Decomposition of Bark as a Part of Logging Slash after Clear-Cutting in Mixed Middle Boreal Forests

The contribution of bark, as a phytomass fraction, to nutrient cycling is studied insufficiently. This study followed six-year dynamics of physical and chemical characteristics of bark residues after clear cutting. The amount of bark present in logging slash was found to be 20.8 m3 ha–1, or one fifth of the volume of coarse woody debris, which varied from 105 to 127 m3 ha–1. The initial area-specific mass of bark was 0.601 g cm–2 for aspen, 0.346 g cm–2 for pine, 0.446 g cm–2 for birch, and 0.233 g cm–2 for spruce. The initial density of bark varied in the range of 0.51–0.71 g cm–3 for aspen, 0.56–0.80 g cm–3 for birch, 0.39–0.64 g cm–3 for pine, and 0.60–0.73 g cm–3 for spruce. The initial concentrations of nitrogen and carbon were 0.23–0.53% and 42–48%, respectively. The changes over time in specific mass, phloem percentage, and bark thickness depended on a particular tree species. The rate of mass loss was the maximal in spruce bark, whereas birch bark showed the maximal rate of phloem loss. The specific mass of bark decreased by 32–38%, the density by 10–17%, and the phloem percentage by 78–99% after six years since cutting. The concentrations of nitrogen and carbon in bark did not change during decomposition. Therefore, the bark layer on a soil surface partially compensates for the nitrogen losses caused by removal of logged wood.