Regional profile
The principle land use in the Kimberley region is cattle
grazing. Significant areas are also taken up by conservation
reserves and parks, and by Aboriginal lands. Weed concerns are
therefore predominantly pastoral and environmental. To an extent
the remoteness and relative aridity of this region has protected it
from major weeds that occur in savanna country to the east such as
mimosa and prickly acacia. Small areas of rubbervine are present,
but are closely monitored. Nevertheless, the soils and climate of
the Kimberley region are well suited to a range of weeds currently
found elsewhere in Northern Australia. Stock movements, and the
effect of tourists moving through areas need to be well monitored
therefore to ensure that the region is protected from weedy
invasion. The checkpoint on the NT/WA border helps keep weeds out
of the Kimberley. All stock entering from interstate are checked
for weed seeds, and trucks are washed out.
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Noogoora burr Photo: Greg Calvert
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Noogoora burr
This broad-leaved weed originally comes from North America.
Noogoora Burr (Xanthium occidental) is a branched, somewhat
sprawling woody herb that grows up to 2 metres and has grapevine
shape leaves which are covered in stiff hairs. It flowers from
April to May and has woody burrs with hooked spines in June to
September. The plant when young is toxic to stock and replaces
other desirable pasture plants, native shrubs and ground covers
that offer better protection against soil erosion. Potential
dispersal mechanisms include stock, feral animals, watercourses and
vehicles.
In the Kimberley region Noogoora burr has invaded grazing land
and formed thick infestations along river banks. Three river
systems, the Fitzroy, the Nicholson and the lower Ord, are infested
with this weed. There are over 360 km of it along the Fitzroy, so
the management aim for producers and authorities is that of
containment, rather than removal. Much of the Fitzroy River and the
lower Ord are currently in quarantine specifically to lessen the
chances of the burr being transported to sheep producing areas down
south. This means that no one outside of station staff and visitors
may go to burr infested areas. Livestock are inspected on their way
out of these areas to ensure that they are burr free. The
Agricultural Protection Board has set up public access areas along
the Fitzroy river which are kept free of Noogoora burr.
While fire can be useful for destroying seed beds and
controlling the spread of Noogoora thickets, it is not generally
used as a management tool. More commonly adopted control methods
are either chemical or hand pulling of plants, both of which are
carried out during the plant's growing season. To see a recent list
of research findings on noogoora burr
click here .
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Bellyache bush Photo: Greg Calvert
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Bellyache bush
The common name of this plant is a fair hint at some of the
problems it can cause. Bellyache bush (Jatropha
gossypifolia) is described as a shrub or small tree, 2-3 metres
high. It has toxic seeds and the mature plants form thick,
impenetrable stands. It displaces favourable grazing species and
infested land becomes unsuitable for grazing. Immediate dispersal
is by explosive opening of the seed capsule. Longer distance
dispersal is likely to occur through mud adhering to vehicles and
animals and in water flow.
In the Kimberley region, bellyache bush is a declared weed in
the west, but not in the east where large populations are beyond
removal, and management is limited to containment. There are
particularly dense stands to be found around Turkey Creek, Bow
River, the top of Lake Argyle, and Halls Creek and surrounding
rivers. Bellyache bush is continuing to spread at an alarming rate
along permanent water bodies. To see a recent list of
research findings on bellyache bush
click here .
Parkinsonia
Stands of parkinsonia (Parkinsonia aculeata) can be found
across the breadth of the Kimberley region. Hundreds of kilometres
of the banks of Lake Argyle, Christmas Creek and the Ord and
Fitzroy rivers are infested with Parkinsonia.
It is another thorny invader that forms dense thickets at the
expense of native species. Stock access to watercourses is often
restricted by these thickets. Parkinsonia has the potential to
colonise vast areas of the Kimberley via the long distance
dispersal of seeds which occurs through ingestion, conveyance and
expulsion by birds and animals. The seeds can also be moved in mud
that sticks to animals and vehicles. To see a recent list on the
research findings of parkinsonia
click here .
Calotrope/ Rubber tree
Calotrope (Calotropis procera) is widespread in the east
of the Kimberley region. It has a waxy appearance and grows 2-4
metres high. Its flowers, which appear between January and
September, are white with purple/pink outer edges on the petals.
Controlling the distribution of this bush is made very difficult by
the fact that its seeds are wind-dispersed.
While no cases of stock poisoning have been recorded, this plant
is regarded as unpalatable. Its milky sap can cause blistering and
irritation in humans. It forms large stands in some areas,
outcompeting native grass species, and thus reduces the grazing
capacity of land, as well as proving a hindrance during musters. To
see a recent list of research findings on Calotrope
click here .
Buffel grass
While this grass is considered as valuable grazing fodder on
pastoral lands, it is viewed as a serious weed in Kimberley
conservation parks and reserves. In fact it has been categorized as
one of Australia's worst 18 weeds because of its capacity to
replace native grass communities. The seeds of buffel grass
(Cenchrus ciliaris) are spread by the wind, which makes
eradication difficult. This grass does provide useful ground cover
however on areas of heavily eroded country. To see a recent list of
research findings on buffel grass
click here .
Conservation zones
Most parks and reserves in the Kimberley have relatively few
problems with weeds due to their remote location and relative
aridity. The parks with the worst problems are Geikie and Windjana
Gorge National Parks where wild passionfruit (Passiflora
foetida ), a rampant climber, smothers native river edge
vegetation. Seeds of this vine are spread by birds and bats which
eat the ripe fruits. Another plant of concern in riparian zones
within conservation areas is known locally as the Darwin pea
(Clitoria ternatea). This sprawling perennial herb forms
dense tangled hedges, and is noticeable for its characteristic
purple/ blue coloured trumpet-shaped flowers.
There are other grass species which are of concern for
conservation zones, some of which are in fact native to the area,
such as cane grass. Changing fire regimes have privileged the
spread of this grass over other native grasses, and monospecific
stands are becoming more common.
While many major weeds are not yet established in Kimberley
reserves, as the movement of tourists through these parks continues
to grow, so too does the threat from introduced plant species. The
peak tourist season, the dry, coincides with the best time for
strategic burning, and so this form of management is often rejected
in favour of those with less impact on the landscape aesthetics.
Nevertheless, some experimental work is being done by park rangers
to test the effectiveness and safety of late dry season burns.
Environmental challenges
There are several weedy plant species present in much of
northern Australia which have not yet appeared on a major scale in
the Kimberley. A very strong legislative emphasis is placed on
keeping these weeds out of the region and on dealing with new
infestations quickly before they spread. Control work is currently
being carried out on mesquite (Prosopis sp. ) with the long
term aim of total eradication from the area, and on limiting the
spread of rubbervine.
Several grasses have potential to become problematic should they
be introduced to the region. These include Para (Brachiaria
mutica), Grader (Themeda quadrivalvis), Mission
(Pennisetum polystachion) and Gamba (Andropogon
gayanus) grasses. One small area of Lion's tail (Leonotis
nepetifolia), which forms dense spiky stands and displaces
native vegetation, has also been identified, but should be
eradicated in the near future.
