Response of antelope bitterbrush to repeated prescribed burning in Central Oregon ponderosa pine forests

Antelope bitterbrush is a dominant shrub in many interior ponderosa pine forests in the western UnitedStates. How it responds to prescribed fire is not well understood, yet is of considerable concern to wildlifeand fire managers alike given its importance as a browse species and as a ladder fuel in these fire-proneforests. We quantified bitterbrush cover, density, and biomass in response to repeated burning in thinnedponderosa pine forests. Low- to moderate-intensity spring burning killed the majority of bitterbrushplants on replicate plots. Moderately rapid recovery of bitterbrush density and cover resulted fromseedling recruitment plus limited basal sprouting. Repeated burning after 11 years impeded the recoveryof the bitterbrush community. Post-fire seed germination following the repeated burns was 3–14-foldlower compared to the germination rate after the initial burns, while basal sprouting remained fairlyminor. After 15 years, bitterbrush cover was 75–92% lower on repeated-burned compared to unburnedplots. Only where localized tree mortality resulted in an open stand was bitterbrush recovery robust. Bycontrolling bitterbrush abundance, repeated burning eliminated the potential for wildfire spread whensimulated using a customized fire behavior model. The results suggest that repeated burning is asuccessful method to reduce the long-term fire risk imposed by bitterbrush as an understory ladder fuelin thinned pine stands. Balancing the need to limit fire risk yet provide adequate bitterbrush habitat forwildlife browse will likely require a mosaic pattern of burning at the landscape scale or a burningfrequency well beyond 11 years to allow a bitterbrush seed crop to develop.