Influences of vegetation on permafrost: A review

Abstract

As the main body of the earth cryosphere, permafrost is formed as a result of heat-moisture exchanges between the lithosphere and atmosphere. The occurrence, distribution and thermal regime of permafrost are affected by many environmental factors of varied spatiotemporal scales. As the medium, a participant and a buffer layer of heat-moisture exchanges between the lithosphere and atmosphere, vegetation and its changes significantly affect the hydro-thermal regimes and distributive features of permafrost. In this paper, the influences of vegetation on permafrost were systematically reviewed. Vegetation has relatively high albedo and capability for water holding and retention, which vary with different types of vegetation and have great impacts on the heat-moisture regimes of permafrost. In vertical structure, there are distinct layers for a given type of vegetation. Each layer has different influences on the thermal regime of permafrost, especially the ground cover layer. Compared to the area above crown canopy, which usually reflects and absorbs probably 40% of solar radiation, the crown canopy significantly affects net radiation and ground surface temperatures in forest. Vegetation, especially the canopy structure, considerably controls the snow accumulation and redistribution through the interception component of the water budget, wind speed, and solar radiation at the snow surface, resulting in a significant impact on the heat-moisture regimes of permafrost. Therefore, deforestation, such as for farming or fuels, may alter snow accumulation, albedo, surface coverage, and capability of water holding of vegetation. This may greatly modify the permafrost environment, induce many types of permafrost hazards, or even result in the thawing and eventually decaying of permafrost patches. Permafrost and vegetation are key components of ecological system in cold regions. They are interdependent and interactive, and have reached dynamic equilibria in the geological and biological evolutionary processes. In permafrost regions, specific vegetation types or their combinations usually present because of appropriate temperatures and moisture conditions. Therefore, the occurrences of specific plant species or a plant community can largely indicate the occurrence of permafrost. Finally, some problems unresolved in the research at present are identified in this paper, and the prospect for further study is also proposed.