Browsing by discipline "Forest Ecology and Management (Forest Sciences and Business)"

Pressure to replace fossil fuels in order to reduce CO2 emissions as well as the increased demand for energy have resulted in more intensive harvesting of forests. The current harvesting practice is to heap the logging residues rather than spread them on skid trails. However, little is known about the effects of modern harvesting techniques on soil fertility and site productivity. The decomposition of and nutrient release from logging residues after clear-cutting has recently been investigated in Finland, but the nutrient dynamics of logging residues after thinning and especially in the residue heaps is less known. In this study the mass loss of and nutrient release from logging residues were explored for three successive years after first thinning of a Scots pine stand in western Finland. The main objective was to identify the effects of heap structure on decomposition and nutrient dynamics. More specifically, the objectives were: 1) To examine how the position within the heaps affects the decomposition rate and nutrient dynamics of residue fractions. It was hypothesised that the decomposition and the release of nutrients are greater under the residue heaps than on top of the heaps and on the ground. 2) To identify temporal changes in decomposition and nutrient release over a 3-year period. 3) To determine how much N, P, K, Ca and Mg are released from logging residues during the first three years after first thinning. 4) To assess whether it is more beneficial for nutrient cycling to concentrate the logging residues in heaps or to spread them out from the standpoint of site fertility. 5) To assess the timing of harvest of logging residues in terms of their role in nutrient cycling of a stand. The decomposition of Scots pine needles, twigs and branches was determined by measuring the mass loss with the litterbag method. The experimental design was randomized blocks with nine treatments and six replicates. The treatments included three logging residue fractions and three locations of logging residue. The influence of logging residue type and locations of residue on mass and contents of nutrients remaining in litter bags over the entire 3-year period were tested by repeated measures ANOVA. In total, 25% of N, 53% of P, 87% of K, 42% of Ca and 49% of Mg were released from logging residues in three years. The treatments in this study had no clear effects on the mass loss of logging residues. The hypothesis was confirmed only with needles, for which the mass loss and nutrient release was significantly faster under the heaps than on the ground and on top of the heaps. Treatments did not have a significant effect on the decomposition of twigs and branches. In the short-term, the logging residues were a minor source of N but a significant source of K. The results indicate that in the short-term logging residues are insignificant for site productivity on sites where the availability of N limits productivity. On peatland sites, where the availability of K limits productivity, logging residues may be significant on site productivity. However, in the long-term logging residues may be an important source of organic matter and nutrients. Great proportion of nutrients was released from needles within the first year of decomposition. The rate of nutrient release from needles was slightly faster from the heaps than on the ground over the first year. If residues are collected for energy, heaping and removal after one year would result in more released nutrients than if they were spread on the ground throughout the harvested stand. In order to avoid possible soil nutrient depletion and negative effects on the growth of remaining trees, it can be preferable to leave residues in the stand after harvest and remove branches after the needles have been shed.