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Edaphic aspects of an ecological classification of the Interior Western Hemlock dry Subzone forests of British Columbia. Smith, Richard Barrie

Abstract

Edaphic information from 168 plots in the Interior Western Hemlock (Tsuga heterophylla (Raf.) Sarg.) Dry Subzone of southeastern British Columbia was used to describe soils and to elucidate some relationships concerning soils and soil-forming factors, and soil and vegetation. Characteristics described from soil pits in each plot included thickness, depth and boundary of horizons, soil texture, structure, consistence and mottling. Color and pH were determined on 1,100 soil samples. In addition, 450 samples from 70 selected profiles were chosen for analysis of exchangeable calcium, magnesium, potassium, and sodium, adsorbed phosphate, total nitrogen, cation exchange capacity, organic carbon and calcium carbonate equivalence. Rock samples were collected and identified to aid in the determination of the nature of the parent material. Seepage water from 40 plots was analysed for calcium, magnesium and potassium content. Observations on physiography, relief, exposure, elevation, slope, drainage and erosion were recorded for each plot. Ninety Colman Fiberglas units were established in 15 plots to determine soil moisture and temperature trends. An estimation of biological activity in 15 plots was made using the loss in breaking strength of cotton duck as the criterion. Nineteen soil monoliths were prepared and over 70 color photographs taken for illustrative and comparative purposes. Soil classification generally followed current Canadian practices to the sub-group level. Certain profiles were found difficult to classify at the sub-group level. These, however, were placed in sub-groups resembling them most closely. Further subdivisions, based mainly on moisture and surface soil conditions and reflecting productivity, were formed by prefixing terms to some of the sub-group names (e.g. Dry Orthic Brown Wooded, I Normal Minimal Podzol, Moist Orthic Podzol). Of the 29 soils distinguished, the Normal Orthic Podzol, Ortstein Podzol, and I Normal Minimal Podzol were considered to represent the zonal soils of the sub-zone. These soils were oligotrophic (base saturations of B generally less than 20 per cent), and were characterized by a felty mor humus, conspicuous Ae, and a bright yellowish brown B, all of which reflected the dominant soil-forming process of the area which is podzolization. Departures from the zonal pattern, however, were numerous. Dry soils tended to have a thin F-H layer and a thin, discontinuous or absent Ae, Seepage influences ranged from an increase of exchangeable bases and humus friability in Moist Orthic and Minimal Podzols, to a build-up (over 30 cm) of organic material in Shallow and Deep Mucks. Soils such as the Dry and Normal Orthic Brown Woodeds, characterized by the absence of Ae and a base saturation generally over 50 per cent, were associated with parent materials rich in calcium especially in dry topoclimates. Where both calcareous parent material and seepage combined, soils most unlike the zonal were produced (e.g. Calcareous Duff Mull Regosol). Podzolization was less effective on steep slopes especially in warm topoclimatic situations. It reached its maximum (Ortstein Podzol) on neutral or slightly concave relief of gentle to moderate inclination, or on coarse, old, excessively drained alluvium or outwash. Brunisolic soils seldom occurred on alluvium or outwash, while strongly podzolized soils were rare in areas underlain by bedrock of the Lardeau series, Sinemurian beds and Rossland formation, or the eastern portion of the Slocan group. Seepage from pits in the vicinity of Lardeau and Slocan bedrock was higher in calcium and magnesium than seepage from other locations. Statistically significant differences occurred between sites in estimated biological activity. Moist and extremely dry sites showed high activity compared to intermediate, well-drained sites with more strongly podzolized soils. A classification of soils by moisture supply (hygrotope) and chemical characteristics (trophotope) was suggested. Associations and ecosytem types determined by an independent investigator from phytocoenotic and general environmental data corresponded fairly closely to the nature of the soil. The correspondence was, however, less apparent in moist than in dry and wet sites.

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