A rare shrub needs to burn to avoid extinction

Banksia conferta, the Glasshouse Banksia, is a critically endangered tree or shrub. You can find it in a few locations in southeast Queensland and the Coorabakh National Park in New South Wales. But as time passes, you can see fewer and fewer of them. Stephen Bell and colleagues investigated if the problem was due to a lack of pollinators. In the Australian Journal of Botany, they describe their search to determine what it is that pollinates Banksia conferta in New South Wales.

The botanists knew that Eastern Pygmy Possums were important to the Queensland plants. The inflorescences of the New South Wales plants show attributes, like the production of a lot of nectar, that indicate that they use vertebrates for pollination. So, they set up camera traps in Coorabakh National Park between June and December 2019 to see what came visiting the plants.

The majority of visits came from just two animals, White-cheeked Honeyeaters, birds up to about 20cm / 8 inches long, and Sugar Gliders, possums that are similar to flying squirrels and a little larger than the honeyeaters. The number of visits seen indicated that a lack of pollinators is not the problem, yet only one site appeared to have many follicles developing seeds, and here say Bell and colleagues is the clue to the problem Banksia conferta faces because this site had a relatively recent fire.

“Flat Nellie, the only site where abundant follicles have been produced in recent years, has burnt twice in recorded history, namely, 63 and 11 years ago,” write Bell and colleagues. “In contrast, Beech Road and Big Nellie last burnt 56 and 63 years ago respectively, and the current individuals at those two sites are now of considerable age. The more recent fire at Flat Nellie explains the prevalence of Banksia individuals of shorter stature (presumably all new germinants, but possibly also older resprouted individuals from lignotubers and/or lateral root suckers), and it is likely that better flowering and fruiting has occurred here because plants (or ramets) are younger.”

Many Banksia plants use fire as part of their reproduction strategy, releasing the seeds after a fire. Because some of the locations in the study hadn’t burned, any new seedlings that tried to establish themselves would be up against strong but ageing opposition.

“[T]he absence of fire from both Beech Road and Big Nellie populations for over 55 years remains a concern, and with observations reported here of low follicle production (despite the presence of pollinators) and decaying older follicles, it seems likely that little new recruitment will occur without intervention. Fortunately, the ability of this species to resprout from lignotubers and subsurface roots should ensure persistence through drought and other stressors while awaiting fire,” write Bell and colleagues.

“The results from this study suggest that a fire (prescribed or wildfire) in one or both of Beech Road and Big Nellie will be beneficial to rejuvenate habitat and promote germination of those viable seeds that remain in the canopy before further follicle decay occurs. Importantly, this should be followed by a fire-free interval of perhaps 10 years to allow maturation and restoration of the canopy seed store.”

READ THE ARTICLE

Bell, S.A.J., Hunter, N. and Steed, A. (2022) “Lack of fire rather than pollinator absence may drive population decline in the critically endangered Banksia conferta (Proteaceae),” Australian Journal of Botany, 70(5), pp. 372–383. https://doi.org/10.1071/BT21143