Population Ecology of Two Endemic, Fire-sensitive, Blue Mountains Banksia Taxa (Proteaceae) in Response to Fire

Abstract

Banksia penicillata (northern Blue Mountains) and Banksia paludosa subsp. astrolux (Southern Highlands) occur in small, isolated populations and occasionally as isolated individuals. We undertook a field study of both species to better understand their population ecology in relation to fire. Both are large, serotinous, fire-sensitive shrubs with plant-stored seedbank and a relatively short lifespan (<50 years); both were impacted by the severe December 2019 fires. Recruitment is generally fire-related, but some recruitment also occurs in the absence of fire. At a landscape-scale, populations of Banksia penicillata occupy dry sandstone ridgetops, providing variable protection from major fires, with occasional intergenerational long-distance seed dispersal establishing populations of variable duration in sites which do not usually act as fire refugia. Banksia paludosa subsp. astrolux has similar responses, but generally smaller populations and more restricted range. Although some plants have been reported as surviving the 2019 fire in nearby rocky ridgetop refugia, all plants were killed in our study populations and seedling recruitment has not replaced all pre-fire occurrences, despite 18 years since the previous fire. Using a precautionary approach, and in the context of a rapidly changing climate, we recommend that both species would benefit by having populations of varying fire histories and ages >15 years old across the landscape, including some sites with fire intervals >30 years, to provide increased opportunities for distance-dispersal and establishment of new fruiting populations. Applying IUCN threatened species criteria, there is a strong case for listing Banksia paludosa subsp. astrolux as Endangered and Banksia penicillata as Vulnerable.