A floristic framework of Australian rainforests

Authors

  • L. J. WEBB,

    1. CSIRO Division of Plant Industry, Long Pocket Laboratories, Indooroopilly, Australia 4068
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      PO Box 338, Alderley, Brisbane, Australia 4051.

  • J. G. TRACEY,

    1. CSIRO Division of Plant Industry, Long Pocket Laboratories, Indooroopilly, Australia 4068
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      CSIRO Division of Forest Research. PO Box 780, Atherton. Australia 4883.

  • W. T. WILLIAMS

    1. CSIRO Division of Tropical Crops and Pastures, Davies Laboratory, Townsville, Australia 4810
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      10 Surrey St., Hyde Park, Townsville, Australia 4812.


Abstract

In the first comprehensive floristic classification of Australian rainforests and monsoon forests, fresh insights made possible by the use of floristic as distinct from structural data are outlined. A set of 561 individual communities, on sites ranging from North Queensland westwards to the Kimberley region and southwards to Tasmania, is defined by the presence or absence of 1316 tree species, or 406 genera. The data have been subjected to numerical classification, first with respect to species, then to genera.

The species classification first divides into three ‘ecofloristic regions’: A, temperate (microtherm) and subtropical (mesotherm) humid evergreen rainforests; B, tropical (megatherm) humid evergreen grading into highly seasonal raingreen (monsoon) forests; and C, subtropical (mesotherm) moderately seasonal humid/subhumid raingreen forests. The sites are further divided into eight ‘ecofloristic provinces’, for each of which a core area is identified and the ten most common diagnostic tree species listed for selected floristic elements, whose ecological relationships are briefly described.

Gradients of quantitative thermal-moisture indices are added to standard climatic typology to provide a more flexible identification of local climates that characterize community-types of each province across a wide latitudinal/altitudinal range. Community disjuncts and outliers of a particular province are interpreted as the results of past environmental sifting (in which ecological factors are not entirely determinate), of previously more continuous rainforest vegetation.

The genera classification first divides into humid eastern coastal and subhumid western and subcoastal sites, then four thermal types, and finally nine groups of floristic ‘paleo-provinces’. Where the species and genera classifications are not in substantial agreement, a wide-ranging generic element across the provinces in northern and northeastern Australia is interpreted in paleogeographic terms.

The relict distribution of existing community types, as the result of climatic sifting of ancient floral stocks, is discussed in support of emerging ideas about the autochthony of Australian rainforests, especially those tropical types that are not intrusive.

It is argued that the unique ecological relationships of Australian rainforests justify the most conservative uses of the relatively small remaining areas.

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