An Individual-Based Model of Chaparral Vegetation Response to Frequent Wildfire

In recent years, the Santa Monica Mountains (SMM) have been plagued by frequent wildfires which threaten the native chaparral species. Nonsprouting chaparral species are completely killed by a fire, but their seeds germinate in response to fire cues. Facultative sprouters both resprout after a wildfire and release seeds that germinate post-fire. This project is based on data collected since 1986 at a biological preserve adjacent to the Malibu campus of Pepperdine University with an average fire return interval of 7.5 years. We present a spatial model that simulates the growth, seed dispersal and resprouting behavior of individual shrubs that compete for space and resources in a domain similar to our study site. The model incorporates varying rainfall and fire frequency as well as the competition between plants for scarce resources. Our simulation reproduces the change in plant community structure at our study site such as the local extinction of Ceanothus megacarpus due to short fire return intervals. Our simulations also predict frequent wildfires will drastically reduce the number and size of individual shrubs. A mathematical model of this system is important because a reduction of vegetation cover can cause a decrease in slope stability that leads to rock and mudslides