California’s coast redwood (Sequoia sempervirens) forests have long been associated with fire, particularly in the southern and interior portions of the species range. The importance of fire in northern coast redwood forests are thought to be reduced because ignitions have been rare and cool coastal temperatures and summer fog ameliorate the fire hazard. Support for this north-south and coast to interior climate gradient hypothesis has been limited due to limited fire history data from the north coast. Moreover, past efforts to test this hypothesis have been challenged by methodological limitations particular to coast redwood. This research revisits the fire history of an area formerly thought to have experienced fire only a few times per millennia: Del Norte Coast Redwoods State Park.
Results/Conclusions
I found that fire frequency was markedly more frequent than previously thought for humid redwood forests. Pre-European fire intervals do not correspond to an east-west climate gradient or a topography-based moisture gradient, but a cultural burning gradient inferred from changing land use practices. Areas close to an aboriginal Tolowa village and resource collection areas burned considerably more often than areas that were less utilized. This spatial and temporal variability in cultural fire altered old growth forest structure and composition. Frequent fire is associated with Pseudotsuga menziesii (Douglas fir) establishment and hardwoods. While variability in coastal fog-stratus and drought may have also influenced fire regimes, particularly at the inland portion of the range, these relationships are difficult to confirm. Changing human and climate influence on old-growth redwood fire regimes suggests that ancient redwood forests are not in equilibrium, but are an artifact of change. Remnant old growth forests are likely to continue to evolve in response to fire exclusion and climate change. Efforts by managers to restore and sustain these remarkable forests can be enhanced by understanding how such complex histories give rise to biodiversity.
