Eucalypt chenopod pastures in the southern rangelands of Western Australia

Pastoral potential – moderate

The pastoral value of eucalypt chenopod pastures in good condition is moderate. The composition of the understorey is the most reliable indicator of grazing impacts. Bladder saltbush and silver saltbush are the most important indicators of pasture condition. Both species respond to season and grazing. One or both species may be present.

Pearl bluebush is a valuable stability desirable plant as it assists in preventing soil erosion and is rarely eaten except where there is heavy grazing pressure. A dramatic loss of pearl bluebush should be regarded as a catastrophe.

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 eucalypt chenopod plain pastures

These pastures do not normally burn readily – they generally have high canopies and lack flammable biomass between tree-based clumps. However, after favourable seasons they may become susceptible to fire due to increased biomass and structural connectivity, which may occur with an abundance of perennial grasses between shrubs.

Pearl bluebush can survive low to moderate fires, but saltbushes rarely survive any type of fire. Saltbush regeneration is from seed, and if grazing pressure after fire kills seedlings, the seed bank may become exhausted, leading to loss of saltbushes and invasion by unpalatable plants such as curara, broom bush, grey cassia and tan wattle.

Eucalypt chenopod pastures are usually stable in good and fair condition. Soil erosion is common where the vegetation is degraded.

Pasture condition

Surveys show that most eucalypt chenopod plain pastures in the southern rangelands are in fair condition and stable. Soil erosion is common where the vegetation is degraded.

Good condition

See Figure 1, 4, 7. In good condition, a mix of palatable low shrub species would be expected in the open and under trees and tall shrubs. Pearl bluebush, bladder saltbush and/or silver saltbush might be co-dominant and plentiful between trees. Young saltbush and pearl bluebush plants are common and other bluebushes will also be present including felty leaf bluebush, golden bluebush, pink-seeded bluebush and sago bush.

The most reliable indication of grazing impact is the diversity and density of palatable low and subshrubs (e.g. ruby saltbush, tall saltbush, tall sida and tar bush), particularly among the tree-based clumps. Perennial grass species, such as palatable speargrasses, may be present and indicate good resource condition when plentiful. There is extensive cryptogamic crusting.

Fair condition

See Figures 2, 5, 8. Fewer saltbushes are present, and bluebushes are dominant. There is reduced species diversity. Long-lived shrubs are small and rounded. Some desert cassia and hop bush are evident, and there might be more cotton bush and old man saltbush. An indication of grazing pressure is a reduction in floristic diversity, firstly in the open areas and then later in the more protected areas under trees and tall shrubs. There is some breakdown of the soil surface crust.

Poor condition

See Figures 3, 6, 9. In poor condition, unpalatable species belonging to the genera Eremophila, Senna and Acacia become abundant. Continued heavy grazing will result in decreasing species diversity. There will be few or no pearl bluebush plants present. Grazing will be evident on old man saltbush plants. Tan wattle, broom bush, desert cassia, silver cassia and hop bush may be present and increasing. The soil surface may be sealed and rilled in places. There will be evidence of water erosion in valley floors.

Eucalypt woodland over saltbush shrubland condition photographs

Figure 1 shows a eucalypt woodland over saltbush shrubland in good condition. There is good density and diversity of palatable shrubs, with an abundance of saltbush. There is no erosion and cryptogamic crusts are common and intact. The site is on a level plain, on a calcareous shallow loam, in the Woolibar land system.

Figure 4 shows a eucalypt woodland over saltbush shrubland in fair condition. Bladder saltbush is present but unpalatable broom bush is increasing in abundance. Cryptogamic crust is still common though there are some patches of soil disturbance and crust loss. The site is on a calcareous loamy plain in the Gumland land system.

Figure 7 shows a eucalypt woodland over saltbush shrubland in poor condition. The saltbush understorey has been drastically reduced and unpalatable shrubs such as broom bush are common. Widespread soil loss through sheetwash erosion is resulting in stony lag strewn across the soil surface. The site is on a level calcareous, loamy plain in the Gumland land system.

Eucalypt woodland over a mixed bluebush-saltbush shrubland condition photographs

Figure 2 shows a eucalypt woodland over a mixed bluebush-saltbush shrubland in excellent condition. There is an abundance of saltbush among patches of bluebush between stands of eucalypts. The soil surface is intact and erosion restricted due to the protection and convoluted flow paths created by so many shrubs. Cryptogamic crusts are abundant and intact. The site is on a level calcareous loamy plain in the Woolibar land system.

Figure 5 shows a eucalypt woodland over a mixed bluebush-saltbush shrubland in fair condition. The density of saltbush and bluebush is reduced between eucalypt stands. The decline in abundance of palatable shrubs has led to unobstructed through-flow, development of erosion cells and some loss of soil. The site is on a level calcareous loamy plain in the Woolibar land system.

Figure 8 shows a eucalypt woodland over a mixed bluebush-saltbush shrubland in poor condition. With the elimination of palatable saltbush, the pasture is reduced to seasonally-dependent bindiis and forbs. Unpalatable shrubs such as broom bush dominate the understorey. Soil loss is occurring. Soil redistribution results in deposits of fine ironstone lag across the surface. The site is on a level calcareous loamy plain in the Gumland land system.

York gum community condition photographs

Figure 3 shows a York gum community in good condition. Saltbush is abundant between stands of eucalypts. Palatable species such as tall saltbush, ruby saltbush and bluebushes are present under the trees. Unpalatable species such as cassias and broom bush may be present at low density.

Figure 6 shows a York gum community in fair condition. Sparse trees are present between stands of eucalypts. Palatable species such as saltbushes and bluebushes are absent. Short-lived cotton bush is present under trees and between stands of eucalypts. Unpalatable Goldfields daisy, cassias and broom bush are present under the trees. The site is on a level plain in the Doney land system.

Figure 9 shows a York gum community in poor condition. Palatable species are lacking under the trees and between stands of eucalypts. Unpalatable species such as cassias and Goldfields daisy (Olearia muelleri) may be present at very low density. There is very little groundcover between stands of eucalypts. The site is on a level plain in the Doney land system.

Vegetation structure and composition

Eucalypt chenopod pastures occur as scattered to moderately close (10–30% projected foliar cover) woodlands. The tree stratum comprises tree or mallee-form eucalypts which vary across the regions. In the Goldfields, prominent eucalypts include salmon gum, gimlet, redwood, Griffith's grey gum, several varieties of blackbutt and many other species – reputedly up to a quarter of all Australian eucalypts.

In the Nullarbor region, giant mallee, yorrell and Yalata mallee commonly dominate the tree stratum of equivalent pastures. In the Sandstone-Yalgoo–Paynes Find and lower Murchison River the prominent eucalypt is York gum.

Shrubs such as broom bush, curara, jam, tan wattle, quandong and sandalwood (Santalum spicatum) occur frequently.

Tan wattle, three-winged bluebush, grey cassia, bead hopbush and broom bush are unpalatable. In some degraded areas kidney saltbush may replace more palatable saltbushes; however, this species doesn’t necessarily indicate a grazing-induced decline as it is the naturally dominant saltbush in some pastures.

The most important forage shrubs are bladder saltbush and/or silver saltbush. Long-lived bluebushes such as pearl bluebush and sago bush have important roles as stabilising shrubs. The salt content in saltbush leaves is generally high, with other plants such as cotton bush, tall sida and tar bush provide some non-saline, perennial forage for herbivores.

Several shorter-lived bluebushes such as felty leaf bluebush, golden bluebush and pink-seeded bluebush and perennial tussock grasses, such as palatable speargrasses, are reliable indicators of good condition.

Occurrence

Eucalypt chenopod plain pastures mainly occur in the southern Goldfields and Nullarbor survey areas, and cover an estimated 2.96 million hectares (3.6% of the southern rangelands).

Figure 10 Estimated distribution of eucalypt chenopod pastures in the Southern Rangelands

In the Goldfields, these pastures are often located on calcareous shallow loams on footslopes and low rises over greenstone or granitic bedrock, and grade down valley floors to alluvial plains on calcareous loamy earths, red loamy earths, clay loams or clays.

In the Nullarbor region these pastures occur on calcareous loamy earths of generally shallow depth over calcrete plains.

Goldfields-Nullarbor eucalypt chenopod pastures occur frequently across the area from south of Menzies to north of Lake Moore, and east of the agricultural vermin barrier fence to Kitchener railway siding on the western edge of the Nullarbor Plain.

Similar pastures also occur in the Sandstone-Yalgoo–Paynes Find and lower Murchison River survey areas on alluvial plains. Soils range from red shallow loams, deep red loamy earths or loamy duplexes to clay soils on clay plains in the eucalypt chenopod pastures of the lower Murchison River.

Associated plants

* D = desirable, U = undesirable, I = intermediate, N = no indicator value