The pioneer work in mapping the vegetation communities of South Australia was carried out in the 1920s and 1930s by T.G.B. Osborn and J.G. Wood, culminating in Wood's The Vegetation of South Australia (1937). Although aerial photography was in its infancy and the mapping of vegetation patterns over wide areas was extremely difficult, their classification and detailed descriptions of plant communities provided a solid foundation for later research.
The next major contribution was R.L. Specht's work for the second edition of The Vegetation of South Australia (1972). In preparing a series of maps for parts of the State, Specht developed a system of classifying vegetation communities on the basis of their dominant life form component; that is, whether tree, shrub, grass or herb. Classification into communities which can be mapped is made on the height and the percentage foliage cover of the tallest stratum of the vegetation. Thus forest is mapped where trees form the tallest stratum and their projective foliage covers more than 30% of the ground. Woodland is mapped where the trees are the tallest stratum but the foliage covers less than 30% of the ground. Open scrub has a tallest stratum of shrubs taller than 2 metres with their projective foliage covering from 30 to 70% of the ground. Tall shrubland has shrubs making up the tallest stratum but their foliage covers less than 30% of the ground. Shrubland is mapped where shrubs form the tallest stratum but are less than 2 metres in height and the foliage cover is less than 30%. Grassland consists of hummock, tussock and other grasses and varies from closed grassland covering up to 100% of the ground to very open grassland covering less than 10%.
From this solid foundation of work on South Australia's vegetation, C.D. Boomsma and N.B. Lewis of the Woods and Forests Department applied Specht's vegetation classification to a map of the State in the publication The Native Forest and Woodland Vegetation of South Australia (1980). The simplified version of their map shows only the major structural categories and a category 'coastal succession' which is a complex of the narrow bands of coastal vegetation which cannot be mapped individually at this scale. The map represents the vegetation of South Australia as it probably existed in 1836.
All forests found in South Australia can be classified as open forest. Such forests can also be described as dry sclerophyll forest; this descriptive title alludes to the low rainfall regime it experiences and the tough leaves of the plants which characterise it, but gives no indication of the density of the trees. The tall open forests (or wet sclerophyll) of eastern and south-western Australia require an annual rainfall of over 1000 mm. Only a few small areas in the Mount Lofty Ranges receive this amount. Open forests are confined to areas of infertile skeletal soils with more than 600 mm of annual rainfall. These occupied only about 1.2% of the State at the time of European settlement and were restricted to the wetter parts of the Adelaide Hills and Fleurieu Peninsula, the southern Flinders Ranges, the western end of Kangaroo Island and parts of the sandy ranges of the South-East.
Open forests, dominated by the stringybarks Eucalyptus obliqua and E. baxteri, had a dense heath understorey of a wide variety of hard-leafed or sclerophyll shrubs, principally of the families Proteaceae, Epacridacceae and Leguminosae.
A large variety of different types of woodland occurs in South Australia and about 100 different formation types have been recognised. Although they generally occur in areas of lower rainfall than the forests, woodlands grow on more fertile soils and have been extensively cleared for grazing and agriculture. At the time of European settlement, the woodlands in the higher rainfall southern areas were dominated by various Eucalyptus species, often with an understorey of native grasses. Further inland, Eucalyptus species are still found in association with or give way to Acacia, Callitris, Casuarina and Melaleuca as the dominant trees.
The open scrub or mallee formations develop in the 250-500 mm rainfall zone on calcareous and infertile sandy soils. The formations are dominated by multi-stemmed Eucalyptus species and, depending on rainfall and soil type, have an understorey of sclerophyll or chenopod shrubs and hummock grasses. The mallee areas were first used for low intensity sheep grazing, mainly on the grassy openings which were scattered through the scrub, but since the 1880s with the development of dryland farming techniques, vast areas have been cleared for cereal growing.
Tall shrubland formations occur in semi-arid areas receiving less than 250 mm of annual rainfall. The shrubs are 2-8 metres tall and often multi-stemmed. Typical of this formation are the extensive stands of mulga (Acacia aneura). Other tall shrublands are dominated by various species of Acacia, Cassia, Dodonaea, Eremophila or Heterodendrum.
Shrublands are almost entirely confined to the semi-arid and arid zones and are dominated by a variety of chenopod shrubs of the genera Atriplex, Maireana, Chenopodium, Halosarcia and Sarcoconia. These often occur as single-species stands with regularly spaced shrubs and are the basis of the rangeland sheep grazing industry of South Australia.
An extensive shrubland of sclerophyll plants also occurs on the infertile sand-dunes in the upper South-East. These were once clothed with heaths of Banksia, Casuarina and Xanthorrhoea. The discovery of the effects of added trace elements on the agricultural productivity of these soils resulted in massive clearance after the Second World War and today only small remnants of this once extensive vegetation complex survived in conservation parks.
Tussock grasslands of the genera Themeda and Danthonia once occurred on the inter-dune flats of the South-East and as an understorey to the woodlands of the Mount Lofty Ranges. There are probably no areas remaining in their pre-European state as they were destroyed by sheep and cattle grazing: however, these grasses still occur along road reserves, railway lines and in country cemeteries. The major grassland formations today are the hummock grasslands of Triodia and Zygochloa of the arid zone, which occur on rocky ranges and on sand dunes.
This category consists of a variety of formations ranging from grey mangrove (Avicennia marina) woodland, through shrublands, to the dune colonising grass Spinifex sericeus. Coastal cliffs support a variety of heath formations, while sandy beaches and dunes support a tall shrubland.
Such was the general pattern of the vegetation of South Australia at the time of European settlement as inferred from present-day remnants and early maps, paintings and descriptions. The State's vegetation has changed in 150 years. No area, with the exception of a few small inaccessible offshore islands, has escaped some alien impact. Generally, the changes to indigenous plant communities decrease in progression from the extensively modified agricultural lands in the south to the Aboriginal lands and vacant Crown land in the extreme north.
The two maps of the South Flinders Ranges (A) and Cooper Creek (B) have been reproduced from large-scale vegetation maps prepared by the Remote Sensing Applications Branch and the National Parks and Wildlife Service of the Department of Environment and Planning.
South Flinders Ranges (A)
This is an area where the mixed composition of the flora and fauna reflects the transition from the high rainfall conditions of the Mount Lofty Ranges to the more arid North Flinders Ranges. The South Flinders Ranges received a mean annual rainfall of 550-600 mm and consist of high ridges of quartzite and rounded ridges of shale. The gorges of Alligator and Mambray creeks make an important contribution to the variety of habitats found here.
To the west of the ranges the plains have been largely cleared and the vegetation consists mainly of introduced grassland species with scattered patches of elegant wattle (Acacia victoriae). On the lower reaches of the intermittently flowing creeks are strips of picturesque river red gums (Eucalyptus camaldulensis) which tap water deep below the sand.
Above the creeks the forest and woodland species depend on slope and aspect. Eucalyptus goniocalyx is associated with either a hummock grassland of Triodia irritans or a diverse heathland of species such as Acacia continua and Pultenaea largiflorens. On the steeper southern slopes the sugar gum (Eucalyptus cladocalyx) occurs as open woodlands with only scattered shrubs such as Bursaria spinosa and Dodonaea viscosa. (The sugar gum is endemic to South Australia. It attracted the attention of the first foresters who encouraged its planting as windbreaks and as a source of firewood on cleared agricultural lands.) Eucalyptus leucoxylon occurs on slopes as an open forest formation with an understorey of either hummock grassland or low heath.
At higher altitude there is a low woodland of Callitris columellaris, the native pine which gives the Flinders Ranges much of their distinctive character. On steep, exposed rocky hill faces there is a low woodland of Allocasuarina verticillata which often has an understorey of low heath.
Cooper Creek (B)
The complex of wetlands, floodplains, dunefields and gibber plains drained by the intermittent flow of Cooper Creek constitutes one of the most important land systems in South Australia. Although the area receives a mean annual rainfall of only 150 mm, the presence of year-round permanent water in the deep water-holes of Cooper Creek means that it supports a much more diverse flora and fauna than the nearby waterless deserts. At times of extreme flooding, the whole floodplain is completely inundated and, as the water recedes, it develops into a complex of floodouts, channels, swamps and terminal lakes. Surrounding the floodplains is a series of sand-dune systems which remain dry even during extreme floods.
The channels and permanent water-holes of Cooper Creek are lined with a band of red river gum. There is a variety of herbaceous plants at the water's edge including Nicotiana velutina and Gnaphalium indutum. The shallow swamps fed by the channels support a low shrubland of lignum (Muehlenbeckia cunninghamii) with a ground cover of common nardoo (Marsilea drummondii), the fern that sustained the ill-fated Burke and Wills expedition for several months in the area. After a flooding of Cooper Creek hundreds of thousands of waterbirds from all over southeastern Australia flock to feed and breed in these tangles of flooded vegetation.
On sections of the floodplain which are inundated less frequently there is a low shrubland dominated by Atriplex nummularia and Chenopodium nitrariaceum. Following rain or flooding, ephemeral herbs grow between the bushes.
On the grey clays of the broad floodouts bordering the main channels there are extensive herblands of Atriplex angulata which merge into shrublands of Atriplex nummularia and woodlands of Eucalyptus microtheca. Many of these areas have been seriously degraded by rabbits and cattle grazing. On the saline soils of episodic lake beds there develops another herbland formation dominated by Sclerolaena intricata and Atriplex spongiosa.
A very open tall shrubland of Acacia ligulata grows on the wide swales of many of the dune systems. The major dune systems support a hummock grassland of Triodia basedowii with sandhill cane-grass (Zygochloa paradoxa) on the mobile dune crests.