Banksia Prionotes - Distribution and Habitat

Distribution and Habitat

Banksia prionotes occurs throughout much of the Southwest Botanical Province, occurring both along the west coast and well inland, and ranging from Shark Bay (25°30′S) in the north, to Kojonup (33°50'S) and Jerramungup (34°24'S 118°55'E) in the south and south-east respectively. It grows among tall shrubland or low woodland, mostly in the swales and lower slopes of dunes, and shows a very strong preference for deep white or yellow sand.

It is most common amongst the kwongan heath of the Geraldton Sandplains north of Jurien; it has a fairly continuous distribution there, often as the dominant species, and extends inland to around the 350 mm isohyet. On the Swan Coastal Plain to the south, its distribution is discontinuous, being largely confined to patches of suitable sand in the narrow transition zone where tuart forest gives way to jarrah forest. With the exception of a population at Point Walter (32°00′S), it does not occur on the sandplain south of the Swan River.

The soils east of the Darling Scarp are generally too heavy for this species, with the exception of some isolated pockets of deep alluvial or aeolian yellow sand. B. prionotes thus has a very patchy distribution east of the scarp. This area nonetheless accounts for around half of its geographic range, with the species extending well to the south and south-east of the scarp. In total, the species occurs over a north–south distance of about 815 km (500 mi), and an east–west distance of about 125 km (80 mi).

The species is almost totally restricted to the swales and lower slopes of dunes. Various reasons for this have been proposed; on the one hand, it has been argued that its dependence on ground water necessitates that it grow only where ground water is relatively near the surface; on the other hand, it has been suggested that it cannot survive in higher parts of the landscape because fires are too frequent there. The latter hypothesis is supported by the recent expansion of B. prionotes along road verges of the Brand Highway, where fires are relatively rare. Despite B. prionotes' occurrence in lower parts of the landscape, it does not occur in areas prone to flooding, because of its intolerance of heavy soils, and because extended periods of flooding kill seedlings. However, recent falls of the water table on the Swan Coastal Plain have seen B. prionotes replace the more water-loving Banksia littoralis in some areas that were previously flood-prone.