Ecology of Banksia
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.
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.
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.
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.
Firstly, the morphology of the Banksia flower makes it virtually inevitable that the stigma will be exposed to its own pollen, since it functions also as a "pollen-presenter".
However abortion rates are difficult to assess because the ovaries are deeply embedded in the "rhachis" (woody spine) of the inflorescence.
[4] 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.
In ecological literature, the species that are killed by fire but regenerate from seed are referred to as "fire-sensitive" or "seeders", while those that typically survive by resprouting from a trunk or underground lignotuber are called "fire-tolerant" or "sprouters".
Serotiny is achieved through the mechanism of thick, woody follicles, which are held tightly closed by resin.
Seeds retained in follicles are protected from granivores and the heat of bushfire, and remain viable for around ten years.
In one study, an estimated 13680 seedlings were counted over June–October following an experimental bushfire, but by January only eleven plants remained.
[5] Other threats to seedling establishment include predation by invertebrates such as grasshoppers and mites; and by vertebrates such as kangaroos and bandicoots.
Three Banksia species are currently declared endangered under Australia's Environment Protection and Biodiversity Conservation Act 1999, and a further two are considered vulnerable.
The most severe disease threat to Banksia is the introduced plant pathogen Phytophthora cinnamomi, commonly known as "dieback".
Banksia's proteoid roots make it highly susceptible to this disease, with infected plants typically dying within a few years of exposure.
Nearly every known wild population of B. brownii shows some signs of dieback infection,[7] and it is said that this species would be extinct within a decade if it were not protected.
For example, in southwestern Australia Banksia often occurs as an understory to forests of jarrah (Eucalyptus marginata), another species highly vulnerable to dieback.
[12] Direct injection of phosphite into tree stems appears to lack this disadvantage, but is costly to administer and restricted to known plants.
Because dieback thrives in moist soil conditions, it can be a severe problem for Banksias that are watered, such as in the cut flower industry and urban gardens.
If bushfires occur too frequently, plants are killed before they reach fruiting age or before they have developed a substantial seed bank.
[14] Longer time intervals also reduce populations, as more plants die of natural attrition between fires.
The proximity of urban areas creates a need to manage the ferocity and rate of occurrence of bushfires, resulting in pressure to prescribe regular low-intensity burns.
