An iconic Australian wildflower and popular garden plant, Banksia is a
genus of around 170 species of the Proteaceae family. Mostly associated
with their long flower spikes and fruiting "cones", they grow as woody
shrubs or trees up to 30 meters tall and occur in most parts of
Australia.Overcoming Ecological Challenges
Banksias relationship and interaction with its environment is unique.
Despite dryness, poor soil, low rates of seed set, high rates of seed
predation and low rates of seedling survival, the adaptability of
Banksias have ensured their survival. Adaptations like proteoid roots,
lignotubers, and specialized floral structures attracting nectariferous
animals for pollination and the release of seed by bushfire help them to
overcome ecological challenges.
How natural bushfire helps in Banksia conservation
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 re-sprouting from a trunk or underground lignotuber are
called "fire-tolerant" or "sprouters". Seeds retained in follicles are
protected from granivores and the heat of bushfire, and can germinate
after ten years. While separator ensures that the seeds fall onto cool
ground, seed is typically released over a period of about 90 days.
Banksia trees can naturally survive bushfires because they have very
thick bark that protects the trunk from fire and they have lignotubers
from which they can resprout after fire. Bushfires promote population of
Banksias through serotiny, though frequent bushfires kill plants before
they attain the fruiting age or before they develop a substantial seed
bank.
If bushfires occur after 20 years then the seed dispersal procedure of
Banksia plants would be most effective. The intensity of fire would also
count. Overly frequent fires prevent the recruitment of new adults, and
populations decline at the rate that adults die. The proximity of urban
areas create a need to manage the ferocity and rate of occurrence of
bushfires, resulting in pressure to prescribe regular low-intensity
burns, which is at odds with the conservation needs of Banksias.
Establishment of seedlings - a threat
Competition for soil moisture endangers the survival of Banksias to
adulthood. Other threats to seedling establishment include predation by
invertebrates like grasshoppers and mites and by vertebrates like
kangaroos and bandicoots. Banksia plants are predated by birds, fungi
and insects on all parts like seeds, stems, leaves, flowers and cones.
The threat of Diseases
Dieback is the most prominent disease affecting Banksias, caused by
the plant pathogen Phytophthora cinnamomi. The roots of the plant make
are more susceptible to this root-rotting disease.
Dieback infestation reached epidemic proportions in southwest Western
Australia, affecting the makeup of plant communities. The B. brownii
species of Banksias is almost at the verge of extinction due to the
constant threat of Dieback. Other vulnerable species include B. cuneata,
B. goodii, B. oligantha and B. verticillata.
Phosphite supplements boost the resistance of both infected and
uninfected plants, and also acts as a direct fungicide, though foliar
spraying of Phosphite adversely affects root and shoot growth. Costly to
administer and restricted to known plants direct injection of phosphite
into tree stems is devoid of such demerits.
Other diseases to which Banksia species are vulnerable include the
aerial canker fungus Zythiostroma and the parasitic fungus Armillaria.
Problem posed by land clearing
Nearly 55% of Banksia woodlands had been cleared by 1986 for
agriculture, mining, urban development and roads. The direct loss of
population and habitat has also led to an increased spread of weeds and
disease. The varieties threatened by clearing include B. hookeriana, B.
cuneata and B. goodii fall into the endangered category.
Exploitation by wildflower industry
Heavy harvesting of blooms substantially reduces harvest of head
production, resulting in a smaller seed bank. Immensely favored by
Australian wildflower industry, blooms are commercially harvested from
around 29 Banksia species, the most popular being B. hookeriana, B.
coccinea and B. baxteri. There were around 1000 licensed commercial
pickers operating in the state, harvesting around 675,000 blooms from B.
hookeriana alone as of 1990.
The Conservation Efforts
Major threats affecting biodiversity of Banksias include disease,
changes in fire frequency, fire intensity, clearing of land for
agriculture, mining, urban development, exploitation of flowers, seeds,
foliage by the cut flower and other industries.
Nearly, 19 Banksias varieties of Western Australia are currently
declared rare, hence they are protected by Australian Environment
Protection and Biodiversity Conservation Act 1999 (EPBC Act), and the
Western Australian Wildlife Conservation Act 1950.
A number of protective measures have been implemented to slow the spread
of disease and boost the survival rates of infected plants. Measures
include restricting access to infected and susceptible sites, the
collection and cold storage of seed, and the treatment of plants with
phosphite.
European colonization of Australia has directly affected Banksia through
deforestation, exploitation of flowers and changes to the fire regime.
Moreover, the accidental introduction and spread of plant pathogens like
Phytophthora cinnamomi (dieback) pose a serious threat to the habitat of
Banksias and biodiversity. Various conservation measures have been put
in place to mitigate these threats, but a number of Banksia varieties
still remain endangered.
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