Ecology of Banksia

Banksia in its environment

The ecology of Banksia is the relationships and interactions among the plant genus Banksia and its environment. Banksia has a number of adaptations that have so far enabled the genus to survive despite dry, nutrient poor soil, low rates of seed set, high rates of seed predation and low rates of seedling survival. These adaptations include proteoid roots and lignotubers; specialised floral structures that attract nectariferous animals and ensure effective pollen transfer; and the release of seed in response to bushfire. The arrival of Europeans in Australia has brought new ecological challenges. European colonisation of Australia has directly affected Banksia through deforestation, exploitation of flowers and changes to the fire regime. In addition, the accidental introduction and spread of plant pathogens such as Phytophthora cinnamomi (dieback) pose a serious threat to the genus's habitat and biodiversity. Various conservation measures have been put in place to mitigate these threats, but a number of taxa remain endangered.

Banksia is a genus of around 170 species in the plant family Proteaceae. An iconic Australian wildflower and popular garden plant, Banksias are most commonly associated with their elongate flower spikes and fruiting "cones", although less than half of Banksia species possess this feature. They grow in forms varying from prostrate woody shrubs to trees up to 30 metres tall, and occur in all but the most arid areas of Australia.

The pollination ecology of Banksia has been well studied, because the large showy inflorescences make it easy to conduct pollination experiments, and the pollination roles of nectariferous birds and mammals makes the genus a popular subject for zoologists. Visits to Banksia inflorescences by western honeybees and nectarivorous birds are often observed and are obviously important to pollination. Also important are visits by nectariferous mammals, although such visits are rarely observed because these mammals are usually nocturnal and reclusive. Studies have found that Banksia inflorescences are foraged by a variety of small mammals, including marsupials (such as honey possums and yellow footed antechinus, Antechinus flavipes), and rodents (such as the pale field rat, Rattus tunneyi). Studies in New South Wales and in Western Australia found that small mammals can carry pollen loads comparable to those of nectarivorous birds, likely making them effective pollinators of many "Banksia" species. Other studies have shown that the relative importance of vertebrates and invertebrates for pollination may vary from species to species, with some Banksia species exhibiting reduced fruit set when vertebrate pollinators are excluded, while others are unaffected by the exclusion of vertebrates and set some fruit even when all pollinators are excluded. Almost all Banksia species studied so far have shown outcrossing rates among the highest ever recorded for plants; that is, very few Banksia plants are found to occur as a result of self fertilisation. In all cases these are rare species that occur in very small populations, which increases the probability of self fertilisation, and may discourage visits by pollinators. Other threats to seedling establishment include predation by invertebrates such as grasshoppers and mites; and by vertebrates such as kangaroos and bandicoots.

Banksia seed is predated by a birds and insects. Insects also feed on stems, leaves, flowers and cones. Some insects cause galls. Many species of fungi live on Banksia plants, including Banksiamyces. Most Banksia species are highly susceptible to Phytophthora cinnamomi dieback.

The biodiversity of Banksia is impacted by a range of processes. Major threats include disease; changes in fire frequency and intensity; clearing of land for agriculture, mining, urban development and roads; and exploitation of flowers, seeds and foliage by the cut flower and other industries. Three Banksia species are currently declared endangered under Australia's Environment Protection and Biodiversity Conservation Act 1999, and a further two are considered vulnerable.