About Australia (Nature)

Areas where eucalypts are notably absent are the tropical and subtropical rainforests of the eastern Australian mainland and the temperate rainforests of Victoria and Tasmania. They are also largely absent from the extensive arid zones of inland, midsouthern (Nullarbor) and northwest Australia, although a few species are abundant along the watercourses in these regions. No eucalypts, in fact no trees at all,grow on the summits of he Australian alps because of the intense cold and high winds. A bushy and often twisted eucalypt, the snow gum, thrives in the snow on the mountain slopes up to an altitude of about 1,500m.

There are about 500 species of eucalyptus. Many are site-sensitive and have particular soil preferences, like black-soil plains, siliceous or gypseous dunes, sandy soils with lime content, sandstone-derived soils, etc., while other species are distributed over wide geographic and environmental gradients and show a relatively wide tolerance to soil type. Generally, however, the species are divided into a northern, summer-rainfall group and a southern, winter-rainfall group although a few species have adapted, probably in different physiological forms, to both low and high latitude regions, particularly on the eastern sea-board. A large, third group is unique to the southwest of Western Australia and has probably been in genetic isolation for a long period due to the barrier of the Nullarbor Plain which is unfavourable for tree growth.

As would be expected in a genus so widespread and comprising hundreds of species, a great range in form is exhibited by members growing under different environmental conditions.

Mountain ash (E. regnans) of Victoria and Tasmania reaches heights of over 100 m making it the tallest species in Australia and the tallest hardwood in the world. Other notable forest trees reaching great size are the Western Australian species karri (E. diversicolor) and the southeastern Australian and Tasmanian species messmate stringybark (E. obliqua), southern blue gum (E. globulus), manna gum (E. viminalis) and alpine ash (E. delegatensis). Tall tree species in the summer-rainfall zone which are conspicuous in the moist forests of New South Wales and Queensland include Sydney blue gum (E. saligna), flooded gum (E. grandis), blackbutt (E. pilularis) and tallowwood (E. microcorys). All these species characteristically dominate tall openforests on the deeper, commonly loamy soils of the higher rainfall areas. Such trees are often over 45 m in height, long-boled and may attain 6 m in girth at breast height.

A considerable number of valuable eucalypts do not attain the giant dimensions of mountain ash and frequently are no more than 35 m in height. Examples of trees of this type are jarrah (E. marginata) of Western Australia, brown stringybark (E. baxteri) from South Australia and Victoria and white stringybark (E. globoidea) from Victoria and New South Wales. Spotted gum (E. maculata) and red bloodwood (E. gummifera) are further examples from the east coast.

Outside the forested country many important eucalypts dominate woodlands over much of northern Australia and in areas of southern Australia receiving less than 750 mm of rain annually. These widely spaced trees are often less than 25 m high with a short thick trunk and with heavy limbs forming a broad, spreading crown. The red gum ironbark and box groups of eucalypts are well represented in these open stands of northern and eastern Australia. Wandoo (E. wandoo) and tuart (E. gomphocephala) are typical woodland species of the southwestern region. Salmon gum (E. salmonophloia) is a remarkable Western Australian woodland species which grows to heights of 30 m on rainfall as low as 250 mm.