Mixed chenopod shrub plain pastures in the southern rangelands of Western Australia

Pastoral potential – high

Pastoral value of mixed chenopod shrub plain pastures is high. Conservative pastoral management, regular winter spelling and retention of critical levels of cover are essential to preserving productivity, dry season reserves, seasonal responsiveness, resistance to soil erosion and unpalatable-shrub invasion.

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 mixed chenopod shrub plain pastures in the southern rangelands

Mixed chenopod shrub plain pastures are very susceptible to overgrazing.

Spelling of pastures, in good and fair condition, after summer rainfall will improve the chances for recruitment of new plants. Maintenance of shrub cover well above the critical threshold (around 7.5% PFC) in the low shrub stratum is recommended. Monitoring changes in low shrub cover is very important.

Scalded areas are a sign that these pastures have degraded to a new state. Scalded patches overlying saline soil are prone to dispersive sealing, inhibiting plant establishment. Regeneration will be a long-term prospect after bare scalds have formed. Poor condition mixed chenopod shrub plain pastures require spelling from grazing for extended periods.

Rehabilitation of poor condition chenopod pastures, with stock exclusion, may take more than 20 years (based on field observations). Grazing poor condition pastures will delay any rehabilitation. Water ponding structures and complete destocking can be effective if regeneration is the priority.

Pasture condition

Survey data show that mixed chenopod shrub plain pastures in the southern rangelands are generally in fair and poor condition and some areas are severely degraded and eroded. Soil erosion is usually associated with a decline in condition in these pastures.

Good

See Figure 1. Mixed chenopod shrub plain pastures support annual and ephemeral herbage of a high quality for livestock in good seasons, in addition to desirable perennials with 10% cover or better in most pastures. Low shrub groups commonly associated with them include other halophytes, poverty bushes, cassias and shrubby wattles. Desirable perennial shrubs will be dominant. Examples include silver saltbush, currant bush, ruby saltbush and golden bluebush. Frankenia-dominated associations will also include relatively desirable plants such as bladder saltbush, sweet samphire and bronze bluebush. Short-lived chenopods such as bindiis, saltbushes and bluebushes are major components of the annual herbage.

Fair

See Figure 2. Cover usually remains above 10% for the low shrub layer. Key decreasers such as saltbushes and bluebushes are reduced and unpalatable species such as needlebush may be present but will not dominate the understorey. Alternatively, key decreasers are present but not dominant, while more resilient plants such as sago bush, tall saltbush and three-winged bluebush dominate. No accelerated erosion is present when mixed chenopod shrub plain pastures are in fair condition.

Poor

See Figure 3. When mixed chenopod shrub plain pastures decline, erosion is generally present and may be accelerated. PFC can fall below 5%. Most of the desirable low shrubs have been lost from the understorey. Some understoreys are dominated by invasive unpalatable species such as silver poverty bush, needlebush, bardie bush and wait-a-while; while other pastures lack understorey perennials.

Heavy stocking and continuous grazing of these pastures has contributed to their near-complete degradation to an ephemeral-only state where no original perennial species remain. Ephemeral plants do not hold the soil together. Excessive grazing pressure and trampling are likely to disturb soil crusting and increase soil loss from scalded and bare areas. Wind erosion can be severe during extended dry periods if shrub cover is lost.

Figure 1 A mixed chenopod shrub plain community in good condition. There is a good mix of palatable species, including saltbushes, golden bluebush, bronze bluebush and frankenia. Cover is close to optimal and the soil surface is stable. The site is hummocky plains with red sand deposits in the Carnegie land system.

Figure 2 A mixed chenopod shrub plain community in fair condition. Shrub density and diversity is reduced to the hardier species like sage, sago bush and frankenia and the soil surface is inflated. The site is an alluvial plain with duplex soils in the Carnegie land system.

Figure 3 A mixed chenopod shrub plain community in poor condition. There is isolated cover and palatable plants are reduced to hardy long-lived species, including silver saltbush and sago. Active scald and rill erosion are occurring. The site is an alluvial plain with sandy-surfaced duplex soil in the Carnegie land system.

Vegetation structure and composition

All mixed chenopod shrub plain pastures have a low shrub stratum of halophytic (salt-tolerant) species (with or without a tree or tall shrub stratum) when in good condition. The mixed chenopod group of pastures comprises two distinct communities: well-mixed halophytic associations and frankenia-dominated communities associated with samphire and saltbush. Mixed halophytic pastures may occur nearby and grade into saltbush and bluebush communities. Perennial grasses are generally sparse to absent.

Projected foliar cover (PFC) ranges from very scattered to moderately close (5–50%). Composition is variable and a function of degree of degradation, soil type, degree of soil salinity, level of development in the overstorey and species biology. Low shrubs may form clumps under larger plants in some pastures.

Occurrence

Mixed chenopod shrub plain pastures occur mostly on alluvial plains with saline texture contrast soil, often over hardpan, covering an estimated 3.93 million hectares (4.8% of the southern rangelands). These pastures are found on broad alluvial plains associated with lake country as well as the margins of salt lakes and drainage lines carrying flow through alluvial and saline plains.

Mixed chenopod shrub plain pastures also occur on the alluvial fans and footslopes below breakaways, in both granite- and greenstone-based landscapes. These pastures are regularly associated with drainage systems that are slow-flowing and sluggish, where local base-levels restrict flow resulting in the deposition of fine sediments and clay formation, with salts accumulating in the soil profile.

The footslopes and the lower plains of the Pillawarra land system (with unique fertile soils of brown loamy earths) also support these pastures.

Frankenia-dominated pastures on saline duplex and clay soils are included in these pastures.

Figure 4 Map of the estimated distribution of mixed chenopod shrub plain pastures

Associated plants

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

Other resources