PATTERNS OF GAP-PHASE REPLACEMENT IN A SUB-ALPINE, OLD-GROWTH FOREST

Small-scale natural disturbances involving the death of one to a few trees and creating gaps in the forest canopy are key processes in the population and community ecology of many forests. I examined the patterns of replacement in gaps in a subalpine old-growth forest in southern coastal British Columbia to assess their role in the forest community. I found no evidence that self replacement or reciprocal replacement act to maintain the current community composition. Gapmaker-gapfiller comparisons indicated preferential replacement of all species by Pacific silver fir (Abies amabilis), suggesting that the community is undergoing successional change. Nor did gap size, location within a gap, or local canopy composition appear to exert a strong influence on the species composition of regeneration within the gap. The only circumstance where Pacific silver fir was not overwhelmingly dominant among gapfillers was on stumps, where almost all successful western hemlock (Tsuga heterophylla) gapfillers were located. These patterns suggest that neither species-specific interactions between gapmakers and gapfillers nor variability in gap environments is adequate to maintain the current composition of the forest canopy. However, caution is indicated in projecting a long-term trend from this short-term assessment of community trajectory.