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Vegetation ecology of rock outcrop ecosystems of the Gulf Islands in the Coastal Douglas-fir zone, British Columbia Sadler, Kella Darleen

Abstract

Rock outcrop ecosystems of the Gulf Islands in the Coastal Douglas-fir (CDF) biogeoclimatic zone of British Columbia were investigated at multiple scales with the following objectives: (1) to refine distribution information for constituent species, (2) to investigate landscape (i.e. site-level) features that influence the patterning of native and introduced plant species of rock outcrop habitats, including (a) geographic position (latitude), (b) geology (rock type), and (c) grazing intensity, (3) to integrate vegetation patterns observed at each sampling scale (site, plot, microplot) to derive a classification scheme for rock outcrop vegetation, and (4) to interpret rock outcrop ecosystem dynamics and address conservation and management implications. A total of 311 plant species were identified from inventoried sites. The majority of plant taxa in rock outcrop ecosystems were herbs and bryophytes, and most of the rare species were mosses. Each landscape feature was associated with unique patterns of coverage and richness for different life form groups (studied by origin and rarity ranking). Uncommon bryophyte species richness was higher in southern sites where exotic vascular species coverage was highest. In contrast, the coverage and richness of native and uncommon graminoids was higher in northern sites. The overall richness of native herbs, and the richness of uncommon herbs was greatest in sedimentary rock sites, where exotic species also had greater coverage and richness. Ungrazed sites showed higher vascular plant species richness, whereas intensely grazed sites revealed higher bryophyte coverage, and greater richness of rare bryophytes. Sequential principal component analyses were used to classify vegetation and characterize scale-related vegetation-habitat relationships. Three major landscape categories were identified, based on the primary environmental gradients found to influence large-scale vegetation patterns: meta-igneous rock sites >49°N (META-N), meta-igneous rock sites

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