Bat activity before and after a severe wildfire in Pilliga forests: Resilience influenced by fire extent and landscape mobility?

Abstract

AbstractWildfires are becoming increasingly severe and common in many parts of the world, yet their effects on certain taxa remain poorly studied. In November 2006, a major wildfire occurred in the Pilliga forests of north‐west New South Wales, Australia. This fire was severe and extensive, burning more than 120 000 ha. Prior to the fire, we conducted a study in the affected area assessing bat activity in relation to flyway size and riparian zones, allowing us to opportunistically compare before – and – after effects of wildfire on bats in burnt and unburnt areas. We assessed how bat activity and bat composition changed from 1 year pre‐fire to 1 year post‐fire and 4 years post‐fire, accounting for the effects of flyway size. A BACI analysis showed that there was an effect of time (year) on bat activity, with activity markedly reduced in both burnt and unburnt sites in the year post‐ fire, before recovering 4‐years post‐fire to levels that approached pre‐burn activity. However, there was no treatment or interaction effect, indicating fire alone did not affect bat activity at our sites. Activity was 50% lower at supplementary sites more remote (~5 km) from the fire edge. Multi‐dimensional scaling and permanova described a strong effect of year but no evidence of fire or stream size‐mediated effects on species composition. The drop in activity post‐fire coincided with a period of drought that subsequently broke in the year prior to our survey 4 years post‐fire. Some species‐specific responses to the fire were evident and depended on the proximity to unburnt forest. We suggest the potential for landscape re‐assortment, whereby some species may move from the unburnt landscape into the burnt landscape, possibly in response to a resource pulse of insects. A landscape pattern of movement could obscure the detection of direct fire effects on mobile bats. We suggest fire extent, proximity to unburnt vegetation and severity are key considerations when interpreting the response of bats to wildfire.