MODEL ANALYSIS OF THE EFFECTS OF SOIL AGE, FIRES AND HARVESTING ON THE CARBON STORAGE OF BOREAL FOREST SOILS

Potential causes for changes in the amounts of carbon. (C) stored in t he soils of boreal forests were studied by measuring the C in the soil along a 5000-year chronosequence in coastal western Finland and using a simple dynamic model of decomposition. The amount of soil C stabili zed at an age of about 2000 years. This suggests that the youth of man y boreal soils does not make them sinks for atmospheric C. Simulated r epeated fires kept the amount of soil C reduced by about 25%, but if f ires were prevented then the C in the soil increased. Stored C may thu s be less than the potential storage where fires are frequent, and it could be increased by preventing fires. Simulated clear-cutting caused a temporary 5-10% decrease in the amount of soil C over a 20-year per iod after the harvesting. It also caused a long term decrease in the a mount of soil C such that, after two 100-year rotations, the amount ha d been decreased by 14%. Stored C is almost certainly less than the po tential storage and decreasing where forests are harvested.