Stony mixed chenopod pastures in the southern rangelands of Western Australia

Pastoral potential – moderate

Stony mixed chenopod pastures are of moderate pastoral value when in good condition. The amount of available forage is low compared to highly productive pasture types such as saltbush and bluebush. However, these pastures are more productive than acacia-cassia short grass forb pastures and will be preferentially grazed where they occur together. They are generally degraded and pastoral value is often well below potential. Where stock water has not been provided, they are under-utilised.

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.

Management

These pastures may support continuous grazing at a conservative level when in good condition. Spelling occasionally for three to six months after rainfall is recommended to maintain good pasture condition. Spelling over a number of consecutive growing seasons is recommended to allow recovery of pastures in poor condition.

These pastures are generally not susceptible to erosion because of soil protection afforded by the stony mantle.

Pasture condition

Survey data show that the condition of stony mixed chenopod pastures in the southern rangelands is about a third each of good, fair and poor condition.

Good

See Figure 1. Indicated by the presence and density of desirable low shrubs concentrated around the bases of larger shrubs and trees, and persisting elsewhere. Ruby saltbush, bluebushes and tall saltbush are common desirable indicator low shrubs and juveniles of these plants should be present. Undesirable shrubs such as bardie bush and wait-a-while are often present at very low densities.

Fair

See Figure 2. Indicated by a loss of desirable species from open areas, but these are still reasonably common under larger shrubs. Ruby saltbush and other sensitive desirable plants occur only as old, heavily grazed individuals. Less palatable species, particularly three-winged bluebush and royal poverty bush, can be expected to increase. The undesirable species such as bardie bush, wait-a-while and grey cassia may occur more frequently as seedlings and young plants increase.

Poor

See Figure 3. Declining cover and density of desirable low shrubs indicate a change from fair to poor condition. Desirable plants are often absent. Intermediate species such as pink-seeded bluebush may be grazed and decline in number. Undesirable species such as grey cassia and bardie bush may increase.

In general, the total PFC remains fairly constant with a decline to poor condition. The removal of desirables may not drastically reduce foliar cover as many grow beneath the canopy of taller shrubs which have remained intact. Increases in the density and size of undesirables will also be compensating for the decline in desirables.

Stony mixed chenopod pastures condition photographs

Figure 1 A scattered stony mixed chenopod community in good condition. There are a number of desirable low shrubs around the bases of larger shrubs and trees and persisting in the spaces between. Desirable bluebushes, ruby saltbush and tall saltbush are present and there is a mix of age classes in the stand. The site is a stony plain in the Sherwood land system.

Figure 2 A stony mixed chenopod community in fair condition. Palatable sago bush, golden bluebush and frankenias are present but density is reduced compared with good condition. Unpalatable needlebush is increasing. Bare areas have increased. Soil erosion is beginning to occur. The site is a stony plain in the Sherwood land system.

Figure 3 A stony mixed chenopod community in poor condition. Hardy sago bush is still present with reduced density. Overall shrub density and diversity are reduced, and the more sensitive palatable plants are at very low density. Unpalatable needlebush is present. Sheet erosion is stripping away topsoil and run-off is increased. The site is a stony plain in the Sherwood land system.

Vegetation structure and composition

Stony mixed chenopod pastures are very scattered tall to low shrubland with projected foliar cover (PFC) of 5–10%. PFC may reach 20%, subject to annual rainfall, the position within the landscape and soil depth.

The upper stratum is generally sparse and may include wait-a-while, mulga, snakewood and bardie bush.

The ground layer supports a diverse range of perennial shrubs, many of which are halophytic. They may include sago bush, three-winged bluebush, grey cassia, ruby saltbush, royal poverty bush, Gascoyne mulla mulla, tall saltbush and others. Low shrub densities are around 25000 per hectare (25 per 10m2). Shrubs are often in clumps concentrated underneath occasional trees or large shrubs with relatively sparse stony areas in the interpatches between. Curly windmill grass is sometimes present among the shrub patches.

Occurrence

1.74Mha, 2.1% of the southern rangelands

Stony mixed chenopod pastures occur on footslopes, stony plains and interfluves with duplex soils of variable depth with moderate to dense surface mantles, and cover an estimated 1.74 million hectares (2.1% of the southern rangelands). The topsoils are sandy or loamy. These pastures frequently occur in a mosaic with acacia-cassia short grass forb pastures and bluebush or saltbush pastures.

Figure 4 Map of the estimated distribution of stony mixed chenopod pastures

Associated plants

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