A model of surface fire, climate and forest pattern in the Sierra Nevada, California

A spatially explicit forest gap model was developed for the Sierra Nevada, California, and is the first of its kind because it integrates climate, fir e and forest pattern. The model simulates a forest stand as a grid of 15 x 15 m forest plots and simulates the growth of individual trees within each plot. Fuel inputs are generated from each individual tree according to tree size and species. Fuel moisture varies both temporally and spatially with the local site water balance and forest condition, thus linking climate wit h the fire regime. Fires occur as a function of the simulated fuel loads an d fuel moisture, and the burnable area is simulated as a result of the spat ially heterogeneous fuel bed conditions. We demonstrate the model's ability to couple the fire regime to both climate and forest pattern. In addition, we use the model to investigate the importance of climate and forest patte rn as controls on the fire regime. Comparison of model results with indepen dent data indicate that the model performs well in several areas. Patterns of fuel accumulation, climatic control of fire frequency and the influence of fuel loads on the spatial extent of fires in the model are particularly well-supported by data. This model can be used to examine the complex inter actions among climate, fire and forest pattern across a wide range of envir onmental conditions and vegetation types. Our results suggest that, in the Sierra Nevada, fuel moisture can exert an important control on fire frequen cy and this control is especially pronounced at sites where most of the ann ual precipitation is in the form of snow. Fuel loads, on the other hand, ma y limit the spatial extent of fire, especially at elevations below 1500 m. Above this elevation, fuel moisture may play an increasingly important role in limiting the area burned. (C) 1999 Elsevier Science B.V. All rights res erved.