Reasons for the relative absence of Thuja plicata regeneration in the old growth Thuja plicata - Tsuga heterophylla forests close to Vancouver, British Columbia, were assessed by measuring seedfall and applying Thuja seeds to small plots. All measurements were replicated in two different sites. The small (0.5 m2) plots were established in 2 canopy cover conditions (clearcut and forest). 3 seedbed conditions (mineral soil, burned forest floor, and undisturbed forest floor), and 2 mammal and bird seed predation conditions (with and without). Each canopy cover, seedbed, and seed predation combination was replicated 15 times in each study site. Large numbers of viable seeds (>200/m2) fell in 1990/91 and again in 1994/95. Seed germination decreased in the order burn > mineral soil > forest floor; forest > clearcut; and without predation > with predation. After 3 growing seasons, of the 100 seeds applied to each plot, an average of only 1-2 seedlings had survived. This number of surviving seedlings decreased in the order - burn > mineral soil > forest floor, and clearcut > forest, but was not influenced by predation. After 3 growing seasons. seedling growth tended to decrease in the order - burn > forest floor > mineral soil; clearcut > forest; and without predation > with predation. It was concluded that the relative lack of regenerating Thuja seedlings in the study area forests was not due to a lack of viable seeds. Although a lack of suitable seedbeds and the presence of the forest canopy reduce the number of seedlings in undisturbed forests, this number should still be substantial. The observed relative lack of regenerating Thuja seedlings must therefore result from other factors which were not considered in the present studyFeller and Klinka "Seedfall, seed germination, and initial survival and growth of seedlings of Thuja plicata in southwestern British Columbia." Northwest Science. 1998; 72(3): 157-16
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