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

A spatially explicit landscape model of disturbance and vegetation successi on, LANDIS, was used to examine the effect of fire regime on landscape patt erns of functional group dominance in the shrublands and forests of the sou thern 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 f unctional groups on an even-aged landscape. Calibration of the three fire r egime treatments resulted in simulation of fire cycles within 7% of these i ntended values when fire cycles were averaged across ten replicated model r uns per treatment. Within individual 500-year model runs, the error in the simulated fire cycle (average area burned per decade) reached 11% for the m oderate and frequent fire cycle treatments and 53% for infrequent. The infr equent fire regime resulted in an old landscape dominated by the three most shade tolerant and long-lived functional groups, while shorter-lived and l ess shade tolerant seeders and resprouters disappeared from the landscape. The moderate fire regime, similar to what is considered the current fire re gime 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 regim e resulted in the persistence of all functional groups on the landscape wit h more even cover, but the same rank order as under the moderate regime. Th e model, originally developed for northern temperate forests, appears to be useful for simulating the disturbance regime in this fire-prone Mediterran ean-type ecosystem. (C) 2001 Elsevier Science B.V, All rights reserved.