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. Lim ited data on fire history and stand structure suggest that there is geograp hical variation in fire regimes and that this variation contributes to regi onal differences in stand and landscape structure. Managers need region-spe cific fire regime data to develop process-based management schemes to manag e 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 (diame ter, age), and fire scars from 75 plots in a 1570 ha area in the northern K lamath 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 short er 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 varie d by historical period. Median FRIs were longer (21.8 years) during the sup pression period (1905-1992) than in the settlement (1850-1904) (12.5 years) or presettlement (1627-1849) (14.5 years) period. The average burn area fo r a fire was 350 ha, and 16 fires larger than 500 ha burned between 1627 an d 1992. Fire rotations varied by century from 15.5 to 25.5 years and were l ongest in the fire suppression period. Stand conditions were multi-aged, an d Douglas-fir recruitment occurred after fire. Patterns of past fire severi ty, inferred from age-classes, indicate that upper slopes, ridgetops, and s outh- 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 top ographic positions to sustain or promote long-term, late-successional condi tions. Prescribed fire will likely be an integral component of management p lans that successfully maintain natural processes and structures in newly e stablished late-successional reserves in the Klamath Mountains. (C) 1998 El sevier Science B.V.