THE FIRE AND FLAMMABILITY NICHES IN PLANT-COMMUNITIES

We construct a model of a multispecies forest that is often affected b y major fires and explicitly incorporates life-history attributes of t rees that are related to fire-flammability and susceptibility to fire. The model is used to explore coexistence mechanisms in forests; two f ire-dependent coexistence mechanisms were identified. The first allows coexistence along a temporal axis since the last fire; this niche axi s is well documented in the literature. The second coexistence mechani sm relies on the influence of tree flammability on the incidence of fi res and/or tree reproductive success. This ''flammability niche'' is e xplored in detail, with particular reference to eucalypt forests in Au stralia and Tasmania. Using the technique of linearized stability anal ysis about a positive equilibrium, we explored the local stability of assemblages with randomly generated life-history attributes. A robust and testable prediction of the model is that two species of fire-adapt ed tree are likely to coexist with a late-successional species if thei r flammabilities are very different, and if the most flammable species is more susceptible to fire but less likely to die as a result of non -fire causes. Our results have implications for managing fire-dependen t ecosystems to maintain biodiversity. Although the motivation for thi s paper is observations on Australian eucalypt forests, the principles of coexistence that we discuss apply to all fire-prone forest and woo dland ecosystems.