Forest vegetation of west-central Vancouver Island, British Columbia

The objective of this study was to quantitatively describe the structure, composition and ecological relationships of old-growth forests of west-central Vancouver Island. Data were obtained by sampling 172 plots, at elevations up to 1000 m, located within thirteen drainage areas. Hypothesized relationships between vegetation and environmental variation were examined using gradient analysis and multivariate methods. Successive reciprocal averaging ordination of the vegetation data led to the recognition of six vegetation groups (floodplain, subalpine, Pinus contorta, Pseudotsuga, Thuja, Abies) and twenty-three community types. Data from the tree, sapling, seedling, shrub, herb and bryophyte-lichen strata were used. Vegetation groups are differentiated along macro-climatic and soil parent material gradients. The vegetation of the Pseudotsuga group, dominant inland, appears to respond to gradients of elevation and soil moisture. The Thuja group is found only near the coast, and its vegetation varies along gradients of soil nutrients and elevation; soil moisture having little effect. The vegetation patterns of the Abies group are correlated to elevation and soil moisture. Canonical variates analyses revealed a close relationship between vegetational and environmental patterns within most vegetation groups. A precipitation continentality gradient was identified as the major determinant of modal vegetation variation. Along this gradient, alpha and beta diversity increased towards the drier and more continental interior as predicted. Tree size-class distribution data indicate that Pseudotsuga menziesii is a seral species in most community types. The dominance of Thuja plicata near the coast may be maintained because of its longevity and, possibly, its wind damage resistance. Attention is drawn to the ecological mechanisms operating in coastal forests which have important implications for their successful management.Science, Faculty ofBotany, Department ofGraduat