This study is designed to distinguish the relative roles of climatic factors and soil properties in determining the outcome of competition among tree and grassland species at the borders of subalpine meadows in mountain regions of the southwestern US. The investigators will conduct observational studies along natural environmental gradients and will perform field experiments to distinguish the effects of cold air drainage vs. soil fertility on tree seedling survival and competition with grasses. They will also develop historical reconstructions of landscape dynamics to complement the gradient and experimental studies. The project results could help to explain historical trends in tree-line (grassland-woodland boundaries) migration in relation to land use practices and climate.
