Banksia Rosserae - Ecology

Ecology

Very little is known of the ecology of B. rosserae. Its massive lignotuber is clearly an adaptation to desert conditions, providing a store of water during extended periods of drought, and a store of energy from which it can resprout after bushfire. Marriott also considers its papery bark to be an adaptation to desert conditions, although he does not elaborate on how the plant benefits from it.

Flowering apparently occurs only after rain, and hence may be separated by periods of many years. Pollinators have not been recorded for the species, but extensive data from other Banksia species suggests that insects, birds and nectariferous mammals would all play a role. There is clearly no shortage of pollinators, as most "cones" contain plenty of follicles. Although most follicles observed are closed, a few open ones have been found, suggesting that the species is weakly serotinous: that is, a few follicles open spontaneously or in response to rain, but most remain closed until burnt.

Seedlings would have little change of surviving in a normal dry season; establishment probably requires several consecutive seasons of good rain. The combination of a bushfire followed by several seasons of cyclonic storms probably only occurs every few hundred years, suggesting that opportunities for seedling recruitment are extremely rare. This would explain why the entire population appears to be over two hundred years old.

There is little information on threats to the species. All known plants appear to be in very good health and free of pests; it seems they are not eaten or damaged by the area's kangaroos, goats and sheep. Bushfire clearly poses no threat; and the area is free from Phytophthora cinnamomi dieback, a scourge of most other western Banksia species. Any concerns about future land use are abated by the fact that the largest population occurs on crown land, which is now being considered for a conservation reserve. In fact, the only perceived threat is the rarity of conditions conducive to seedling recruitment: "it may well be that this banksia has become so adapted to its harsh environment that its long-term future in the wild is in doubt."

Because of the absence of any specific threat to the species, it has not been declared rare or threatened. However, Olde and Marriott declared it to merit Priority One listing on the Department of Environment and Conservation's Declared Rare and Priority Flora List. Consequently they withheld the precise location of their specimens "for conservation reasons".