Canopy Disturbances over the Five-Century Lifetime of an Old-Growth Douglas-Fir Stand in the Pacific Northwest: A Reconstruction from Tree-Ring Records

Tree ring records from old growth Douglas fir forests in the western Cascade range, WA, were examined to reconstruct canopy disturbances in a mapped plot. The reconstruction revealed pulses indicating abrupt and sustained increases in many western hemlock ringwidths (growth increases) due to medium-sized or larger events. At least three such disturbances were evident that resulted in thinning (but not clearing) of canopy areas >0.8 ha. These occurred in about the late 1500s, 1760s, and 1930s. None promoted regeneration of Douglas fir, which became established from about 1500-1521, but those events may have promoted regeneration and growth of western hemlock. Canopy disturbances create patchiness. The utility of such reconstructions for guiding restoration and management strategies is discussed.