A review of revegetation techniques in the tropics
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Internal Report 333
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approach is extremely important if large areas are to be kept weed-free. This will allow the use of available resources to be concentrated on eradication of more aggressive species. For example, Kakadu National Park (KNP) has a number of exotic weeds (Cowie and Finlayson 1986, Cowie and Werner 1987 and 1988, Brock and Cowie 1992). The eradication of two of these weed species Salvinia molesta and Mimosa pigra is a high priority at present (J. Russell-Smith, pers. comm.). Control of other weeds such as Pennisetum polystachion, Hyptis, Sida etc is considered a lower priority (I. Garven; pers. comm.). Mining companies in the ARR have small areas on which to control weeds by comparison with KNP. However, mine sites are more prone to infestation by exotic weeds than undisturbed sites elsewhere in the Region. This is due to increased human and vehicular traffic within mine leases, and changes in the properties of disturbed soils viz soil nutrition (eg higher P on Ranger WRD) and water availability. The mining companies therefore adopt intensive methods of weed control. At Nabarlek, stockpiled clay, top soils and retention pond bunds are treated with herbicides (R. Hinz; pers. comm.) early in the Wet season. The areas are then monitored and any clumps left un-affected by herbicide are removed manually. Natural areas adjacent to disturbed sites may also be infested by exotic weeds such as mission grass (Pennisetum polystachion). These isolated plants are monitored during their flowering stage. Seed heads are bagged and the entire plant removed and burnt (P. Bailey; pers. comm.). At Ranger, Pennisetum polystachion is commonly found on many disturbed sites (eg Jabiru East and some sites on waste rock dumps), and other weeds also appear occasionally. Burning is followed to control the former while the latter are eradicated by herbicide application and/or hand removal (C. Unger; pers. comm.). The waste rock dumps and RP2fRP4 areas are also infested with buffel grass (Cenchrus ciliaris), but no control measures seem to have been taken. At Coronation Hill, rubber bush (Calotropis procera) occurs in isolated bushes and clumps. Use of herbicides and hand pulling are being employed to eradicate this species (J. Russell Smith; pers. comm.). Many studies have been carried out, or are currently underway to investigate eradication procedures for exotic weeds from range lands, pastoml lands and park lands of the ARR. These studies primarily concentrate on the control of Mimosa pigra (Harley 1992), Salvinia molesta (M. Julien and M. Storrs; pers. comm.), Sida acuta and Pennisetum polystachion (Mott 1980). The methods tested include biological methods such as the use of insects and fungi, and chemical methods (use of herbicides, salinity) and cultural methods (ploughing, burning). An integrated approach is used to control exotic weeds within Kakadu National Park (KNP). This includes the use of quarantine procedures as weIl as mechanical, chemical and biological 32 I I I I I I I I I I I I I I I I I I I I I