Gaston R. Oñatibia

Understanding the drivers of plant community stability is crucial for predicting ecosystem responses to extreme drought events. In grasslands, drought resistance supports the maintenance of key functions such as above‐ground primary productivity, making the identification of resistance drivers essential to guide management under climate change. Proposed factors contributing to grassland stability include multiple diversity facets, functional traits and long‐term climate, but most assessments focus on temporal invariability under historical disturbance regimes, leaving mechanisms of extreme drought resistance and their variation across climatic contexts relatively underexplored. Here, we analysed data from 54 grassland sites of the International Drought Experiment to examine the resistance of above‐ground net primary productivity to a short‐term (i.e. 1 year) extreme drought. We investigated the relative importance and joint influence of functional composition (i.e. community‐weighted means of leaf and root traits), plant diversity facets (taxonomic, functional and phylogenetic) and climate (aridity and rainfall variability) on drought resistance. We used structural equation models to disentangle direct, indirect, and moderating pathways linking these drivers to drought resistance. Long‐term aridity appeared as one of the most important drivers of grassland resistance to drought, with more arid sites showing lower resistance. Moreover, aridity impacted resistance through indirect effects by shaping functional composition and plant diversity, and by moderating the influence of plant diversity and functional composition. Functional composition related to dehydration avoidance and dehydration tolerance was also positively associated with resistance, while diversity had a weaker relationship with resistance, mostly through functional and phylogenetic facets. Interannual rainfall variability also influenced resistance, with different effects in more arid versus humid and less arid sites. Synthesis . Widely studied stability drivers such as plant diversity and functional composition have only partial explanatory power for short‐term drought resistance of above‐ground productivity in grasslands at a global scale. The abiotic context, particularly long‐term aridity, is crucial for understanding ecosystem responses to rainfall variation and can improve predictive models for advancing the study of ecosystem resistance to drought. Along with management practices that target high species diversity or specific traits, restoration and conservation practices should support vulnerable sites experiencing high aridity

Drylands worldwide are predominantly used for animal husbandry and provide critical ecosystem services such as forage provision and carbon sequestration. Sustainable livestock grazing management in these ecosystems relies on accurate forage dynamics assessments. Forage dynamics largely result from the characteristics of the plant populations composing the community, the traits of domestic herbivores and the management strategies that influence consumption and selectivity. However, traditional forage evaluations often focus on total productivity, plant cover or biomass measurements, overlooking plant‐size population structures that control forage dynamics as perceived by grazers. We developed species‐specific allometric equations for dominant perennial grasses of the Patagonian steppes to estimate aboveground biomass categories related to the provision of forage and other ecosystem services—including total, green, senescent, standing‐dead and crown biomass—based on plant size. Then, we applied the equations to assess the effects of sheep grazing intensity on population plant‐biomass structures and forage biomass in commercial‐sized paddocks. The non‐destructive allometric method was highly accurate ( R ² ranged 0.77–0.90; p < 0.001 for green and total biomass models), allowing efficient biomass estimations across different plant morphologies under varying grazing pressures. Notably, grazing intensification did not affect total grass green biomass, but significantly reduced forage biomass by 70% ( p < 0.001) due to the substantial population decline in sheep‐preferred species, highlighting the differential impacts of selective grazing on specific biomass components. By enabling a finer understanding of plant–animal interactions and species‐specific biomass dynamics, our method supports informed management strategies to sustain critical ecosystem services in Patagonian steppes and other drylands grazed by selective herbivores.

Drivers of non-native plant success in drylands are poorly understood. Here we identify functional differences between dryland native and non-native perennial plants and assess how biotic, abiotic and anthropogenic factors shape the success of the latter. On the basis of plant community and functional trait data from 98 sites across 25 countries, we report a total of 41 non-native plant species at 31 sites. Non-natives tend towards faster growth strategies than natives. Non-native plant richness is higher at sites with greater grazing pressure and under environmental conditions associated with higher soil fertility, decomposition and fungal richness—conditions that tend to occur in less arid regions—and lower where native plant and herbivore richness are greater. Non-native plant cover correlates positively with grazing pressure and negatively with native plant richness. Taken together, our results suggest that non-native plant success in drylands is facilitated when high grazing pressure coincides with elevated resource availability. Such context-dependence of non-native plant success and linkages with native plant and herbivore diversity highlight the need for managing grazing and conserving biodiversity across the world’s drylands.

Land cover data are commonly used to model the terrestrial carbon (C) sink, yet these data have wide margins of error that significantly alter estimates of global C storage. Here we demonstrate this data vulnerability in grasslands, which are critical to C cycling but whose estimated distribution has varied by >50 million km ² (3.5–42% of the Earth’s terrestrial surface). Comparing multiple high-resolution land cover products with expertly annotated grassland data from six continents, we show sources of mapping error and discuss C implications based on 2023 United Nations (UN) FAO estimates. Past misidentification arose from inconsistent definitions on grassland identity and classification flaws especially relating to woody plant cover. Correcting these errors adjusted grassland coverage to 22.8% of the terrestrial land base (30.1 million km ² ), elevating UN projections of soil C stocks to 155.02 Pg (0–30 cm depth). These findings underscore the challenges of biome mapping for ecosystem accounting and policy, when lacking field-validated remotely sensed data.

Understanding the mechanisms that shape ecosystem resistance to increasing livestock grazing pressure, a major driver of land degradation, is essential for predicting its impacts and informing sustainable land management strategies. This issue is particularly relevant in drylands, which host half of the world’s livestock production and are highly vulnerable to desertification caused by overgrazing. Here we conduct a standardized field survey across 73 dryland sites in 25 countries to simultaneously evaluate how climatic, edaphic, vegetation and grazing-related factors influence ecosystem resistance—defined here as the capacity to maintain vegetation cover under increasing grazing pressure. We found that increasing grazing pressure reduced vegetation cover in 80% of sites, with an average decline of 35%. Plant species richness emerged as the strongest predictor of ecosystem resistance, with higher richness associated with lower vegetation cover loss. Functional trait data indicated that this positive effect was mainly explained by complementarity in trait values among plants, rather than by functional redundancy. Our results indicate that conserving plant diversity is key to strengthening ecosystem resistance and sustaining dryland functioning under intensifying grazing pressure.

Rangelands are vital ecosystems with high biodiversity that provide forage for livestock and help mitigate the negative impacts of climate change. However, they are increasingly threatened by more frequent and intense drought events. Understanding the key factors influencing forage sensitivity to droughts of varying durations is essential for promoting sustainable livestock production. In this study, we analysed data from multiyear drought experiments conducted across nine contrasting rangeland sites, spanning arid to humid environmental conditions. Our findings reveal that climatic variables related to water availability are the primary drivers of forage sensitivity to drought, regardless of its duration. However, biotic factors, such as plant richness and the proportion of grasses, play a particularly important role in determining sensitivity to prolonged droughts. These results offer novel insights into how rangeland forage production responds to droughts of different lengths across diverse environmental gradients. Our study advances the understanding of rangeland vulnerability to climate change and underscores the importance of species diversity in buffering the impacts of drought.

Questions: Biological invasions significantly impact plant communities, affecting and threatening biodiversity at regional and local scales worldwide. The invasion process may be influenced by climate change, particularly by the increasing frequency of extreme droughts. Here we evaluate (1) the level of exotic plant invasion along an aridity gradient and its relationship with environmental variables, and (2) the cumulative effect of prolonged droughts on native plant communities and the invasion of exotic species. Location: Rangelands located along an aridity gradient from the arid Patagonian steppe to the humid Pampa region in Argentina, South America. The study sites (11) encompass a wide range of mean annual precipitation (170–950 mm year ⁻¹ ) and diverse vegetation physiognomic characteristics. Methods: We conducted floristic surveys to assess plant community composition, diversity, and the cover of native and invasive exotic species in (1) 11 sites located along an aridity gradient, and (2) a 4‐year drought simulation experiment established in nine sites. At each experimental site, rain‐out shelters intercepted 50%–60% of incoming rainfall to simulate drought conditions. We then used linear mixed models to analyze the effects of drought on the cover, richness, and dominance of the plant community. Results: Our findings reveal (1) a positive relationship between plant invasion and rangeland humidity at the regional scale. In the humid extreme, invasive exotic species dominated the plant community, whereas in the arid extreme native species were more abundant than invasive exotic species. (2) Experimental droughts reduced native plant cover in arid and semi‐arid rangelands and promoted the cover, dominance, and richness of invasive exotic species in humid counterparts, reducing native species richness. Conclusions: This study suggests a potential intensification of biological invasions in response to increased occurrences of droughts predicted by climate change. Management strategies for invaded humid rangelands are imperative, and early warnings are crucial during dry years in arid and semi‐arid rangelands, where droughts could enhance the abundance of invasive exotic species.

As droughts become longer and more intense, impacts on terrestrial primary productivity are expected to increase progressively. Yet, some ecosystems appear to acclimate to multiyear drought, with constant or diminishing reductions in productivity as drought duration increases. We quantified the combined effects of drought duration and intensity on aboveground productivity in 74 grasslands and shrublands distributed globally. Ecosystem acclimation with multiyear drought was observed overall, except when droughts were extreme (i.e., ≤1-in-100-year likelihood of occurrence). Productivity losses after four consecutive years of extreme drought increased by ~2.5-fold compared with those of the first year. These results portend a foundational shift in ecosystem behavior if drought duration and intensity increase, from maintenance of reduced functioning over time to progressive and profound losses of productivity when droughts are extreme.

Plant biomass tends to increase under nutrient addition and decrease under drought. Biotic and abiotic factors influence responses to both, making the combined impact of nutrient addition and drought difficult to predict. Using a globally distributed network of manipulative field experiments, we assessed grassland aboveground biomass response to both drought and increased nutrient availability at 26 sites across nine countries. Overall, drought reduced biomass by 19% and nutrient addition increased it by 24%, resulting in no net impact under combined drought and nutrient addition. Among the plant functional groups, only graminoids responded positively to nutrients during drought. However, these general responses depended on local conditions, especially aridity. Nutrient effects were stronger in arid grasslands and weaker in humid regions and nitrogen-rich soils, although nutrient addition alleviated drought effects the most in subhumid sites. Biomass responses were weaker with higher precipitation variability. Biomass increased more with increased nutrient availability and declined more with drought at high-diversity sites than at low-diversity sites. Our findings highlight the importance of local abiotic and biotic conditions in predicting grassland responses to anthropogenic nutrient and climate changes.