• Energy Research

Le pâturage représente l'utilisation la plus étendue des terres dans le monde. Pourtant, ses impacts sur les services écosystémiques restent incertains car des interactions omniprésentes entre la pression de pâturage, le climat, les propriétés des sols et la biodiversité peuvent se produire mais n'ont jamais été traitées simultanément. En utilisant une enquête standardisée sur 98 sites sur six continents, nous montrons que les interactions entre la pression du pâturage, le climat, le sol et la biodiversité sont essentielles pour expliquer la fourniture de services écosystémiques fondamentaux dans les zones arides du monde entier. L'augmentation de la pression de pâturage a réduit la prestation de services écosystémiques dans les zones arides plus chaudes et pauvres en espèces, tandis que les effets positifs du pâturage ont été observés dans les zones plus froides et riches en espèces. La prise en compte des interactions entre le pâturage et les facteurs abiotiques et biotiques locaux est essentielle pour comprendre le sort des écosystèmes des terres arides sous le changement climatique et l'augmentation de la pression humaine. El pastoreo representa el uso más extenso de la tierra en todo el mundo. Sin embargo, sus impactos en los servicios ecosistémicos siguen siendo inciertos porque las interacciones generalizadas entre la presión del pastoreo, el clima, las propiedades del suelo y la biodiversidad pueden ocurrir, pero nunca se han abordado simultáneamente. Utilizando una encuesta estandarizada en 98 sitios en seis continentes, mostramos que las interacciones entre la presión del pastoreo, el clima, el suelo y la biodiversidad son fundamentales para explicar la prestación de servicios ecosistémicos fundamentales en las tierras secas de todo el mundo. El aumento de la presión del pastoreo redujo la prestación de servicios ecosistémicos en las tierras secas más cálidas y pobres en especies, mientras que los efectos positivos del pastoreo se observaron en las zonas más frías y ricas en especies. Considerar las interacciones entre el pastoreo y los factores abióticos y bióticos locales es clave para comprender el destino de los ecosistemas de tierras secas bajo el cambio climático y el aumento de la presión humana. Grazing represents the most extensive use of land worldwide. Yet its impacts on ecosystem services remain uncertain because pervasive interactions between grazing pressure, climate, soil properties, and biodiversity may occur but have never been addressed simultaneously. Using a standardized survey at 98 sites across six continents, we show that interactions between grazing pressure, climate, soil, and biodiversity are critical to explain the delivery of fundamental ecosystem services across drylands worldwide. Increasing grazing pressure reduced ecosystem service delivery in warmer and species-poor drylands, whereas positive effects of grazing were observed in colder and species-rich areas. Considering interactions between grazing and local abiotic and biotic factors is key for understanding the fate of dryland ecosystems under climate change and increasing human pressure. يمثل الرعي الاستخدام الأوسع للأراضي في جميع أنحاء العالم. ومع ذلك، لا تزال آثاره على خدمات النظام الإيكولوجي غير مؤكدة لأن التفاعلات المنتشرة بين ضغط الرعي والمناخ وخصائص التربة والتنوع البيولوجي قد تحدث ولكن لم تتم معالجتها أبدًا في وقت واحد. باستخدام مسح موحد في 98 موقعًا في ست قارات، نوضح أن التفاعلات بين ضغط الرعي والمناخ والتربة والتنوع البيولوجي ضرورية لشرح تقديم خدمات النظام الإيكولوجي الأساسية عبر الأراضي الجافة في جميع أنحاء العالم. أدى الضغط المتزايد للرعي إلى تقليل تقديم خدمات النظام الإيكولوجي في الأراضي الجافة الأكثر دفئًا والفقيرة بالأنواع، في حين لوحظت آثار إيجابية للرعي في المناطق الأكثر برودة والغنية بالأنواع. يعتبر النظر في التفاعلات بين الرعي والعوامل المحلية اللاأحيائية والأحيائية أمرًا أساسيًا لفهم مصير النظم الإيكولوجية للأراضي الجافة في ظل تغير المناخ وزيادة الضغط البشري.

Le pâturage représente l'utilisation la plus étendue des terres dans le monde. Pourtant, ses impacts sur les services écosystémiques restent incertains car des interactions omniprésentes entre la pression de pâturage, le climat, les propriétés des sols et la biodiversité peuvent se produire mais n'ont jamais été traitées simultanément. En utilisant une enquête standardisée sur 98 sites sur six continents, nous montrons que les interactions entre la pression du pâturage, le climat, le sol et la biodiversité sont essentielles pour expliquer la fourniture de services écosystémiques fondamentaux dans les zones arides du monde entier. L'augmentation de la pression de pâturage a réduit la prestation de services écosystémiques dans les zones arides plus chaudes et pauvres en espèces, tandis que les effets positifs du pâturage ont été observés dans les zones plus froides et riches en espèces. La prise en compte des interactions entre le pâturage et les facteurs abiotiques et biotiques locaux est essentielle pour comprendre le sort des écosystèmes des terres arides sous le changement climatique et l'augmentation de la pression humaine. El pastoreo representa el uso más extenso de la tierra en todo el mundo. Sin embargo, sus impactos en los servicios ecosistémicos siguen siendo inciertos porque las interacciones generalizadas entre la presión del pastoreo, el clima, las propiedades del suelo y la biodiversidad pueden ocurrir, pero nunca se han abordado simultáneamente. Utilizando una encuesta estandarizada en 98 sitios en seis continentes, mostramos que las interacciones entre la presión del pastoreo, el clima, el suelo y la biodiversidad son fundamentales para explicar la prestación de servicios ecosistémicos fundamentales en las tierras secas de todo el mundo. El aumento de la presión del pastoreo redujo la prestación de servicios ecosistémicos en las tierras secas más cálidas y pobres en especies, mientras que los efectos positivos del pastoreo se observaron en las zonas más frías y ricas en especies. Considerar las interacciones entre el pastoreo y los factores abióticos y bióticos locales es clave para comprender el destino de los ecosistemas de tierras secas bajo el cambio climático y el aumento de la presión humana. Grazing represents the most extensive use of land worldwide. Yet its impacts on ecosystem services remain uncertain because pervasive interactions between grazing pressure, climate, soil properties, and biodiversity may occur but have never been addressed simultaneously. Using a standardized survey at 98 sites across six continents, we show that interactions between grazing pressure, climate, soil, and biodiversity are critical to explain the delivery of fundamental ecosystem services across drylands worldwide. Increasing grazing pressure reduced ecosystem service delivery in warmer and species-poor drylands, whereas positive effects of grazing were observed in colder and species-rich areas. Considering interactions between grazing and local abiotic and biotic factors is key for understanding the fate of dryland ecosystems under climate change and increasing human pressure. يمثل الرعي الاستخدام الأوسع للأراضي في جميع أنحاء العالم. ومع ذلك، لا تزال آثاره على خدمات النظام الإيكولوجي غير مؤكدة لأن التفاعلات المنتشرة بين ضغط الرعي والمناخ وخصائص التربة والتنوع البيولوجي قد تحدث ولكن لم تتم معالجتها أبدًا في وقت واحد. باستخدام مسح موحد في 98 موقعًا في ست قارات، نوضح أن التفاعلات بين ضغط الرعي والمناخ والتربة والتنوع البيولوجي ضرورية لشرح تقديم خدمات النظام الإيكولوجي الأساسية عبر الأراضي الجافة في جميع أنحاء العالم. أدى الضغط المتزايد للرعي إلى تقليل تقديم خدمات النظام الإيكولوجي في الأراضي الجافة الأكثر دفئًا والفقيرة بالأنواع، في حين لوحظت آثار إيجابية للرعي في المناطق الأكثر برودة والغنية بالأنواع. يعتبر النظر في التفاعلات بين الرعي والعوامل المحلية اللاأحيائية والأحيائية أمرًا أساسيًا لفهم مصير النظم الإيكولوجية للأراضي الجافة في ظل تغير المناخ وزيادة الضغط البشري.

Increasing aridity associated with climate change may lead to the crossing of critical ecosystem thresholds in drylands, compromising ecosystem services for millions of people. In this context, finding tools to detect at early stages the effects of increasing aridity on ecosystems is extremely urgent to avoid irreversible damage. Here, we assess shifts in plant community functional structure along a spatial aridity gradient in tropical dryland (Brazilian Caatinga), to select the most appropriate plant functional groups as ecological indicators likely useful to predict temporal ecosystem trajectories in response to aridity. We identified seven plant functional groups based on 13 functional traits associated with plant establishment, defense, regeneration, and dispersal, whose relative abundances changed, linearly and non-linearly, with increasing aridity, showing either increasing or decreasing trends. Of particular importance is the increase in abundance of plants with high chemical defense and Crassulacean Acid Metabolism (CAM) photosynthetic pathway, with increasing aridity. We propose the use of these functional groups as early warning indicators to detect aridity impacts on these dryland ecosystems and shifts in ecosystem functioning. This information can also be used in the elaboration of mitigation and ecological restoration measures to prevent and revert current and future climate change impacts on tropical dry forests.

Increasing aridity associated with climate change may lead to the crossing of critical ecosystem thresholds in drylands, compromising ecosystem services for millions of people. In this context, finding tools to detect at early stages the effects of increasing aridity on ecosystems is extremely urgent to avoid irreversible damage. Here, we assess shifts in plant community functional structure along a spatial aridity gradient in tropical dryland (Brazilian Caatinga), to select the most appropriate plant functional groups as ecological indicators likely useful to predict temporal ecosystem trajectories in response to aridity. We identified seven plant functional groups based on 13 functional traits associated with plant establishment, defense, regeneration, and dispersal, whose relative abundances changed, linearly and non-linearly, with increasing aridity, showing either increasing or decreasing trends. Of particular importance is the increase in abundance of plants with high chemical defense and Crassulacean Acid Metabolism (CAM) photosynthetic pathway, with increasing aridity. We propose the use of these functional groups as early warning indicators to detect aridity impacts on these dryland ecosystems and shifts in ecosystem functioning. This information can also be used in the elaboration of mitigation and ecological restoration measures to prevent and revert current and future climate change impacts on tropical dry forests.

Drylands occupy 47% of the world’s terrestrial area and comprise important biodiversity hotspots such as the Mediterranean Basin, where one can find high levels of plant diversity and endemism. At the same time, they provide resources for human populations, being cattle grazing one of the main activities in dryland ecosystems. Mediterranean woodlands and pastures are currently under threat with increasing aridity due to climate change. Aridity, together with human exploitation, pushes these ecosystems towards land degradation, leading to decreased diversity, ecosystem functioning, and economical value. Understanding how plant communities respond to climate in the long-term, as well as climatic fluctuations, is crucial to anticipate the impacts of climate change in these ecosystems and build a knowledge base to design adaptation and restoration measures and promote their resilience. In the western Mediterranean Basin dryland areas are commonly occupied with oak open woodlands. It is an agro-silvo-pastoral system with a savannah-like structure, dominated by oaks with a species-rich understory of pastures and shrubs. In Portugal, this system is called montado, and due to its socio-economic and ecological importance, it is currently monitored within the LTsER montado platform. The herbaceous layer, dominated by annual species, is a major component of this system’s diversity. While these pastures are adapted to dryland climatic conditions, its annual turnover may make these communities quick responders to environmental changes, providing a good model system to study the effects of climate on diversity and ecosystem functioning. In this work, we aim to assess the effects of long-term climate and yearly climatic fluctuations on plant taxonomic and functional diversity and on pasture productivity, as well as the relationship between diversity and productivity. We sampled the understory plant community of 10 holm-oak open woodlands along a spatial aridity gradient in southern Portugal in multiple years, 5-7 times, between 2012 and 2022. A stratified random selection of sites was made, avoiding as much as possible confounding effects, namely from differences in slope, elevation and fire occurrence. The plant community was sampled in spring, at the peak standing biomass, with the point-intercept method along six 20 m transects per site. Pasture productivity was measured by collecting the aerial herbaceous biomass in three 30 cm squares placed randomly in each site. Functional diversity was calculated using mean trait values per species retrieved from online databases. We fit linear mixed-effects models to assess the relationship between long- and short-term climate variables and taxonomic and functional diversity. We further explored the role of diversity on productivity with structure equation modeling. To assess the patterns of compositional changes along space and time, we determined compositional and functional dissimilarity among sites and among years. Preliminary results show that both productivity and species diversity increase with annual precipitation and winter temperature, while long-term aridity does not seem to be a main driver. On the other hand, species compositional changes between years suggests that more arid sites have higher species turnover, and possibly a higher species richness considering both dry and more wet years, while less arid sites are more stable along time. In this presentation, we will further explore these patterns and assess the role of functional traits and functional diversity as a means by which communities adapt to climatic conditions, and how these influence pasture productivity. These findings may then contribute to a discussion on the projections on future scenarios for these ecosystems and which adaptation and restoration measures may be adopted to promote its sustainability and resilience.

Drylands occupy 47% of the world’s terrestrial area and comprise important biodiversity hotspots such as the Mediterranean Basin, where one can find high levels of plant diversity and endemism. At the same time, they provide resources for human populations, being cattle grazing one of the main activities in dryland ecosystems. Mediterranean woodlands and pastures are currently under threat with increasing aridity due to climate change. Aridity, together with human exploitation, pushes these ecosystems towards land degradation, leading to decreased diversity, ecosystem functioning, and economical value. Understanding how plant communities respond to climate in the long-term, as well as climatic fluctuations, is crucial to anticipate the impacts of climate change in these ecosystems and build a knowledge base to design adaptation and restoration measures and promote their resilience. In the western Mediterranean Basin dryland areas are commonly occupied with oak open woodlands. It is an agro-silvo-pastoral system with a savannah-like structure, dominated by oaks with a species-rich understory of pastures and shrubs. In Portugal, this system is called montado, and due to its socio-economic and ecological importance, it is currently monitored within the LTsER montado platform. The herbaceous layer, dominated by annual species, is a major component of this system’s diversity. While these pastures are adapted to dryland climatic conditions, its annual turnover may make these communities quick responders to environmental changes, providing a good model system to study the effects of climate on diversity and ecosystem functioning. In this work, we aim to assess the effects of long-term climate and yearly climatic fluctuations on plant taxonomic and functional diversity and on pasture productivity, as well as the relationship between diversity and productivity. We sampled the understory plant community of 10 holm-oak open woodlands along a spatial aridity gradient in southern Portugal in multiple years, 5-7 times, between 2012 and 2022. A stratified random selection of sites was made, avoiding as much as possible confounding effects, namely from differences in slope, elevation and fire occurrence. The plant community was sampled in spring, at the peak standing biomass, with the point-intercept method along six 20 m transects per site. Pasture productivity was measured by collecting the aerial herbaceous biomass in three 30 cm squares placed randomly in each site. Functional diversity was calculated using mean trait values per species retrieved from online databases. We fit linear mixed-effects models to assess the relationship between long- and short-term climate variables and taxonomic and functional diversity. We further explored the role of diversity on productivity with structure equation modeling. To assess the patterns of compositional changes along space and time, we determined compositional and functional dissimilarity among sites and among years. Preliminary results show that both productivity and species diversity increase with annual precipitation and winter temperature, while long-term aridity does not seem to be a main driver. On the other hand, species compositional changes between years suggests that more arid sites have higher species turnover, and possibly a higher species richness considering both dry and more wet years, while less arid sites are more stable along time. In this presentation, we will further explore these patterns and assess the role of functional traits and functional diversity as a means by which communities adapt to climatic conditions, and how these influence pasture productivity. These findings may then contribute to a discussion on the projections on future scenarios for these ecosystems and which adaptation and restoration measures may be adopted to promote its sustainability and resilience.

Forests contribute directly to ecosystem structure and functioning, maintaining biodiversity, acting as a climate regulator and reducing desertification. To better manage forests, it is essential to have high-resolution forest models and appropriate spatial-explicit variables able to explain tree cover at different scales, including the management scale. Most tree cover models rely only on broad-scale variables (>500 m), such as macroclimate, while only few studies include also local-scale variables (<500 m). This study aimed to identify the importance of local-scale factors relative to broad-scale factors and identify the environmental variables at different scales that explain tree cover in oak woodlands in Mediterranean drylands. Sixty sites previously identified as being covered with Holm oak or Cork oak were stratified by precipitation. Normalized Difference Vegetation Index, used here as a surrogate of tree cover, was modelled using simultaneously broad-scale factors (macroclimate) and local-scale factors (microclimatic and edaphic conditions). The percentage of variance explained by local- and broad-scale factors and the effect size of each environmental variable on tree cover was determined for the study site. It was found that local-scale factors and their interaction with broad-scale factors explained more variance than broad-scale factors alone. The most important local-scale factors explaining tree cover were elevation, potential solar radiation, used as a surrogate of microclimatic conditions, and wetness evaluated terrain used as an indicator of water flow accumulation. The main broad-scale factors were related to temperature and precipitation. The effect of some local-scale variables in tree cover seems to increase in areas where water as a limiting factor is more important. This study demonstrates the critical importance of including local-scale factors in multi-scale modelling of tree cover to obtain better predictions. These models will support well-suited forest management decisions, such as reforestation and afforestation plans to reverse evergreen oaks decline in Mediterranean drylands.

Forests contribute directly to ecosystem structure and functioning, maintaining biodiversity, acting as a climate regulator and reducing desertification. To better manage forests, it is essential to have high-resolution forest models and appropriate spatial-explicit variables able to explain tree cover at different scales, including the management scale. Most tree cover models rely only on broad-scale variables (>500 m), such as macroclimate, while only few studies include also local-scale variables (<500 m). This study aimed to identify the importance of local-scale factors relative to broad-scale factors and identify the environmental variables at different scales that explain tree cover in oak woodlands in Mediterranean drylands. Sixty sites previously identified as being covered with Holm oak or Cork oak were stratified by precipitation. Normalized Difference Vegetation Index, used here as a surrogate of tree cover, was modelled using simultaneously broad-scale factors (macroclimate) and local-scale factors (microclimatic and edaphic conditions). The percentage of variance explained by local- and broad-scale factors and the effect size of each environmental variable on tree cover was determined for the study site. It was found that local-scale factors and their interaction with broad-scale factors explained more variance than broad-scale factors alone. The most important local-scale factors explaining tree cover were elevation, potential solar radiation, used as a surrogate of microclimatic conditions, and wetness evaluated terrain used as an indicator of water flow accumulation. The main broad-scale factors were related to temperature and precipitation. The effect of some local-scale variables in tree cover seems to increase in areas where water as a limiting factor is more important. This study demonstrates the critical importance of including local-scale factors in multi-scale modelling of tree cover to obtain better predictions. These models will support well-suited forest management decisions, such as reforestation and afforestation plans to reverse evergreen oaks decline in Mediterranean drylands.