Australia: The Land Where Time Began

A biography of the Australian continent 

Quaternary Vegetation

In Australia the climate had been evolving towards greater aridity for about 10 million years before the boundary of the Quaternary, and with no sudden glacial onset, the boundary is not a dramatic break with the previous Tertiary. As the climate dried, there were still suitable habitats for those species that were capable of migrating to them. Remnant rainforests remained in areas such as southwest Tasmania and the northeast coast of the mainland. The expansion of the longitudinal dunefields was the most dramatic event at this time, with indications of a vegetational cover of less than 10 %, and the winds were strong about 700,000 years ago. Since then the vegetation of the arid areas has been adapting to survive some very severe conditions of water stress and nutrient deficient soils, making them less susceptible to further drying. The biota had adapted to slow, complex climatic cycles of change, and the short growing seasons in the south.

Some species have developed increased levels of ecological plasticity, and probably genetic plasticity, allowing them to be elements of different kinds of vegetation and to have varying levels of dominance in the different communities. Many Australian environment are notable for their variability, and this has encouraged the levels of plasticity found in many species. Australian arid area plants have developed special features such as mallee (lignotubers), shrubs, trees and hummock grasses. It is believed that highly stressed environments over wide areas in the past may have led to the simple floristic of many semiarid and woodland communities. Communities with many local species probably survived as intact stands that have been isolated for long periods,

The vegetation will by of a relict type that occupies habitats that have cores that have been relatively stable throughout the Quaternary where important elements are comprised of endemic species from isolated taxonomic groups (palaeoendemics).

Species that adapted well to the variability of the Pleistocene, developing mechanisms of fire tolerance and avoidance and the ability to migrate have been favoured by the arrival of humans. It is believed that the eucalypts may have been favoured by the arrival of humans, replacing some other taxa in woodland and open forest. Some areas have been moved towards shrubland growth, while some landscapes have been stabilised by the removal of all large predators and many large browsers and grazers. Since the introduction of a range of placental species, not including large carnivores, the interference has been reversed. The vegetation cover is now being shifted towards a lower cover and mainly ephemeral species.

Sources & Further reading

  1. G.S. Hope in Hill, Robert S., (ed.), 1994, History of the Australian Vegetation, Cambridge University Press.
 
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                                                                                           Author: M.H.Monroe  Email: admin@austhrutime.com     Sources & Further reading