Disturbance regimes favor alternative plant communities in the natural grasslands of the Pampa Austral (Argentina)

The Austral Pampa hosts extensive and diverse grasslands, which, over the last century, have been exposed to climate change and unprecedented disturbance regimes, including domestic herbivory and a novel fire regime. Predicting community responses to these changing conditions and designing appropriate conservation plans requires dissociating the individual contribution of each factor to community filtering. We ask whether fire, herbivory, temperature and drought, favor distinct communities in Pampean grassy ecosystems and which plant traits. Field surveys were conducted in three areas of the Ventania Mountain System in Pampa Austral (Argentina) exposed to varied fire, herbivory, and drought regimes. A total of 140 plant species were examined across 8 sampling areas, selected as representing different disturbance regimes. We measured 17 functional traits related to plant height, reproduction, and leaf area. The relationships between these traits and environmental variables were analyzed using RLQ and fourth-corner methods. RLQ analysis revealed that temperature, rainfall, and herbivory influenced plant communities, while fire frequency had less impact. We identified five distinct plant functional groups (PFGs) that differed in perenniality, type of pollination, resprouting capacity, spinescence, leaf hairiness and leaf area. Separating the effects of herbivory, fire, and drought reveals that multiple stresses could influence communities, resulting in higher resprouting and shorter life cycles. Analyzing how functional traits respond to environmental factors and disturbances provides insights into the conservation challenges posed by these changing disturbance dynamics in the Pampa biome.