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United States Department of Agriculture

Agricultural Research Service

Title: Radiative Exchange Near-Surface Temperature, and Soil Water of Forest and Cropland in Interior Alaska

Author
item Sharratt, Brenton

Submitted to: Agricultural and Forest Meteorology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 25, 1997
Publication Date: N/A

Interpretive Summary: Subarctic forest lands may be susceptible to clearing to support agricultural production enterprises if shortages occur in world food supplies. Clearing these forest lands may adversely affect radiant energy and heat transport processes and therefore regional climates. Clearing forest lands reduced the amount of radiation absorbed at the earth's surface and therefore suggests that regional temperatures will decrease as forest land is converted to cropland in the subarctic. Societal concerns about global warming caused by deforestation appear not to be valid in the subarctic where radiational and evaporative cooling are likely to be enhanced by deforestation. Therefore, the agricultural and logging industry may be expanded in the subarctic region of the United States without adversely warming global climates.

Technical Abstract: The expansion of the agricultural resource base in Alaska during the early 1980's allowed for clearing 50000 ha of boreal forest. Little is known, however, about the impact of clearing boreal forest on surface energy exchange processes. This study assessed radiative and heat exchange, temperature, and soil water at a boreal forest and grassland site near Delta Junction, Alaska. The sites, located 5 km apart, were on a nearly level alluvial terrace. The grassland site was cleared in 1978 and seeded to grass in about 1985. At both sites, sensors were installed to measure the albedo, net radiation, surface heat flux, near-surface temperatures, and soil water content from September 1991 to April 1993. Seasonal variations in albedo were more apparent for grassland (0.19 to 0.85) than for forest (0.08 to 0.18). Net radiation over forest was 20% greater during the summer and 25% smaller during winter compared with grassland. Surface heating consumed 13 and 6% of net radiation during the growing season at the grassland and forest sites, respectively. Soil temperatures at the 0.5-m depth ranged from -14 to 10 deg C at the grassland site and from -2.5 to 0.5 deg C at the forest site. The soil at the grassland site was drier and exhibited greater seasonal variation in water content compared with the soil at the forest site. Ice lenses were apparent in the forest soil at a depth of 0.3-0.6 m as the water content exceeded the porosity. This study indicated that clearing forest land will alter the radiative, thermal, and water balance of soils in the subarctic.

Last Modified: 8/21/2014
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