PS 3-34 - Post-fire recovery of native and introduced plant species across an elevation gradient in the sagebrush steppe

Abstract: Millions of US dollars are spent annually on ecosystem restoration following wildfires in order to restore critical ecosystem services. However, non-native species that invade following fires can be a major challenge for establishing desired native species, especially along environmental gradients. Understanding natural revegetation potential of a site is therefore critical for maximizing dollars spent on restoration, prioritizing key species that do not return following a disturbance like fire and understanding the interactions of native and non-native species along environmental gradients. In this study, we monitored natural revegetation of native desirable and non-native invasive species following a 2012 wildfire in the sagebrush steppe along an elevational gradient. Five sites were selected for each elevation (7 elevations x 5 sites = 35 total sites) and plant density was measured in 2014, 2015 and 2016 for all species. We used a generalized linear mixed effects model with a negative binomial distribution to assess plant densities with fixed effects of elevation and year, and a random effect of aspect. We found that native desirable species had higher densities at higher elevations (5500-7000 ft, p < 0.001), and this trend was particularly true for native perennial grasses (6000 ft, p = 0.015; 7000 ft, p < 0.001). Conversely, non-native species had lower densities at high elevations (7000 ft, p = 0.007), which was most apparent in the exotic annual grasses (6000 ft, p = 0.012; 6500 ft, p = 0.035; 7000 ft, p = 0.009). A year effect was most apparent with the exotic annual grasses wherein high precipitation in the winter of 2015-2016 likely drove higher emergence across all elevations (2016, p < 0.001). This study provides evidence to guide land management decisions on areas to prioritize post-fire restoration efforts.