and to a lesser extent latitude, were the most important environmental predictors of beta diversity. Metrics related to species identity [percentage of singletons and β(W)] were most sensitive to soil fertility, whereas those metrics related to environmental gradients and abundance [(β(R2) and β(MV)] were more associated with climate variability. Interactions among soil variables, climatic factors and plant cover were not important determinants of beta diversity. Sites receiving less than 178 mm of annual rainfall differed sharply in species composition from more mesic sites (> 200 mm).Main conclusionsSoil fertility and variability in temperature and rainfall are the most important environmental predictors of variation in plant beta diversity in global drylands. Our results suggest that those sites annually receiving c. 178 mm of rainfall will be especially sensitive to future climate changes. These findings may help to define appropriate conservation strategies for mitigating effects of climate change on dryland vegetation.

Les forêts saisonnièrement sèches des néotropiques sont fortement menacées par une combinaison de perturbations humaines et de changement climatique ; cependant, la gravité de ces menaces est rarement contrastée. Cette étude vise à quantifier et à comparer les effets de la déforestation et du changement climatique sur les aires spatiales naturelles de 17 espèces d'arbres caractéristiques des forêts sèches décidues du sud de l'Équateur, qui sont fortement fragmentées et soutiennent des niveaux élevés d'endémisme dans le cadre de l'écorégion tumbésienne. Nous avons utilisé 660 enregistrements de plantes pour générer des modèles de répartition des espèces et des données sur la couverture terrestre pour projeter des fourchettes d'espèces sur deux périodes : un scénario de déforestation simulé de 2008 à 2014 avec conversion des forêts indigènes en utilisation anthropique des terres, et un scénario de changement climatique extrême (CCSM4.0, RCP 8.5) pour 2050, qui supposait un changement nul des activités humaines. Pour évaluer les deux menaces potentielles, nous avons comparé les taux annuels estimés de perte d'espèces (c.-à-d. les changements d'aire de répartition) affectant chaque espèce. La perte de déforestation pour toutes les espèces était en moyenne d'environ 71 km2/an, tandis que la perte potentielle attribuée au climat était de près de 21 km2/an. De plus, les taux annuels de perte de surface dus à la déforestation étaient significativement plus élevés que ceux attribués au changement climatique (P < 0,01). Cependant, les projections dans le scénario futur montrent des preuves de modèles de déplacement divergents, indiquant la formation potentielle de nouveaux écosystèmes, ce qui est cohérent avec les prévisions d'assemblage d'autres espèces en raison du changement climatique. En outre, nous fournissons des recommandations pour la gestion et la conservation, en donnant la priorité aux espèces les plus menacées telles que Albizia multiflora, Ceiba trichistandra et Cochlospermum vitifolium. Los bosques estacionalmente secos en los neotrópicos están muy amenazados por una combinación de perturbaciones humanas y cambio climático; sin embargo, la gravedad de estas amenazas rara vez se contrasta. Este estudio tiene como objetivo cuantificar y comparar los efectos de la deforestación y el cambio climático en los rangos espaciales naturales de 17 especies de árboles característicos de los bosques caducifolios secos del sur de Ecuador, que están muy fragmentados y soportan altos niveles de endemismo como parte de la ecorregión Tumbesiana. Utilizamos 660 registros de plantas para generar modelos de distribución de especies y datos de cobertura de la tierra para proyectar rangos de especies durante dos marcos de tiempo: un escenario de deforestación simulado de 2008 a 2014 con conversión de bosques nativos a uso de la tierra antropogénico, y un escenario de cambio climático extremo (CCSM4.0, RCP 8.5) para 2050, que suponía un cambio cero de las actividades humanas. Para evaluar ambas amenazas potenciales, comparamos las tasas anuales estimadas de pérdida de especies (es decir, cambios de rango) que afectan a cada especie. La pérdida de deforestación para todas las especies fue de aproximadamente 71 km2/año, mientras que la pérdida potencial atribuida al clima fue de casi 21 km2/año. Además, las tasas anuales de pérdida de área debido a la deforestación fueron significativamente más altas que las atribuidas al cambio climático (P < 0.01). Sin embargo, las proyecciones sobre el escenario futuro muestran evidencia de patrones de desplazamiento divergentes, lo que indica la posible formación de nuevos ecosistemas, lo que es consistente con las predicciones de ensamblaje de otras especies como resultado del cambio climático. Además, proporcionamos recomendaciones para el manejo y la conservación, priorizando las especies más amenazadas como Albizia multiflora, Ceiba trichistandra y Cochlospermum vitifolium. Seasonally dry forests in the neotropics are heavily threatened by a combination of human disturbances and climate change; however, the severity of these threats is seldom contrasted. This study aims to quantify and compare the effects of deforestation and climate change on the natural spatial ranges of 17 characteristic tree species of southern Ecuador dry deciduous forests, which are heavily fragmented and support high levels of endemism as part of the Tumbesian ecoregion. We used 660 plant records to generate species distribution models and land-cover data to project species ranges for two time frames: a simulated deforestation scenario from 2008 to 2014 with native forest to anthropogenic land-use conversion, and an extreme climate change scenario (CCSM4.0, RCP 8.5) for 2050, which assumed zero change from human activities. To assess both potential threats, we compared the estimated annual rates of species loss (i.e., range shifts) affecting each species. Deforestation loss for all species averaged approximately 71 km2/year, while potential climate-attributed loss was almost 21 km2/year. Moreover, annual area loss rates due to deforestation were significantly higher than those attributed to climate-change (P < 0.01). However, projections into the future scenario show evidence of diverging displacement patterns, indicating the potential formation of novel ecosystems, which is consistent with other species assemblage predictions as result of climate change. Furthermore, we provide recommendations for management and conservation, prioritizing the most threatened species such as Albizia multiflora, Ceiba trichistandra, and Cochlospermum vitifolium. الغابات الجافة موسمياً في المناطق المدارية الحديثة مهددة بشدة بسبب مزيج من الاضطرابات البشرية وتغير المناخ ؛ ومع ذلك، نادراً ما تتناقض شدة هذه التهديدات. تهدف هذه الدراسة إلى تحديد ومقارنة آثار إزالة الغابات وتغير المناخ على النطاقات المكانية الطبيعية لـ 17 نوعًا مميزًا من الأشجار في جنوب الإكوادور، وهي غابات نفضية جافة مجزأة بشدة وتدعم مستويات عالية من التوطن كجزء من منطقة تومبيز البيئية. استخدمنا 660 سجلاً نباتيًا لتوليد نماذج توزيع الأنواع وبيانات الغطاء الأرضي لنطاقات أنواع المشروع لإطارين زمنيين: سيناريو محاكاة إزالة الغابات من عام 2008 إلى عام 2014 مع تحويل الغابات الأصلية إلى استخدامات الأراضي البشرية، وسيناريو تغير المناخ الشديد (CCSM4.0، RCP 8.5) لعام 2050، والذي افترض صفر تغيير من الأنشطة البشرية. لتقييم كلا التهديدين المحتملين، قارنا المعدلات السنوية المقدرة لفقدان الأنواع (أي تحولات المدى) التي تؤثر على كل نوع. بلغ متوسط خسارة إزالة الغابات لجميع الأنواع حوالي 71 كم 2/سنة، في حين بلغت الخسارة المحتملة المنسوبة للمناخ حوالي 21 كم 2/سنة. علاوة على ذلك، كانت معدلات فقدان المساحة السنوية بسبب إزالة الغابات أعلى بكثير من تلك المنسوبة إلى تغير المناخ (P < 0.01). ومع ذلك، تظهر التوقعات في السيناريو المستقبلي أدلة على أنماط النزوح المتباينة، مما يشير إلى التكوين المحتمل لنظم بيئية جديدة، وهو ما يتوافق مع تنبؤات تجميع الأنواع الأخرى نتيجة لتغير المناخ. علاوة على ذلك، نقدم توصيات للإدارة والحفظ، مع إعطاء الأولوية للأنواع الأكثر تهديدًا مثل Albizia multiflora و Ceiba trichistandra و Cochlospermum vitifolium.