Reestablishing natural fire regimes to restore forest structure in California’s red fir forests: The importance of regional context

Abstract The reestablishment of natural fire regimes can have numerous benefits for forest ecosystems, including the restoration of stand structure through a reduction in tree densities and increased representation of large diameter trees. However, fire effects may depend on how departed the ecosystem is from its historical fire frequency. Red fir (Abies magnifica) forests occupy a broad geographic area across which historical fire return intervals and stand structures vary. Using historical stand inventory data from the Vegetation Type Mapping (VTM) project, we evaluated red fir forests in the Sierra Nevada in California and the Cascade-Klamath region of northwestern California and southern Oregon to determine how reintroduced fire effects vary regionally and if these differences are related to historical fire return intervals or structural conditions. We sampled a total of 29 overlapping fires and found that reestablishing fire in red fir forests consistently restored historical forest structure across a wide geographic range by reducing the density of small trees and maintaining large trees. However, the effect of fire was most evident in the Sierra Nevada where the percent difference in total tree density between unburned and burned plots was significantly greater (77% difference) than in the Cascade-Klamath (53% difference), and burned plots in the Sierra Nevada had significantly lower densities of both small (