Chemical properties of decaying wood in an old-growth spruce forest and effects on soil chemistry

Live trees influence the nutrient status of the soil by the interception of substances from the atmosphere, the uptake of nutrients from the soil, and the deposition of litter. In an unmanaged old-growth spruce mountain forest on acidic soil, we analyzed how the death and decay of spruce trees affects the acidity and element concentrations of the soil, tree bark (or outermost stemwood) and stemflow. Key study objective was to examine whether the element release from decaying deadwood significantly increases the available soil nutrient stocks in the senescence phase of coniferous forests. Bark and stemflow chemistry responded to the death and decay of the trees with lowered acidity and reduced nutrient concentrations, which was attributed to the gradual loss of the intercepting canopy surface. Bark and stemflow concentrations of base cations (K, Ca, Mg) showed a transient peak in the course of wood decay. Published evidence suggests that the variability in bark and stemflow chemistry detected across the sequence of wood decay stages was sufficient to shape the epiphytic lichen and bryophyte communities. The death and decay of spruce trees also resulted in elevated base saturation near standing deadwood. Downed deadwood had a negligible effect on soil chemistry, among others due to slow decomposition in the studied cold mountain forest. Soil acidity was not significantly affected by deadwood. The release of base cations from standing deadwood to the soil suggests that sparing part of the trees in managed forests from logging could counteract nutrient depletion through timber harvesting.