COS 55-2 - Extreme Event Succession Dynamics: A Dryland Plant Community Response to Widespread Drought-Induced Mortality

Abstract: Extreme climate events are becoming more frequent and have the potential to directly or indirectly alter disturbance regimes. While succession following indirect effects, such as wildfire or landslides are well-studied, disturbances associated with the direct effects often present novel conditions. Widespread plant mortality caused by extreme dry or wet soil water conditions are an increasingly common example occurring across a range of ecosystems from temperate forests to shrub steppe ecosystems. While some work has been done to characterize factors that influence the resistance of plant communities to mortality, we do not yet understand what influences the resilience of plant communities. In this study we asked, what influences the resilience of big sagebrush (Artemisia tridentata Nutt.) plant communities following a large-scale mortality event? Specifically, do interactions between site level abiotic factors change plant community trajectory or resilience? To answer these questions, we sampled big sagebrush plant communities using 100m² plots ten years after a mortality event. Our design included two landscape positions, uplands and lowlands, across sites with variable soil textures. In each landscape position we sampled control plots and plots with varying degrees of big sagebrush mortality. We sampled canopy and understory communities to assess big sagebrush seedling re-establishment and plant community response to mortality. Our results showed that landscape position and soil texture influence plant community resilience to extreme climate event induced mortality. The number of big sagebrush seedlings in lowlands was not significantly different between mortality and control plots (p = 0.90), whereas seedling numbers in uplands were higher in mortality plots (p = 0.004). We found that the density of small sagebrush individuals was higher post-mortality than pre-mortality (p < 0.001), and sagebrush density was negatively related to clay content in lowlands (p < 0.001). At the community level, clay content was positively related to non-native forb cover (p = 0.03). Perennial bunchgrass cover in lowlands decreased with clay content (p = 0.005). Upland plant communities were resilient to morality regardless of soil texture. Our findings indicate that landscape position and soil texture can influence the resilience of plant communities to mortality events. According to our results, the most vulnerable areas in big sagebrush plant communities are clay rich lowlands.