Together we stand, divided we fall: Effects of livestock grazing on vegetation patches in a desert community

Abstract

Questions: Vegetation patches formed by interacting xeric species are the main drivers of dryland structure and function. Plant aggregation enhances microclimatic conditions and triggers abiotic and biotic processes, such as nutrient cycling and accumulation, and species interactions. However, vegetation patches may be modified by disturbances in unpredictable ways. We tested whether livestock grazing affects vegetation structure and plant spatial associations in a desert community, by considering the role of plant species in ecological succession. Location: Patagonian Monte Desert, Argentina. Methods: We used high-quality standardized photographs along transects to characterize plant community structure (i.e., cover, abundance, richness), spatial patterns (i.e. plant-plant associations), and classified species based on their successional role (i.e. early, intermediate and late species). We used regression models and network analysis to evaluate the effect of grazing on vegetation. Results: In general, grazing modified community structure, reducing total cover, abundance and richness. Grazing modulated community spatial patterns, simplifying and removing vegetation patches. The impact of grazing depended on the species successional role. The abundance and cover of early species were less affected by grazing than intermediate and late species, the latter being the most affected. However, species richness significantly decreased with increasing stocking rates, regardless of their successional role. Late species were present in most plant spatial associations, indicating a major contribution to multi-specific vegetation patches formation. Conclusions: The reduction in species richness and low abundance of late species highlights the need to prevent irreversible degradation caused by overgrazing. Late species emerge as key structures of vegetation in desert rangelands facilitating the establishment and protecting other plant species. Due to the critical role of vegetation patches in maintaining desert ecosystem functioning, conservation and management practices should focus on late species, while early species, responsible for vegetation patch formation in overgrazed situations, should be preferred for restoration practices.