Long-term influence of prescribed burning on subsequent wildfire in an old-growth coast redwood forest

Background: Prescribed burning is an effective tool for reducing fuels in many forest types, yet there have been few opportunities to study forest resilience to wildfire in areas previously treated. In 2020, a large-scale high-intensity wildfire burned through an old-growth coast redwood (Sequoia sempervirens) forest with a mixed land management history, providing a rare opportunity to compare early post-wildfire data between areas with and without previous application of prescribed burning. The purpose of this study was to analyze the differences between these two treatments in terms of tree mortality, stand structure, fuel composition, and post-wildfire regeneration. Field data were collected approximately 1 year after the wildfire using a total of fifty 20 m plots in three sites previously treated with prescribed fire more than 9 years prior to the wildfire, and fifty plots in three adjacent sites without a history of prescribed fire. Data regarding the influence of prescribed burning on forest structure and composition following wildfire were assessed using generalized linear mixed effects models (GLMMs).

Results: Prescribed burning was positively associated with greater canopy cover, tree survival, counts of early post-fire coast redwood seedlings, and lower stand density, following subsequent wildfire. In addition, the mortality of individual trees was lower within areas treated with prescribed fire and negatively associated with tree height. Topkill was also lower within treated areas and was negatively correlated with tree diameter and tree height for all basal sprouting species combined and for S. sempervirens individually.

Conclusions: Results suggest that prescribed fire improved coast redwood forest stand resistance and resilience to wildfire and that these benefits were maintained after a significant wildfire event in areas treated more than 9 years prior to the wildfire. Further research is recommended in areas where prescribed fire has been applied repeatedly, to better understand long-term effects and guide best practices for future prescribed fire use in coast redwood forests.