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Weeds in the Gulf

Overview

The gulf region contains great variation in land types and intensity of land use. Given that weed invasion tends to be directly related to either human traffic or to intensity of land use, there is a parallel variance in weed presence across the region. Limited financial and human resources on the ground has severely constrained the amount of weed survey work carried out in the Gulf region. The NT Department of Primary Industries and Fisheries has recently begun a survey of weeds throughout the Northern Territory's portion of the Gulf.

Major weeds

The major weed threatening the biodiversity and productivity of riparain systems on the Queensland side of the border (Morgan 1999: 2/9) is rubber vine (Cryptostegia grandiflora), which now infests areas of most river systems, and has had a particular strangle hold on the Mitchell-Gilbert system in the far north-east of the region. It also infests dunes and scrubs along the coastal zone in the east of the region. It has currently advanced as far west as the Nicholson River system in the Northern Territory, although it has since been eradicated from the area.

Rubber vine is a serious weed of the riverbanks of north Queensland

In the south of the region between the Leichardt and Flinders catchments are areas of black soil plains. In this part of the gulf region, weed problems are distinct and include encroachment of woody natives such as coolibah (E. microtheca), whitewood (Endospermum medullosum) and gutta percha (Excoecaria parvifolia) . Exotics such as Parkinsonia (Parkinsonia aculeata) and, in the most southerly reaches, prickly acacia (Acacia nilotica) also are becoming problems. These areas are considered prime grazing country and as such are often protected from fire. This may be a major factor in the weedy invasion.

Noogoora burr (Canthium pungens) and hyptis (Hyptis sauveolens) are also considered high priority weeds throughout the region. They reduce the value of pastoral land and are a threat to native plant communities. Mesquite (Prosopis spp.) occurs, sometimes as dense infestations, throughout the southern parts of the Gulf Country around Cloncurry, the southern Nicholson River and on northern sectors of the Barkly Tableland.

Salvina (Salvina molesta), water hyacinth ( Eichhornia crassipes) and callotropie (Calotropis procera) are also locally significant.

Introductions

Plants currently being introduced to the area which have been identified as having significant potential to become weeds include neem trees (Azadirachta indica) which are being planted around, and to the north east, of Cloncurry. The concern is that if these trees were to spread to the marine floodplains, they could become unmanagable.

Ponded pasture species which are being planted on the fan of the Mitchell-Gilbert system and along coastal floodplains to the west of this system are also of conern. These plants have the potential to invade native wetlands and displace local plants and animals.

Other invaders

Mexican poppy (Argemone ochroleuca) occurs in some river catchments including the McArthur, the Calvert and Settlement Creek. Khaki weed (Alternanthera pungens) and Star burr (Acanthospermum hispidum) are two nuisance plants that occur in settled areas throughout the Gulf region. Similarly, chinee apple (Zizyphus mauritiana) is not a major concern at present, but has potential to become a problem on sandy country.

Weeds on Aboriginal lands

There are significant areas of Aboriginal land in the gulf region, especially on the Northern Territory side of the border. While weed problems are known to exist on many of these lands, there is limited knowledge of the extent of the weed problem in many of these areas (Smith 2001).

Overall Aboriginal lands have less weeds than other areas, mostly by virtue of their isolation and lack of infrastracture. In addition, the requirement for permits to enter these areas may further decrease the traffic. In general, those catchments on Aboriginal lands with the greatest number of weeds are those traversed by major roads, those with significant agricultural or pastoral activities and those containing large settlements.

It is important that traditional owners be kept informed of new weeds which may threaten their country, and be informed of control methods. Aboriginal lands close to the Queensland border, for example on the Nicholson River, may be under threat from rubber vine in adjacent catchments. These areas are extremely strategic in ensuring that weeds from Queensland do not advance further to the west.

References

Morgan, G. (1999). Gulf Plains. In: Sattler, P. & Williams, R. (eds), The Conservation Status of Queensland’s Bioregional Ecosystems, page 9, Chapter 2. Environmental Protection Agency, Brisbane. 

 Smith, N.M. (2001) Not from here: Plant invasions in Aboriginal lands of the Top End, TS–CRC, Townsville, Qld.