Native pastures are simply grazing environments that are usually dominated by native grasses and may occur as grasslands or woodlands. These pastures contain native grasses and many other native herbs and shrubs. Even healthy, relatively undisturbed native pastures also commonly have a mix of introduced species, such as annual and perennial grasses, clovers and herbs.
Not all native pastures are the same and include: largely undisturbed native swards with few introduced species; pastures topdressed and oversown with, for example, clovers and superphosphate; pastures disturbed by ploughing or heavy grazing and containing many introduced species; or introduced pastures that have declined and be re-colonised by native species. The composition, grazing value and conservation value of each pasture type will vary, as will their management; depending on the goals of the manager.
A healthy native pasture may contain up to 100 species, of which 25-30% are typically grasses; the rest consist of lilies, daisies, sedges, rushes and herbs from many other families. Although perennial grasses may not form the majority of the species present; they usually dominate the pasture bulk. Even in a healthy native pasture, introduced species are often present, but form only a minor component of the biomass.
Many regions have mosaics of different dominant native species that are favoured by landscape differences, even within the one paddock. For example, differences in soils, slope, aspect, tree density and the presence of boulders and fallen logs all influence the composition of species and which will dominate.
THE VALUES OF NATIVE PASTURES
Native pastures have many different values, the importance of which will vary depending on the structure of the pasture and the goals of the manager. The values include:
- habitat for endangered flora and fauna;
- well adapted to the variable Australian climate;
- habitat for endangered flora and fauna;
- have low input requirements compared with exotic counterparts;
- carry fewer stock, but require fewer inputs;
- provide shelter for stock; and
- provide drought feed.
Original pastures in Australia were most likely a mix of both tall tufted warm-season (C4) and year long green (C3) perennials, such as kangaroo grass (Themeda triandra), wild sorghum (Sorghum leiocladum), spear grass (Austrostipa species) and Poa species. The dominant species would have varied with altitude, rainfall and soil type. Shorter grasses, such as red grass (Bothriochloa macra), purple wiregrass (Aristida ramosa), wallaby grass (Austrodanthonia species) and weeping grass (Microlaena stipoides) were mostly subsidiary species.
Many of the original dominant species were favoured by regular burning and very light, or no, grazing pressure. With the introduction of yearlong grazing by cattle and sheep and late winter burning in many areas, pastures composed of shorter warm-season perennials become more common as they are either more resilient to grazing (e.g. red grass) or are avoided by stock (e.g. purple wiregrass). This also commonly leads to an increase in naturalised cool-season annuals. Where heavy summer grazing and/or fertiliser are used, the abundance of native yearlong green perennials (e.g. wallaby grass and weeping grass) and naturalised cool-season annuals is favoured. Combining heavy yearlong grazing and increased soil fertility generally degrades native pastures to dominance by naturalised cool–season annuals.
These changes can work in the opposite direction to achieve the desired composition if the right management is used, and sufficient plant numbers are present. Long rests and reduced grazing pressure can move a pasture dominated by short yearlong green species towards one dominated by taller erect species. Increasing the grazing pressure in winter and not fertilising will tend towards a short warm-season perennial dominated pasture. Achieving these changes, depends on the season (good rains are needed for germination or growth) and the timing of the management relative to the desirable and undesirable species. For example, rests from grazing need to coincide with the flowering and seeding of the desired species to be effective.
PASTURE COMPOSITION IN NATIVE PASTURES
Most historical changes to pasture composition were not done by design. Now better understanding of the requirements of species can enable management to push composition in a more predictable direction. However, understanding of native species dynamics is far from complete and caution in management is advised.
In some situations, degradation of native pastures has gone too far to permit grazing or fertiliser management to restore the desired pasture composition (e.g. lack of seed bank, change in soil condition, invasion of weeds or other factors). In these cases, seed sowing and/or chemical weed control may be valid options to aid the re-establishment of native species.