For more than 30 years, scientists have suggested that the first human immigrants into Australia dramatically changed the continent's vegetation with the use of fire. However, few vegetation records from the vast Australian interior exist, and none extend beyond the last 18,000 years. The traditional tools for reconstructing vegetation - such as imprints and remnants of plants and the accumulation of pollen grains - are not preserved in the harsh outback environment.
A report in the May 14 issue of Science, describing a novel approach to reconstructing paleovegetation, presents the first continuous vegetation record from the Australian interior extending back 65,000 years. This, in turn, serves as a proxy for the predominent season of rainfall. The evidence is consistent with a human over-print on environmental change, the authors say.
The paper was authored by Beverly Johnson, a post-doctoral fellow with the University of Washington's School of Oceanography; Gifford Miller of the University of Colorado at Boulder; Marilyn Fogel of the Carnegie Institution of Washington (D.C.); John Magee and Michael Gagan of the Australian National University; and Allan Chivas of the University of Wollongong in Australia. To reconstruct changes in vegetation, and the season of predominant rainfall, the research team analyzed the stable carbon isotope composition of fossilized eggshells laid by emus, large flightless birds that are still found today in Australia.
The eggshells reflect the emu's diet, including the relative amounts of
vegetation consumed with a C3 signal (mostly trees, shrubs, and winter grasses)
or a C4 signal (tropical grasses). Modern emu eggshells have a stronger C3
signal if the animals live in regions where the plants predominately receive
winter precipitation. The shells of modern emus have a stronger C4 signal if
they live in areas dominated, instead, by the summer monsoon and the resulting
weather systems carrying rain into the interi
Contact: Sandra Hines
University of Washington