About three-quarters of the VRD-Sturt region lies inside the
Northern Territory, with the remainder in Western Australia. Land
use in the region is dominated by pastoralism but Aboriginal lands
and conservation reserves also occupy substantial areas. The area
of intensive agriculture associated with the Ord River Irrigation
Scheme is increasing, and there is also a large military training
The long history of pastoral use has left a legacy of land
degradation in many of the region's most productive areas. There
has been erosion and widespread replacement of preferred grasses by
less palatable species including exotic weeds. In some areas,
overgrazing and changes in fire regimes have combined to increase
the density of native shrubs and trees and lower the land's
carrying capacity. This combination has also left large areas
vulnerable to invasion by weeds, including exotic woody species
such as parkinsonia (Parkinsonia aculeata) and castor oil
plant (Ricinus communis ).
Parkinsonia forms thorny thickets in the
Photo Greg Calvert
Parkinsonia forms impenetrable thorny thickets that compete with
and exclude native species and cut off access to creeks and rivers.
It is widespread in the region. Castor oil plant, a tall branching
shrub, displaces more desirable native species and can lead to
significant losses in grazing land. It can become locally abundant
after rains or flooding. Noogoora burr (Xanthium strumarium)
is another weed that excludes native shrub species and the spines
of the burr can cause injury to animals' feet.
Devil's claw (Martynia annua) is also present, and poses
a major threat within the region. This plant invades disturbed
ground where it prevents the regeneration of native species. The
clawed fruits can work their way into soft body parts of animals,
causing injury and discomfort. Lion's tail (Leonotis
nepetifolia ) is another weed likely to become much more
serious in the region.
Neem tree (Azadirachta indica), widely planted as a shade
tree around settlements and towns, is spreading rapidly in the
region. Rubber bush (Calotropis procera), sicklepod
(Senna obtusifolia), coffee senna (Senna
occidentalis), spiny head sida (Sida acuta) and flannel
weed (Sida cordifolia ) are also causing concern.
Prickly acacia (Acacia nilotica) and mesquite have been
reported in the region, and both have the potential to become major
problems. Mimosa (Mimosa pigra ) also poses a serious threat
to the region, although only a few occurrences have been reported
Gamba Grass is potentially a major problem
Weeds in National Parks
In Gregory National Park, devil's claw (Martynia annua),
cobbler's peg (Bidens bipinnata), parkinsonia
(Parkinsonia aculeata) and rubber bush (Calotropis
procera) are the weeds causing most concern at present. Gamba
grass (Andropogon gayanus) and mission grass (Pennisetum
polystachion) are major potential problems, because they lead
to very hot fires that can seriously damage native vegetation.
Mimosa (Mimosa pigra) could also be a huge problem if it
Weeds are both a symptom and a cause of land-management
problems. They interact with fire, feral animals and grazing
management. Therefore it is vital that strategic weed management is
fully integrated into all long term management programs.
As in all regions, prevention is the most desirable and
cost-effective approach to weed management. Legislation prohibits
introduction of potentially damaging weed species into the NT, but
we also need to avoid moving weed seeds from infected areas into
ones that are still 'clean'. It is important that we minimise an
area's susceptibility to weed invasion. Examples are by reducing
disturbance due to overgrazing, feral animals and unnecessary
vehicle traffic, and rehabilitating and revegetating disturbed
sites with local native plants.
Education and awareness are vital if we are to recognise weed
infestations at an early stage when eradication is still
practicable. Knowing how to deal effectively with existing
infestations will minimise weed problems. Keep up to date with
latest control methods, and implement long-term plans.