Extinction Australian megafauna caused vegetation change

30-06-2013   About 45,000 years ago, the extinction of large animals in Australia was followed by abrupt changes in vegetation as well as by substantial forest fires, and not the other way around. This is the result of a study of researchers from the NIOZ Royal Netherlands Institute for Sea Research, together with Australian colleagues. Their findings appear online in the journal Nature Geoscience of June 30.

There has been a long and heated debate in Australia about the timing and cause of the extinction of the Australian megafauna, large animals which includes a variety of large marsupials and the giant flightless bird, and which happened ca. 50,000 to 45,000 years ago. The debate has concerned whether early humans are the direct cause (through hunting) or were indirectly responsible (by setting fires causing burning of the landscape and changing vegetation). Or was there a shift of climate that led to the disappearance of the large animals, or a combination of any of these factors?

NIOZ researchers, together with Australian colleagues, reconstructed past climate conditions as well as vegetation for South East Australia, home for a large part of the Australian fauna. They used specific molecules present in sediments from the coast of South East Australia which were deposited there by the large Murray-Darling rivers. Using this, it was possible to determine the relative importance of the so-called C3 vegetation (shrubs, trees) and C4 vegetation (mainly grasses). This revealed an extensive period (68,000-31,000 years) of generally high C4 plant abundance that was punctuated by an abrupt increase in C3 vegetation at ~43,000 years. This sharp increase in C3 vegetation lasted for ~5,000 years and directly followed the period in which the large animals in Australia became extinct.

The cause for the vegetation change was not climate change as no evidence was found for any abrupt, strong changes in temperature or precipitation. Instead, the extinction of the megafauna allowed the expansion of C3 vegetation such as shrubs and trees, which were normally consumed by these large animals. The researchers also found specific molecules which indicated that large parts of the vegetation were burned at this time. These fires were likely engendered by humans and aided by the fact that the C3 vegetation is more prone to fire than C4 vegetation. Remarkably, the nature and relative timing of these events is exactly as first hypothesized by Professor Tim Flannery, one of Australian’s most well-known climate scientists, already in 1992. The project was performed at NIOZ Texel and was funded through a Vici grant to Stefan Schouten by the Netherlands Organization for Scientific Research (NWO-ALW).

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Article:
Raquel A. Lopes dos Santos, Patrick De Deckker, Ellen C. Hopmans, John W. Magee, Anchelique Mets, Jaap S. Sinninghe Damsté and Stefan Schouten. Abrupt vegetation change after the Late Quaternary megafaunal extinction in southeastern Australia. Nature Geoscience June 30.

More information:
Prof. Dr. Ir. S. Schouten, +31 (0)222 369 565
Nienke Bloksma, NIOZ Communication: +31 (0)222 369 460 or +31 (0)6 53 49 47 14

High-resolution pictures are available upon request from Nienke Bloksma.

Pictures:
Intense crown fire in a Eucalyptus dominated wet sclerophyll forest, Kilmore area, Victoria, February 2nd, 2009. © Richard Alder AFSM, National Aerial Firefighting Centre.
Example of typical vegetation occurring in South East Australia. © Raquel Lopes dos Santos