Factors associated with post-fire butterfly occupancy and nectar attributes in the Sierra Nevada, California

Fire can change the quality of habitat for endangered species, including butterflies. Different nectar sources and host plants for butterflies may have distinct responses to gradients of both vegetation and soil burn severities. Our study was the first to examine post-fire butterfly occupancy as a function of covariates including nectar abundance and sugar content, as well as vegetation structure and composition. In 2014 and 2015, we conducted butterfly and vegetation surveys within the Rim Fire boundary on the Stanislaus National Forest (Tuolumne County, California). We surveyed eight sites throughout the butterfly flight season in both years and four additional sites in 2015. Burn severities of the sites, as measured by federal resource agencies, ranged from low to high. We used occupancy models implemented in Program MARK to analyze butterfly occupancy. We found that fire severity was associated with the distribution and abundance of nectar sources used by butterflies in the first two years after the fire. Fire severity was also correlated with covariates of butterfly occupancy, including canopy cover, live ground cover, and nectar abundance. These results will inform assumptions about the extent to which plant or butterfly species, and their responses to wildfire or prescribed fire, may serve as surrogates for management of related species. Such insights are directly applicable to development of conservation guidelines by the US Fish and Wildlife Service and other agencies.