A SOIL-TEMPERATURE MODEL FOR CLOSED CANOPIED FOREST STANDS

We developed a soil temperature model to predict hourly temperatures at the litter-soil interface and at soil depths of 0.10 m, 0.20 m, and 1.25 m in hardwood forest stands with closed canopies. The model, which was written in BASIC on a microcomputer, uses a numerical solution for the partial differential heat-flow equation. Litter-soil interface temperature was predicted from air temperature by multiple regression. Daily temperatures at the litter-soil interface and in the soil were predicted for 2-month periods in summer, late fall, and early spring. Predictions were most accurate in summer and late fall but tended to be high in late spring. Results were in general agreement with measured values when approximate soil thermal characteristics were used. Predicted values were within 1 to 3-degrees-C of measured soil temperatures. Soil temperature prediction could be improved by using actual thermal characteristics; however, sensitivity analyses indicate that only large variations in thermal characteristics significantly affect soil temperature predictions. The model predicts soil temperatures within the bounds (+/- 5-degrees-C) of most microbial activity assays and should be suitable for regulating rate functions in nutrient and carbon cycling models.