THERMAL-CONDUCTIVITY AND WATER-RETENTION OF A BLACK SPRUCE FOREST FLOOR

The forest Boor of black spruce (Picea mariana (Mill.) B.S.P.) stands is typified by a thick layer of moss and organic material overlying th e soil, This layer is an important source of nutrients and water for s pruce and provides thermal insulation of permafrost, However, little i s known about the water retention characteristics and thermal conducti vity of black spruce forest Boors, Near Fairbanks, Alaska, in situ the rmal conductivity and water content of a black spruce forest floor (0- 0.05 m depth) were assessed during the 1992 growing season, In additio n, core samples were taken for laboratory estimates of bulk density, w ater retention, and thermal conductivity, Bulk density was about 0.035 Mg m(-3) at the 0 to 0.10-m depth and 0.050 Mg m(-3) at the 0.10 to 0 .20-m depth, In situ thermal conductivity of moss was generally smalle r than previously estimated and ranged from 0.03 to 0.09 W m(-1) K-1 o ver the growing season, Thermal conductivity varied linearly with wate r content at the 0 to 0.10-m depth and exponentially with water conten t below 0.10 m. Water retention differed within the forest Boor profil e, with an apparently smaller air-entry matric suction and pore size d istribution index below the 0.1-m depth, This study suggests that vari ations in bulk density within a forest Boor profile, which result from changes in organic material composition, affect both the thermal and hydrologic properties of black spruce forest floors.