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United States Department of Agriculture

Agricultural Research Service

Title: Thermal Conductivity and Water Retention of a Black Spruce Forest Floor in Interior Alaska

Author
item Sharratt, Brenton

Submitted to: Arctic and Alpine Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 12, 1997
Publication Date: N/A

Interpretive Summary: The forest floor is an important source of water and nutrients for tree growth in the subarctic. In addition, the occurrence of permafrost in subarctic regions is largely controlled by the thermal insulation of the forest floor. Thermal insulation of the forest floor was shown to be affected by the density and water content of the floor. Increasing the density of the forest floor will cause permafrost degradation in the subarctic, and consequently enhance erosion of landscapes as well as alter groundwater and surface water resources. State and federal agencies such as the Bureau of Land Reclamation, Forest Service, National Park Service, and Parks and Recreation must regulate activities in subarctic woodlands to curtail trafficking of the forest floor by selective logging operations, agricultural enterprises that utilize woodlands for confinement of animals, or private and public enterprises that utilize woodlands for recreation. This research emphasizes the need for the development of regulations in utilizing subarctic woodlands to minimize the threat of erosion and changes in groundwater resources in the North American subarctic.

Technical Abstract: The forest floor of black spruce (Picea mariana (Mill.) B.S.P.) stands in interior Alaska is characterized by a thick layer of moss and organic matter. This layer is important in providing water and nutrients for spruce stands as well as maintaining permafrost in the region. Yet, little is known concerning water retention characteristics and thermal conductvity of the black spruce forest floor. This study was conducted in a black spruce stand near Fairbanks, Alaska. The forest floor was about 0.3 m thick. In-situ thermal conductivity and water content of the forest floor (0-0.05 m depth) was assessed during the 1992 growing season. In addition, 0.15-m diameter core samples were taken to a depth of 0.2 m for determining bulk density, water retention, and thermal conductivity. Bulk density was about 0.035 Mg m-3 at the 0-0.10 m depth and 0.050 Mg m-3 at the 0.10-0.20 m depth. In-situ thermal conductivity ranged from 0.03 to 0.09 W m-1 K-1 during this study. Thermal conductivity of the core samples varied linearly with water content at the 0-0.10 m depth whereas conductivity varied exponentially at the 0.10-0.20 m depth. The greater slope of the water retention function of the 0.10-0.20 m samples indicated that matrix pore size was more variable at this depth than at the 0-0.10 m depth. This study suggests that variations in bulk density with forest floor depth alter the thermal conductivity and water retention characteristics of the black spruce forest floor.

Last Modified: 8/22/2014
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