Tree mortality patterns following prescribed fires in a mixed conifer forest

During the late fall of 2002 we administered three burns in mixed conifer forest sites in the north-central Sierra Nevada. Eight months later we measured fire-induced injury and mortality in 1300 trees. Using logistic regression, an array of crown scorch, stem damage, fuels, and fire-behavior variables were examined for their influence on tree mortality. In Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), white fir (Abies concolor (Gord. & Glend.) Lindl.), and incense cedar (Calocedrus decurrens (Torr.) Florin), smaller trees with greater total crown damage had higher mortality rates. Smaller stem diameters and denser canopies predicted mortality best in ponderosa pine (Pinus ponderosa Dougl. ex P. Laws. & C. Laws). Duff consumption and bark char severity increased model discrimination for white fir and incense cedar and California black oak (Quercus kelloggii Newberry), respectively. In tanoak (Lithocarpus densiflorus (Hook. & Arn.) Rehd.), greater total crown damage in shorter trees resulted in higher mortality rates. Along with tree diameter and consumption of large (> 7.6 cm diameter at breast height, DBH) rotten downed woody debris, fire intensity was a significant predictor of overall tree mortality for all species. Mortality patterns for white fir in relation to crown damage were similar among sites, while those for incense cedar were not, which suggests that species in replicated sites responded differently to similar burns. Our results demonstrate actual fire-behavior data incorporated into mortality models, and can be used to design prescribed burns for targeted reduction of tree density in mixed conifer forests.