Greenstone stony plain pastures in the southern rangelands of Western Australia

Pastoral potential – moderately high

The pastoral value of the greenstone stony plain pastures is moderately high, grading upslope into greenstone hills (crests and upper hillslopes) with low pastoral value acacia shrubland.

These pastures are suitable for year-round use by all classes of livestock under conservative stocking rates.

Suggested levels of use (per annum)

Table 1 provides a rough guide to the range of pastoral values for good condition pastures, which must be checked against conditions in each region and paddock. Carrying capacities for fair condition pastures might be 75% to 50% of good, and poor condition pastures less than 50% of good.

See Introduction to pastures in the southern rangelands of Western Australia for an explanation of how carrying capacities are estimated.

¹ DSE is based on the feed energy required to maintain a 45 kilogram liveweight Merino wether with zero weight change, no wool growth additional to that included in maintenance, and walking 7 km/day. 1 DSE has an energy requirement of approximately 8.7 MJ ME/day.
² CU in the southern rangelands is based on a 400 kg steer at maintenance and equivalent to 7 DSE.
³ AE is based on the feed energy to maintain a 450 kg Bos taurus steer 2.25 years of age, walking 7 kilometers each day. 1 AE has an energy requirement of approximately 73 MJ ME/day and equivalent to 8.4 DSE.

Managing greenstone stony pastures

Moderate grazing can stimulate some low shrub growth. Heavy grazing pressure kills the desirable perennial shrubs.

We recommend fencing off large areas of bluebush/saltbush pasture from other pasture types, to manage grazing pressure. Good quality water supplies must be provided to maximise pasture utilisation and animal productivity.

Conservative use and favourable seasons may lead to the recruitment of palatable shrubs although this requires a seed source. More commonly, conservative use results in more George’s bluebush, sago bush and cotton bush. When shrubs are lost, the annual spear grass and bindii numbers increase.

Pastures in fair or poor condition will require periodic spelling to improve condition. Spelling is recommended during and immediately after the growing season until seedlings are well established and mature plants have set seed.

Pasture condition

Surveys show that greenstone stony plain pastures in the southern rangelands are mostly in fair condition, with bladder saltbush being absent or at low levels, and the long-lived species such as pearl bluebush present and dominating the community. Greenstone stony plain pastures are usually stable in good condition, but are fragile and susceptible to rapid decline with overgrazing.

Good condition

See Figure 1. Saltbushes are co-dominant with the long-lived bluebushes. There is a diversity of low and medium shrubs present such as golden bluebush, sago bush, sage, bladder and silver saltbush. A range of mixed age plants is present on non-stony surfaces. Very few to no young unpalatable plants are present.

Well-developed soil surface crusting is evident on non-stony areas. Feather speargrass is a common perennial grass where land is in good condition and neverfail often grows in drainage foci. Juvenile saltbushes, George’s bluebushes, sago bushes will be present. Low and medium shrubs are well-branched (not hedged) and bush mounds are healthy and joined together.

Fair condition

See Figure 2. Survey data show that greenstone stony plain pastures in the southern rangelands are predominantly in fair condition, due to bladder saltbush being absent or much reduced, but the long-lived species such as pearl bluebush still present and dominating the community.

Vegetation is dominated by long-lived shrubs such as pearl bluebush, sago bush and sage. There is some loss of bladder and silver saltbush and small bluebushes, and very little change in the number of pearl bluebush and perhaps some increase in sago bush. Vegetation is resilient and protects the soil surface from erosion.

Few young palatable species are present. Three-winged bluebush and cotton bush may increase. Soil surface crusting is evident on non-stony areas, but might be partially developed. Bush mounds might be small and there are usually signs of water flow between mounds. The country is comparatively fragile where the stone mantles are not heavy.

Poor condition

See Figure 3. There are few or no saltbushes, few low shrubs, and might be many woody and other weeds such as desert cassia, tan wattle (south of Menzies), needlebush, three-winged bluebush and hop bush. Three-winged bluebush might dominate the community. 

Sago bush might dominate sites that previously supported more palatable species such as bladder saltbush. If pearl bluebush or sago bush is the only shrub in the understorey it usually reflects previous overgrazing. The moderately palatable pearl bluebush and sago bush may be the only desirable plants remaining; the loss of all shrubs with only bindiis and other short-lived species remaining is possible. Needlebush, desert cassia and hop bush are likely to be present.

Soil surface crusting is poorly developed, and minor sand piling against fallen trees might be evident. Bush mounds are largely absent, and there is evidence of trampling, wind erosion and water erosion.

Greenstone stony plain pastures condition photographs

Figure 1 shows a greenstone stony plain community in good condition. There is a diverse range of chenopod shrubs with the structurally important sago bushes exhibiting a range of different-aged individuals. The site is on a saline stony plain on a duplex soil in the Gundockerta land system in the southern rangelands.

Figure 2 shows a greenstone stony plain community in fair condition. There is a reduction in species diversity with the more resilient sago bush dominating. A number of juvenile sago bushes are present. Bare areas have increased. The site is a saline stony plain on a duplex soil in the Gundockerta land system, southern rangelands.

Fugure 3 shows a greenstone stony plain community in poor condition. Shrub density and diversity are reduced with few desirables. Bush mounds are deteriorating, sheet erosion is stripping away topsoil and the site is shedding water. The site is a saline stony plain in the Gundockerta land system, southern rangelands.

Vegetation structure and composition

Greenstone stony plains support a varied population of tall and low shrubs with variations resulting from different environmental impacts, primarily caused by grazing and/or mining.

The projected foliar cover (PFC) of these pastures is very scattered to scattered (10–20% PFC), occasionally moderately close (<30% PFC), shrublands with a pearl bluebush dominated low shrub stratum, a well-developed mid-shrub stratum, and very scattered tall shrubs and trees.

In good condition, bladder saltbush is co-dominant with pearl bluebush. Broom bush appears on the less alkaline sites, usually on rising ground. A wide range of eremophilas may also be present including pixie bush, poverty bush and weeooka. The most sensitive palatables are golden bluebush and the saltbushes. Annuals in season may include everlastings and tall mulla mulla.

Occurrence

Greenstone stony plains occurs over extensive areas of upland country on metamorphosed volcanic rock occur through the Murchison and Goldfields, and cover an estimated 0.61 million hectares (0.8% of the southern rangelands) (Figure 4). These are known as the greenstones or greenstone belts, and contain the major gold and nickel deposits of Western Australia, plus minerals beneficial for plant growth. The country can be very productive and is usually considerably more naturally fertile than similar granite or stony bluebush country.

Some basalt and dolerite is hard and resistant to erosion while ultramafic rocks are softer. Land systems which typify this country include Gundockerta, Nubev and Violet in the Goldfields.

Some of the most typical and distinctive examples of greenstone country are found in the Goldfields around Leonora, Laverton and Menzies. The land has been used extensively for both mining and pastoralism, which historically focused on sheep production. Greenstone belts are less frequent west of a line from Meekatharra, Cue to Yalgoo.

Figure 4 Map of the estimated distribution of greenstone stony plain pastures

Associated plants

¹ Mulga as Acacia aneura has been split into multiple species including: A. aneura, A. aptaneura, A. caesaneura, A. fuscaneura, A. incurvaneura, A. macraneura, A. mulganeura, A. pteraneura.
* D = desirable, U = undesirable, I = intermediate, N = no indicator value

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