Invasion of native plant communities by exotic perennial grasses - key threatening process listing

The Scientific Committee, established by the Threatened Species Conservation Act, has made a Final Determination to list the Invasion of native plant communities by exotic perennial grasses as a KEY THREATENING PROCESS in Schedule 3 of the Act. Listing of key threatening processes is provided for by Part 2 of the Act.

NSW Scientific Committee - final determination

The Scientific Committee has found that:

1. A number of exotic perennial grasses including Cenchrus ciliaris (Buffel Grass),  Hyparrhenia hirta (Coolatai Grass),  Eragrostis curvula (African Lovegrass),  Nassella neesiana (Chilean Needlegrass) and  Nassella trichotoma (Serrated Tussock) invade and may dominate native plant communities competing with, and displacing, many native species. Some other perennial grasses (in alphabetical order) that invade smaller areas of native plant communities include  Agrostis capillaris (Browntop Bent),  Andropogon virginicus (Whisky Grass),  Chloris gayana (Rhodes Grass),  Cortaderia spp. (Pampas Grasses),  Ehrharta erecta (Panic Veldgrass),  Melinis minutiflora (Molasses Grass),  Panicum repens (Torpedo Grass),  Paspalum urvillei (Vasey Grass),  Pennisetum clandestinum (Kikuyu),  Phalaris aquatica (Phalaris),  Setaria sphacelata (South African Pigeon Grass),  Sporobolus fertilis (Giant Parramatta Grass),  Sporobolus natalensis (Giant Rats Tail Grass) and  Urochloa mutica (Para Grass). Other exotic perennial grasses not specified may, or have the potential to, adversely affect native plant communities and native species.

2. Exotic perennial grasses have been both deliberately and accidentally introduced to New South Wales. Hyparrhenia hirta and forms of  Eragrostis curvula were introduced for soil stabilisation while species such as  Cenchrus ciliaris and  Phalaris aquatica have been introduced for pasture. These species as well as accidentally introduced  Nassella neesiana and  Nassella trichotoma have spread to become dominant species in some native grasslands and woodlands.

3. The characteristics of vigorous growth, prolific seed production and effective seed dispersal enable many exotic perennial grasses to compete strongly with, or in some places displace, native vegetation. Exotic perennial grasses may also change the fuel load in plant communities. The changed structure and fire regimes of the habitat is likely to adversely impact on both native vertebrate and invertebrate fauna.

4. Dense monocultures of perennial grasses that develop after invasion threaten local vegetation at all sites that are affected. This may result in local and regional declines of many native species and communities, possibly to the extent that they become endangered. Many of the perennial exotic grasses establish following disturbances such as overgrazing, road works and management of roadside areas. Spread of these grasses is often aided by slashing, weed control, forestry and mining operations, movement or addition of fertilisers and nutrients, changes to drainage and fire regimes. Some species, such as Hyparrhenia hirta,  Sporobolus fertilis, Sporobolus natalensis Nassella neesiana,  Nassella trichotoma, and forms of  Eragrostis curvula, are also considered a problem in pastures. These grasses are not favoured grazing species and selective grazing results in a rapid increase in numbers of these less palatable grasses.

5. Invasion of native plant communities by exotic perennial grasses is an identified threat to a number of communities listed in Schedule 1 of the Threatened Species Conservation Act including, but not restricted to:

• White Box, Yellow Box, Blakely's Red Gum Woodland
• McKie's Stringybark/Blackbutt Open Forest in the Nandewar and New England Tableland Bioregions
• Howell Shrublands in the Northern Tablelands and Nandewar Bioregions
• Cumberland Plain Woodland

These grasses are also an identified threat to a number of plant species listed in Schedule 1 and Schedule 2 of the Threatened Species Conservation Act, including:

• Calystegia affinis
• Desmodium camplocaulon
• Dichanthium setosum
• Digitaria porrecta
• Eucalyptus mckieana
• Goodenia macbarronii
• Polygala linariifolia
• Rutidosis heterogama
• Thesium australe

Many terrestrial orchid species listed in Schedule 1 and Schedule 2 of the Threatened Species Conservation Act are also threatened by exotic perennial grasses.

A number of bird, reptile and invertebrate species listed on Schedule 1 and Schedule 2, and dependent on plants that are being displaced by exotic perennial grasses are also likely to be threatened. Examples of some listed bird species are:

6. In view of above the Scientific Committee is of the opinion that the Invasion of native plant communities by exotic perennial grasses adversely affects two or more threatened species, populations or ecological communities.

Associate Professor Paul Adam
Chairperson
Scientific Committee

Proposed Gazettal date: 12/09/03
Exhibition period: 12/09/03 - 24/10/03