Nature and distribution of rain-forests in New South Wales

Abstract

Rain-forest has a discontinuous distribution along the coast and adjoining ranges of New South Wales, extending to altitudes of over 4000 ft. Four major subformations can be recognized, along with two other structural forms which may deserve subformation status. The subformations have been defined as tropical, subtropical, temperate, and dry rain-forest. Six floristic alliances and their associations are briefly described.

For the widespread development of rain-forest an annual rainfall exceeding 60 in. is required, though rain-forest is found under much lower rainfalls in places favoured by the soil or topography. The Hernicyclia alliance (dry rain-forest) is found in areas showing a distinctly seasonal rainfall distribution, while the Nothofagus alliance (temperate rain-forest) requires cold and very moist conditions. The Castanospermum alliance occurs along creek banks, usually away from the main rain-forest patches, and the Cupaniopsis alliance is found close to the coast, apparently requiring wind-borne supplies of moisture and mineral nutrients for its development. The Argyrodendron (tropical) and Ceratopetalum (subtropical) alliances occur under similar climatic conditions in the north, but with the Ceratopetalum alliance restricted by competition to the less fertile soils. In the south of the State, where climatic sifting has removed many tropical rain-forest species, the Ceratopetalum alliance occurs on the richer soils.

The discontinuity of the rain-forest distribution has been brought about by past climatic changes. Human influence has always restricted rain-forest spread, and since European settlement the area of rain-forest in New South Wales has been reduced by about half.