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Phytogeocoenoses of the coastal western Hemlock zone in Strathcona Provincial Park, British Columbia, Canada Kojima, Satoru

Abstract

A vegetation-environmental relationships study, based on the concept and approach of biogeoclimatology established and developed by Krajina and his students, was conducted in Strathcona Provincial Park, British Columbia, where the vegetation showed special ecosystematic peculiarities resulting from a unique geological substratum. The purposes of the present study were, therefore, 1) to clasisify the vegetation in the park according to the methods of the Zurich -Montpellier school as modified by Krajina, 2) to analyze as many environmental factors as possible, 3) to correlate the environmental factors with the plant communities at the association level, and 4) to discover the factors that contribute conspicuously to the development of the vegetation units. A total of ninety-nine plots were established to represent the phytogeocoenoses. These plots were later grouped into associations according to their floristic homogeneity and environmental similarity. In the study area, four orders, eight alliances and eight associations with three variants were established and described. In order to obtain general information concerning climate in the study area, three weather stations and ten rain gauges were installed and maintained for the summers of 1968 and 1969. Several pebbles were identified from each plot. They were found to be predominantly basalt and its allies, and the whole area was geologically fairly homogeneous. A total of 377 soil samples were analyzed for physical and chemical properties such as soil texture, field moisture, field capacity, cation exchange capacity, exchangeable cations (Ca, Mg, Na and K), total nitrogen, carbon content, available phosphorus, and pH. Some selected samples were analyzed for iron and aluminum. Soils were generally coarse in texture; most of the soils were found to be loamy sand while some were sand and sandy loam. They were especially high in base status, reflecting the influences of the base-rich parent material. Thus, most of the soils examined were found to be Brunisols which were equivalent to "pararendzina" soils (sensu Kubiena 1953). In spite of high precipitation, Podzols were rather rare. To the environmental factors which had been measured and estimated quantitatively, one way analysis of variance was applied to detect significant differences among the five forested associations. Of twenty-two factors taken into consideration, fourteen factors were found to be significant at the 1% level, one factor at the 5% level, and seven factors were not significant. Duncan's new multiple range test was applied to the factors which were significant either at the 1% or 5% level, and the associations were grouped and ranked using the result of this test. The factors most influential on the development of the associations were selected by the multiple regression analysis. The twenty-two factors were treated as independent variables, while vegetation was processed as a dependent variable. In order to quantify the vegetation, "likeliness value" was devised and used. It is a numerical assessment signifying how likely a plot is to be a member of a certain association, based on the species significance of some selected species. A species constellation involving fifty-five species was constructed based on the Chi-square test and Cole's indices. Three assemblies of species were detected, which characterized 1) xeric and mesic habitats of the drier subzone (CWHa) as well as xeric habitats of the wetter subzone (CWHb), 2) seepage habitats of both subzones, and 3) mesic habitats of the wetter subzone. In conclusion, it became apparent that the uniqueness and complexities of the vegetation in the study area rested in the considerable intermingling of species of quite different ecological character resulting from the high base status of the soils. Because of base rich edaphic conditions, some of the calciphiles commonly occur free from their normally hygrotopic restriction. At the same time, a considerable number of acido-philes grow on humus, supported by the mor humus which is already very acid due to the strong leaching by rain water. This kind of double structure makes the vegetation particularly complex and consequently more difficult to understand. Such an understanding, however, has been made possible, using the procedures followed in the present thesis.

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