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Savanna Explorer > Darwin-Kakadu > Grazing > Native Pastures

Native pastures

Distribution

The species composition and growth of native grass communities in the Darwin-Kakadu region is primarily determined by plant available moisture. Seasonality of rainfall, drainage and flooding regularity all impact on the distribution of native grass species. Native legumes and forbs form only a minor part of the pasture communities in this region although they may be locally significant during their short growing season.

Dominant pastures

The dominant native pasture types are a mixture of fast-growing perennial medium height grasses grading into medium and taller species (2-3m) as the rainfall and length of growing season increases from south to north. Local ground cover can vary considerably in dominant species and relative density, generally in response to soil moisture, and to a lesser degree soil fertility. Major mid grass species include golden beard grass (Chrysopogon fallax), whitegrass (Sehima nervosum), and black spear grass (Heteropogon contortus) in areas with annual average rainfall of 1100 mm or less. Kangaroo grass (Themeda triandra) and perennial sorghum (Sorghum plumosum) occur throughout the region, while cockatoo grass (Alloteropsis semialata), ribbon grass (Crysopogon latifolius) and Cymbopogon spp. are found in wetter areas. Tallgrass species common in the north include giant spear grass (Heteropogon triticeus) and northern cane grass (Mnesithea rottboelloides). On deep sandy soils annual Sorghum species may form virtually monospecific stands or mix with sparse tall perennial species.

Rocky hilltops and sandstone country

Significant areas of the region are not subject to grazing. These include Kakadu and Nitmiluk National Parks, smaller parks such as Litchfield and the largely cattle-free areas of Arnhen Land which lie within this bioregion. A large proportion of this consists of escarpment country, rocky hilltops and deep pale sands which support curly spinifex (Plectrachne pungens) and Triodia spp. Where these pastures do occur on pastoral leases, they tend to form small or rarely utilised pockets, either due to terrain or accessibility.

Poorly drained soils

Alluvial plains of the coastal rivers, such as the Adelaide and Mary systems, support a low to mid grass cover of annual species which are of limited nutrient value. These include kerosene grass (Eriachne burkitii), kangaroo grass (Themeda triandra), Chrysopogon spp. and northern cane grass (Mnesithea rottboelloides) on river levees and higher ground within and adjoining the plains.

Coastal floodplains

Pasture composition of floodplain country depends mostly on wet season flood depth.Shallower zones tend to support a variety of annual forbs and grasses. Wild rice (Oryza spp.), native hymenachne (Hymenachne acutigluma) and swamp rice grass (Leersia hexandra) are found in the intermediate zone, while native hymenachne  will dominate the deepest flooding areas. Grazing of floodplain country occurs only in the dry season, in direct contrast to other native pastures which are at their best in the wet.