The study describes an integrated impact assessment tool for the net carbon dioxide (CO₂) exchange in forest production. The components of the net carbon exchange include the uptake of carbon into biomass, the decomposition of litter and humus, emissions from forest management operations and carbon released from the combustion of biomass and degradation of wood-based products. The tool enables the allocation of the total carbon emissions to the timber and energy biomass and to the energy produced on the basis of biomass. In example computations, ecosystem model simulations were utilized as an input to the tool. We present results for traditional timber production (pulpwood and saw logs) and integrated timber and bioenergy production (logging residues, stumps and roots) for Norway spruce, in boreal conditions in Finland, with two climate scenarios over one rotation period. The results showed that the magnitude of management related emissions on net carbon exchange was smaller when compared with the total ecosystem fluxes; decomposition being the largest emission contributor. In addition, the effects of management and climate were higher on the decomposition of new humus compared with old humus. The results also showed that probable increased biomass growth, obtained under the changing climate (CC), could not compensate for decomposition and biomass combustion related carbon loss in southern Finland. In our examples, the emissions allocated for the energy from biomass in southern Finland were 172 and 188 kg CO₂ MW h⁻¹ in the current climate and in a CC, respectively, and 199 and 157 kg CO₂ MW h⁻¹ in northern Finland. This study concludes that the tool is suitable for estimating the net carbon exchange of forest production. The tool also enables the allocation of direct and indirect carbon emissions, related to forest production over its life cycle, in different environmental conditions and for alternative time periods and land uses. Simulations of forest management regimes together with the CC give new insights into ecologically sustainable forest bioenergy and timber production, as well as climate change mitigation options in boreal forests.

The impacts of alternative forest management scenarios and harvest intensities on climate change mitigation potential of forest biomass production, utilization and economic profitability of biomass production were studied in three boreal sub-regions in Finland over a 40-year period. Ecosystem modelling and life cycle assessment tools were used to calculate the mitigation potential in substituting fossil materials and energy, expressed as the net CO₂ exchange. Currently recommended management targeting to timber production acted as a baseline management. Alternative management included maintaining 20% higher or lower stocking in forests and final felling made at lower breast height diameter than used in the baseline. In alternative management scenarios, logging residues and logging residues with coarse roots and stumps were harvested in final felling in addition to timber. The net CO₂ exchange in the southern and eastern sub-regions was higher compared to the western one due to higher net ecosystem CO₂ exchange (NEE) over the study period. Maintaining higher stocking with earlier final felling and intensified biomass harvest appeared to be the best option to increase both climate benefits and economic returns. Trade-offs between the highest net CO₂ exchange and economic profitability of biomass production existed. The use of alternative displacement factors largely affected the mitigation potential of forest biomass.

A gap-type ecosystem model was used to assess how climate change may affect the growth (stemwood production), timber production (sawlogs and pulpwood) and carbon stocks in the forest ecosystem (trees and soil) under varying thinning regimes in Finland. Simulations were carried out over a 100-year period under current and changing climate for seven thinning regimes by changing both the basal area threshold when the thinning is performed and the remaining basal area after the thinning. The management recommendations, currently applied in Finnish forestry, were used to define the “business-as-usual” treatment. The results indicated that climate change may substantially increase the growth, timber production and carbon stocks in the forest ecosystem. The largest relative changes were found in northern (above 64° N) Finland (south: growth 37–45%, timber production 23–40%, carbon stocks 8–10%; north: 75–78%, 59–70%, 21–23%, respectively, depending on the thinning regimes applied), although the absolute (mean) values were higher in southern (below 64° N) Finland. Regardless of climate scenarios, a reduced level of tree stocking in thinnings may result in cuttings exceeding the growth and result in lower carbon stocks in the forest ecosystem. Conversely, increased tree stocking level up to 30% reduced timber production, but did not remarkably affect the growth and carbon stocks under the current or changing climate. Hence, it may be suggested that if thinning is made at 15–30% higher stocking than current level it would result in a positive compromise; beyond that, timber production could be reduced drastically.