Burn severity and non-native species in Yosemite National Park, California, USA

We examined non-native species density three years after the Tuolumne Fire, which burned 1540 ha in upper montane forest in California, USA. We sampled 60 plots, stratified by burn severity (low, moderate, or high severity) and landscape position (lowland or upland). We detected non-native species in 8 of 11 (73 %) of high severity lowland sites and in 5 of 10 (50 %) of moderate severity lowland sites but, overall, richness and abundance was low. We detected only five non-native species, of which bull thistle (Cirsium vulgare [Savi] Ten.) was the most common. Although non-native abundance is currently low, we recommend continued low intensity monitoring, especially on high severity burned lowland sites.