Tropical, Subtropical and Temperate Woodlands
Melaleuca woodland in Northern Australia
Melaleuca woodland in Northern Australia
PROTECTING THE NORTHERN WOODLANDS
Every year, as the summer months approach, the humid north-west monsoonal winds build up and then in roll across northern Australia, bringing the monsoon rains and occasional associated cyclone. Flooding rains drench the north most years. However by March the winds begin to recede, replaced by dry south-easterly trade winds and
‘The Dry’ replaces ‘The Wet’… until the next summer.
This harsh, highly seasonal climate has produced a distinct landscape of tropical savannas, Australia’s northern woodlands. The woodlands stretch right across northern Australia, from the Kimberley through the Northern Territory to Cape York. Superficially, the woodlands of the north are similar throughout their range. But varying rainfall, soils and fire regimes have produced a range of types – from tall
open forests, to the more common open woodlands, through to open grasslands. The dominant trees are mostly eucalypts and the understorey is dominated by a range of summer growing grasses, which grow spectacularly during the Wet, and then rapidly brown off during the Dry. Along rivers and in areas sheltered from fire, small
patches of rainforest grow.
The popular image remains in Australia of a vast Outback wilderness across the north. The tourism ads focus on a Crocodile Dundee land unscathed by change – wild rivers, dangerous (man-eating!) crocodiles, abundant birds, endless tracts of country inhabited only by the traditional indigenous owners and a thin scattering of romantic ‘whitefella’ stockmen.
In part this is true. The northern woodlands still stretch in an unbroken line across the north of the continent. Residents and visitors can still drive for days through unbroken woodlands and see teeming wildlife on billabongs. No species seem to have been
completely lost from the region.
However, all is not as stable as it seems. Recent research has shown that at least 16 bird species, nearly all of them grass-seed eaters, have declined greatly in range. Some, such as the stunning Gouldian Finch and Golden-shouldered Parrot are now highly endangered. Some mammals such as the gorgeous big Black-footed Rat and the northern Brown Bandicoot have also declined.
Yet less than one percent of the northern woodlands have been cleared? So why the declines?
Most of the declining animals are ground feeders and seed-eaters. There are correlations between the declines and the intensity of cattle grazing. However, it may not be simply grazing intensity.
Such areas have also been settled by whites for the longest period of time and have consequently been the longest without Aboriginal burning practices. The interactions
between cattle grazing and fire practices and animal populations have still not been fully disentangled, but research to date indicates that these factors are involved in the declines in complex ways.
Added to this is the great new threat of broad-scale clearing across the north. An important new report from the Environment Centre of the Northern Territory found that clearing for agriculture and plantations is a major and increasing threat in the north. The latest estimates are that tens of thousands of hectares are being
cleared annually in the Northern Territory.
The Ord River district in the Kimberley is planning a major expansion. In addition the cotton industry has a range of proposals at various stages to grow cotton in the Gulf Country in Queensland, the Top End in the Northern Territory and in the Kimberley.
The risk is that the unsustainable clearing of the southern woodlands will repeat itself in the north. Many of these woodlands across the north are ‘protected’ by being on infertile soils. However, the risk is that major river systems will be targeted for water extraction to irrigate woodlands on more fertile soils. This gives biodiversity a double hit. The crucial wet/dry flooding regimes of the rivers will be broken, affecting freshwater and coastal ecosystems – such as important fisheries. In addition the most fertile valleys, generally the richest in biodiversity and with the highest animal populations, will be cleared.
In summary, there are two problems for the northern woodlands. The first is the current decline of some birds and mammals under current grazing and fire regimes. More research is needed to determine the causes and to implement changes.
The second, encroaching land clearing requires a vigorous public response to stop a ‘development’ agenda for the north which replicates the problems of the south.
PROTECTING THE BRIGALOW AND THE COOLABAH IN THE SUBTROPICS
Wedged between north and south, the sub-tropical woodlands of Queensland and Northern New South Wales have biological and social characteristics of both.
In large part this rests on the climate. The sub-tropical woodlands receive both summer, monsoon-influenced rains, and the winter rains more typical of the south. Like the tropics most of the woodland types have summer-growing grasses under an overstorey of eucalypts.
Unique, are the large areas dominated by Brigalow, a beautiful silvery leafed wattle. This special habitat occurs largely on cracking clays, soil too heavy for eucalypts. With the eucalypt woodlands, open grassy downs country and taller riverine forests, the Brigalow formed part of a habitat mosaic unique to the sub-tropics.
As was the case in the southern woodlands, sheep and cattle were introduced at an early date and, after some of the bloodiest fighting in Australia, Aboriginal control of the country was lost. Burning and other indigenous land management practices suddenly altered. The changes created by this alone were marked. Australia’s only extinct bird, the Paradise Parrot, occurred only in the grassy valleys of this region. It had gone before land clearing really commenced. A range of other birds and some mammals, all largely ground-feeders, declined or disappeared.
While some species have gone, large intact woodland areas remain as functioning ecosystems with dingoes, quolls and other top order predators remaining. This is unlike the southern temperate woodlands, where essentially no fully functional wilderness areas remain.
Until the Second World War, clearing of the country was mostly restricted to the more open eucalypt woodlands on better soils. Postwar this changed, with the development of new machinery and new techniques to clear and to crop the land.
The cracking clays of the Brigalow country were found to be especially fertile, so the ‘Brigalow Scheme’ was set up – a joint Commonwealth-Queensland initiative to clear and closely settle the Brigalow lands. While the Brigalow tree itself is still common,
intact areas of Brigalow habitat are very rare.
The region remains the clearing hotspot for the nation, with clearing now largely focussed on the remaining eucalypt woodlands – associations of Coolabah, Poplar Box, Silver-leafed Ironbark and Mulga. Most of the clearing is to increase cattle production, with some significant areas being bulldozed or chained for cotton and
other crops.
RESURRECTING THE SOUTHERN WOODLANDS
They were stunningly beautiful. In a moist warm spring the grassy wooded hills and plains of southern Australia were covered with lilies and orchids, filled with the song of the spring migrants.
In the inland foothills of the Great Dividing Range, from Tamworth to Albury to Bendigo and to the Grampians, were thicker woodlands of White Box, Yellow Box, with Ironbark and Stringybark on the poorer slopes. On the plains leading out along the Murray, Murrumbidgee, Loddon and Lachlan were millions of hectares of rolling plains of Grey Box, Belah and Red Gum. In the south-west of Western Australia, and in the drier rainshadow areas of central and western Tasmania, were distinct woodlands with unique species, such as Salmon Gum in the west.
The first white settlers eulogised its beauty, but especially admired its grass. The grassy woodlands required no clearing to be immediately economically productive. The sheep and the cattle came quickly; the grazing bought losses. On the mainland, most of the ground mammals disappeared very quickly. Other major ecological changes followed the second wave of European settlers. Broad-scale clearing in all the southern woodlands accelerated towards the latter part of the Nineteenth Century, and continued for the next hundred years, accelerating in many areas from the 1950’s onwards with the increasing use of machinery to clear and develop land.
Since European settlement more than 80 percent of the southern temperate woodlands have been cleared. In some districts more than 95 percent has been cleared and what is left has been grossly altered.
Because of this loss, the woodlands now contain a very high proportion of threatened and declining species, more than the better known, wetter forests and rainforests. These declines are still in rapid progress and are particularly noticeable amongst temperate woodland birds such as the Hooded Robin, Grey-crowned Babbler, Diamond Firetail and Black-chinned Honeyeater. What is happening in many areas now is that small, non-viable populations are disappearing from small isolated remnants, often decades after clearing in a district has ceased.
For more information, please contact:
Barry Traill
Land Clearing Ecologist
Email Barry Traill
Created: 20 Jun 2001 | Last updated: 20 Jun 2001