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Soils of three grassland-forest ecotones north of Kamloops, British Columbia Jakoy, Andrew Geza

Abstract

Soils and vegetation of a grassland - forest ecotone north of Kamloops, British Columbia, were studied on three systematically selected transects. This investigation was to determine the pedogenesis and taxonomy of these transitional soils and to check the stability of the grassland - forest boundary. The transects ranged in length of 1.0, 0.8 and 0.4 km, and the elevation ranged from 740 to 890, from 900 to 1000 and from 920 to 940 m respectively. Along the three transects fourteen pedons were sampled. The soil climatic subclasses ranged from cool-subarid to cold-subhumid throughout the area, depending on elevation and physiographic location. The associated vegetation was Agropyron - (Artemesia) grassland and Pinus ponderosa - (Pseudotsuga menziesii) savanna - like forest at 740 to 890 m elevations. The vegetation, at 900 to 1000m elevation, was Agropyron - Festuca - (Stipa) grassland, bordering Pseudotsuga menziesii park-like forest. Physical analyses of soil samples determined particle size, including fine clays and moisture retention for all sampled horizons. Mineralogy of < 2.0 μm clays was checked by X-ray diffraction. Chemical analyses determined soil reation, organic carbon contents, carbon/nitrogen ratios, exchangeable cations and total base saturations for each sampled horizon. Organic fractions of nine selected Ah horizons were analyzed for humic, fulvic acid contents and absorption spectra between 400 and 700 μm. Micromorphology of the Bm(Bt) horizons of each pedon was analyzed to detect clay illuviation. Phytolith contents and grass species composition of silt extracts of nine sola were examined to find correlation with past vegetations. No forest influence was detected in the present grassland areas established on compacted or on locally dry, ice-disintegration moraines. These grasslands have orthic subgroups of Dark Brown and Black soils. At the present forest edge, a tension zone exists where scattered ponderosa pines and Douglas-firs may encroach upon the grasslands having Ghernozemic soils of low bulk density, at elevations between 820 - 850 m. At elevations of 900 - 930 m, aspen groves occupy Orthic Ghernozemic soils in depressions. Forests of ponderosa pine and Douglas-fir occupy slopes steeper than 20° above 850 to 900 m on colluvium. All-aged Douglas-fir forests occupy morainal materials above 930 m on stable surfaces. The soils of these forests are Eutric and Melanic Brunisols.

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