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Summary1. Drylands cover about 41% of Earth's land surface, and 65% of their area supports domestic livestock that depends on the above-ground net primary productivity (ANPP) of natural vegetation. Thus, understanding how biotic and abiotic factors control ANPP and related ecosystem functions can largely help to create more sustainable land-use practices in rangelands, particularly in the context of ongoing global environmental change. 2. We used 311 sites across a broad natural gradient in Patagonian rangelands to evaluate the relative importance of climate (temperature and precipitation) and vegetation structure (grass and shrub cover, species richness) as drivers of ANPP, precipitation-use efficiency (PUE) and precipitation marginal response (PMR). 3. Climatic variables explained 60%, 52% and 12% of the variation in grass cover, shrub cover and species richness, respectively. Shrub cover increased in areas with warmer, drier and winter rainfall climates, while the response observed for both grass cover and species richness was the opposite. Climate and vegetation structure explained 70%, 60% and 29% of the variation in ANPP, PUE and PMR, respectively. These three variables increased with increasing vegetation cover, particularly grass cover. Species richness also increased with ANPP, PUE and PMR. ANPP increased, and PUE decreased with increasing mean annual precipitation, whereas PMR increased with the proportion of precipitation falling in spring-summer. Temperature had a strong negative effect on ANPP and PUE, and a positive direct effect on PMR. Standardized total effects from structural equation modelling showed that vegetation structure and climate had similar strengths as drivers of ecosystem functioning. Grass cover had the highest total effect on ANPP (0.58), PUE (0.55) and PMR (0.41). Among the climatic variables, mean annual precipitation had the strongest total effect on ANPP (0.51) and PUE (À0.41), and the proportion of the precipitation falling in spring-summer was the most influential on PMR (0.36). 4. Synthesis. Vegetation structure is as important as climate in shaping ecosystem functioning Patagonian rangelands. Maintaining and enhancing vegetation cover and species richness, particularly in grasses, could reduce the adverse effects of climate change on ecosystem functioning in these ecosystems.

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.

Over 65% of drylands are used for grazing of managed livestock. Understanding what drives grazing effects on the structure and functioning of rangelands is critical for achieving their sustainability. We studied a network of 239 sites across Patagonian rangelands (Argentina), which constitute one of the world's largest rangeland area. We aimed to (i) evaluate how aridity and grazing affect ecosystem structure and functioning and (ii) test the usefulness of the landscape function analysis (LFA) indices (stability, infiltration and nutrient cycling) as surrogates of soil functioning. Aridity decreased species richness and the cover of palatable grasses but increased the cover of palatable shrubs. Grazing pressure negatively impacted the cover of palatable grasses and species richness but did not affect the cover of shrubs. Aridity had direct and indirect negative relationships with the LFA indices. Grazing pressure had no direct effects on the LFA indices but had an indirect negative effect on them by affecting vegetation structure. The LFA indices were positively and negatively correlated with soil organic carbon and sand contents, respectively, suggesting that these indices are useful proxies of soil functional processes in Patagonian rangelands. Our findings indicate that aridity and overgrazing have convergent effects on the structure and functioning of ecosystems, as both promoted reductions in species richness, the cover of palatable grasses and soil functioning. Rangeland management activities should aim to enhance species richness and the cover of palatable grasses, as these actions could contribute to offset adverse effects of ongoing increases in aridity on drylands. Copyright © 2017 John Wiley & Sons, Ltd.

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