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AUSTRALIA
Land degradation in Australia is, from the standpoint of area affected, a problem of overgrazing of range lands.
Window and water erosion and salinization of irrigated and nonirrigated land are serious locally, primarily in
small areas across the southern part of the continent, and their economic impact probably exceeds that due to
overgrazing. Land degradation is usual around farming communities and popular tourist areas such as Ayers
Rock.
Overgrazing began 50 to 100 years ago with settlement of the interior arid lands at a time when there was no
information on the carrying capacity of range land, and little knowledge of climatic averages and extremes.
During the first quarter of the 20th century, problems of wind and water erosion, salinization and waterlogging of
irrigated land, and saline seepage of dryland areas arose as cultivation spread into the drier areas. Remedial
action was undertaken on a concerted basis in the 1930s and l940s when states enacted soil conservation
legislation and established units to correct land abuses and prevent further deterioration. At present, it probably
is safe to say that overgrazing is much less of a problem than it was before 1940, that wind and water erosion
still occur but to a lesser degree than before, that salinization of irrigated land in the Murray River catchment
(watershed) is increasing, and that saline seepage of semiarid and subhumid lands is expanding steadily.
Desertification Characteristics
About 25 percent of Australia's arid regions are unoccupied (Condon, 1978) due to the unpalatability of spinifex
grasses or to the remoteness of the land from population centers. Most of the remaining 75 percent is
moderately desertified (Figure 4). Severe desertification is most extensive in the saltbush-bluebush
(Atriplex-Maireana) vegetation type occurring in New South Wales and South Australia, where overgrazing has
caused degeneration of the plant cover. Degradation of the vegetation due to overgrazing has also been
severe on the fine-textured lowland soils (Vertisols) of eastern Australia and in the flood plains and surrounding
slopes of coastal river valleys, particularly the Gascoyne, Ord, and Victoria catchments in Western Australia
and the Northern Territory. Gully erosion has been severe on the Ord River catchment and significant on the
other catchments, with greatly increased runoff where the trampling of livestock has developed water-repellent
surface crusts. The presence of large numbers of feral donkeys in the Victoria River watershed compounds the
problem of grazing control there.
Areas delineated on the map as severely desertified are not uniformly degraded. The typical spotty character of
desertification shows up in river catchments as badly overgrazed and gullied land on flood plains and on the
gentle slopes adjoining them, with moderately desertified areas in the less accessible parts of those shrub
steppe zones.
Distribution of saline seeps on drylands, and salinized and waterlogged irrigated lands (Mabbutt, 1978), is also
spotty. Seepage of salt-laden water on slopes has plagued cultivated lands in the semiarid and subhumid
regions of Western Australia, South Australia, New South Wales, and Victoria for decades. The resulting saline
soils on lower slopes and in waterlogged depressions ordinarily cover a few or several hectares and are
surrounded by nonsaline soils. In Western Australia where the problem is most acute, seepage of saline
groundwater into streams has also had a significant adverse effect on water quality.
Waterlogging in the Murray River and its tributaries is characterized by groundwater mounds affecting tens of
thousands of hectares of irrigated land (Pels, 1978). The high groundwater levels lead to secondary salinization
of soils as the salts originally present in the subsoils are carried to the surface through evaporation from the
shallow water tables. Since waterlogging and salinization are functions of the irrigation water management and
the presence or absence of a drainage system, salty land is interspersed with nonsalty land.
Wind and water erosion have been severe in the past but are less so now, by and large. Wind erosion is an old
problem in the grazing and cultivated lands of New South Wales (Wagner, 1978) and the wheat lands of the
Murray Mallee (Matheson, 1978). One of the special problems in the semiarid Australia is the appearance of
"scalds," when sandy surface soils are blown or washed away and the slowly permeable subsoil of
texture-contrast (duplex) soils is exposed. Revegetating scalds is difficult unless steps are taken to impound
water on the surface. Mining towns such as Broken Hill have experienced accelerated wind erosion and dust
storms as the land around the towns was denuded of vegetation.
Magnitude of Desertification
A 1969 report on land degradation in Australia (Newman and Condon, 1969) included an estimate that about 14
percent of the arid rangelands were severely degenerated in pastoral value, 23 percent were moderately
degenerated, and 63 percent showed minor, little, or no degradation. Condon (1978) notes that much of the
serious erosion and degeneration of rangelands that was evident until the late 1940s was a consequence of
heavy use during the late 1800s. Since the 1940s there has been considerable improvement in range
conditions, partly due to abnormally favorable rainfall over the last thirty years. The magnitude of desertification
in Australia is shown in Table 5.
About 1 percent of the cultivated land in Western Australia is affected by saline seepage, with lesser
percentages affected in the other states. Northcote and Skene (1972) estimate that 85,000 hectares of irrigated
land in Australia are salt-affected, most of it in the Murray Basin. They also state that at least 197,000 hectares
of dryland are affected by secondary salinization. Waterlogging and salinization go hand-in-hand in the Murray
region.
Techniques to control desertification are well-known in Australia, the problem is recognized as a serious one,
and state agencies are available to assist in carrying out reclamation and prevention programs. Grazing
pressure probably has been reduced by half since the late 1800s and early 1900s and wind and water erosion
in the more populous southern part of the continent is much less of a problem now. Soil salinity and
waterlogging are more difficult to control because of the cost arising from the special conditions in the Murray
irrigated area. One method used to dispose of saline drainage water without increasing the salinity of the
Murray River water downstream is to divert it into evaporation basins. The principle is good but the cost is high
and there are uncertainties about future contamination of groundwater by effluents from the basins.
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