The effects of terrestrial ecosystems on the climate system have received most attention in tropical forests, where extensive deforestation and burning have released carbon to the atmosphere, altered atmospheric chemistry, and may warm temperatures and decrease precipitation. Land-atmosphere interactions may also be important in arctic and sub-arctic regions. Much of this interest is related to the release of large soil carbon pools to the atmosphere with a warmer, drier climate. However, biophysical land-atmosphere interactions may be as important as these biogeochemical interactions. By masking the high albedo of snow and through the partitioning of net radiation into sensible and latent heat, boreal forests significantly warm climate (in some months and some regions by more than 5C to 10C) compared to climate model simulations in which the boreal forest is replaced with bare ground or tundra vegetation. This winter and spring warming extends into the summer because of oceanic influences.
This means that large-scale past and future geographic changes in the location of treeline can result in significant climate change. In other words, the northern expansion of boreal forest into tundra in response to climate warming is likely to feedback and further warm the climate. Past changes in treeline associated with the glacial retreats are also likely to have significantly affected climate. Foley et al. (1994) showed that paleovegetation feedbacks may be as important as the altered orbital geometry when simulating the climate of high-latitudes 6,000 years before present.
These results also have implications for our undestanding of climate-vegetation interactions. Historically, ecologists have looked for climate variables that correlate with vegetation biogeography, assuming these are the climate variables that determine the biogeographical patterns. However, these results suggest that climate and vegetation exist in a dynamic equilibrium in which vegetation both responds to and affects climate.
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