Mass loss and nutrient dynamics of coarse woody debris in three Rocky Mountain coniferous forests: 21 year results

Mass loss and changes in C, N, and P concentrations were measured in 20 cm long log segments of lodgepole pine (Pinus contorta Dougl. ex Loud.), white spruce (Picea glauca (Moench) Voss), and subalpine fir (Abies lasiocarpa (Hook.) Nutt.) that had been placed in three Rocky Mountain coniferous forests 21ayears earlier. Pine, spruce, and fir lost 76%, 39%, and 64%, respectively, of their initial mass during the 21years. The corresponding mean decay rates (k) were 0.072, 0.024 and 0.052 center dot year(-1). The decay patterns of pine and spruce were similar with the highest k between 6 and 14 years. Fir k increased during the course of decomposition with the highest rate between 14 and 21 years. The correlation between original dry mass and k was negative for pine (r = -0.28), positive for fir (r = 0.35), and not significant for spruce. C/N, C/P, and N/P ratios declined and converged to a similar value in relation to mass loss for all three species. The N/P ratios of logs of all three species stabilized at about 19. These findings indicate that patterns of wood decay are difficult to predict (even with 14 year data), and so models that incorporate wood-decay estimates will be associated with considerable uncertainty.