Buffel grass pastures in the southern rangelands of Western Australia

Pastoral potential – high to very high

The pastoral value of buffel grass pastures is high to very high, but varies according to the season.

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. Carrying capacity expressed as 36–69/<35 is the estimated range for high and very high pastoral potential.

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 buffel pastures in the southern rangelands

Grazing and adjacent pasture types

Buffel and birdwood grasses can tolerate heavy grazing after good rains, but feed value declines as the grass hays off. Livestock then seek other forage on adjacent native pastures, such as bluebush or acacia-cassia short grass forb pastures. Buffel grass pastures in favourable seasons support higher grazing pressure than the surrounding native vegetation, which leads to overgrazing in adjacent pastures. Stock should be removed before the shrubs are overgrazed.

Buffel grass pastures in hard and soft spinifex pastures are easier to manage, as both pasture types are resilient under grazing, and the rapid growth of buffel after rain and the value of spinifex in dry times complement each other.

Stabilising degraded sites

Many riparian habitats were degraded prior to buffel grass establishment. Buffel and birdwood grasses have had a significant role in stabilising surfaces and preventing further erosion. Grazing aids establishment through soil disturbance and reducing competition from other plants.

Ecosystem changes and fire

Ecosystem processes may be altered as buffel or birdwood grasses become established and out-compete native species in a variety of habitats.

Riparian and adjacent buffel grass-dominated plant communities in the southern rangelands are increasingly susceptible to fire. A feedback loop is promoted in the fire cycle, as there is more biomass (and therefore, higher fuel load) than in native pastures and increased connectivity to carry fire into pastures where fire is less common. Fire-sensitive species such as chenopods may disappear. Affected landscapes become inherently fire-prone and are left with exposed surfaces after fire. The risk of erosion to exposed soil surfaces is increased after fire. Weed invasion risk increases after fire.

Figure 1 Buffel grass invasion diagram. The dominant process is the invasion, indicated by red arrows. Undisturbed (intact) good condition pastures within the range can be colonised and may become buffel grass pastures.

Figure 78 Buffel grass invasion diagram. The dominant process is the invasion, indicated by red arrows. Undisturbed (intact) good condition pastures within the range can be colonised and may become buffel grass pastures.

Pasture condition

Survey data show that buffel grass pastures in the southern rangelands are predominantly in fair condition.

Good

See Figure 2. There is an even coverage of buffel and/or birdwood grass with a basal density of  more than 4%. Other desirable perennial plants are present and vigorous.

Fair

See Figure 3. Buffel grass basal density is between 1 and 3% with patchy tussock distribution and possibly some small bare scalded areas. Some woody weeds may be present, for example, bardie bush, wait-a-while.

Poor

See Figure 4. Buffel grass frequency declines. Tussocks will lack vigour and may be stunted. Buffel plants may behave as annuals lacking tussock development and seeding as small prostrate plants with little root development. Other desirable perennial plants may be hard to find and bare ground will be evident.

Figure 2: A buffel grass community in good condition. There is a strong, even coverage of buffel grass and the tussocks are vigorous and healthy. Other perennials include limestone wattle. The site is a floodplain in the Gascoyne land system.

Figure 3: A birdwood grass community in fair condition. Tussock density is reduced with frequent small bare areas. Unpalatable crinkle leaf cassia has increased. The soil surface is stable. The site is a sandy-surfaced plain in the Mary land system.

Figuire 4: A buffel grass community in poor condition. Buffel grass frequency has declined to below 20% of the stand and the small tussocks lack vigour. There are very few other surviving perennial plants and even the bardie bush is showing signs of stress. The site is on a level plain in the Wandagee land system.

Vegetation structure and composition

Buffel grass pastures have varying structure and composition. They occur as open tussock grassland or as tall shrublands/low woodlands with grassy understoreys. The projected foliar cover (PFC) of the shrubs is correspondingly variable (0≥30%). Widespread tall shrubs include limestone wattle, wanyu and curara, while on stabilised alluvial areas, wait-a-while, bardie bush and needlebush may be dominant. A sparse overstorey of coolibah may be present on floodplains. Low shrubs include silver saltbush, grey cassia, crinkle leaf cassia, ruby saltbush, Wilcox bush, cotton bush, Gascoyne bluebush and currant bush. Buffel grass is the dominant understorey and occurs with basal cover 1≥8%. Other perennial grasses include birdwood grass, curly windmill grass and silky browntop, all of which normally occur with basal cover <1%, although birdwood grass may co-dominate with a basal cover up to 2%. See Table 2 for a list of the common and important species in buffel grass pastures.

Occurrence

Buffel grass pastures (including birdwood grass) cover an estimated 0.34 million hectares (0.4% of the southern rangelands) in the semi-arid and arid environments of Western Australia. These introduced grasses have spread significantly in recent decades to become naturalised in many areas. Suitable areas for buffel grass have annual rainfall of 300–750 mm or may occur in areas with a lower rainfall but in locations receiving water run-on.

These pastures occur on a range of soils, but prefer alkaline or neutral soils with relatively high nutrient levels; they do not tolerate flooding or waterlogging. Buffel and birdwood grasses have the capacity to adapt to hostile growing conditions over time and may hybridise, potentially increasing the expected range.

Associated plants

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