Structural – compositional variation in three age-classes of temperate rainforests in southern coastal British Columbia

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Abstract
Relationships between forest structure and species composition were examined in three age-classes of temperate rain forest in southern coastal British Columbia. Old forests (> 250 years) exhibited greater structural and compositional heterogeneity than young (31–60 years) and mature (61–80 years) forests. Size-class distributions of living and dead standing trees in the three age groups suggested both qualitative and quantitative differences in regeneration and mortality processes. The canonical correlation between structure and composition was high (Rc = 0.84), but a substantial amount of total variation remained unexplained by the analysis. Principal component analysis (PCA) axis 1 of species composition separated the lower elevation (warmer and drier) mature forests from the higher elevation (cooler and wetter) young and old forests. PCA axis 1 of structure separated the young and mature forests as a group from the old forests. PCAs of the separate age-classes indicated weaker compositional – structural linkages than with all age-classes combined. Study area differences explained greater proportions of variation in young and mature forests (up to 53%) than in old forests (< 10%). The results indicate a slow recovery process following impacts from human disturbance in coastal forests. Key words: canonical correlation analysis, old-growth temperate rain forest, principal component analysis, species composition, forest structure.