Scaling up our knowledge of grazing impact on plant diversity and ecosystem functioning in Andean grasslands

In this thesis, I focus on the intricate dynamics between grazing, biodiversity, and ecosystem functioning in grasslands. As the global decline in biodiversity reaches critical levels, it becomes urgent to conserve diverse ecosystems, such as grasslands, which are subjected to widespread land use through livestock grazing. One of the central debates in grassland ecology is whether grazing promotes or reduces plant diversity, and how this, in turn, affects ecosystem stability. Rather than addressing this question in isolation, in Chapter 2 I approach the topic comprehensively by examining how grazing influences multiple facets of biodiversity—including alpha and beta diversity, functional trait diversity, and functional groups —across spatial scales. I find that local plant diversity is driven by soil pH, with acidic soil reducing diversity, while increased grazing intensity may homogenize communities and favor resourceacquisitive species. Furthermore, in Chapter 3 I explore the broader impacts on the stability of plant productivity at the local and larger spatial scales and the role of spatial asynchrony in stabilizing productivity at the larger spatial scale. Results reveal that higher grazing intensity and elevated soil nitrogen were associated with greater stability at both local and broader scales. Increased gamma stability, despite biotic homogenization, was driven by enhanced spatial asynchrony in productivity among communities at higher grazing intensities. In Chapter 4 I highlight the importance of considering the social and economic aspects of land use. In the study area, traditional livestock herding is gradually being replaced by mining, which introduces further complexity into land-use management. The results emphasize the need for tailored management strategies that balance biodiversity conservation with local livelihoods, particularly in indigenous communities. I suggest prioritizing the conservation of the wild camelid vicuña. For this, indigenous communities that depend on livestock for their livelihoods could reintroduce traditional herding activities or reduce the current stock rates. Furthermore, communities that depend on mining should quantify the negative impact of this activity on grasslands diversity and functioning. Furthermore, a key challenge in studying these relationships lies in the difficulty of controlling abiotic factors. I discuss how uncontrolled environmental variables can obscure the true effects of grazing on biodiversity, drawing attention to the complexities of real-world landscapes. Despite these challenges, the research highlights the value of observational studies, particularly in remote, biodiverse regions like Andeangrasslands, where experimental studies are limited due to a lack of infrastructure and financial support. In Chapter 5 I conduct a meta-analysis of experiments excluding livestock grazing to assess its impact on plant diversity and productivity across mountainous grasslands in South America. I find that herbivore exclusion led to higher aboveground biomass but lower species richness and Shannon diversity, with effects intensifying over time while remaining unaffected by climatic conditions or the evolutionary history of grazing. Altogether, my findings deliver key insights into the interplay between grazing, biodiversity, and ecosystem functioning, providing essential science-based guidelines for the conservation, management, and restoration of (sub) tropical mountainous grasslands. By integrating ecological research with socio-economic realities, this work contributes to the development of novel strategies for sustaining biodiversity,