Australia's own grass

Australian map showing mitchell grass country

Map 1: Mitchell grass grows mainly in northern Australia where summer rainfall is dominant, and where average annual rainfall is between 250 mm and 550 mm. Queensland has the largest area of Mitchell grass country

Introduction

Mitchell grasses (Astrebla spp.) were first discovered near Bourke in New South Wales by the explorer Sir Thomas Mitchell in 1835. The four species of Mitchell grass (curly, barley, hoop and bull) were named in his honour. Curly Mitchell (Astrebla lappacea) and hoop Mitchell (Astrebla elymoides) are generally regarded as having the better feed value with barley Mitchell (Astrebla pectinata) next best and bull Mitchell (Astrebla squarrosa) regarded as the least nutritious and palatable.

Distribution

Mitchell grass grows mainly in northern Australia where summer rainfall is dominant, and where average annual rainfall is between 250 mm and 550 mm. Queensland has the largest area of Mitchell grass country.

Mitchell grass country is generally open, treeless rolling downs, especially in the dry tropics of northern Australia and the arid inland. The relative absence of trees is partly due to the heavy clay soils which Mitchell grass prefers to grow in, and partly due to the bushfires which would have swept through the countryside prior to the start of pastoralism in the 1860s.

Mitchell grass and drought

Individual Mitchell grass plants live for 20 to 30 years. Mature plants produce new seedlings once or twice over this period, because of the erratic nature of rainfall and droughts in outback Australia. Mature plants are well adapted to this harsh environment. They cope well with droughts through a deep root system, and by maintaining reserves of starch in rhizomes at the base of tussocks. These reserves are used to promote new growth when sufficient rainfall occurs to allow plant growth.

Grazing Mitchell grass

A graph showing mitchell grass yield perkg/ha of dry material

Figure 1: Mitchell grass tends to die out over time if neither grazed nor burnt

Mitchell grass is very well adapted to moderate grazing pressure because it evolved with intermittent grazing and wildfires prior to European settlement. In fact, Mitchell grass tends to die out over time if it is neither grazed nor burnt, resulting in lower plant density and yield (Figure 1).

Continued overgrazing also results in reduced Mitchell grass density, with plant survival reduced under high grazing pressure. High grazing pressure during drought is very detrimental to Mitchell grass. The combined stresses of heavy grazing and drought lead to the death of a large proportion of Mitchell grass plants in the pasture.

Acknowledgement

Support for this project was provided by Australian woolgrowers and the Australian Government through the Australian Wool Research and Promotion Organisation.

Further information

See also:

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Last updated 01 March 2013