Australasian Science: Australia's authority on science since 1938

Nullarbor’s Ancient Forests Uncovered

Rather than being the treeless, limestone expanse that the Nullarbor Plain is today, dating of fossilised pollen has revealed that five million years ago it received up to four times as much rain as it gets now and was an expanse of gum and eucalyptus trees, banksias and other flowering plants that are now confined to Australia’s east coast.

The finding, published in PNAS (www.tinyurl.com/jcu7hyv), sheds new light on the environmental history of the Nullarbor, a former seabed that was lifted above the sea 14 million years ago.

“The Nullarbor region had a relatively dry climate until five million years ago, but then the vegetation suddenly changed,” said Dr Kale Sniderman of The University of Melbourne. “In just 100,000 years it became a forest of gums and banksias, which suggests a rainfall of two or up to four times higher than today.”

The Nullarbor Plain covers 200,000 km2 bordering the Great Australian Bight between South Australia and Western Australia. It receives an average of 250 mm of rain each year, but before five million years ago the annual rainfall was approximately 480 mm and 3.5–5 million years ago it rose to an estimated 1220 mm.

Investigating the climate history of Australia’s desert regions is traditionally difficult for scientists given the scarcity of fossils and the difficulty in accurately dating them.

The researchers dated speleothems – stalagmites, stalactites and flowstones deposited in caves – and then dissolved them to examine any ancient pollen trapped within.

“Most didn’t contain any pollen, which isn’t surprising since many speleothems grew in caves that had no openings to the surface,” Sniderman said. “But some did contain fossil pollen, which revealed the nature of the vegetation growing at those times. Through that we’ve been able to develop a new understanding of the history of the Nullarbor’s climate.”