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Multivariate analysis of terrestrial bryophyte-habitat relationships in a subalpine forest of coastal British Columbia Sadler, Kella Darleen

Abstract

This thesis had two general objectives: to describe the patterns of distribution and abundance of terrestrial bryophytes in old growth subalpine forests at two study areas (Cypress and Mt. Seymour Provincial Parks) in southern coastal British Columbia, and to determine the scale at which environmental factors influence these patterns. Using principal components analyses, it was demonstrated that regional scale ("biogeographical") plant associations correspond only weakly to the patterns of distribution and abundance of terrestrial bryophytes. Thus, bryophytes may "sense" the environment differently than is the case with vascular plants, i.e. their distribution may be more related to microclimate characteristics. Patterns of bryophyte diversity and abundance were examined at the scale of 20m x 20m study plots using canonical correlation analysis and Pearson correlation coefficients. At this scale, bryophyte diversity and coverage were found to be positively correlated with variables relating to increased light availability. Plots with a northern aspect, reduced canopy coverage, more abundant vascular vegetation, lower abundance of woody debris, and lower LFH depth and organic matter content were associated with higher bryophyte diversity and abundance. The microscale (i.e. 0.1m² microplots) environmental preferences of individual bryophyte species were examined using Pearson correlation coefficients, and by examining the range of microhabitat conditions in which species were noted to occur. Species in open habitats exhibited narrower ranges of soil surface layer (LFH) characteristics (pH, C:N ratios) than those in closed habitats, possibly because of greater flux in soil surface conditions (e.g. litterfall) in closed sites. The substratum affinities of bryophytes were examined using their microscale frequencies on available substrata. To investigate the combined influence of substratum and microhabitat, the species associations on different substratum types were investigated using principal components analysis. Microscale features (environment and/or substratum) were found to be closely related to the distributions of some bryophyte species. Assemblages on fine litter and woody debris in open, "stable" habitats with abundant bryophytes and vascular plants differed from those in closed-canopy, steeper, "unstable" habitats with lower bryophyte and vegetation cover. Bryophyte assemblages occurring on exposed humus and creeping stems were most closely related to the availability of the substratum types. The relationship of bryophyte species to stable and dynamic types of microenvironments was investigated using logistic regression. Bryophytes associated with unstable environments (i.e. dynamic surface layer) had a more random distribution than species that were associated with open, stable habitats, or that displayed strong substratum affinities. The physiological tolerance of species for microhabitat features (environment and/or substratum), and the degree of microhabitat stability seem to play important roles in determining the structure and dynamics of terrestrial bryophyte vegetation.

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