Temporal fire disturbance patterns on a forest landscape

Potential temporal fire disturbance patterns on a forest landscape were investigated using a fire regime model with four different fire probability functions: (1) forest age-independent; (2) hyperbolic increase with forest age; (3) sigmoid increase with age; and (4) linear increase with age. Different combinations of parameter values for a logistic equation were used to approximate different fire probability functions. An extensive model behavior study suggested that fire regimes similar to the observations in Ontario could result from any of the fire probability functions, but with different parameter values. Simulation results on the case study area indicated that when the fire rotation period was fixed to 200 years (corresponding to fire regimes in the southern part of northwestern Ontario), the predicted temporal disturbance patterns (average interval between two successive fires) were similar for small and intermediate fires, but different for large and severe fires. The results from the fire probability function with a sigmoid shape appeard the most appropriate among the four tested fire probability functions. The average interval between two successive fires for each size group is: small fires every 5.8 years, intermediate fires every 34.4 years, and large fires every 151.6 years. Better prediction of a temporal disturbance pattern, especially for large and severe fires, will require an explicit understanding of the quantitative relationship between fire probability and forest age.