10 The current global decline in biodiversity is a matter of pressing concern, necessitating the 11 conservation of diverse ecosystems across various spatial scales. Regions such as the 12 tropical Andes face the imminent threat of biotic homogenization due to intensive 13 livestock grazing, posing a significant risk to biodiversity. This study is focused on the 14 sub-humid grasslands of northwestern Bolivia, within the the National Park Apolobamba. 15 We investigate the influence of environmental factors on plant diversity within and among 16 communities across seven distinct sites. Our research reveals that local plant diversity, 17 quantified by species richness and the inverse Simpson index, is predominantly shaped by 18 soil pH. Notably, more acidic soil is associated with diminished diversity. Furthermore, 19 our findings highlight that the dissimilarity in species composition among local 20 communities may be linked to grazing intensity. This suggests that intensified grazing may 21 have the potential to homogenize plant communities across the landscape. A concerning 22 implication is the likelihood of communities becoming dominated by acquisitive species, 23 leaving them more susceptible to the impacts of climate variability. The study underlines 24 the necessity to analyze multiple facets of diversity for a comprehensive understanding of 25 the environmental factors regulating and therefore to address potential drivers of diversity 26 loss. To mitigate these threats, managers may consider adjusting livestock quantities and 27 the spatial range used by grazers, aiming to sustain multiple aspects of plant diversity and 28 prevent homogenization and degradation of grasslands in a changing world. 29

Mountainous grasslands in South America represent highly diverse ecosystems that offer a broad spectrum of benefits to people. These include the regulation and purification of water, prevention of soil erosion, provision of livestock feed, and preservation of cultural heritage. Previous research has underscored the significant role of grazing in shaping the diversity and productivity of grassland ecosystems, particularly in highly productive, eutrophic systems. In such systems, grazing has been demonstrated to restore grassland plant diversity by reducing primary productivity. However, it remains unclear whether these findings are applicable to South American mountainous grasslands, where plants are adapted to different environmental conditions. To address this gap, we conducted a meta-analysis of experiments that excluded livestock grazing. The goal was to quantify the impact of grazing exclusion on plant diversity and productivity across mountainous grasslands in South America. Our findings, akin to studies conducted in temperate grasslands, revealed that herbivore exclusion led to an increase in aboveground biomass. Nevertheless, it also resulted in a reduction in species richness and Shannon diversity. Interestingly, the effects of grazing exclusion became more pronounced with longer exclusion durations, yet remained robust to various climatic conditions, including mean annual precipitation and mean annual temperature, as well as the evolutionary history of grazing. In contrast to results observed in temperate grasslands, the reduction in species richness due to herbivore exclusion was not correlated with increased aboveground biomass. This suggests that the processes regulating (sub)tropical grassland plant diversity may differ from those in temperate grasslands. Further research is imperative to better comprehend the specific factors influencing plant diversity and productivity in South American montane grasslands and to discern the ecological implications of herbivore exclusion in these unique ecosystems..