Managing Carnarvon's grasslands

Joss Bentley is currently preparing the Carnarvon Station Reserve Management Plan

Expansive bluegrass grasslands at Carnarvon. PHOTO: JULIA SHAW

The purchase of Carnarvon Station in central Queensland, with its endangered bluegrass (Dichantheum sericeum) communities and other grasslands, presents Bush Heritage with the challenge of managing these important natural resources.

Grassland management as a science is still developing, but we know that the species composition and structure of grassland is easily changed by different management techniques. Such changes also affect the animals and birds which depend on it.

Choosing the management actions which will ensure that Carnarvon’s grasslands maintain the greatest biodiversity, while key species are protected, is not straightforward. For example, the existing bluegrass downs, which are of such high conservation value, are a rich mixture of grasses and smaller herbs and forbs. Although we wish to encourage the healthy growth of all these species, the survival of the understorey plants depends upon the management of the dominant grasses. If the grasses are allowed to form a dense and moribund sward, the species beneath will not survive. Many of the small understorey plants have conservation significance themselves as well as being an important food source for wildlife.

Preventing the grasses from completely dominating the ecosystem may be achieved by the use of grazing or fire. Both of these management tools need to be used carefully however, as they can have both beneficial and detrimental effects and can change the composition of the grassland. Over-grazing may result in the loss of understorey species such as the threatened austral cornflower Stemmacantha australis (see Species Update). Such species are highly palatable to stock and may be preferentially eaten. Similarly, some plants, such as those found in the endangered vine scrubs, may be eliminated by fire if the fire escapes from the grasslands into these scrubs. Furthermore, if burning is either too frequent or not frequent enough species may be lost.

Yassom Flora and Fauna Reserve and Terrick Terrick National Park in Victoria, provide interesting examples of how management actions can modify native grassland.

Left: Female plains-wanderer stands tall to look over the grass tussocks. Photo:Tom Wheller Above: Carnarvon grassland at sunset. Photo: Wayne Lawler/Ecopix.

Before being declared reserves, both properties grazed sheep on “unimproved” native pastures.Terrick Terrick was grazed at low to moderate stocking rates and Yassom was grazed heavily at times. A balance between stock, vegetation and wildlife had been established over more than 100 years and the properties supported an abundance of rare and threatened species. The nationally endangered plains-wanderer was one of them. This small bird lives only in sparse native grasslands where bare ground between plants enables it to forage for insects and seeds and run from danger.

When the reserves were established, stock was removed completely from Yassom Flora and Fauna Reserve, but not from Terrick Terrick National Park.Within four years, the thickening vegetation had eliminated the plains-wanderers and crowded out some threatened plants at Yassom. Low stocking densities have been maintained at Terrick Terrick and so have plains-wanderers, threatened plants and threatened reptiles.

Both these case studies are relevant to Carnarvon Station Reserve, where our aim is to maintain high levels of diversity within the grasslands, while protecting individual species of high conservation value. Cattle have been on Carnarvon for many years now, and have been an integral part of the ecosystem. Although Bush Heritage had intended to maintain grazing by cattle, we have recently decided to manage the grassland biodiversity primarily through the use of fire. To this end we have developed a fire management plan for the Reserve.

Nevertheless, given the current state of knowledge, management will necessarily be partly by trial and error, hence the absolute necessity of a thorough and rigorous monitoring program, the results of which will feed back into our management programs. This raises the possibility that at some point in the future, our monitoring results may suggest that the reintroduction of low intensity grazing may be appropriate. We will keep you informed as the work continues and share our progress in protecting Carnarvon’s grassland biodiversity.