Short fire-interval and drought lead to decline in an obligate seeding Banksia

Abstract

Context Fire frequency is predicted to increase with climate change and represents a major threat to plant communities around the world. Despite this, there are few published examples quantifying impacts of short fire-intervals, even for those species most at risk. Aims We examined the impact of the 2019/2020 Black Summer megafires (and associated fire regime) on the highly restricted, obligate seeding shrub Banksia paludosa subsp. astrolux from south-eastern Australia. Methods We surveyed sites after the 2019/2020 megafires to quantify plant survival, pre-fire plant size, canopy seed bank, number of growth whorls, and the level of seedling recruitment after the fires. Key results We found no plants in areas with a short interval (4–5 years) between recent fires (burnt in both 2015 and 2019/2020), likely due to death of standing juvenile plants during the most recent fire. Where the interval between recent fires was longer (10+ years), we found estimated population declines of 44% (range 0–93% across sites, with a small increase at one site). Declines were influenced by poor post-fire seedling recruitment due to low canopy seed bank availability at the time of the 2019/2020 megafires. Reduced seed availability was likely influenced by pre-fire drought and/or low levels of serotiny. Conclusion Ongoing management of the obligate seeding serotinous subspecies in fire-prone systems needs to ensure that future fire regimes maintain intervals long enough between fires for sufficiently large canopy seed banks to accumulate. Implications Interactions with other climate-driven changes, such as increased fire severity or more intense drought, need to be incorporated into studies for more robust assessment into the future.