Early postfire response of a northern range margin coast redwood forest community

Abstract

Projected increases in fire occurrence and severity in the western United States have created heightened interest in postfire ecological research in Pacific Northwest forest communities. A 2017 mixed-severity fire event at the northern range margin of Sequoia sempervirens (coast redwood) provided a rare opportunity to analyze early postfire data on the interacting effects of burn severity, stem size, and species biology on survivorship and recovery of coast redwood and three forest community associates (Pseudotsuga menziesii var. menziesii, “Douglas-fir”; Notholithocarpus densiflorus, “tanoak”; and Rhododendron macrophyllum, “coast rhododendron”). We employed recursive partitioning to build decision trees that accurately classified (80–88% prediction accuracy) the postfire response of the four primary woody species present in this community. Species specific postfire responses were variable across stem diameters and burn severities, but the ability of three of the four primary woody species to resprout resulted in a resilient postfire community that quickly initiated recovery. Large coast redwood parent stems most typically survived and resprouted from their bole and base, regardless of fire severity, and even the smallest redwood individuals resprouted from their base. Basal sprouting characteristics of coast redwood including sprout presence, growth, and abundance were found to be positively correlated with increasing burn severity. Douglas-fir showed considerable fire resistance at low to moderate burn severities, but high severity fire killed trees of all sizes. Tanoak and coast rhododendron parent stems typically died and resprouted from the base except where burn severity was very low. We conclude by using our findings to discuss the utility and role of fire in forest management, and consider future research avenues that could help to solidify our understanding of the impact and role of fire in these and similar communities.