CANOPY GAPS IN DOUGLAS-FIR FORESTS OF THE CASCADE MOUNTAINS

In mature (100-150-yr-old) and old-growth (>200-yr-old) Douglas-fir Pseudotsuga menziesii/western hemlock Tsuga canadensis forests in W Oregon and Washington, most canopy trees died without disrupting the forest in both mature (87.6%) and old-growth stands (73.3%). Amount of forest area per year representing new gaps was 0.7% in mature stands and 0.2% in old-growth stands. Most regeneration (>1 m tall) in gaps was western hemlock; Douglas-fir regeneration did not occur. The ratio of seedling density in gaps to density under canopies was c3 for the mature stand and 9 for the old-growth stand. Seedling density was correlated with measures of gap age but not gap size. In addition to gap size, canopy structure and disturbance severity are important determinants of gap response. -from Authors