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Kellerberrin
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Fragmentation has been linked to habitat and species loss through the physical process of removal of vegetation structure and the loss of niche space but fragmentation can also cause changes to ecosystem processes which result in further habitat decline.
Structural changes to vegetation cover associated with fragmentation can alter the radiation balance within the habitat patch, and temperature and humidity gradients become apparent at the edges between remnants and agricultural land.
Changes also occur in physical and chemical fluxes across the landscape eg radiation, wind, water and nutrients. A lack of perennial cover (the result of removal and replacement with arable crops) increases wind speed near ground, which can cause increased soil erosion.
Another common impact of fragmentation is that it produces a mosaic of patches with different nutrient statuses. The radiation balance in the region is changed because of the replacement of predominantly perennials with annuals. Native vegetation in this region is largely evergreen sclerophyllous species, whereas vegetation on agricultural land varies greatly and reflection tends to vary accordingly.
Land clearance of the wheatbelt has caused a reduced area occupied by native vegetation, resulting in fragmentation of habitat, habitat loss and insularisation of biota (Hobbs, 1993).
This landscape transformation has resulted in the known extinction of 24 species of plant, and has one of the highest lists of rare and endangered species of all regions in Australia: 348 species of plant are classed as rare or endangered.
Many of the species found in this region also have restricted ranges and their long-term viability is thought to be limited.
Because clearing was selective and preferential the remnant vegetation that is present is not representative of vegetation before clearing. While some floral communities have been removed entirely others have been left.
Changes to ecosystem processes caused by fragmentation (for example, metapopulations) are as important, if not more important, than biogeographic changes for long term conservation.
In Kellerberrin shire, 187 ha per year of once productive land became saline over the 15 years leading up to 1993. This equates to 3.5% of previous arable land now affected by salinity (Saunders et al., 1993, Hobbs, 1993).
There have also been changes in changes in nutrient cycling, energy balances and wind regimes (Hobbs, 1993), and there has also been increased run off and ground water recharge. It has been estimated that over 15% of agricultural land in wheatbelt may be affected by salinity in next 30 years (Nulsen, 1993).
Since intensification of agriculture in this region, big changes in hydrological balance and ecosystem processes have been observed in the wheatbelt, along with widespread loss of native species (Saunders et al., 1993).
Removal of native vegetation and replacing it with annual crops has led to changed hydrological balance, soil salination, wind and water erosion, flooding, acidification of soil, soil compaction and decline in soil structure (Saunders et al., 1993).
Rising water tables will affect remnants. Many formally wooded areas in the wheatbelt are now very saline or under water leading to further losses of woodland vegetation. Some fresh watercourses are also becoming increasingly saline, which is a problem for the local biodiversity.
The wheatbelt has the highest rate of mammal decline and extinction in WA. due to loss of habitat.
Of the 43 species of native mammals thought to have been present at the time of European settlement only 12 were common, 13 had disappeared from the region and 9 were totally extinct in Australia by the 1970s.
Of the 15 species of mammals, excluding bats, now found in the Kellerberrin study area, only the grey kangaroo, the euro, the fattailed dunnart and the echnida are thought to have any security of prevalence in the medium term, and this is dependant on no future clearing.
CSIRO studies suggest that mammals are still being lost from remnants in the wheatbelt.
Declines are not restricted to mammals; bird populations are also suffering a decline. Of the 131 species of birds recorded in the Kellerberrin area since European settlement, 38 species have declined in range and/or abundance over the last 90 years, and of these, 16 species have disappeared all together from the Kellerberrin area within the few years prior to 1993 (Saunders et al., 1993).
Habitat loss and fragmentation can be blamed for the loss in bird populations in the wheatbelt because the purple crowned lorikeet, western rosella, Gilberts whistler, chestnut quail thrush and rufous tree creeper which were once common in Kellerberrin, have now disappeared but are still common in the area of extensive uncleared native vegetation around Yellowdine (200km east of Kellerberrin) (Hobbs, 1993).
Yates et al. (1994) examined the response of unfragmented woodlands dominated by E. salmonophloia, like the woodlands once found in the wheatbelt, to landscape scale disturbances such as fire, floods, windstorms and drought.
The results of his study indicate that landscape scale disturbances of several scales are important drivers of dynamics in these semi-arid woodlands. This means that the lack of regeneration of fragmented woodlands in the wheatbelt is likely to be due to altered disturbance regimes along with altered physical and biotic conditions within remnant patches.
The results of this study are a reflection of general trends that have been observed in Australian rangelends.
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