By John Woinarski, Parks & Wildlife Commission
of the NT
The Arnhem Land region shares many of the biological features of
the Darwin-Kakadu region. The major blip on the relatively flat
landscape of the north of the Northern Territory is the sandstone
plateau of western Arnhem Land, which is bissected by these two
regions. The biota of this plateau and escarpment has been
relatively well documented in its western half (i.e. within
Kakadu), but is essentially the same across the Arnhem Land border
up to about the headwaters of the Mann River. Further east, into
central Arnhem Land, the headwaters are far less rugged, and the
sandstone biota accordingly much diminished.
Open forests
The eucalypt open forests (typically dominated by Darwin
stringybark and Darwin woollybutt, Eucalyptus tetrodonta and
E. miniata respectively) which form the dominant landscape
element of the lowlands in the Darwin-Kakadu region also dominate
extensive areas of Arnhem Land. There are some differences in
floristic composition, probably mainly related to differences in
soil structure (most notably with large areas of Arnhem Land
forests being on either very sandy or lateritic soils) and/or fire
management.
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This broad vegetation map shows the similarity
of vegetation in the Arnhem and Darwin/Kakadu regions divided by
the sandstone country
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Sorghum understorey
Annual sorghum is a far less dominant component of the
understorey of these forests in Arnhem Land than in the
Darwin-Kakadu region. Cypress pine Callitris intratropica is
generally more prevalent, with typically better recruitment than in
other areas of the Top End. Many of the animals associated with
these eucalypt forests such as the
brushtail possum Trichosurus vulpecula ,
northern brown bandicoot Isoodon macrourus ,
agile wallaby Macropus agilis ,
delicate mouse Pseudomys delicatulus ,
red-collared lorikeet Trichoglossus haematodus ,
brown honeyeater Lichmera indistincta ,
silver-crowned friarbird Philemon argenticeps ,
weebill Smicrornis brevirostris and
white-bellied cuckoo-shrike Coracina papuensis -are
widespread in Arnhem Land. (Click on the species name to see a list
of research findings).
In contrast, some species common in eucalypt forests elsewhere
in the Top End are either comparatively rare or absent from most of
Arnhem Land: these include many of the finches, some raptors and
the fawn antechinus Antechinus bellus.
Rivers and floodplains
East of the East Alligator River, most of the rivers of Arnhem
Land are relatively small, and the floodplains relatively
restricted. The Goyder/Glyde system is the most distinctive,
including the vast Arafura Swamp, the most extensive melaleuca
wetland in Australia. This is an important breeding site for
magpie geese and other waterfowl, and the swampland and
adjacent areas contain many highly restricted plant species.
Coastal areas
Coastal areas of Arnhem Land include some of the best developed
sandsheet and sand-dune formations in northern Australia,
especially at Cape Arnhem Peninsula and on Groote Eylandt. These
support some distinctive heathlands, and some localised animal
species, including the
Northern Hopping-Mouse Notomys aquilo and the burrowing
skinks Lerista stylis and L. carpentariae . Mangroves
are also well-developed along much of the shoreline of Arnhem Land,
and support a rich associated biota including the
False Water-rat Xeromys myoides , Mangrove Monitor
Varanus indicus ,
Chestnut Rail Eulabeornis castaneoventris and
Mangrove Golden Whistler Pachycephala melanura .
