Media Release - 27 July 2003

Woody invasion attributed to European grazing techniques

A new study demonstrates that the invasion of Australia's tropical grazed grasslands by trees and shrubs followed the introduction of European land-management practices such as livestock grazing and fire suppression.

The study, by scientists from Australia's Cooperative Research Centre for Greenhouse Accounting, uses innovative analysis of carbon isotopes in soil to trace changes in vegetation cover back through time.

It concludes that, at a test site in north-eastern Australia's grazed lands, woody thickening - the invasion of grasslands by trees and subsequent growth of the trees - commenced after European management practices were introduced.

Study leader Dr Evelyn Krull said that woody thickening had long been observed worldwide, particularly in the grasslands and savannas of Australia, America and Africa. “Until now there has been little information on when woody thickening began or its cause,” Dr Krull said.

Dr Krull said remote imaging from satellites could give information on invasion, but only over the past 30 years or so. “The technique developed in this study allows us to trace back further in time to see when it began,” she said.

“This study not only confirmed that soil organic matter provides a record of past vegetation change in tropical rangelands, but also established that increases in tree cover followed changes in land management,” she said.

The Chief Executive of the Cooperative Research Centre for Greenhouse Accounting, Dr Chris Mitchell, said Dr Krull's work provided a means by which scientists could probe into the past to improve understanding of processes involved in ecosystem change.

“In effect we can now look back through time to see what changes have occurred in these areas and when they occurred,” Dr Mitchell said.

“The Cooperative Research Centre for Greenhouse Accounting iscontinuing work to analyse the impact of soil and vegetation type onthe role woody plants play in removing the greenhouse gas carbon dioxide from the atmosphere and storing carbon.

“This technique should give us a better understanding of the role woody invasion plays in these processes in the tropics.

“If other grazed grasslands and savannas around the world are found to be similar to those in Dr Krull's study, they will play a significant role in the global carbon cycle.

“The ability to trace past changes in these tropical rangelands will also help in efforts to improve understanding of productivity, changing bio-diversity, and fire-risk,” Dr Mitchell said.

Cooperative Research Centres are created through an Australian program that brings together researchers from universities, government agencies and private industry in long-term collaborative arrangements to support research, development and education activities achieving outcomes of national economic and social significance.

Partners of the Cooperative Research Centre for Greenhouse Accounting in the woody thickening studies include the Commonwealth Scientific and Industrial Research Organisation and the Queensland Department of Primary Industries.

Dr Krull will present her work on Tuesday 29 July at the 16th Congress of the International Union for Quarternary Research in Nevada, USA.

(Paper No. 78-2 Presentation Time: 1:30 PM-4:30 PM Tuesday 29 July 2003. Tracing Recent Vegetation Changes In Australia's Grazed Woodlands By D13c Analyses Of Soil Organic Matter KRULL, Evelyn S.¹, SKJEMSTAD, Jan O.¹, BURROWS, William H.², and BRAY, Steven G.³, (1) CSIRO Land & Water, CRC for Greenhouse Accounting, PMB 2, Glen Osmond SA, 5064, Australia, Evelyn.Krull@csiro.au, (2) Queensland Department of Primary Industries, CRC for Greenhouse Accounting, PO Box 5545, Rockhampton QLD, 4702, Australia, (3) Queensland Department of Primary Industries, CRC for Greenhouse Accounting, PO Box 6014, Rockhampton QLD, 4702, Australia.)