Australia: The Land Where Time Began

A biography of the Australian continent 

Cainozoic Vegetation in Tasmania - macrofossil evidence

Tasmania has had microthermal rainforests dominated by Nothofagus and conifers since at least the Early Oligocene, about 35 Ma. In more recent times much of the floristic diversity of these forests has been lost, probably because of changing climate, leading to a greater temperature and rainfall variation, diurnally and seasonally. The macrofossil record from Tasmania has shown that in the past, plant communities that are now unknown in the present vegetation. This supports the proposal by (Jablonski, 1991) that it is common for plant species to exhibit individualistic responses to a particular climate change.

The nature of the Tasmanian vegetation, with its large component of elements that left no descendants, and growing under totally different conditions from those at very high latitudes at the present, is more obscure before the Late Eocene.

The Tertiary macrofossil record is sparse for typical coastal heathland and woodlands dominated by eucalypts with many diverse Myrtaceae, Epacridaceae and the legumes are common in the relatively dry eastern and nutrient-deficient wet southwestern region of present-day Tasmania. This has been partly attributed to taphonomic factors, as well as the apparent spread of the vegetation types during the Quaternary as the frequency of fire increased (Hope in Hill, 1994). Evidence has been found for these floral elements, as well as possible a similar structural vegetational type. It is believed an oligotrophic edaphic complex, similar to that found in the Cethana region at the present,  probably existed there in the Palaeogene. At the present there is a stunted sclerophyllous flora in the area that includes Eucalyptus, epacrids, legumes, Lomatia tinctoria, Banksia, Gleichenia and Sticherus. Macrofossils have been found in the deposit that show affinity with the last 4 taxa.

Small-leaved sclerophyllous shrubs or small trees are typically present in the alpine and subalpine vegetation of Tasmania. Taxa present include, Taxodiaceae, Myrtaceae, Proteaceae, Epacridaceae, Microstrobos, Microcachrys, and Nothofagus gunnii. Isoetes, a fern ally, is commonly found in the high country in many small lakes. Most of these taxa are found as macrofossils in the Monpeelyata site at high altitude. This has been seen as an indication that Tasmanian mountains have supported a similar vegetation for at least 22 Ma. Tasmania has sites such as Regatta Point, Little Rapid River and Cethana, where there are many angiosperm leaves that still await identification.

Sources & Further reading

  1. R.J. Carpenter, R.S. Hill & G.J. Jordan in Hill, Robert S., (ed.), 1994, History of the Australian Vegetation, Cambridge University Press.
  2. Jablonski, D., 1991, Extinctions: a palaeontological perspective. Science, 253, 754-7.
  3. Hope in Hill, 1994).
 
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                                                                                           Author: M.H.Monroe  Email: admin@austhrutime.com     Sources & Further reading