Relationships among forest strata and environment in southern coastal British Columbia

Abstract

Data from coastal forests on west-central Vancouver Island were used to examine correlations between compositional variation in six forest strata among themselves (trees, saplings, tree seedlings, shrubs, herbs, and bryophytes) and with site environmental variables. These relationships were examined with data from three geographical areas: (i) a dry inland area dominated by Pseudotsugamenziesii, (ii) a wet coastal area dominated by Thujaplicata, and (iii) the entire study area including a few sites dominated by Abiesamabilis. Principal component analysis was used to summarize the main compositional variation within the strata of each of the three areas. Canonical correlation analysis was then used to assess the degree of correlation among strata, as well as between strata and several environmental variables. Patterns of correlation among strata differed in the three geographical areas analysed. The most strongly correlated strata were commonly associated with similar environmental factors, although the total variance in the data explained by the correlations was low (< 18%). Strata growing on rotting logs, in many parts of the study area (saplings, tree seedlings, shrubs, and bryophytes), tend to be highly intercorrelated. These same strata are weakly correlated with the herb stratum, which does not occur on rotting logs.