Ecology

Land systems

Land systems: an Australian 'invention'
Geomorphology
Geology
Vegetation
Botanical history
Mulga-Eucalypt line
Lakes

It was beautiful country for botanists and tourists but useless for sheep! Alan Payne 2006, recalling the 1993 Whitewells Rangeland Survey

Charles Darwin Reserve is a diverse landscape. It has a number of ecosystems that cross the Mulga-Eucalypt line, a biogeographical line which marks a major change in climate and ecosystems. The junction of four biological and geographic regions of Australia is neaby. On its northern side lies the sparse mulga country of the hot arid zone. To the south lies the woodlands and sandplain shrublands of the Avon Wheatbelt bioregion of south-western Australia which experience relatively wet winters and dry summers. This southern region is now mostly cleared for broadacre wheat and sheep farming .

Charles Darwin Reserve is an relatively intact remnant of the vegetation at the interface of these two zones. It is one of a group of properties along this transitional line which are now being managed for nature conservation, by both private and government organisations. The million or so hectares provide a large enough area to maintain habitats and species that are declining to the north and the south. Active land management for conservation and monitoring is underway, and weeds and feral animals are being controlled.

Much of the palaeo-valley system on which the reserve and its neighbours lie is still fully vegetated. It offers contemporary scientists and land managers sites on which to learn the workings of the regions valleys before they were cleared of bush and affected by rising salt water tables.

The work of botanists and ecologists in describing and identifying its natural values was critical to making the case for conserving this area. Over a period of about 130 years, many of the ecosystems on either side of the reserves were lost to clearing for cultivation or overgrazing by sheep flocks. Only recently has its importance been recognised sufficiently to allow its conversion from pastoralism to conservation. Much of the knowledge of the country accumulated by its Indigenous guardians over the last 40,000 years was ignored by the colonial occupiers and may have been lost.

The current conservation management is now building on previous work, such as the vegetation mapping done in the 1960s and land system analysis and mapping done in the 1990s for pastoral management.

 

 

Ecology

Charles Darwin Reserve is roughly 20 km by 36 km in size and lies in a larger ‘island’ of natural vegetation approximately 70 km by 60 km. It is surrounded by a moat of normally dry saltlakes lying in paleo-valleys; old river systems which ceased flowing to the ocean when the western edge of the continent was uplifted. They have filled in and dried up over millenia. These lakes still fill occasionally after heavy rains, with a flourish of aquatic and bird life.

 
 

Although relatively flat, Charles Darwin Reserve is very diverse. It is comprised of fifteen land systems, based on vegetation, soils and landform.

Most of the reserve is in the Avon Wheatbelt bioregion of Western Australia in which only about 10 per cent of the original vegetation remains. Much of it still looks as it did when the British colonists began their first explorations of the area in 1868, when in search of grazing lands.

The south-west of Western Australia was listed by Conservation International in 1999 as one of 25 International Biodiversity Hotspots in the world. These ‘hotspots’ are selected for their richness of species and high degree of threat. www.biodiversityhotspots.org

The Avon Wheatbelt area was listed by the Australian Government as one of fifteen national biodiversity 'hotspots' in 2003.

The reserve and the surrounding properties that lie on the dry side of the 300 mm isohyet, contain ecosystems from both the arid zone (the Eremean Botanical Province) and the south-west ecosystems (South West Botanical Province). The arid zone is characterised by hot summers (October to March) with erratic cyclonic downpours and thunderstorms, and cool winters with some rain. It is dominated by open shrublands of acacias including mulga on hard red earths. The south-west is driven by cool winter rains (April to September) coming from westerly fronts driving in from the Southern Ocean and moving across the south-western corner. The vegetation is largely woodlands of large eucalypts, and dense shrublands of other myrtaceaeous species, acacias and Proteaceae such as hakeas and grevilleas. These shrublands are adapted to fire usually ignited by summer lightning strikes. The cycle of burning is usually greater than 30 years.

 

 
 
   

This country, with its fragile soils, is very sensitive to changes in the sheet flow of water across the country. This is a landscape driven by erratic cycles of flood and drought. But it was financial, rather than ecological, considerations that governed the use of the land, especially under pastoralism. The impacts on the land of extracting the land’s resources under the extreme variation in seasons and rainfall were not understood or were ignored. In many areas the land was driven beyond its capacity to regenerate. Even where grazing was light, fences and tracks were oftern located to channel water with detrimental effects on the ecosytems.

Charles Darwin Reserve has however retained most of its its integrity as a natural landscape. It is recognised as one of the few remaining areas of bush in south-western Australia that is large enough for ecosystems to function naturally, if weeds and exotic predators are controlled, fire is kept out of long unburnt ecosystems and drainage patterns are restored.


 
 
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