Novel fire regimes are increasing due to human activity, including the increasing frequency of megafires. The mosaic patterns of these megafires create burn patches of varying size and severity across the landscape that likely affect patterns of herbivory and forest regeneration success. We asked the following question: How does the burn mosaic within a megafire scar alter patterns of herbivory and regeneration in multiple forest types? We installed a transect network across aspen-conifer, oak-maple, and pinyon-juniper forests burned in central Utah’s 2018 Pole Creek megafire complex. Transects were geographically paired in burn severity stands and adjacent unburned stands with 6 replications per forest type, leaving us with thirty-six 50-meter transects across the 61,000-hectare burn. Sapling height, density, cover, and herbivory were measured along each transect.
Results/Conclusions
Our results suggest that high severity fires promote sapling regeneration, as there were 1.7 times more total individuals in high severity burn areas than in unburned areas. We observed faster overall regeneration in aspen-conifer and oak-maple forest types, likely due to their clonal and vegetative growth, as compared to the pinyon-juniper forests that regenerate largely via seeds. Forests that regenerate quickly post-disturbance are critical in avoiding invasion that may result in regenerative failure, especially in the case of megafires that may span multiple ecotones. Herbivory also interacted with fire severity to impact the observed regeneration, as browse pressure was seen to be 1.2, 1.9, and 14.4 times higher in burned areas than in unburned areas for aspen, oak, and maple trees, respectively. However, oak trees were found to be 1.3 times taller on average in burns than unburned areas, which is likely due to the increased resource availability and decreased competition in burned areas. Aspen showed the opposite trend, with the average sapling height in unburned areas 1.3 times taller than the average height in burned areas, which is likely due to the aspen browsing pressure being 2.3 times that of oak. Our study suggests that high severity fire may promote regeneration of multiple forest types yet may also pose a threat in areas with chronic ungulate herbivory.