UBC Theses and Dissertations
The relationships between the ecological site quality and the site index and stem form of red alder in southwestern B.C. Courtin, P. J.
Site, soil, tree form, vegetation and foliar data were collected from thirty-seven natural stands of red alder (Alnus rubra Bong.) from three biogeo climatic subzones on Vancouver Island and the adjacent mainland of British Columbia. Based on temperature and precipitation normals, three subzones of the Coastal Western Hemlock zone are suggested as being the most suitable for the growth of red alder. The results of quantitative analyses between different site variables indicate that a major factor accounting for the majority of variance in the data is soil reaction. When the stands were divided into two groups based on pH, the majority of variation in site index was explained for both soil and foliar nutrient variables. Other variables had weak correlations with site index. Soil morphological and physical data were not sufficient to predict site index, and the use of soil moisture and nutrient regimes as categorical variables in site index regressions gave insignificant results. Diagnostic criteria applied to the understory vegetation of the stands could not differentiate site classes nor were stands differentiated on the basis of soil reaction group which seemed to dominate the separation of both soil and foliar variables. This is due to red alder's N-fixing ability, which tends to promote species having nutrient rich indicative value regardless of site. Tentative vegetation associations are proposed but the irrecognition needs further testing. The relationship between four measures of tree form of red alder with other variable domains did not indicate meaningful results. The hypothesis that form of alder differs with site cannot be accepted based on these data. The synthesis of a qualitative site assessment for estimating the potential productivity of red alder was approached from the recognition of soil parent materials while incorporating soil physical and morphological properties already in use infield guides.
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