DECOMPOSITION OF ASPEN, SPRUCE, AND PINE BOLES ON 2 SITES IN MINNESOTA

Boles of quaking aspen (Populus tremuloides Michx.), white spruce (Picea glauca (Moench) Voss), red pine (Pinus resinosa Ait.), and jack pine (Pinus banksiana Lamb.) were sampled after decomposing for 11-17 years. Mass loss and changes in chemical composition were determined. Density decreased by 40-73%, and the decomposition constant (k) decreased in the order aspen > spruce > red pine > jack pine. Although the decomposition rate was strongly species dependent, it did not differ between the two sites. The decomposition constant was weakly related to lignin and phosphorus concentration in the original stems (r2 = 0.44 and 0.49, respectively) and not significantly related to original nitrogen concentrations. Nutrient concentration increased during decomposition, particularly for nitrogen and phosphorus. Nitrogen content increased during decomposition, and potassium content decreased. Calcium and magnesium content changed little during decomposition, whereas phosphorus content increased or decreased, depending on species. In general, species with the lowest initial nutrient contents had the greatest nutrient increases during decomposition. Nutrient content of boles of all species became similar during decomposition.