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Community and regional scale patterns of native and exotic plant species in sand beaches of Vancouver Island, British Columbia Page, Nicholas Alexander

Abstract

I compared the distribution and abundance of native and exotic plant species at two spatial scales using vegetation data from eighteen beaches on the west coast of Vancouver Island, BC. I found that native and exotic plant species have similar patterns of distribution and abundance at both community and regional scales. This suggests that despite some biological differences between native and exotic species they share common ecological patterns. Within sand beach plant communities, I found that spatial patterns of native and exotic plant species richness were similar; both were low near the shore, reached a maximum approximately 50 m inland, and then declined in the dunes behind. The results support the generalization that increased invasibility from exotic species is associated with sites of high native species richness within plant communities. This pattern is a major conservation concern because it indicates that sites with the highest biological diversity are at the greatest risk from exotic species invasion. Native and exotic species richness peaked in plots with the most fertile soils. At a regional scale, native and exotic plant species also have similar ecological patterns. Regional distribution-local abundance relationships, which were analyzed using data from sand beaches together with seven other plant communities, for native and exotic plants species in regional patch networks were statistically coincident or similar. As well, the proportions of native and exotic species in patch occupancy classes were statistically equal in all regional patch networks. Most native and exotic species were both regionally rare and locally sparse. Collectively, the results indicate that the distribution and abundance of native and exotic plant species are not independent at a regional scale. I also described and named seven sand beach plant associations from the west coast of Vancouver Island: 1) Cakile edentula - Atriplex gmelinii Sparse Vegetation; 2) Leymus mollis spp. mollis - Lathyrus japonicus Herbaceous Vegetation; 3) Festuca rubra - Fragaria chiloensis Herbaceous Vegetation; 4) Ammophila arenaria Herbaceous Vegetation; 5) Arctostaphylos uva-ursi Dwarf Shrubland; 6) Eurhynchium oreganum / Gaultheria shallon Shrubland; and, 7) Poa macrantha Sparse Vegetation. All are of potential conservation concern because the limited development of beach vegetation in coastal British Columbia.

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