Burning for biodiversity or burning biodiversity? Prescribed burn vs. wildfire impacts on plants, lizards, and mammals

Fire is a large-scale phenomenon that affects ecosystems in many parts of the world. Wildfires can have highly destructive effects on habitats and the biota they support, and land managers frequently use prescribed burning to reduce the extent of wildfires and to benefit biodiversity. Underpinned by the predictions of the intermediate disturbance (IDH) and patch mosaic burn (PMBH) hypotheses, small-scale prescribed fires are thought to maximize biodiversity by creating heterogeneous mixes of early-, mid-, and late-successional habitats across the landscape. However, evidence supporting the positive effects of prescribed burning for biodiversity is mixed. We conducted a before-after control-impact study assessing the effect of prescribed burns and a wildfire on the alpha and beta diversity of plants, mammals, and lizards in hummock grassland in arid central Australia. Diversity was assessed for up to one year after each fire. Applying the IDH and PMBH we predicted that (1) small-scale, patchy, prescribed burns, by increasing habitat heterogeneity, would increase the alpha diversity and decrease the beta diversity of our study taxa in burned patches and (2) wildfire, by creating large, homogeneous burned patches, would reduce the alpha diversity of the study taxa in burned patches but promote beta diversity at the landscape level due to the differing assemblages expected to inhabit the burned and unburned areas. In accordance with our predictions, we found that fires of differing spatial scale and heterogeneity affected alpha and beta diversity in different ways, but also that the effects were taxon dependent. In contrast to our predictions, we found a surprisingly high level of congruence between alpha and beta diversity within taxa. Our results provide little support for the application of the intermediate disturbance and patch mosaic burn hypotheses and highlight instead the importance of stochastic events such as rainfall in influencing biodiversity over the immediate postfire period in arid environments. We suggest that prescribed fire is of little utility for the broadscale conservation of biodiversity due to taxon-dependent and unpredictable species responses, but that it may be useful in creating fire breaks that serve to protect the habitats of fire-sensitive species from the effects of broadscale wildfire.