Hemispheric- and Continental-Scale Patterns of Similarity in Mountain Tundra

Understanding the full range of biodiversity patterns from local to global scales, through the study of the drivers of multiscale plant community composition and diversity, is a current goal of biogeography. A synthetic understanding of to what extent vegetation compositional patterns are produced by biotic factors, geography, or climate and how these patterns vary across scales is needed. This lack hinders prediction of the effects of climate change in global vegetation. Variation in community composition is examined in relation to climatic difference and geographic distance at hemispheric and continental scales. Vascular plants and bryophytes in thirteen mountain regions were analyzed: eight in Europe and five in North America, nine midlatitude and four oroarctic. Species composition differed between continents and between oroarctic and midlatitude regions. Patterns of paired regional similarity with distance were significant for all pairs and intercontinental pairs but not for those within Europe and North America. Climatic variables accounted for most of the variance in vegetation patterns revealed by general linear models of ordinations, but geographic variables of Moran eigenvectors and latitudinal zones were also important and significant. The effects of geography were typically twice as strong for vascular plants as for bryophytes. The importance of geography at these scales suggests that past evolutionary and ecological processes are as important as current fit to any climatic niche. Interpretation of observations of the impacts of global climate change should recognize geographic context and phylogeny, and policies to mitigate them, such as assisted migration, should be cautious. Key Words: Alpine, beta diversity, climate, distance, oroarctic.