Responses of mammals to time since fire are indirect and dependent on fire-driven habitat resources

Background/Question/Methods

Fire regime changes threaten biodiversity globally, but our understanding of how this threat manifests is still developing. For example, direct relationships between Australian mammal abundance and time since fire (TSF) can be unclear and are seldom found. Instead, some evidence suggests that mammals respond more directly to habitat resources, which may have their own relationship with TSF. Predictions about animal occurrence based on the fire regime are therefore difficult. Previous studies have examined how mammal occurrence responds to fire history or to habitat structure, or habitat structure to fire history, but rarely considered these three factors together.We used a network modelling approach to explore these relationships in fragmented and fire-prone heathy woodlands in South Australia. We related ground-dwelling mammal species activity to habitat structure, habitat structure to TSF, and mammal species activity to TSF simultaneously. This allowed us to find direct effects of TSF, as well as indirect effects as mediated by habitat resources. We also contrasted these effects against those of the underlying landscape structure, measured by the overall proportion of the landscape surrounding sites covered by native heathy woodland vegetation.

Results/Conclusions

None of the seven mammal species analysed were related directly to time since fire. However, most mammal species responded to at least one of the measured habitat structure variables, three of four of which did vary with TSF. Of the mammals that were related to habitat structure, some also showed indirect responses to growth stage as a result of changes to habitat structure. All but one species was related to the surrounding extent of heathy woodland.Responses of ground dwelling mammal species to time since fire may therefore not be obvious, unless accounting for the processes underlying such relationships (i.e. the importance of habitat resources). In addition, other environmental factors such as landscape structure may play an important role.Fire management planning for fauna conservation should closely incorporate plant community responses to capture the whole-system response, as mammal responses to the fire regime may be mediated by such fire-driven habitat resources. Our results will help land managers understand the immediate and longer-term impacts of their fire management activities, as well as changes to mammal communities after wildfires, by identifying the direct and indirect effect of fire in a landscape with multiple threats to native biodiversity.