Changes in carbon stores in Swedish forest soils due to increased biomass harvest and increased temperatures analysed with a semi-empirical model

We have used a combination of conventional forest yield tables and a theory for carbon cycles to analyse consequences of climatic change and changes in forest management for carbon stores in Swedish forest soils. The yield tables provide us, for different forest stands, with growth and litter production, which are then fed into a decomposition model from which time series of soil carbon development are obtained. The decomposition model is developed on the basis of the continuous-quality theory and takes into account effects of temperature and substrate quality differences. Complete removal of all needles, branches, and tops, which are normally left during harvesting operations, decreases the soil carbon store with 59 Tg after 150 years or 0.4 Tg per year, which should be compared to the annual carbon harvest of I I Tg and the total soil carbon store of 1700 Tg. Leaving the needles, which should be done to decrease nutrient losses, changes the carbon budget almost imperceptibly. A temperature increase by 4 degreesC, which is predicted in climate scenarios, will increase decomposition and carbon losses from the soil with 0.9 Tg per year. Only increasing forest production would counter-balance this loss with 0.7 Tg per year, but the net loss of carbon from the forest soils is around 0.5 Tg per year when changes in both production and decomposition are taken into account. The most important factors determining the balance between gains and losses in the carbon budget is the distribution of Norway spruce and Scots pine within the country because of the interaction between management and growth. (C) 2002 Elsevier Science B.V. All rights reserved.