GLOBAL CHANGE AND BRITISH COLUMBIA NATIVE FLORA Richard Hebda Botany Unit Royal British Columbia Museum Victoria, B.C. V8V 1X4 Presented at the "British Columbia Native Plants, their current Status and Future Colloquium at Botany Dept., University of British Columbia, May 12, 1990 ****************************************************************************** Abstract The profound climatic and physical changes predicted as a result of the "greenhouse effect" may have major impact on British Columbia's vascular plants and vegetation. Potential warming of 2ūC-4ūC, reduction of summer soil moisture by 30-40%, and a rising seal level from 0.5-1.5m could strongly alter or eliminate major vegetation types and lead to expansion or shrinking of species ranges and in extreme cases extirpation of species. The relatively warm and dry interval between 10,000 and 6,000 years ago provides an analog for predicting the impact and global warming. Alpine zones may shrink significantly as timberline rises possibly as much as 100-200 m. Species areas will be reduced, populations will become isolated, and some species may be lost. Small alpine and subalpine patches in the south are at greatest risk. Wetlands will change in character, and shrink. Hydrological gradients will change and there may be a shift from acidic bog-wetlands and species to neutral or even alkaline fens and marshes and species. Demand for water by people will increase and further stress wetland habitats. Major vegetation adjustments will occur in the dry interior where grassland communities may expand up-slope and northward. Grassland area may increase 400%, and grassland communities may become vertically differentiated. Arid habitat species, including rare taxa, may become more abundant and widespread providing there are migration corridors. Sea levels will rise and drown estuaries. The size of confined estuaries will be severely reduced and rare species may disappear. Forest composition and extent will change as species respond individually and re-assemble into new forest types. Weedy, adventive species will likely expand and become permanent elements of new vegetation types. In general, impacts on plant populations will likely be sudden, precipitated by extremes of climate. Recommendations include: 1. a long-term project to inventory, study the biology of, and monitor the flora, especially rare species, 2. protection of populations and areas of concentration of rare plants as reservoirs of raw material for future vegetation types, 3. Conservation of ecological gradients for future dispersal. 4. Paleoecological studies to provide predictive data. Introduction The richest, vascular flora in Canada, that of the province of British Columbia, comprising about 2 500 species (Straley et al. 1985) may be at great risk. In the next 50-100 years the profound climatic and physical changes predicted by many experts as a result of the "Greenhouse Effect" can be expected to significantly affect this native flora. In this paper, I will briefly outline the expected climatic and physical changes resulting from anticipated global warming, and how these might directly impact the native flora. I will focus on four major ecosystems liable to change dramatically: the alpine (cf. Alpine Tundra Biogeoclimatic Zone of Krajima et al. 1982); wetlands; interior grassland and sagelands (cf. Ponderosa Pine Biogeoclimatic Zone and Bunchgrass Biogeoclimatic Zone; Research Branch 1988) and marine shoreline vegetation. I will note some rare or threatened species potentially at risk. Then I will propose some future strategies to soften the potential impact of global change on the native flora.