Synthesizing the Impacts of Natural Disturbances and Climate on Patagonian Semiarid Grasslands: Insights From an 18-Year Long-Term Monitoring Study

Abstract

Question: How does the vegetation of northwestern Patagonia grasslands respond to climate fluctuations and disturbances? Location: Northwestern Patagonia, Argentina. Methods: Our study was carried out in livestock- grazed grasslands affected by drought (1998), wildfire (1999), and volcanic ash deposition (2011). We analyzed annual precipitation trends, rainfall-use efficiency, and the relationship between ENSO events and seasonal climate. Before a severe drought, we monitored vegetation at three sites over 18 years (1999–2017). Only the North and South sites were affected by fire, while the unburned Control site was impacted by grazing and volcanic ash deposition. We used linear mixed-effects models to assess the relationships between vegetation cover and species richness with precipitation, temperature, and disturbances. We calculated species turnover, diversity, evenness, and similarity, and constructed a native reference community. Results: Precipitation showed a negative trend from 1991 to 2018. Rainfall-use efficiency was low in 2006 and high in 2016. ENSO signals were stronger in spring than in winter. Spring precipitation and temperature enhanced both cover and richness. Annual species responded positively to annual and spring precipitation. In the Control site, plant cover recovered faster post- drought than post-eruption, whereas species richness showed the opposite pattern. Grassland recovers fast after fire compared to other disturbances. Species turnover was lowest 8 years post-drought and 6 years post-eruption. Diversity and evenness increased over time, and were higher in burned sites compared to the Control. The community most similar to the native reference com- munity was the recently burned grassland. Conclusions: Our long-term study shows that seasonal climate and disturbances shape grassland dynamics, which can be interpreted within the framework of Mediterranean-climate grassland ecology. Grassland managers in northwestern Patagonia could benefit from our findings by adapting livestock management practices to enhance grassland post- disturbance recovery and reduce the invasion of opportunistic species.