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UBC Theses and Dissertations

Soils and forest growth in the Sayward Forest, British Columbia Keser, Nurettin

Abstract

The sustained-yield policy presently practiced in British Columbia necessitates intensive management of forest land especially in the coastal region of the province. Soils, their nature and distribution, provide an ideal framework for a successful implementation of such management. A mapping system encompassing geology and soil and providing units interpretable for forestry practices was developed for the coastal forested lands of British Columbia. The system contains several steps of mappings corresponding to different intensities or levels of abstraction. These levels are: 1. Bedrock geology, 2. Surficial geology, 3. Geologic units, 4. Geologic unit - drainage classes, 5. Soil associations, and 6. Soil catenas. Mapping employs air-photo interpretation extensively and can be directly undertaken at any desired level for inventory of interpretation purposes. Grouping of units can also be made from any level of mapping. Maps showing the distribution of bedrock types, surficial materials and soils were prepared. Vancouver volcanics, Coastal intrusives and Cretaceous sandstones are the main bedrock formations. The surficial materials encompass the inter-glacial, glacial, post glacial and recent deposits, and consist of glacial tills, glaciofluvial, alluvial and marine sediments. The soils encountered represent the Podzolic, Brunisolic, Regosolic, Gleysolic and Organic Orders. The area is comprised of primarily Douglas-fir plantation, 20 to 30 years of age. Studies involving the soil-stand growth relationship were undertaken on the well drained soils developed on the major surficial materials. Morphological, physical, chemical and minera1ogica1 characteristics of soils and the growth statistics of stands were determined. The growth performance of Douglas-fir varied with the kind of soil. Growth was best on soils developed from marine clay. Soils developed from stony outwash exhibited the slowest growth and lowest productivity. Till soils had productivity between these two extremes. The textural components of soil (coarse sand, medium sand, total sand, total silt, coarse clay, fine clay and total clay), were correlated to growth. With respect to chemical nutrients, organic matter, calcium and magnesium, phosphorus and zinc appeared to be important factors. The soil moisture retention characteristics such as field capacity and available water showed correlation with growth. The relationship between the growth and soil characteristics became more apparent as stand age advanced. Interpretation of soil series and mapping units at different levels was carried out for: productivity for Douglas-fir, species suitability, logging hazard, slash burning hazard, natural regeneration probabi1ity, brush hazard, browsing hazard, thinning prescription, fertilizer recommendation, road construction suitability, and erosion. Two groupings, potential productivity and thinning recommendation for Douglas-fir, were undertaken. The study indicated that knowledge of soils and their distribution are prerequisite to the operational and economical management of forest and soil resources. Consequently, a classification scheme such as the one presented is the first and essential step towards the intensive management of the coastal forested lands in British Columbia.

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