Effects of Forest Management on Total Biomass Production and CO2 Emissions from use of Energy Biomass of Norway Spruce and Scots Pine

Abstract

The aim of this study was to analyze the effects of forest management on the total biomass production (t ha-1a-1) and CO2 emissions (kg CO2 MWh-1) from use of energy biomass of Norway spruce and Scots pine grown on a medium fertile site. In this context, the growth of both species was simulated using an ecosystem model (SIMA) under different management regimes, including various thinning and fertilization treatments over rotation lengths from 40 to 120 years in different pre-commercial stand densities. A Life Cycle Analysis/Emission calculation tool was employed to assess the CO2 emissions per unit of energy from the use of biomass in energy production. Furthermore, the overall balance between the CO2 uptake and emission (carbon balance) was studied, and the carbon neutrality (CN) factor was calculated to assess environmental effects of the use of biomass in energy production; i.e., how much CO2 would be emitted per unit of energy when considering direct and indirect emissions from forest ecosystem and energy production. In general, the total annual biomass production for both species was highest when management with fertilization and high pre-commercial stand density (4000–6000 trees ha-1) was used. In the case of Norway spruce, the highest annual biomass production was obtained with a rotation length of 80–100 years, while for Scots pine a rotation length of 40–60 years gave the highest annual production. In general, the CO2 emissions decreased along with an increasing rotation length. The reduction was especially large if the rotation length was increased from 40 years to 60 years. Scots pine produced remarkably smaller net CO2 emissions per year (on average 29%) than Norway spruce over all different densities and rotation lengths. The value of the CN factor was highest if a rotation of 100 years was used for Norway spruce stands and a rotation of 120 years for Scots pine. The CO2 emission per energy unit was substantially less than that from the use of coal, which was used as reference to assess environmental effects of the use of biomass in energy production. The use of higher density of pre-commercial stand than that currently recommended in the Finnish forestry, together with timely thinning and fertilization, could increase the total biomass production, but also simultaneously decrease the net CO2 emissions from the use of energy wood.