The fire and flammability niches in plant communities

We construct a model of a multispecies forest that is often affected by major fires and explicitly incorporates life-history attributes of trees that are related to fire—flammability and susceptibility to fire. The model is used to explore coexistence mechanisms in forests; two fire-dependent coexistence mechanisms were identified. The first allows coexistence along a temporal axis since the last fire; this niche axis is well documented in the literature. The second coexistence mechanism relies on the influence of tree flammability on the incidence of fires and/or tree reproductive success. This “flammability niche” is explored in detail, with particular reference to eucalypt forests in Australia and Tasmania. Using the technique of linearized stability analysis 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-adapted tree are likely to coexist with a late-successional species if their 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-dependent ecosystems to maintain biodiversity. Although the motivation for this paper is observations on Australian eucalypt forests, the principles of coexistence that we discuss apply to all fire-prone forest and woodland ecosystems.