Bitou Bush - Its Effects on Biodiversity

Points covered:

• What is Bitou Bush?
• Why is it a problem?
• What effect has Bitou Bush had on native plants and animals?
• What effects might occur by controlling Bitou Bush with herbicides?

Words to know:

• BALLAST WATER - water carried in ships to provide stability.
• ARTHROPODS - animals with an exoskeleton, including insects,spiders, crabs, centipedes and millipedes.

Bitou Bush, (Chrysanthemoides monilifera), is a native of South Africa. It was intentionally imported into Australia as early as 1858. However, it was also unintentionally imported, probably in the dumped ballast water of a South African ship.

Bitou Bush has only become a problem in Australia in the last few decades, since being used to stabilise coastal sand dunes after sand mining. In the absence of the South African organisms which usually feed on it, Bitou Bush has choked native Australian vegetation. In the early 1970s, it was discontinued from use but by then it was too late: Bitou Bush was firmly established along more than half of the coastline of New South Wales. Ironically, one of the plants being choked - Golden Wattle (Acacia longifolia) - has become a major pest of coastal dunes in South Africa, where it was introduced to serve much the same purpose as Bitou Bush in Australia.

Many groups of organisms are dependent on native vegetation and are not adapted to survive on Bitou Bush. To find out the effect Bitou Bush has on the diversity of native organisms, such as arthropods, scientists at the Australian Museum are studying the differences between areas which are infested with Bitou Bush and areas which still have native vegetation. Scientists at the Australian Museum are now also studying the effects of controlling Bitou Bush with herbicides. In recent years, the New South Wales Department of Agriculture has embarked on a campaign to control Bitou Bush by aerial spraying of herbicides from a helicopter. The herbicides kill the Bitou Bush but don't affect the native vegetation. However, the herbicide might be toxic to certain groups of animals, such as arthropods, and the spraying also causes dramatic short-term changes to the environment.

It is hoped that these studies will give us further insight into the effects of introduced species on native biodiversity, while also giving us an opportunity to assess our attempts to rectify the mistakes of the past.

Lance Wilkie
CBCR
Australian Museum