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United States Department of Agriculture

Agricultural Research Service

Title: Surface Energy Budget of Forest Versus Crop Land in the Subarctic

Author
item SHARRATT, BRENTON

Submitted to: Agricultural and Forest Meteorology Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: February 2, 1996
Publication Date: N/A

Interpretive Summary: Subarctic forests may be vulnerable to clearing if economic policies of polar regions shift toward development of renewable resources. Clearing these forests will affect regional climates, yet the magnitude of change and the mechanism by which change will occur is poorly understood. A study was conducted to assess the impact of clearing a subarctic forest on the surface energy balance. Clearing the forest reduced the amount of energy absorbed at the earth's surface and consequently the energy available for heating processes. The forest ecosystem was more efficient at utilizing energy for growth processes while the crop ecosystem released much of the absorbed energy as sensible heat. Clearing subarctic forests will result in regional warming and drying.

Technical Abstract: Agricultural development in the North American Subarctic during the early 1980's necessitated clearing forest land that was laden with permafrost. Land clearing altered the surface energy balance as evidenced by extensive thaw consolidation. This study assessed the impact of clearing a Subarctic forest on surface energy partitioning. A cleared (grass) and non-cleared phase (forest) of a Pergelic Cryaquept in interior Alaska was instrumented to ascertain net radiation and latent, sensible and ground heat flux. Albedo of the forest was smaller than that of the grass land throughout the year; being 0.08 for forest and 0.2 for grass land during the summer and 0.2 for forest and 0.8 for grass land in winter. The smaller albedo of forest contributed to a greater availability of radiant energy (2.1 MJ m**-2 d**-1)during summer to drive processes such as photosynthesis, transpiration, and heating. Nearly 100% of the available energy over the forest was dissipated through evapotranspiration. Soil heat flux was negligible in the forest and accounted for 20% of crop land net radiation. The remaining 80% of crop land net radiation was equally dissipated through latent and sensible heat flux. In winter, more radiant energy (0.8 MJ m**-2 d**-1) was lost from the forest compared to the cropland, thus indicating substantial heat loss from the forest canopy. This study demonstrated that clearing a Subarctic forest results in sensible heating of the atmosphere and that permafrost is maintained largely through dissipation of energy through evapotranspiration.

Last Modified: 9/29/2014
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