Are forest gullies refuges for birds when burnt? The value of topographical heterogeneity to avian diversity in a fire-prone landscape

In forest ecosystems, uniformity in fire spread may be moderated by topography such that sheltered areas (e.g. gullies) escape fire. However, gullies are not immune to fire and, under extreme fire weather conditions, can burn. This may compromise their habitat value, and diminish differences in faunal communities across topographical gradients. We investigated the extent to which differences in avian communities persist when subjected to uniform fire severity and fire history across the gully and slope components of a forest site. We predicted that there would be less difference with increasing fire severity or long absence of fire. Birds were surveyed at 91 paired gully/slope sites in foothill eucalypt forests, two to three years after a large, severe wildfire in south-eastern Australia. Sites were stratified in relation to four levels of fire severity (unburnt through to crown burnt) and two levels of fire history prior to the wildfire (burnt < 3 years, or > 20 years). Under similar conditions of fire severity and fire history, gullies maintained greater species richness and abundance than did slopes; averaging 13% greater species richness and 32% greater abundance, along with a distinct bird assemblage. However, contrary to predictions, topographical differences for most avian responses did not diminish with increasing fire severity or in the long absence of fire prior to the wildfire. This study highlights the value of forest gullies in maintaining or facilitating the recovery of distinct avian communities after wildfire, even when the gullies themselves have been burnt.