Indicator value of pasture condition
Buffel grass (Cenchrus ciliaris) and birdwood grass (C. setiger) are considered desirable for their fodder value, but have limited use as an indicator of pasture condition. They are preferentially grazed when green and actively growing.
Buffel grass is not waterlogging tolerant and extended inundation (floods from monsoonal rain) of buffel grass–dominated pastures can kill the buffel grass, leaving very little forage reserve.
Buffel grass pastures are highly productive and buffel grass is preferentially grazed when green and actively growing. These actively growing plants have higher protein, phosphorus and digestibility than many other native grasses. Buffel grass is generally highly palatable when green, although there is variation from moderately low to high between sites and perceptions by managers (Bohning & Wilkie 1999).
As buffel grass hays off, the protein content, digestibility and palatability drop rapidly. Palatability when dry can range from low to high, depending on the site and perception of managers (Bohning & Wilkie 1999), with most managers reporting moderate palatability. Where other desirable and more-palatable perennials are present, grazers move to those species, allowing buffel grass to produce abundant seed. This grazing pattern favours the survival of buffel and birdwood grasses over other palatable pasture plants, resulting in buffel grass stands becoming stronger and other grasses being crowded out. Buffel grass can quickly become rank and less palatable if ungrazed for too long. Areas of useful pasture can be maintained by grazing heavily and then spelling to allow regrowth.
Buffel grass has diverse forms and cultivars with ongoing hybridisation resulting in new forms developing in the wild. This diversity of types means that buffel grass can adapt to a wide range of growing conditions. Birdwood grass is similar but occurs less commonly.
Some cultivars are more palatable than others. The less-palatable forms may gradually become dominant in grazing lands through selective grazing, progressively reducing long-term productivity. Pastoralists at pasture identification workshops in northern WA in April 2015 observed that the pastoral value of C. ciliaris cv. Gayndah is good; C. ciliaris cv. USA (aka American) is "awesome"; and C. ciliaris cv. Biloela is "bad". However, these ratings are likely to differ in different areas and conditions.
Buffel grass contains oxalates and, in buffel grass–dominated paddocks, can cause oxalate poisoning and calcium deficiency. Young sheep and horses are more susceptible, and it is not usually a problem in mature ruminants or in mixed pasture types. Calcium deficiency can be reduced or prevented by providing a mixture of other grasses and feeds or calcium and phosphorus supplements. These conditions are rare in WA.
Buffel grass was introduced to north-western Australia and central Australia, and probably elsewhere, in the 1870s by Afghan cameleers. The cameleers restuffed worn harnesses and saddle packs, discarding the original buffel grass stuffing brought from their homelands, and also hand spread it as they travelled. Much later, it was deliberately introduced to improve pasture production in the rangelands. Buffel grass occurs naturally in northern Africa, the Middle East and across to India, and in Indonesia (Friedel et al. 2006)
Buffel grass is suited to areas with an annual rainfall of 300–750mm and will grow in areas up to 1200mm where winter rainfall is less than 400mm, and in areas with lower rainfall where soils receive water run-on. Buffel and birdwood grasses respond quickly to even small amounts of rain. Buffel grass can do well on a range of soils, although it prefers lighter alkaline or neutral acidity soils with moderate to high nutrient levels, and does not tolerate waterlogging or flooding.
Buffel grass has different productivity and appearance in different environments, and visual separation of the cultivars is very difficult. Buffel grass has naturalised over most of northern Australia and as far south as Perth and Kalgoorlie in WA.
Modelling based on climatic and soil requirements has predicted that 25% of Australia is potentially ‘highly suitable' and '43% is suitable for buffel grass growth’ (Weed Management CRC 2008).
Disadvantages for pastoralism
There are number of potential disadvantages for pastoralism with native pastures being replaced by buffel grass–dominated systems:
- Fire risk is increased because buffel grass forms a relatively continuous flammable ground layer that can carry extensive and intense fires at more frequent intervals than that experienced in native plant communities. More-common and more-intense fires can lead to loss of established trees and shrubs, death of recruitment before they have produced seed, and loss of fire-sensitive species, such as the Chenopodiaceae, as landscapes become inherently more fire prone.
- Pasture diversity can be lost through competition with native species. Buffel grass can displace desirable native grasses that are highly valued fodder. This decreases the grazing value of the pasture in dry spells.
- Desirable native species and pasture types can be overgrazed. Buffel grass becomes less palatable than some of the desirable native species when it is dry and livestock seek supplementary forage. This can lead to overgrazing of fertile patches and shrubs with high protein content resulting in degradation of these areas as a forage source. This can then lead to buffel grass colonising these areas.
- The grazing value of buffel grass–dominated pasture may run down over time because less-palatable forms gradually become dominant through selective grazing.
- Buffel grass contains oxalates and can cause oxalate poisoning in young and hungry sheep, and ‘Big head’ in horses if there is a lack of diversity of pasture types. This is not usually a problem in mature ruminants or with the mixed pasture types commonly found in the WA rangelands.
- Buffel grass has strong environmental weed characteristics and has invaded environmentally sensitive areas. Native plants have been affected by competition, altered soil nutrients and water availability, constraints to recruitment such as shading, altered fire regimes, changes in availability of dispersal or pollination agents, allelopathy and increased grazing pressure (Friedel et al. 2006, p. 9).
Buffel and birdwood grasses are dense, perennial tussock grasses. The plants can grow up to 1.2m tall and there are many local varieties of buffel and birdwood grasses with different forms. The leaves are bluish green and flat, up to 30cm long and tapered to a fine point. The seed heads can be up to 5cm long and may turn white as they mature. The individual seeds of buffel grass generally have soft bristles. Birdwood grass is a close relative of buffel grass and is usually distinguished by the hard bristles on the seed head.
Bohning, G, & Wilkie, A 1999, Palatability scoring of forage plants in central Australia, Technote 106, Department of Primary Industries and Resources, Nothern Territory, https://dpir.nt.gov.au/__data/assets/pdf_file/0020/233444/tn106.pdf.
Friedel, M, Puckey, H, O’Malley, C, Waycott, M, Smyth, A & Miller, G 2006, Buffel grass: both friend and foe. An evaluation of the advantages and disadvantages of buffel grass use and recommendations for future research, Desert Knowledge Cooperative Research Centre, Alice Springs, http://www.nintione.com.au/resource/DKCRC-Report-17-Buffel-Grass.pdf.
Weed Management CRC 2008, Weed management guide: buffel grass (Cenchrus ciliaris), archive.dpi.nsw.gov.au/__data/assets/pdf_file/0005/347153/buffel-grass-weed-management-guide.pdf.