Gamba grass (Andropogon gayanus) is a serious threat to savannas of northern Australia and is regarded as an environmental weed in the northern parts of Western Australia, the Northern Territory and Queensland. It forms dense stands which out-compete native plants and is of most concern in savanna woodlands where rainfall is over 600 mm per annum. However, it is also regarded by many in the grazing industry to be a highly productive pasture grass, and is still widely grown for this purpose in northern Australia. It has a low palatability when mature and requires constant slashing or grazing to be of significant use in pastures.In the Northern Territory, gamba grass (Andropogon gayanus) currently occurs in the Darwin, Palmerston and Litchfield Shires, the Coomalie Community Government, and the Mary River, Douglas River and Lower Daly River regions. It is spreading rapidly along roadsides and other disturbance corridors throughout the northern parts of the territory, and from these initial infestations it then invades relatively undisturbed vegetation, including significant conservation areas (e.g. Wildman River National Park and Kakadu National Park). In Queensland, the first naturalised specimen of gamba grass (Andropogon gayanus) was collected in 1992, from Bamaga on Cape York Peninsula. Since this collection was made, it has been found in sites to the north and south of Weipa, along the road to Hopevale in the Cooktown area, in the Lakeland Downs area, at Sudley to the east of Weipa, at Kalinga Station about 80 km north of Laura, on the Mitchell River near Kowanyama, at Kendell River west of Coen, at Batavia Downs, on aboriginal land in the Northern Peninsula Area (NPA) and near Mareeba. It has also been reported to be spreading into parks and reserves in northern Queensland (e.g. Heathland National Park and Keatings Lagoon Conservation Park). Compared with native grasses, gamba grass (Andropogon gayanus) forms much taller and denser stands of vegetation that dry out later in the season, and therefore invaded areas contain much higher fuel loads than native grasslands. Native grass fuel loads are typically 3-5 tonnes per hectare while gamba grass (Andropogon gayanus) fuel loads are typically 11 to 15 tonnes per hectare, and may sometimes be as high as 30 tonnes per hectare. These higher fuel loads support more frequent fires that are much more intense than those fuelled by native grasses, and the flame heights of fires in stands of gamba grass (Andropogon gayanus) fires are typically higher than the tree canopy. These hotter fires have the potential to severaly damage native plants and may also dramatically alter the structure of the native vegetation over time. In particular, the number of trees are reduced resulting in a change from native woodland into exotic grassland.This is illustrated by the fact that gamba grass (Andropogon gayanus) invasion has been shown to produce a phenomenon known as a "grass-fire cycle" in northern Australia. This occurs when the amount of gamba grass (Andropogon gayanus) increases, causing an increase in the amount of fuel, which increases fire frequency and fire intensity. This then causes a decline in native tree and shrub cover, which aids further gamba grass (Andropogon gayanus) invasion and in this way a self-perpetuating cycle of invasion develops. For example, at one site in the Northern Territory, it was found that gamba grass (Andropogon gayanus) invasion had caused a 53% reduction in the native tree canopy in the last 12 years. If this sort of change occurs on a landscape scale, it could totally transform northern Australia's savannas from wildlife-rich woodlands into biologically impoverished monocultures of gamba grass (Andropogon gayanus) carrying regular hot fires. Because of this, invasion of gamba grass (Andropogon gayanus) in northern Australia has been nominated for listing as a "key threatenening process" under the Environment Protection and Biodiversity Conservation Act.Gamba grass (Andropogon gayanus) invasion has also been shown to have a variety of other impacts on native flora and fauna, and even ecosystem function. For example, invaded areas generally have about half the number of plant species as native grassland areas. Its higher biomass also alters the structure of invaded areas and can change ecosystem processes such as nutrient cycling and water cycling. Daily water use in the wet season is three times higher in gamba grass (Andropogon gayanus) invaded sites than it is in nearby native grasslands, and this reduces the drainage of water through the soil profile. Though gamba grass (Andropogon gayanus) invades and establishes more easily with disturbance, it can grow quite readily in burnt and unburnt savanna habitats regardless of whether the soil surface is broken. It is also not restricted to savannas, as it has been reported to invade upland melaleuca forests, riparian areas, and wetland and floodplain margins in northern Australia.As well as affecting ecosystems, and the native flora and fauna in general, gamba grass (Andropogon gayanus) is also a significant threat to numerous rare and endangered native plants and animals. Its impact on the following species in the Northern Territory has been documented: the endangered Atlas moth (Attacus wardi). This species is found only in the Darwin region, where its larvae survive in remnant grasslands. Invasion of gamba grass (Andropogon gayanus) is a threat because in displaces the native food plants of this species and fuels hotter fires which destroy its habitat.the vulnerable Cycas armstrongii. This species is endemic to the north-western corner of the Northern Territory. While it is locally common, inappropriate fire regimes caused by the invasion of gamba grass (Andropogon gayanus) and other exotic grasses is a major threat. Mortality in excess of 50% of adult stems per fire event have been recorded when subject to fuel loads of 20 tonnes per hectare.the threatened Darwin palm (Ptychosperma bleeseri). The Darwin palm is only found in eight small rainforest patches east of Darwin, within the Adelaide and Howard River system.