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Vegetational and environmental variations in the ecosystems of the coastal western hemlock zone Orlóci, László

Abstract

This thesis describes the biogeoclimatic zones on the southwestern British Columbia mainland and gives a detailed analysis of the vegetation-environmental patterns within the Coastal western hemlock zone. Ecosystem classifications are proposed utilizing coordination techniques and stratification. The major underlying causes of variations in the floristic structure among individual ecosystems are identified by four environmental gradients: regional climate, parent material, local climate (exposure), and soil-moisture regime. The orographic influence of Vancouver Island and the Coast Mountains results in a regional climatic gradient from low to high elevations. Natural segments of this gradient, recognized on the basis of zonal (climatic climax) vegetation and mesic soils, constitute the biogeoclimatic zones and subzones. Land types are separated from within the Coastal western hemlock zone on the basis of parent materials. The rock outcrop land type includes a mosaic of peaks, knolls, and crevices characterized by a coincident pattern of the vegetation types. All glacial drift deposits, except those of the swampy habitats, belong to the glacial drift land type. Maximum floristic variations in the glacial drift land type occur along a soil-moisture gradient. A lesser variation in the floristic structure is attributed to a local climatic gradient from cool to warm exposure. These gradients signify different sets of vegetation types in the different subzones of the Coastal western hemlock zone. The spring-water swamp land type includes waterlogged mineral soils and waterlogged woody peats in the vicinity of spring lines. The vegetation of the spring-water swamps has remarkable uniformity throughout both subzones. Narrow valley-like depressions with permanent or semipermanent streamlets and intermittent overflow water constitute the ravine alluvial land type. The vegetation of the ravines shows little variation among the two subzones. The flood-plain communities of the Squamish alluvial plain land type reflect the influence of overflow water and post-flood drainage. The basic unit of classification used is the ecosystem type, a segment in a simple vegetation-environmental gradient. A vegetation-environmental gradient is simple if it consists of a single set of vegetation types along an environmental gradient. Ecosystem type mapping involved approximately 85 acres in the southwestern part of the University of British Columbia Research Forest; a map is enclosed (in the thesis).

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