The potential for forestry to reduce net CO2 emissions

Forestry may have an important role to play in attempts to reduce atmospheric CO2 levels, since countries may choose to account for forest management activities to fulfil their commitments under the Kyoto Protocol. However, the effectiveness of such efforts may depend on the forest management strategies applied. This thesis is based on four separate studies in which the potential for forest management strategies to decrease net CO2 emissions was considered. Long-term field experiments and models were used to: evaluate the impact of different thinning regimes; study broadleaved stands growing on abandoned farmland with different rotation lengths; predict the effects of using different rotation lengths on carbon accumulation and fossil fuel substitution; and perform an integrated analysis of forest management practices and the potential to substitute fossil fuels by wood products. To evaluate the effects of the management regimes considered, carbon stocks in the investigated stands and the potential of the resulting biomass to substitute fossil fuel were estimated. No significant differences were found in biomass production between the thinning regimes for Norway spruce (Picea abies (L.) Karst.) stands, but the standing biomass was significantly larger in unthinned stands, indicating that to maximize the carbon stock in tree biomass thinnings should be avoided. For Scots pine (Pinus sylvestris L.), thinned and fertilized stands produced significantly more biomass (2.60-2.72 ton d.w. ha-1 yr-1) than unthinned and unfertilized stands (2.17-2.34 ton d.w. ha-1 yr-1) in the northern regions. These findings indicate that fertilization might be a viable measure to increase production of biomass with the potential to replace fossil fuel and energy-intensive material. In addition, for broadleaved trees stands on abandoned farmland, management regimes with a short rotation were found to be better for maximizing the substitution of fossil fuel than regimes with a long rotation. However, the trees have to be grown on good sites; otherwise long rotations could be better options for broadleaved stands. In coniferous stands, a shortened rotation period resulted in lower carbon stocks than a prolonged rotation period, but the amount of residues that could substitute fossil fuel increased with a shorter rotation. However, annual rates of carbon accumulation in biomass might decline in both short- and long-rotation stands in the future. If so, carbon sequestration in biomass would not be the best option. In a long-term perspective, wood products could have high potential to reduce net CO2 emissions, since wood can replace energy-intensive materials like cement, plastics and aluminium. Intensively managed forests (e.g. fertilized forests or shortened rotation lengths) could contribute more to reductions in CO2 emissions than current forest management. Using forest products (i.e. wood products and biofuel) is probably more important than storing carbon in biomass and soil, but it is necessary to conserve the existing stocks. Intensive forest management and increased use of biomass may, however, conflict with environmental quality objectives