UBC Theses and Dissertations
Vegetation development on recent alpine glacier forelands in Garibaldi Park, British Columbia Fraser, Bruce Erland Clyde
This thesis attempts to devise a classification of ecosystematic units which reflect the rates, patterns and environmental determinants of plant community formation on recently deglaciated terrain. A series of three glacial valleys located in Garibaldi Park, approximately 60 miles east of Vancouver, British Columbia, and lying between elevations of 4800 and 5000 feet above sea level, were studied. The valleys lie in a transition area between coastal and interior biogeoclimatic zones and thus derive their pioneer flora from elements of the Coastal Subalpine Mountain Hemlock Zone, the Coastal Alpine Zone and the Interior Engelmann Spruce - Subalpine Fir Zone. Climate, geology and soil development in the three valleys were studied in order to provide an understanding of the macroenvironmental conditions under which the vegetations was developing. Temperature, humidity, and rainfall were measured for three field seasons (1965 through 1967) to determine the degree of climatic homogeneity of the study area, to examine the effect of glacial proximity on microclimate within the valleys and to establish a gross moisture balance for the growing season. Snow duration was noted for all vegetated sites. A brief description of the parent rocks contributing to the glacial till in the valleys is provided. The chronology of ice retreat in each valley is documented by growth ring analysis of trees established on differently aged surfaces and by reference to studies of synchronous glacial movements in western North America. Soil development was studied by chemical analysis of soil samples taken from pits associated with various plant communities. Changes in total nitrogen, organic matter, C:N ratio, cation exchange capacity and macronutrient cations have been noted with advancing substrate age and altered vegetation cover. Vegetation was sampled using 16 m² sample plots in which vegetation stratification, floristic composition and species abundance-dominance, sociability and vigour were estimated. A classification of ecosystematic units was then synthesized by grouping samples on the basis of overall floristic similarity, dominance by a characteristic combination of species and uniformity of ecotope. The phytosociological synthesis was compared with a cluster analysis of the sample plots using species presence and cover, a method which yielded a similar but not identical set of groups to the ecosystem units. A total of twelve ecosystem units was delimited representing a number of pathways in plant succession and ranging in age from 40 - 150 years since ice retreat. Detailed ecological relationships with the ecosystematic units have been determined from microenvironmental measurements, soil nutrient analyses, sap pressure studies, and autecological analyses associated with the original sample plots. Variations in soil moisture content, surface temperature extremes and snow duration were recorded and correlated with plant community development. Soil nutrient availability was determined for soil samples from pits within sample plots representing the various ecosystematic units. Apparatus and field methods were developed to monitor the diurnal variation of internal moisture stress for a number of successionally important species. Sap pressure, negative tension on the water stream in the xylem, was correlated with net radiation to the plants and atmospheric moisture deficits. A statistical comparison of sap pressure regimes and distribution of four Salix shows that their distribution into different ecosystem types is predictable from their mean sap pressures. For all species of significant coverage an autecological summary has been prepared from plot analysis records showing their modalities to hygrotope, snow duration and age of substrate since ice retreat. Climate, geology, substrate chronology, soil development, microenvironment, autecological relationships, and phytosociological units with their successional roles have been combined to provide a synecological summary for each ecosystematic unit. Maps of the glacial valleys are presented which show the actual distribution of individual communities within each unit.
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