A BIOPHYSICAL SURFACE-ENERGY BUDGET ANALYSIS OF SOIL-TEMPERATURE IN THE BOREAL FORESTS OF INTERIOR ALASKA

Observed soil degree-days (SDD) for 20 forest stands in the discontinuous permafrost zone of interior Alaska range from 483 to 2217. These stands differ in terms of forest structure, topography, and soils. A biophysical model that solves the surface energy budget of a multilayer forest canopy was used to examine which site factors were most important in controlling the observed soil temperature gradient. Simulated soil temperature averaged 851 SDD for the 20 sites. Sensitivity analyses indicated that this average could vary by 0-88 SDD (0-10% of the mean) because of possible parameter error. Removing the forest canopy and the moss cover caused the soil to warm, on average, by 408 and 345 SDD, respectively. Elevation and soil drainage differences among sites were of secondary importance, causing SDD to deviate by 71 and 66 SDD, respectively. Slope and aspect had little effect on soil temperature.