Decomposition and nutrient release from Picea abies (L.) Karst. and Pinus sylvestris L-logging residues

We analyzed the long-term dynamics of the decomposition of different fractions of forest litters by using models derived from a theory on decomposition and element cycling in organic matter. The analysis of decomposition was done (i) by measuring decomposition rates of and nutrient changes in needles, twigs, and branches in field experiments, and (ii) by estimating parameters used in the models with information derived from these experiments. The analysis showed that variability in decomposition rate decreases with increasing substrate diameter. We also used the models to predict the long-term dynamics of carbon, nitrogen, and phosphorus in logging residues. Our predictions suggest that from a short-term perspective the nutrient-rich needles and twigs are a more important nutrient source for the subsequent forest, generation compared with branches. However, in the long run the nutrient concentration of the coarse litter fractions will also be important. The predicted amounts of carbon and nitrogen in logging residues were compared with measured amounts in humus layer. On a productive Norway spruce site remaining logging residues were, 16 years after clear-felling, predicted to increase carbon amounts in the forest floor by 50% and on a low productive Scots pine site by 100%. The corresponding nitrogen amounts in the forest floor should have been 30% higher at the spruce site and 70-80% higher at the pine site. (C) 2000 Elsevier Science B.V. All rights reserved.