Fire regimes and stand dynamics in an upper montane forest landscape in the southern Cascades, Caribou Wilderness, California

Fire is the most frequent and widespread disturbance affecting forests in the Pacific Northwest and identifying the frequency, extent, and severity of fires is essential for understanding the role of fire in longterm forest dynamics. This study quantifies presettlement fire regimes (i.e. fire return interval, fire extent, fire severity, fire rotation) and successional patterns in a 950 ha upper montane forest using 39 cross-dated fire scar samples, tree ages and radial growth patterns in cores, and tree diameter distributions in 112 plots. Forest species composition varied with potential soil moisture and there was variation in some fire regime parameters among forest compositional groups. Mean fire return intervals were shortest in red fir-white fir forests (41 yr), and longer in white fir-Jeffrey pine, lodgepole pine, lodgepole pine-red fir, and red fir-western white pine forests (59-70 yr). Lodgepole pine and lodgepole pine-red fir forests experienced more high severity (38-75%) fire than other forest types (13-25%). Fire rotation varied by time period, and was shortest in the pre Euro-American period (76 yr), longer in the settlement period (177 yr), and longest in the fire suppression (577 yr) period. The average extent of a fire was small (150 ha). Lodgepole pine-red fir, white fir-Jeffrey pine, and red fir-white fir forests are changing in composition but lodgepole pine and red fir-western white pine forests are compositionally stable. Recurring fire in the presettlement period maintained fire-dependent pines but fire suppression is now causing shifts in species composition and changes in landscape scale vegetation patterns similar to those in lower montane forests.