Climate and vegetation change in Alaskan tundra.
Studies of tundra vegetation changes in recent decades have predicted an increase in the relative abundance of shrubs in response to climate warming. In contrast, a detailed analysis of a 20-year record of tundra vegetation structure and composition from a set of permanent monitoring plots at Toolik Lake and Imnavait Creek on the Alaskan North slope indicate a general increase in above ground biomass, occurring in several growth forms of vascular plants. Specifically, graminoids, herbaceous dicots, and shrubs all increased significantly in abundance (graminoids by 20%, herbaceous dicots by 19%, and shrubs by 12%). The overall proportion of graminoids and shrubs in the community shifted from 20% and 27% respectively in 1989 to 25% and 31% in 2008. Over the last two decades the relative abundance of vascular vegetation (grasses, herbs, shrubs) increased by 16% while the relative abundance of nonvascular vegetation (mosses) decreased by 18%. The height, extent, and complexity of the canopy have been increasing over time, with the landscape area covered by multiple layers of vegetation increasing from about 60% to 80%. The spread of canopy overstory represents a significant increase in above ground standing crop and a shift in carbon allocation to vascular plants vs. bryophytes. The increase in the abundance of vascular vegetation and in canopy height and complexity will likely affect snow redeposition because shrubs capture drifting snow. Shrubs and snowdrift should result in a deeper, looser snowpack that insulates soil surface layers, changing winter biological processes, nutrient allocation, and carbon cycling.