Demographic impacts of low- and high-intensity fire in a riparian savanna bird: implications for ecological fire management

ABSTRACT

1. Climate change is driving changes in fire frequency and intensity, making it more urgent for conservation managers to understand how species and ecosystems respond to fire. In tropical monsoonal savannas – Earth’s most fire-prone landscapes – ecological fire management aims to prevent intense wildfires late in the dry season through prescribed low-intensity fire early in the dry season. Riparian habitats embedded within tropical savannas represent critical refuges for biodiversity, yet are particularly sensitive to fire. Better understanding of the impact of fire – including prescribed burns – on riparian habitats is therefore key, but requires long-term detailed post-fire monitoring of species’ demographic rates, as effects may persist and/or be delayed.

2. Here, we quantify the multi-year impacts of prescribed low-intensity and high-intensity fire on the density, survival, reproduction and dispersal of the threatened western purple-crowned fairy-wren (Malurus coronatus coronatus), in an exceptionally well-studied individually-marked population.

3. Following low-intensity fire, bird density was reduced in the burnt compared to adjacent unburnt riparian habitat for at least 2.5 years. This was a result of reduced breeding success and recruitment for two years immediately following the fire, rather than mortality of adults or dispersal away from burnt habitat.

4. In contrast, a high-intensity fire (in a year with low rainfall) resulted in a sharp decline in population density 2-8 months after the fire, with no signs of recovery after 2.5 years. The decline in density was due to post-fire adult mortality, rather than dispersal. Breeding success of the (few) remaining individuals was low but not detectably lower than in unburnt areas, likely because breeding success was poor overall due to prevailing dry conditions.

5. Hence, even if there is no or very low mortality during fire, and no movement of birds away from burnt areas post-fire, both low- and high-intensity fire in the riparian zone result in reduced population density. However, the mechanism by which this occurs, and recovery time, differs with fire intensity. To minimise the impacts of fire on riparian zones in tropical savannas, we suggest employing low-intensity prescribed burns shortly after the breeding season in years with good rainfall.