Disturbance response strategies open coexistence opportunities in fire-prone heathlands

Disturbance is a popular hypothesis for the maintenance of high plant species diversity, but may potentially operate in different ways in different systems in nature. It is thus not a single mechanism, but may be involved in a variety of different diversity maintenance mechanisms. We investigate the nature of the diversity maintenance mechanism in a model of disturbance by fire in mediterranean heathlands. We have in mind the Fynbos and Kwongan, which are examples of plant communities which maintain high levels of diversity in the presence of a frequent fire disturbance regime. In such a community, shrub species commonly respond to fire by either re-seeding from a seed bank, or re-sprouting from surviving structures. Our model shows how these two complementary strategies can form the basis of stable coexistence under the stochastic disturbance of fires. Using a general approach to quantifying coexistence mechanisms, we show that the underlying coexistence mechanism is the spatial storage effect, and elucidate the dependence of mechanism strength on underlying life history traits. While many mechanisms of coexistence may be present in an actual community, the storage effect generated by these strategic responses to disturbance is sufficient to stabilize competitive coexistence of species with complementary life-history traits.