Fire history and landscape dynamics in a late-successional reserve, Klamath Mountains, California, USA

The frequency, extent, and severity of fires strongly influence development patterns of forests dominated by Douglas-fir in the Pacific Northwest. Limited data on fire history and stand structure suggest that there is geographical variation in fire regimes and that this variation contributes to regional differences in stand and landscape structure. Managers need region-specific fire regime data to develop process-based management schemes to manage new late-successional reserves (LSR). This study quantifies fire regimes and stand structural patterns in a LSR in Douglas-fir-dominated forests in northern California. We analyzed tree species composition, structure (diameter, age), and fire scars from 75 plots in a 1570 ha area in the northern Klamath Mountains. Tree species composition varied with elevation and aspect, and median fire return intervals were similar (12-19 years) among species composition groups. However, median fire return intervals (FRI) were shorter on south- (8 years) and west-facing (13 years) slopes than on northern (15 years) or eastern (16.5 years) aspects. Fire return intervals also varied by historical period. Median FRIs were longer (21.8 years) during the suppression period (1905-1992) than in the settlement (1850-1904) (12.5 years) or presettlement (1627-1849) (14.5 years) period. The average burn area for a fire was 350 ha, and 16 fires larger than 500 ha burned between 1627 and 1992. Fire rotations varied by century from 15.5 to 25.5 years and were longest in the fire suppression period. Stand conditions were multi-aged, and Douglas-fir recruitment occurred after fire. Patterns of past fire severity, inferred from age-classes, indicate that upper slopes, ridgetops, and south- and west-facing slopes experienced more severe fires between 1850 and 1950 than lower slopes or east- and north-facing slopes. Implications are that lower slopes and north and east aspects are more likely than other topographic positions to sustain or promote long-term, late-successional conditions. Prescribed fire will likely be an integral component of management plans that successfully maintain natural processes and structures in newly established late-successional reserves in the Klamath Mountains.