Review of the management of feral animals and their impact on ...

Impacts
Much is known about <strong>the</strong> <strong>impact</strong> <strong>of</strong> rusa deer because <strong>the</strong>y have been studied in Royal
National Park near Sydney. The damage consists <strong>of</strong> ‘overgrazing, browsing,
trampling, ring-barking, dispersal <strong>of</strong> weeds… creation <strong>of</strong> trails, concentration <strong>of</strong>
nutrients, exposing soils to erosion/accelerating erosion, <strong>and</strong> <strong>the</strong> subsequent
degradation <strong>of</strong> water quality in creek <strong>and</strong> river systems’ (Jesser 2005). There is also a
‘significantly lower diversity <strong>and</strong> abundance <strong>of</strong> plant species’ where deer density
high.
Mahood (1981), writing <strong>of</strong> this area, noted ‘extensive erosion associated with “deer
tunnels” on coastal ridges’, <strong>and</strong> ‘signs <strong>of</strong> gully erosion formation <strong>of</strong> ridge sides [sic]
which may have been caused by deer breaking <strong>the</strong> surface’. He recorded that rusa
maintain grassl<strong>and</strong> areas by preventing regeneration, <strong>and</strong> that ‘<strong>the</strong>re are considerable
areas beaten down to form camps <strong>and</strong> trails…’ These deer ringbark trees when <strong>the</strong>y
rub <strong>the</strong>ir antlers to remove velvet, <strong>and</strong> impede regeneration in burnt areas.
A Deer Management Plan for <strong>the</strong> park, published in 2002, found that ‘deer are
browsing on rare <strong>and</strong> threatened plant species <strong>and</strong> having significant <strong>impact</strong>s on <strong>the</strong>
diversity <strong>of</strong> threatened ecological communities within <strong>the</strong> park’ (NSW National Parks
<strong>and</strong> Wildlife Service 2002). Some <strong>of</strong> <strong>the</strong> <strong>impact</strong>s recorded included significantly
lower density <strong>and</strong> diversity <strong>of</strong> plant species in threatened plant communities, <strong>and</strong>
rainforest patches with 70 per cent less under storey plant species. The report
identified an ‘urgent need for deer numbers to be reduced’. The deer population,
estimated at 2 900 in 2001, is descended from seven deer that escaped almost a
hundred years ago.
On <strong>the</strong> Torres Strait isl<strong>and</strong>s, where <strong>the</strong>ir numbers are high, rusa, along with pigs <strong>and</strong>
goats, ‘have caused significant environmental degradation’ (Jesser 2005).
In New Guinea, in a review <strong>of</strong> <strong>the</strong> Tonda Wildlife Management Area on <strong>the</strong> south
Coast, Chatterton (1996) nominated invasive species as <strong>the</strong> worst threat to <strong>the</strong> area
<strong>and</strong> listed rusa first. According local people <strong>the</strong> rusa have “moulded <strong>the</strong> whole area”
by causing change in herbaceous species <strong>and</strong> through soil compaction.
Bioclimatic modelling indicates that rusa deer could establish substantial <strong>feral</strong>
populations in Arnhem L<strong>and</strong>, <strong>the</strong> Top End <strong>and</strong> north Queensl<strong>and</strong>, with lesser
populations establishing around <strong>the</strong> Gulf <strong>of</strong> Carpentaria <strong>and</strong> along <strong>the</strong> central
Queensl<strong>and</strong> coast (Moriarty 2004). In <strong>the</strong>se regions, rusa could contribute to <strong>the</strong>
l<strong>and</strong>scape degradation caused by <strong>feral</strong> horses, donkeys, buffalo <strong>and</strong> by domestic
cattle.
In a Queensl<strong>and</strong> Government report, Jesser (2005) proposed that all deer colonies
found outside <strong>the</strong>ir historic range in Queensl<strong>and</strong> should be declared class one pests,
which would require l<strong>and</strong>holders to eradicate <strong>the</strong>m. If his recommendation is adopted
by <strong>the</strong> Queensl<strong>and</strong> Government rusa deer could be eliminated from <strong>the</strong> Rangel<strong>and</strong>s.
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