Appendix A. Methods for creating current-observed, current-predicted, and future-predicted species distribution models for whitebark pine within British Columbia, Canada.
In 2006, species distribution models for whitebark pine within British Columbia were created by Tongli Wang (University of British Columbia, unpublished) using the climate-envelope modeling technique of Hamann and Wang (2006). The current-observed range for whitebark pine was determined using 479 presence observations from the botanical inventory used to create the BC Ministry of Forests and Range’s Biogeoclimatic Ecological Classification (BEC) system (Fig. 1a). The BEC system is a hierarchical classification system that divides BC’s landbase into 14 zones, 97 subzones and 152 variants based on vegetation, soil, climate and topography (Meidinger and Pojar, 1991). The variant level describes land units comprising relatively homogeneous ecological and geoclimatic features.
To create current-observed species ranges, Hamann and Wang (2006) extrapolated the occurrence data from one-dimensional observation points to two-dimensional BEC variant polygons, under the assumption that a species should be able to grow anywhere within a variant in which it is observed. Variant-level divisions had not been delineated for the alpine tundra BEC zone at the time that Hamann and Wang created the SDMs, so instead they created alpine tundra pseudo-variants based on geographic divisions between mountain ranges. High-elevation areas with permanent icefields were excluded, and polygons with low (< 1/100 of average) predicted species frequencies eliminated.
ClimateBC v3.1 (Wang et al., 2006) was then used to generate biologically-relevant normal (1961-1990) climate variables associated with whitebark pine’s current-observed range. ClimateBC interpolates weather station data using high-resolution digital elevation models that accurately capture climatic variance in BC’s mountainous terrain. Whitebark pine’s current-predicted range (Fig. 1b) was extrapolated by selecting all areas in the province with normal climate conditions in the range of those currently experienced by the species, accounting for climatic interactions. Future-predicted ranges for 2025, 2055 and 2085 were then projected using “middle of the road” (IS92a) Coupled Global Circulation Model ensemble mean (CGCM1 GAX) carbon scenarios developed by the Canadian Centre for Climate Modeling and Analysis (Flato et al., 2000, accessed using ClimateBC). Recently, whitebark pine’s present and future distributions were remodelled using a classification and regression-tree procedure called Random Forests, yielding broadly similar predictions (T. Wang, University of British Columbia, pers. comm.)
Flato, G. M., G. J. Boer, W. G. Lee, N. A. McFarlane, D. Ramsden, M. C. Reader, and A. J. Weaver (2000). The Canadian centre for climate modelling and analysis global coupled model and its climate. Climate Dynamics 16(6):451–467.
Hamann, A., and T. Wang (2006). Potential effects of climate change on ecosystem and tree species distribution in British Columbia. Ecology 87:2773–2786.
Meidinger, D., and J. Pojar (1991). Ecosystems of British Columbia. Special Report Series 6, B.C. Ministry of Forests and Range, Victoria, BC. B.C. Ministry of Forests and Range, Victoria.
Wang, T., A. Hamann, D. L. Spittlehouse, and S. N. Aitken (2006). Development of scale-free climate data for western Canada for use in resource management. International Journal of Climatology 26(3):383–397.