摘要 : Fire history and forest age structure were reconstructed at Point Reyes National Seashore on the central California coast to document changes in forest conditions over the past\approx.\200 years. Surface fire history was reconstru... 展开 Fire history and forest age structure were reconstructed at Point Reyes National Seashore on the central California coast to document changes in forest conditions over the past\approx.\200 years. Surface fire history was reconstructed from dendrochronologically-crossdated fire-scarred trees in two stands of Douglas fir (Pseudotsuga menziesii var. menziesii) and one stand of coast redwood (Sequoia sempervirens). Age structure in an approximately 2000 ha area of Douglas fir forest was examined for tree recruitment patterns. Reconstructed mean surface fire intervals and Weibull median probability intervals ranged from～7 to～13 years. Fires generally occurred late in the growing season or after growth had ceased for a year. Spatial patterns of historic fires and those reconstructed from the fire-scar record document often widespread fires in the central Olema Valley. It is suggested that many, if not most, of the fires reconstructed from Point Reyes were ignited by humans given the long history of intensive use of this area, first by the Coast Miwok and later by European ranchers. Age structures of stands suggest that much of the Douglas fir overstorey is multiaged with little evidence of stand-replacing fire or other disturbance events. Ages of trees in Douglas fir stands document increasing landscape coverage of Douglas fir forest at Point Reyes and broadleaved recruitment under older Douglas fir canopies. It is concluded that loss of surface fires is having cascading effects on landscape vegetation patterns, community relationships, and probably related ecosystem processes. 收起