Effects of forest management on sustainability of integrated timber and energy wood production - scenario analysis based on ecosystem model simulations

Abstract

The main aim of this thesis was to study the effects of forest management on the sustainability of integrated timber and energy wood production in Norway spruce (Picea abies (L.) Karst.), on fertile and medium fertile sites, and Scots pine (Pinus sylvestris L.), on medium fertile and less fertile sites. In this context, an ecosystem model was used in scenario analyses, which considered the effects of management on the total stem wood production, timber and energy wood production. Furthermore, the management implications for net present value (NPV) and net CO2 emissions of the use of energy wood was addressed. The management included varying pre-commercial stand density, timing, and intensity of energy wood thinning, N fertilization (Papers II-IV), and rotation length (Paper IV). In addition, the effects of the genetic entry on above-ground biomass production of Norway spruce were studied based on experimental data (Paper I). In general, the management with higher pre-commercial stand density than that used in basic management and N fertilization clearly increased stem wood production (i.e. sawlogs, pulp and small-sized stem wood), energy wood production (logging residuals, small-sized stem wood, stump wood and roots) and also NPV over the rotation for both Norway spruce and Scots pine, regardless of site fertility type and rotation length used in the simulations (Papers II-IV). However, the total stem wood production and energy wood production were also affected by the timing of energy wood thinning. Fertilization had a positive effect, but the effects of number of applications and amount of N fertilization were negligible on the total stem wood and energy wood production. Additionally, in the case of net CO2 emissions, the increase of pre-commercial stand density and fertilization clearly decreased the net CO2 emission in energy production over the rotation regardless of tree species, site fertility type and rotation length used in simulations (Papers III-IV). In general, high stem wood production indicated concurrently, on average, higher NPV and lower CO2 emissions per energy unit regardless of tree species and site fertility type. At the landscape level, the highest amount of timber and energy wood and the NPV was obtained in Norway spruce on landscape dominated by older stands (Paper IV). The lowest net CO2 emissions were obtained with the landscape dominated by younger stands with rotation length of 60 and 80 years, regardless of site fertility type. The same was observed with the normal age-class distribution with rotation length of 120 years. The use of higher density of pre-commercial stand than that currently recommended in Finnish forestry together with timely thinning and fertilization could increase the stem wood production and the economic profitability of the management remarkably, but also simultaneously decrease the net CO2 emissions from the use of energy wood. Furthermore, the proper selection of genetic entries could increase also the productivity and potential of biomass recovery at least in Norway spruce (Paper I).