Introduced grasses

Introduced or exotic grasses can displace native vegetation and have a negative impact on native animals and agriculture.

Many perennial grass species have been introduced to Australia since 1788. Some species have adverse impacts on biodiversity and agriculture and are recognised as weeds.

Some introduced grasses, such as serrated tussock and Chilean needlegrass, are recognised as Weeds of National Significance. Many others have been listed in regional weed strategies as threats to biodiversity.

Why are introduced perennial grasses a threat?

Features of introduced perennial grasses include:

  • vigorous growth
  • prolific seed production
  • effective seed dispersal.

These characteristics enable many exotic grasses to compete strongly with, or even displace, native vegetation. Exotic perennial grasses may also change the fuel load in plant communities. The changed structure and fire regime of the habitat is likely to have a negative impact on both native animals and insects.

In September 2003 the NSW Scientific Committee made a final determination to list the 'invasion of native plant communities by exotic perennial grasses' as a key threatening process (KTP) in NSW.

Exotic perennial grasses are those which are not native to New South Wales and have a life-span of more than one growing season. More than 100 species of exotic perennial grasses occur in NSW. A relatively small number of these perennial grasses threaten native plant communities. Exotic perennial grasses of special concern include the following:

Increasing evidence that some perennial grass species have significant adverse impacts on biodiversity has led to the listing of 'invasion of native plant communities by exotic perennial grasses' as a key threatening process. A few examples follow:

  • Coolatai grass grows vigorously, forming an almost complete monoculture and replacing native grass and wildflower species. It tolerates drought, heavy grazing and many herbicides. It has invaded large areas of grassy woodlands and native pastures in north-west NSW and is spreading rapidly in other regions.
  • Chilean needlegrass has several features which give it a competitive advantage over many native species, such as its ability to produce a large, long-living seed bank, high survival of seedlings, tolerance to drought and effective animal-borne and water-borne dispersal mechanisms for seeds.
  • Serrated tussock infests more than a million hectares in southern Australia, but has the potential to spread over a much larger area. It invades native grasslands, grassy woodlands, dry forests and rocky shrublands. Serrated tussock forms large tussocks, with individual plants capable of producing more than 10,000 seeds annually. Some seeds remain viable in the soil for more than 10 years. Mature plants droop across the ground, smothering other species.
  • Pampas grass readily tolerates saline conditions, salt spray, drought, periodic inundation, severe frosts and strong winds. It can grow on a wide range of soil conditions and light conditions, from shaded areas through to full sunlight. Pampas grass is an aggressive coloniser and can form dense stands which prevent other plants from growing. Individual flower heads produce more than 100,000 seeds, and wind may disperse seed for several kilometres.
  • Perennial grasses, such as perennial veldtgrass, pampas grass, Coolatai grass and buffel grass, produce large amounts of plant matter which dries quickly and causes fuel loads to increase. This fuel results in fire regimes that favour the spread of these perennial grasses. Hotter and more frequent fires may lead to changes in the structure of the vegetation and in some cases to local extinctions of some plant and animal species.
  • Species such as Coolatai grass, Chilean needlegrass, serrated tussock, and invasive forms of African lovegrass are undesirable in pasture because of their low palatability to stock or low nutritional value at certain times of the year.
  • On Montague Island, the proliferation of kikuyu interferes with the nesting of adult fairy penguins. Kikuyu forms dense mats across the surface of the ground and blocks burrow entrances. Consequently, some chicks die of starvation.

Threatened species and endangered ecological communities include:

  • ‘Box-gum woodland' (White box yellow box Blakely's red gum woodland) is threatened by Coolatai grass. Coolatai grass dominates large areas of pasture, roadsides, travelling stock routes and areas of remnant vegetation in the North-Western Slopes, especially in the Manilla area north of Tamworth.
  • Serrated tussock, African lovegrass and Chilean Needlegrass are a major threat to native grasslands, particularly the endangered communities 'Natural temperate grasslands of the South Eastern Highlands' and 'Bega Dry Grass Forest'.
  • In the Sydney area, pampas grass threatens 'Duffys Forest Ecological Community'. Threatened species at risk include Persoonia mollis and the orchid Microtis angusii.

For more ecological communities and species impacted upon by the invasion of exotic perennial grasses, see the Scientific Committee’s final determination.

Perennial grasses such as phalaris are important components of pastures in many areas of the tablelands and higher rainfall areas of the western slopes. They are valued because of their productivity under grazing, and the amount and nutritional value of the herbage they produce. When grown in swards containing one or more complementary species, for example annual or perennial legumes or annual grasses, they also resist invasion by weed species such as vulpia and thistles.

Kikuyu is an important pasture species for dairy cattle in some coastal areas and is used widely as a lawn.

Pastures containing perennial grasses have important environmental benefits. In comparison with pastures and crops based on annual species, they reduce deep drainage (groundwater recharge) and thereby reduce the development of dryland salinity. Pastures based on perennial grasses also have reduced the rates of soil acidification.

Some of these perennial grasses will continue to be grown widely in pastures or lawns, and have the potential to spread into natural ecosystems where they can adversely affect biodiversity.

Many introduced grasses have origins in Australia as agricultural or ornamental species and some have become a threat to biodiversity. One of the challenges associated with managing these grasses is that many will be retained as agriculturally beneficial species.