The forests of Siberia play an important role in absorbing carbon dioxide. Resent increases in forest fires, due to both human negligence and global warming, appear to cause significant damage to the forests. In the present research, basic models were established to evaluate changes in land area and carbon flux by forest fires and by disturbances of permafrost. Basic data necessary for the analysis are also summarized and presented. The characteristic of the model is a solution to the problem with probabilities in statistic space, rather than detailed simulation. The results of the simulation shows the significance of forest fires on the net carbon flux, which maintains the present level with a sensitive balance between large positive and negative fluxes. It was also shown that forest areas keep decreasing over a thousand-year time span even after a fire rate becomes constant. This implies that changes of land features are quite slow and that there may be irreparable situations at the time when changes are actually recognized. The effect of fire control and planting of the areas exposed to fires is also evaluated. (c) 2004 Elsevier Ltd. All rights reserved.