Finding the facts of life in the bush

David Freudenberger with his travelling case of woodland birds

By Brad Collis

The revegetation of farmland to improve the biodiversity of the cropping landscape, and ultimately lift the grainbelt’s long-term sustainability, is shifting up a gear through a three-year study into the real needs of threatened flora and fauna species.

The project, ‘Testing Approaches to Landscape Design in Cropping Lands’, is building on CSIRO research in WA and NSW into the ‘focal species’ concept.

This was developed as a way to actually measure the effects of clearing, loss of biodiversity, and dryland salinity. To save time, given the urgency of the situation, the approach identifies species that are the most sensitive to particular threats, rather than trying to determine the health of a whole range of plants and animals.

By responding to the needs of these ‘focal species’ it not only allows a more strategic approach to revegetation, but hopefully creates an ecological umbrella under which the needs of many other species are also covered.

The initial focal species chosen as bioindicators are woodland birds because they require a dense understorey, which means revegetation has to be more comprehensive than just tree-planting.

“We find that woodland birds tend to disappear from the landscape once the bush becomes fragmented and the understorey over-grazed,” says project leader, Dr David Freudenberger. “They need a lot of threedimensionality; trees and shrubs of varying height and density.

“So an early rule of thumb we use to define habitat quality is if you can see through it, then it isn’t a very useful habitat. It usually means the understorey which these birds need for nesting, feeding and for protection from predators, has been grazed out.”

Photo: Disappearing treasures: David Freudenberger with his travelling case of woodland birds.

The other early finding is that birds need larger areas of dense bush than previously thought – anything from 10 to 100 hectares.

This is the threshold that has emerged from surveys of the Riverina, the western slopes of NSW, the WA wheatbelt and central NSW. Below this figure, the bush seems incapable of providing woodland birds with the habitat diversity needed for breeding and feeding.

Armed with this information, a new project – a joint Land and Water Australia/ CSIRO initiative – is moving beyond a single focal species like the small woodland birds, to identifying the requirements of a range of fauna, such as insects and reptiles; to see at what levels of revegetation a more complex and more viable web of life begins to interlink.

Dr Freudenberger and his team hope to develop a guide for growers interested in revegetating poor cropping country to assist the long-term survival of remaining biodiversity. They will evaluate methods for assessing where to put revegetation, for determining whether or not revegetation designed for one species or genus meets the needs of others, and for assessing how much revegetation is required.

“So far the research has shown us that planting a few rows of trees does not provide the habitat needed to protect species, such as birds, that are declining because of land clearing. But now we have to extend our knowledge to a wider range of taxa – to the threatened plants and the creepy crawlies on the ground and up in the trees,” says Dr Freudenberger.

“We also have to measure the impact of bush fragmentation across larger areas. For example, is a 10 hectare patch still enough if it’s in isolation? How many 10-hectare patches are needed in say, 10 or 100 square kilometres.”

Dr Freudenberger hopes the project will convey to the community what biodiversity really means. Biodiversity embraces a wide range of organisms and if land users are going to try and recreate useful habitats then it needs to accommodate all of them.

For more information:
Dr David Freudenberger, david.freudenberger@csiro.au