Simulation modelling of greenhouse gas balance in continuous-cover forestry of Norway spruce stands on nutrient-rich drained peatlands

Abstract

We used a simulation model to analyse the effect of continuous-cover forestry on the carbon dioxide (CO2) and methane (CH4) emissions from nutrient-rich drained peatland sites in southern Finland. The simulation scenarios were constructed by varying harvesting interval and post-harvest basal area in a typical mature Norway spruce (Picea abies (L.) H. Karst.) stand. A process-based model of soil organic matter dynamics supplied with some additional empirical routines was used for calculation of emission due to decomposition of fresh litter and peat. The amount and chemical properties of litter inputs, as well as the hydrothermal conditions and the water table depth in the peat layer were used as predictors. We estimated the net ecosystem production as a difference between carbon sequestration in stand biomass and carbon losses due to decomposition of dead organic matter, and the net biome production as the net primary production minus losses due to harvesting. Simulations showed that the peatland forest acted as a carbon sink with low and middle harvest intensity, while it turned into a carbon source with high harvesting intensities. This was mostly because intensive harvesting raised the water table level, thus decreasing tree production and increasing soil methane emission. Carbon dioxide emissions from peat and litter, in turn, correlated negatively with the intensity of harvesting. Correlation of site carbon balance with harvested roundwood indicated that there is a significant trade-off between maintaining carbon in drained peatland forests and providing harvest revenues. The simulations provide novel results and fill a gap of knowledge in ecosystem responses to alternative management regimes in continuous-cover forestry on drained peatlands.