UBC Theses and Dissertations
Vegetational composition and regeneration in three forest associations after logging in the coastal Western Hemlock zone Houseknecht, Stephan J.
The study was initiated to determine the composition and structure of vegetation and natural tree regeneration invading logged areas within three major forest associations that were subjected to different site treatments in coastal British Columbia. To accomplish the above objectives, 50 one-fortieth acre plots were established in logged areas ranging in age from 2 to 14 years following logging and the accompanying site treatment. The number of trees per acre by height class, rooting substratum of the coniferous trees, and qualitative coverage estimates of the trees, shrubs, herbs and mosses encountered on each plot were sampled. These data were grouped into associations and analyzed using the relevé method for the vegetation arid analysis of variance to assess the role of natural regeneration in each association and treatment class. Distance to the seed source and the type of seed source were measured to provide adjacent stand information. Environmental parameters such as slope, aspect, topographic position, seedbed type, parent material and depth, and altitude were measured to determine their significance in forming each association and their effect on natural regeneration. The results of the study indicate that the three forest associations are identifiable in the early stages of secondary succession. The identification of the sword-fern - western redcedar and salal - Douglas-fir associations was possible from vegetation characteristics alone. Identification of the moss - western hemlock association necessitated the use of physiographic position, soil depth, and vegetation. Structurally, all associations contained the same average total cover, but differed considerably in species composition and layer dominance. The salal - Douglas-fir association had a very well developed shrub layer dominated by a low cover of Gaultheria shallons a well developed moss layer, dominated by Hylocomium splendens, and a poorly developed herb layer. The moss - western hemlock association followed a similar trend. The swordfern - western redcedar association was characterized by a well developed shrub layer dominated by Rubus spectabilis, a herb layer that was well-developed both in species composition and cover, and a poorly developed moss layer. It was found that factors such as the degree of disturbance, spacing of the planted trees, age, and parent material caused changes in structure and species composition within each association and between associations. In addition, site treatment, especially slashburning, affected the species composition by eliminating many of the low growing indicator species normally found in an association that had had no treatment. Slashburning decreased the number of species in the salal - Douglas-fir association the greatest, while in the swordfern - western redcedar association, this reduction was of a lesser extent. The results of the statistical analysis indicate that associations coupled with site treatment are more important in determining the number and species of coniferous trees invading a logged site than the association type. Coniferous trees preferred the salal - Douglas-fir and moss -western hemlock associations that had no treatment or were piled and burned. Douglas-fir, western hemlock, and western redcedar were all decreased in numbers by slashburning. The regeneration of deciduous trees was found to be more strongly controlled by the association type. The swordfern - western redcedar association was the favoured association. All coniferous species preferred a mineral soil seedbed for germination, however, survival was low except for Douglas-fir. Western hemlock preferred a decaying wood substratum and western redcedar was found most often on rapidly decomposing organic matter in moist pockets. The study indicated that an adequate number of coniferous trees existed in all associations and site treatments according to normal restocking standards. Western hemlock was the dominant tree species and generally occurred in an uneven clumped pattern. Douglas-fir and western redcedar were relatively poorly stocked in all associations and site treatment classes. Indications are that supplemental planting of Douglas-fir would be needed to reach a desirable level of stocking of Douglas-fir in all associations studied.
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