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Plant associations of the Cariboo - Aspen - Lodgepole pine - Douglas-Fir parkland zone Beil, Charles Edward

Abstract

The objectives of this study were to obtain quantitative and qualitative data on the vegetation and environmental factors of the Cariboo Zone and to synthesize these data into an ecosystematic classification. Sample plots were chosen selectively according to criteria based on uniformity and discreteness. Vegetation was studied using the phyto-sociological methods of the Zürich-Montpellier School. On all plots data were also obtained for edaphic and physiographic factors. Based on floristic composition and environmental data the 131 plots were synthesized into a flexible ecosystematic classification in which eight orders, twelve alliances, twenty associations and six subassociations were described. The order Pseudotsugetalia menziesii with three associations dominated most of the forested areas, occurring on subhygric to subxeric habitats. The order Piceetalia glaucae with three associations occurred only marginally; always on subhygric to subhydric habitats. The order Koelerio -Agropyretalia spicati with eight associations dominated the grassland areas, occurring on fine textured soils of aeolian origin. The order Puccinellietalia airoidis with two associations dominated the saline-alkaline habitats. The orders Betuletalia glandulosae, Salicetalia, Scirpetalia validi, and Caricetalia rostratae were represented by single associations of restricted distributions. Soils representative of all six orders of the Canadian Soil Classification system were distinguished with Chernozemic and Brunizolic soils the most common. Melanization appeared to be the dominant soil-forming process and the soils were generally rich having high cation exchange capacities, high amounts of exchangeable cations and alkaline reactions. An examination of the population structures of the major tree species showed that Pseudotsuga menziesii had the widest amplitude and formed the climax forest cover over much of the Cariboo Zone. Picea glauca had a narrower amplitude and Pinus contorta and Populus tremuloides reached dominance only as pioneer species. Selected ecosystem units were characterized microclimatically. The Agropyrion spicati occupied microclimatically warm areas while the floristically related Stipion columbianae was present in areas with a cool microclimate. The Antennario - Poetum secundae and Stipetum richardsonii, although bordering associations, occupied microclimately distinct habitats. Forest communities were shown to develop at higher elevations where a cool microclimate prevails. Based on species significance data, plots were objectively grouped by the weighted-pair-group and the weighted-variable-group methods of cluster analysis. The resulting hierarchical arrangements of plots paralleled very closely the subjectively derived ecosystematic classification. On the dendrogram obtained by the weighted-variable-group method, associations were distinguished and their degree of homogeniety and ecological relationships were demonstrated. The forest-grassland boundary in the Cariboo Zone was assessed to be relatively stable and to be controlled by available soil moisture as related to soil texture. It was apparent though, that minor fluctuations in the boundary as a result of grazing and fire occur. Detailed topographic relationships of the associations were demonstrated and it was apparent that topography, which represents a complex of physiographic factors, is important in controlling the distribution of associations. Successional changes appeared to be operating at a slow rate and thus most of the associations described were in a stable condition. The Agropyretum spicati most closely approximated the climatic climax association, occurring on ridges and slopes. Other stable associations were rated as edaphic or topographic climaxes. The successional relationships of the associations were demonstrated within a monoclimax concept in which it was assumed that ultimately all associations would change into the climax as a result of soil weathering and peneplanation of the land. It was concluded that the gynecological approach and classification methods used allowed the presentation of data in an ecosystematic format which could be directly applied to range or forest management but could also serve as a basis for more detailed scientific studies.

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