Climate-vegetation interaction

Abstract
The climate exerts the dominant control on the spatial distribution of the major vegetation types on a global scale. In turn, vegetation cover affects climate via alteration of the physical characteristics of the land surface like albedo, roughness, water conductivity (biogeophysical mechanisms) and atmospheric gas composition, for example, CO ₂ and CH ₄ (biogeochemical effects). The chapter covers biogeophysical interactions between the land surface and the atmosphere. Recent progess in vegetation and land surface modelling is briefly discussed. Research on climate-vegetation interaction is mostly concentrated on "hot spots" where the interaction is the most significant: boreal forests, North Afiica, and Amazon forest. Boreal forests, even deciduous ones, significantly reduce the albedo of snow-covered surfaces. Simulations with different climate models reveal that positive feedback between forest and surface air temperature in the boreal region is not strong enough to establish multiple steady states. Nonetheless, the simulations show a significant cooling trend due to historical land cover changes, mainly as a result of temperate and boreal deforestation. In general, the climate models agree that tropical deforestation exerts a net regional warming while an effect on extratropical regions is more uncertain. In the Sahel/Sahara region, several models are able to simulate ,,green Sahara" phenomenon during the mid-Holocene. Some models reveal multiple steady states in the region due to a strong interaction between vegetation and monsoon precipitation. Sensitivity simulations show that some expansion of vegetation cover into the Sahara is possible under CO ₂-induced climate changes.