Ecological facets of plant species rarity in rock outcrop ecosystems of the Gulf Islands, British ColumbiaThis paper is one of a selection of papers published as part of the special Schofield Gedenkschrift.

Abstract

Rare plants and their habitats are integral to the conservation of biodiversity in many areas. With increasing habitat destruction and fragmentation, there is an urgent need to identify elements of diversity that are at risk, to adequately address conservation priorities, and successfully implement management strategies. In this research project, plant species rarity in rock outcrop ecosystems occurring on the Gulf Islands in southwestern British Columbia was examined at 13 study sites (3000 m2 area examined per site). Bryophytes comprised the largest portion of rare taxa; 18 of the 20 provincially rare taxa were mosses, including two species new to Canada. Challenges facing rare plant species conservation were considered from a landscape management perspective. Rock outcrops represent non-equilibrial, primary successional systems; some form of perpetual large-scale disturbance (e.g., climate and (or) grazing) may be integral to maintaining these ecosystems, their constituent habitats, and the occurrence of many rare moss species. In contrast with vascular plants, which are of focal concern in relatively deeper-soiled Garry oak meadows (i.e., native herbs and grasses), bryophytes have limited competitive ability. As such, the rare bryophytes of rock outcrop ecosystems are likely to be highly sensitive to successional development within sites (i.e., factors reducing the availability of early successional habitats) that may arise through land use modifications and (or) changes in local climatic conditions related to global warming.