Concurrent Permafrost Aggradation and Degradation Induced by Forest Clearing, Central Alaska, U.S.A

• Published in: Arctic and alpine research 1996-08, Vol.28 (3), p.294-299
• Main Authors: James R. J. Nicholas, Hinkel, Kenneth M.
• Format: Article
• Language: English
• Subjects: Boreal forests; Coniferous forests; Forest soils; Ice; Mineral soils; Peat; Permafrost; Shrubs; Surface temperature; Vegetation
• ISSN: 0004-0851; 2325-5153
• DOI: 10.1080/00040851.1996.12003181

Temporal variations in the annual depth of the active layer above permafrost reflect changing thermal and hydrological conditions that can occur at local and regional spatial scales. Among the most important local factors responsible for permafrost maintenance in the discontinuous and sporadic permafrost zones is a surficial layer of peat which, when dry, acts as a superb thermal insulator. The impact of this organic layer on the local soil energy balance is exemplified at a site near Fairbanks, Alaska. The natural cover of spruce trees and moss were cleared by bulldozing to prepare for land development, and the debris deposited in a number of large piles on the same property. This action resulted in permafrost degradation and development of thermokarst in the 12.7-ha cleared area within several years. In adjacent undisturbed regions, permafrost is encountered 0.4 to 0.5 m below the surface in late summer, but cannot be detected to depths of 1.2 m in the cleared section. Concurrently, permafrost underlying the debris piles was protected and has aggraded about 1.0 m upward into the core of a trenched mound. This study highlights the sensitivity of permafrost in this environment to anthropogenic surficial change.