Mitchell grass upland pastures of the Kimberley, Western Australia

Mitchell grass upland pastures

These pastures are part of the Kimberley 'black' soils group of pastures, and the perennial Mitchell grasses are the identifier grasses. Use the interactive key to pasture condition to help identify pasture type.

Pastoral value

Pastoral value is high when in good condition, although the uplands are slightly less productive than the alluvial plains. As Mitchell grass presence declines, pasture value also declines because the desirable grasses are replaced by less-palatable perennial grasses or undesirable species, such as feathertop. Increased amounts of annual grasses can provide good feed for livestock, particularly early in the year, but the bulk depends on the season. In below-average rainfall years, the bulk and vigour of annual grasses will be much reduced.

Occurrence

Mitchell grass upland pastures are tussock grasslands with scattered small trees that occur on flat to undulating upland plains. The soils of the uplands are drier and stonier than those of black soil alluvial plains.

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Pasture condition

Very good–good: Desirable Mitchell grasses (barley Mitchell and hoop Mitchell) are usually dominant when this pasture type is in good condition. Mitchell grass tussocks are healthy and evenly spaced. There may be small amounts of other desirable perennial grasses, such as bundle-bundle and ribbon grass. Isolated plants of feathertop, an undesirable perennial grass, are usually present, even in good condition (Figure 1).

Annual grasses and herbs will occupy the ground space between perennial tussocks in the late wet to early dry season. As grazing of palatable annual species (such as Flinders grasses) progresses into the dry season, small bare areas are created between the perennial tussocks.

Figure 1 Mitchell grass upland pasture in good condition in the Kimberley (photograph taken in September 2006).  A There is a dense coverage of Mitchell Grass and other desirable species.  B Red Flinders Grass (an intermediate species) and other annual grasses are growing between the perennial grass tussocks.

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Fair: A reduction in density and vigour of Mitchell grasses and other desirable perennial grasses will occur as pasture condition declines from good to fair, and the tussocks will not provide an even cover. Less-palatable perennial grasses, such as native millet, become more apparent, and the stand is likely to be dominated by this and other intermediate species, such as bull Mitchell grass or silky browntop (Figure 2).

Annual sorghum can occupy the increased space between the perennial tussocks. Unpalatable perennial grasses, such as feathertop, increase in frequency and may occupy up to an equal amount of ground space as the desirable species present.

Figure 2 Mitchell grass upland pasture in fair condition in the Kimberley (photograph taken in May 1998).   A There is a reduced density of desirable Mitchell grasses.   B Native millet, an intermediate species, is more apparent.   C Woody plants, in this case rubber bush, are taking up some of the ground space; the increased space between perennial grass tussocks is occupied by annual grasses.

Poor–very poor: Further deterioration to poor condition results in the almost complete loss of Mitchell grasses and other desirables, and a significant increase in bare ground. The pasture is dominated by feathertop or annual grasses, though some intermediate perennial grasses can still be present. Non-grass plants (woody and/or weedy species) may increase (Figure 3).

Figure 3 Mitchell grass upland pasture in poor condition in the Kimberley (photograph taken July 1996).  A Undesirable feathertop and annual species dominate.  B There are large areas lacking any perennial grass cover.  C Desirable species are not easy to find, and intermediate species, such as native millet, lack vigour.  D Prickle bush, an indicator of heavily used black soils, is present.

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Associated plants