Effects of afforestation and deforestation on boreal soil carbon stocks-Comparison of measured C stocks with Yasso07 model results

Land use changes like afforestation and deforestation are known to affect stocks of carbon in soils. We measured changes in soil carbon stocks in afforested and deforested sites. Repeated measurements were made at six sites which had been afforested with three different tree species 17-18 years before this sampling. The deforestation sites consisted of six field soils that were taken to cultivation 1-200 years before the sampling and adjacent forest sites representing the same soil types as the fields. The performance of the Yasso07 model in predicting the soil carbon stock changes in afforestation and deforestation was evaluated by simulating the changes in the carbon stocks and comparing the measured and simulated results for these sites. The mean observed 20-year carbon stock change after the land use change was -9% in the afforested sites and -19% in the deforested sites. The decrease in the mean carbon stock after afforestation was most pronounced during the first 9-10 years and was probably due to low rates of litter production in the early growth phase of the forests. The stock change in deforestation was lowest in fields with grasses as the main crop and highest in cereal monoculture. The simulation results were well in accordance with the measured carbon stocks on most sites. (C) 2011 Elsevier B.V. All rights reserved.