Low- and high-intensity fire in the riparian savanna: demographic impacts in an avian model species and implications for ecological fire management.
Abstract
Climate change is driving changes in fire frequency and intensity, making it more urgent for conservation managers to understand how species and ecosystems respond. 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 burns early in the dry season. Riparian habitats embedded within tropical savannas represent critical refuges for biodiversity, yet are particularly fire-sensitive. 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. We analyse impacts of (prescribed) low-intensity and (prescribed but escaped) high-intensity fire in northern Australian riparian and adjacent savanna habitat. We quantify multi-year impacts on density, survival, reproduction and dispersal of an endangered riparian bird, the western purple-crowned fairy-wren (Malurus coronatus coronatus), in a well-studied individually marked population. Following low-intensity fire, bird density was reduced by >20% in burnt compared to adjacent unburnt riparian habitat for ≥2.5 years. This was a result of reduced breeding success and recruitment for 2 years immediately following fire, rather than mortality or dispersal of adults. In contrast, high-intensity fire (in a dry year) resulted in a sharp decline in population density by 50% 2-8 months after 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. Synthesis and applications. Even if there is no or very low mortality during fire, and no movement of birds away from burnt areas, both low- and high-intensity fire in the riparian zone reduce population density. However, the mechanism by which this occurs, and recovery time, differs with fire intensity. To minimise impacts of fire on riparian zones in tropical savannas, we suggest employing low-intensity prescribed burns under optimal conditions shortly after the breeding season.