Functional and compositional diversity display a maximum at intermediate levels of fire frequency when modeling the plant-fire feedback

Abstract

Fires are generally considered to promote biodiversity, although the exact relationship is unclear, because it can be affected by several factors, including fire regime and ecosystem type. Given the ongoing global change, a better understanding of this connection is needed to assess the extent to which projected increases in fire frequency may affect current biodiversity trends. A major challenge lies in vegetation-fire feedback, which often mediates changes in fire regimes. To shed light on the role of fires in promoting or limiting biodiversity, we studied the compositional and functional diversity of simulated plant communities along a gradient of fire frequencies. We extended an existing model to include a large number of species. The model reproduces plant successional dynamics and is parameterized to represent Boreal and Mediterranean communi-ties. Fire events are stochastic, with frequencies that depend on community flammability, and plants have different fire responses, thus creating a vegetation-fire feedback. For both ecosys-tems, we found that fires generally had a positive effect on both compositional and functional diversity. Furthermore, in most cases, both peaked at intermediate fire frequencies. Interestingly, compositional and functional diversity were correlated but did not reach their maximum values in the same communities. This seemingly underlines that a certain degree of functional similarity may be necessary to achieve maximum species richness. These results stem from the vegetation-fire feedback, highlighting its importance for predicting ecosystem responses to global change, including biodiversity losses and wildfire regime shifts.