Effects of a short fire-return interval on resources and assemblage structure of birds in a tropical savanna

Fire frequency is a key land management issue, particularly in tropical savannas where fire is widely used and fire recurrence times are often short. We used an extended Before-After-Control-Impact design to examine the impacts of repeated wet-season burning for weed control on bird assemblages in a tropical savanna in north Queensland, Australia. Experimentally replicated fire treatments (unburnt, singularly bunt, twice burnt), in two habitats (riparian and adjacent open woodland), were surveyed over 3 years (1 year before the second burn, 1 year post the second burn, 2 years post the second burn) to examine responses of birds to a rapid recurrence of fire. Following the second burn, species richness and overall bird abundance were lower in the twice-burnt sites than either the unburnt or singularly burnt sites. Feeding group composition varied across year of survey, but within each year, feeding guilds grouped according to fire treatment. In particular, abundance of frugivores and insectivores was lower in twice-burnt sites, probably because of the decline of a native shrub that produces fleshy fruits, Carissa ovata. Although broader climatic variability may ultimately determine overall bird assemblages, our results show that a short fire-return interval will substantially influence bird responses at a local scale. Considering that fire is frequently used as a land management tool, our results emphasize the importance of determining appropriate fire-free intervals.