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Weeds

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.

Noogoora burr

 Noogoora burr Photo: Greg Calvert

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 .

Bellyache bush

Bellyache bush Photo: Greg Calvert

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.