Australia: The Land Where Time Began

A biography of the Australian continent 

Australian Vegetation Types

• Plant Formations in Australia
• Closed Forest Formation
• Tropical Closed Forests
• Subtropical-Warm Temperate Closed Forests
• Cool Temperate Closed Forests
• Open Forest
• Woodland

The earliest record of the flora of Australia as a separate continent is pollen deposited in the sediment of the growing rift between Australia and Antarctica. These sediments are from the the Late Cretaceous rocks of the Otway Basin & Duntroon Basin. These pollen indicate that the rift was the focus of diversification of the Proteaceae & Aquifoliaceae, now found in Australia, New Zealand, Papua New Guinea, and New Caledonia, as well as some in Chile. Other families of plants found in the Late Cretaceous sediments of the Otway Basin include Gunneraceae, Winteraceae, Epacridaceae, Trimenaceae. There are also 3 genera of podocarp, Araucareae, and Nothofagus.

Ocean mud from the northern margin of Antarctica have been found to contain pollen showing that the Late Cretaceous forests consisted of podocarp and Araucarian species, but these forests also included species of angiosperm.

As the Eromanga Sea retreated it left behind a variety of habitats where the angiosperms could proliferate and evolve. There were many estuaries, swamps, saltwater and fresh water marshes, brackish lagoons and the sand of the sea bed, now left high and dry. The angiosperms took advantage of the large number of niches becoming available and all the families of angiosperm diversified rapidly.

The Otway Basin and Gippsland Basin of Victoria provide a  picture of the biota in and around these basins between 116 and 106 million years ago. Great dpths of sediment waere deposited when they were part of the rift zone. More than 50 plant taxa have been identified from these sediments. So far, no definite angiosperms have been found. The southern forests were made up mostly of Ginkgoes and southern conifers.

Fossil tree trunks have been found that display growth rings. This implies seasonal growth, or seasonal dormancy, probably due to winter months of darkness. There was an understorey of such plants as pentoxylalen cycadophytes, tree ferns, horsetails and mosses. There were also bracken-like ferns, clubmosses and peat mosses. In the Cretaceous podocarp forests there is some evidence of catastrophic fires in New South Wales parts of the Murray Basin. Some of the charcoal of these trees still had their cell structures preserved.

The major Australian plant formations are described here, as well as some typical alliances contained within them.

Sources & Further reading