Use of forest resources for bioenergy is expected to increase considerably in Norway in the next 10-20 years. Forest residues such as branches and tops are likely to be harvested, as in Finland and Sweden today. As a large part of the nutrients in trees a re located in the needles and branches, removing these might lead to nutrient depletion and increase the risk for future nutrient imbalance, reduced forest production and changes in biodiversity and understory species composition. The extent of these proc esses will differ with soil type and climatic conditions. There is at present little knowledge about which factors determine the contrasting effects found in different field experiments on increased biomass removal, or of how variation in these controllin g factors will affect long-term site sustainability.
We will (1) quantify the effects of harvesting of branches and tops from Norway spruce forests on the supply of nutrients/organic substances in the soil, as well as on vegetation, soil water, forest reg eneration and production, and (2) use data from field trials, monitoring plots and literature to model where such harvesting can be carried out in an ecologically sound way and to produce policy and management recommendations. This will be achieved throug h five closely connected work packages, of which WP1-3 will deal with Point (1) through coordinated field trials, including experimental stands in Norway spruce forests in both eastern and western Norway, while WP4-5 will aim at estimation of nutrient bal ances, modelling and synthesizing results into recommendations and predictions based on current knowledge, and, along with WP1-3, identify further gaps in knowledge of key controlling factors. A close coordination with national and international colleague s and adaptation of existing models will help to fulfil these goals. This project will increase the knowledge basis for policy formulation regarding sustainable management of forest resources for bioenergy.