摘要 : The frequency, extent, and severity of fires strongly influence development patterns of forests dominated by Douglas fir (Pseudotsuga menziesii var. menziesii) in the Pacific Northwest USA. Limited data on fire history and stand s... 展开 The frequency, extent, and severity of fires strongly influence development patterns of forests dominated by Douglas fir (Pseudotsuga menziesii var. menziesii) in the Pacific Northwest USA. 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. Tree species composition, structure (diameter, age), and fire scars were analysed from 75 plots in a 1570-ha area in the northern Klamath Mountains. Tree species composition varied with altitude and aspect, and median fire return intervals were similar (12-19 yr) among species composition groups. However, median fire return intervals (FRI) wereshorter on south- (8 yr) and west-facing (13 yr) slopes than on northern (15 yr) or eastern (16.5 yr) aspects. Fire return intervals also varied by historical period. Median FRIs were longer (21.8 yr) during the suppression period (1905-1992) than in thesettlement (1850-1904) (12.5 yr) or presettlement (1627-1849) (14.5 yr) 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 yr 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, ridge tops, and S.- and W.-facing slopes experienced more severe fires between 1850 and 1950 than lower slopes or E.- and N.-facing slopes. Implications are that lower slopes and N. and E. aspects are more likely than other topographic positions to sustain or promote long-term, late-successional conditions. Prescribed fire will be likely to be an integral component of management plans that successfully maintain natural processes and structures in newly established late-successional reserves in the Klamath Mountains. 收起