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Vegetation-environment relationships of sub-boreal spruce zone ecosystems in British Columbia Wali, Mohan Kishen

Abstract

An environmental study using the association concept and the 'ecological groups' within the biogeoclimatic zonal framework was conducted in the Sub-Boreal spruce zone in British Colimbia [sic]. Quantitative information on the vegetation and environment of the zone has, hitherto, been lacking. Seventy seven stands have been studied. From the six upland associations, delimited by the methods of Zurich-Montpellier School using Domin-Krajina scale, soils from seventeen different Soil Great Groups have been distinguished and described. The relation between vegetation and soil morphology are obvious at the zonal and association levels but are less distinct at lower levels. Based on fourteen sample plots, four low moor associations on nine Mesisols, four Fibrisols and one Humisol are also described. Microclimatic data, air and soil temperatures, humidity, precipitation and snow cover have been recorded from five stands that differed in canopy density, ground cover, species composition, in soil conditions and topography. Air and soil temperature patterns show a remarkable similarity. Diurnal temperature fluctuations are most pronounced under Pinetum contortae while such fluctuations are much less under Alnetum tenuifoliae and Piceetum glaucae. Chemical analyses of 280 soil samples include a wide range of both macro- and micronutrients as well as some toxic heavy metals. Analyses involved water soluble and replaceable major cations, total nitrogen and available phosphorus, and water soluble, replaceable, EDTA- and HCl-extractable trace metals. The soils under white spruce-devil's club and river alder-ostrich fern are the richest in both macro- and micronutrients, followed by aspen and black spruce. Seemingly soils of the black spruce sites sampled show a high nutrient content but it looks doubtful if all these are readily available because of impeded drainage and low base saturation. From the study of the sites, nutritional requirements of subalpine fir appear to be high and those of lodgepole pine very low. Neither the chemical characteristics of the low moor organic soils nor the water chemistry seem to show any distinct relationship with the vegetation of these sites. Using multiple regression analyses eight statistically significant environmental gradients have been used in the study. The soil texture gradient is based on the weighted averages of the sum of percentage silt and clay content calculated for the rooting depth. The water gradient has been established on the available water capacity expressed as a percentage of the rooting volume of the soil. Five nutrient gradients have been established. The calcium and magnesium gradients are based on the replaceable content expressed as equivalents per square meter of the soil rooting volume. Nitrogen gradient based on total nitrogen analysis are expressed as grams per square meter of the rooting volume. Gradients based on EDTA-extractable manganese and iron are expressed the same way as nitrogen. The light gradient is based on observations from fiftyeight plots, extended over a period of two years, using a chemical light meter. All gradients are quantified and the correlations of associations along these gradients are shown. Of all the gradients considered in the study, plant communities showed better correlations with soil texture, water and replaceable calcium. Using relative species significance rather than presence, distributional patterns of individual species along these gradients have been illustrated. Predictive equations based on regression analyses using both transformed measured values and their logarithms have been given for a number of plant species.

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