Vegetation in the Australian Tertiary in Response to Climatic and Phytogeographic Forcing Factors*

Abstract

Nancy Burbidge's 1960 paper on the phytogeography of the Australian region would make a fitting starting point for a review of the impact of the plant fossil record on understanding Australian vegetation history. However, a number of reviews were published in the late 1970s and early 1980s, so that the present overview takes its starting point from that time and considers the advances in research since then. In the interval since, information has accrued from both palynology and plant macrofossils, so that the fossil evidence must now be considered a primary source of data for interpreting the evolution of Australian vegetation.

There have also been major advances in understanding the geological framework of the Tertiary, against which the fossil data must be set. For instance, the timescale against which advances must be measured has been refined, there have been comprehensive syntheses of Tertiary palaeogeography, and a better understanding of the relationships, through time, of Australia with continents to the north, and between Australia and Antarctica. Our understanding of the climatic factors affecting the continent and its vegetation has also improved.

The record now available, in spite of its many limitations, gives a general picture of transition from widespread, very diverse rainforests in the early Tertiary, to predominantly open vegetation with rainforest restricted to wetter regions. Some aspects of the early forests remain insufficiently understood; for instance, the effects of high latitude position on forest growth. The development of sclerophylly may go back as far as the Eocene, with Banksia and Acacia now having records that extend back that far. The development of open vegetation types was probably linked with changing fire regimes; we know that by the mid-Miocene, heath-like vegetation was established locally in coal swamps. Rainforests of drier aspect were established early too, probably first at inland localities, and there are hints of wet sclerophyll forest by the late Miocene. The history of grasslands and savannah remains sketchy, and no modem analogues can be identified for vegetation types in the Pliocene that were rich in Asteraceae and grasses. The history of the eucalypts, and their links to specific fire regimes, is a more recent story.

* The Nancy Burbridge Memorial Lecture, which was presented at the 'Southem Temperate Ecosystems' conference, held in Hobart, Tasmania, 18–22 January 1993.