CHANGES IN NUTRIENT CONCENTRATIONS AND NUTRIENT RELEASE IN DECOMPOSING NEEDLE LITTER IN MONOCULTURAL SYSTEMS OF PINUS-CONTORTA AND PINUS-SYLVESTRIS - A COMPARISON AND SYNTHESIS

Scots pine (Pinus sylvestris) and lodgepole pine (Pinus contorta) need le litters were compared in terms of nutrient composition and its chan ge during decomposition. Initial nutrient composition differed between the species, with lodgepole pine needle litter having significantly h igher concentrations of P, Mg and Mn. However, no difference was found for concentrations of N, Ca or K. Increases in concentrations of N, P and K during decomposition were significant in both litter types. For Ca the pattern of concentration changes followed a quadratic function as decomposition proceeded. Concentrations of Mg and Mn decreased in lodgepole pine needle litter. In Scots pine litter there was also an i nitial decrease, but it was followed by an increase in most incubation s. For both Mg and Mn, changes in concentrations during decomposition differed significantly between species. In the late decomposition stag es, concentrations of ME and Mn became similar in both litter types. N utrient concentrations generated by the models were compared with thos e of the humus (F and H) layer in the stands. The model was quite accu rate in predicting concentrations of N and P for both species and the concentration of Mg for lodgepole pine. By contrast, it was not accura te in predicting concentrations of Ca and Mn. Nutrient release was est imated for the two species using both measured litterfall data and lon g-term estimates, and regression models were used to predict concentra tion changes. Rates of release of P, Mg and Mn in the lodgepole pine s tands were found to be about twice as high compared with those in Scot s pine. Calcium was also released to a greater extent although the dif ference was not significant.