Wildfire Impact on Coastal Groundwater-Dependent Heathland: Structural and Floristic Responses and Management

Abstract

Fire is a critical driver of many Australian ecosystems, including the groundwater-dependent heathlands on Australia's east coast. However, the effects of intense wildfires under drought conditions, associated with depletion of groundwater and soil moisture, are poorly documented, and mechanisms of vegetation recovery, particularly for obligate seeders and resprouters, are unclear. We aimed to assess the impacts of an intense wildfire on vegetation structure and species composition in a long-unburnt groundwater-dependent heathland, focusing on the responses of obligate seeder and resprouter species and the role of environmental factors in post-fire recovery. A before–after control–impact study was conducted at Bribie Island, Queensland, following a 2019 wildfire. Vegetation responses were analysed using a generalised linear model, with environmental factors such as rainfall, soil moisture and groundwater levels evaluated for their influence on recovery. Our results demonstrated that shrub counts recovered and exceeded pre-fire levels within 3 years. Species richness returned to pre-fire levels after 2 years but did not reach the peak observed during high-moisture conditions 3 years before the fire. The post-fire response included a slow species richness rebound and incomplete recovery. Obligate seeders showed a variable response, with some dominant populations failing to recover, while resprouters exhibited significant declines. These outcomes are linked to the varying capacity of heathland flora to cope with intense fire during low soil moisture and groundwater deficits. The results of this study suggest that intense wildfires during dry conditions may adversely affect some obligate seeder and resprouter populations, even after long fire intervals. Full consideration of fire intensity, timing and environmental conditions such as soil moisture and groundwater levels are essential for effective vegetation management. Furthermore, prescriptive fire management should focus on burning during periods of high soil moisture to reduce fire severity and enhance post-fire regeneration.