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Recession of Permafrost in a Cultivated Soil of Interior Alaska¹

ABSTRACT

Soil temperatures above and within the perennially frozen zones of Tanana silt loam, a member of the subgroup of Pergelic Cryaquepts, were measured twice weekly over a period of 3 years in undisturbed, cleared, perennial grass, and potato (Solanum tuberosum L.) plots. The permafrost table receded rapidly from a depth of about 1 m to almost 5 m after clearing. Refreezing in autumn and winter takes place simultaneously downward from the surface and upward from the new permafrost table. In the potato plot, an unfrozen zone remained throughout the winter. Mean annual temperatures above the new permafrost table are warmer than 0C. Some revision in the definition of Pergelic subgroups in the Comprehensive Classification System seems necessary to avoid a change in classification of the soil as a result of clearing and cropping.

¹ Contribution from Alaska Agr. Exp. Sta., and the Soil Conservation Service, USDA.

² Research Horticulturist, Alaska Agr. Exp. Sta., College, and State Soil Scientist, SCS, Palmer, Alaska, respectively. The authors wish to acknowledge the assistance of Michael D. Hill and Burton L. Clifford, SCS, and Carl Mock, Alaska Agr. Exp. Sta., in preparation and installation of equipment and recording of the data.

Received for publication November 4, 1968. Accepted for publication January 29, 1969.