Fire Feedbacks with Vegetation and Alternative Stable States

Positive feedbacks between vegetation and fire disturbance may lead to nonlinear ecosystem responses to variation in fire regime. We used a cellular automaton model of fire|vegetation dynamics based on pine savanna communities to explore the potential for fire|vegetation feedbacks to lead to ecological thresholds and abrupt transitions between alternate ecosystem states. We show that (i) ecosystems can rapidly move between grassland and forest states in response to gradual changes in fire regimes or initial landscape composition and that (ii) hurricane disturbances can mediate the frequency of fire that leads to ecological thresholds. Nonlinear ecosystem dynamics lead to sensitivity to initial conditions and bistable ecological communities that can exist in either a grassland or forest state under the same disturbance frequency. Our results indicate that gradual changes in global climate that influence disturbance frequency may result in the rapid transformation of landscapes through feedbacks between fire and vegetation.