MODELING THE EFFECT OF SPATIAL SCALE AND CORRELATED FIRE DISTURBANCESON FOREST AGE DISTRIBUTION

With the exponential model, Van Wagner (1978) gave us valuable insight in understanding stand age and forest age distribution in fire-distur bed landscapes. He showed that, under certain conditions, the probabil ity distribution of the age of a stand subject to periodic renewal by fire is exponential, The extension of this model to the landscape-leve l results, also under certain conditions, in an exponential shape for the forest age distribution. Empirical studies have supported this hyp othesis in some landscapes and not in others, The results are believed to depend on the size of the landscape in question, the patterns of f ire disturbance, and changes in the disturbance regime over time and s pace. In this paper, we present additional insight into some of the fu ndamental factors that determine the forest age distribution. We analy zed some alternative spatial models of fire disturbance, and used a sp atial simulation model (FLAP-X) to explore whether the forest age dist ribution has an exponential shape, and whether it would be stable or v ariable over time under different conditions. We use different spatial and temporal disturbance patterns, some of which represent correlatio n due to fire growth and episodes of high fire disturbance. We describ e FLAP-X and give the results of computational tests based on hypothet ical data. We found that, under characteristic boreal fire disturbance regimes, we should not expect to find forest age distribution stabili ty even at very large spatial scales due to the spatial and temporal c orrelation of disturbances. (C) 1997 Elsevier Science B.V.