Simulating the effects of different fire regimes on plant functional groups in Southern California

A spatially explicit landscape model of disturbance and vegetation succession, LANDIS, was used to examine the effect of fire regime on landscape patterns of functional group dominance in the shrublands and forests of the southern California foothills and mountains. Three model treatments, frequent (35 year), moderate (70 year), and infrequent (1050 year) fire cycles, were applied to the landscape for 500 year. The model was calibrated and tested using a dataset representing an initial random distribution of six plant functional groups on an even-aged landscape. Calibration of the three fire regime treatments resulted in simulation of fire cycles within 7% of these intended values when fire cycles were averaged across ten replicated model runs per treatment. Within individual 500-year model runs, the error in the simulated fire cycle (average area burned per decade) reached 11% for the moderate and frequent fire cycle treatments and 53% for infrequent. The infrequent fire regime resulted in an old landscape dominated by the three most shade tolerant and long-lived functional groups, while shorter-lived and less shade tolerant seeders and resprouters disappeared from the landscape. The moderate fire regime, similar to what is considered the current fire regime in the southern California foothills, resulted in a younger landscape where the facultative resprouter persisted along with the long-lived shade tolerant functional groups, but the obligate seeder with low fire tolerance disappeared, despite its moderate shade tolerance. The frequent fire regime resulted in the persistence of all functional groups on the landscape with more even cover, but the same rank order as under the moderate regime. The model, originally developed for northern temperate forests, appears to be useful for simulating the disturbance regime in this fire-prone Mediterranean-type ecosystem.