Effects Of Very Intensive Forest Biomass Harvesting On Short And Long Term Site Productivity

Abstract

Intensified forest biomass utilisation causes export of substantial amounts of nutrients from the forest ecosystem. Compared to conventional stems-only harvesting, the most intensive biomass sce nario causes increases in nutrient exports of up to 6-7 times whereas the biomass export increases only up to 2 times (Stupak et al. 2007a). High concentrations of nutrients in small branches, twigs, and leaves compared to stems are the main reason. The extensive export of nutrients related to intensive biomass extraction have for many years caused concern for the long-term fertility of the system among forest ecologists (Burger 2002, Blanco et al. 2005, Dyck et al. 1994, Egnell et al. 1998, Egnell et al. 2006). In this chapter we focus on the nutritional consequences of intensified biomass utilisation by use of the nutrient balance approach. Specific attention is given to quantification of the nutrient export and to the soil nutrient release capability. We suggest distinction of sensitive and robust soils. Six case studies are used to exemplify the approach and illustrate the importance of deposition, harvesting and soil properties. The distinction of sites and the quantification of nutrient balances are used for compensation recommendations. We do not discuss effects like decrease in soil organic matter, or other indirect effects like soil compaction, weed problems, and microclimatic effects.