Nandewar - biodiversity
The vegetation of the Nandewar Bioregion is influenced primarily by geology and the influence of altitude on temperature and rainfall. The bioregion is characterised by box woodlands that occur on clay or loam soils, typically at low to mid elevation in agriculturally productive areas. The principal dominants of these box woodlands are white box (Eucalyptus albens), yellow box (Eucalyptus melliodora), Blakely's red gum (Eucalyptus blakelyi) and grey box (Eucalyptus mollucana). Bimbil box (Eucalyptus populnea subsp. bimbil), fuzzy box (Eucalyptus conica) and western grey box (Eucalyptus microcarpa) also occur, particularly in the western half of the bioregion.
With decreasing soil fertility and increasing topographic relief the box woodlands are replaced by ironbark/cypress pine communities which characterise much of the agriculturally less productive parts of Nandewar. These communities are common at mid elevations, particularly on sedimentary hills and ranges, and form woodlands and open forests typically consist of silver-leaved ironbark (Eucalyptus melanophloia), white cypress pine (Callitris glaucophylla) and tumbledown red gum (Eucalyptus dealbata).
Canopy combinations vary in relation to environmental factors, with narrow-leaved ironbark (Eucalyptus crebra) common on sediments and Caleys ironbark (Eucalyptus caleyi) and black cypress pine (Callitris endlicheri) favouring granitic areas. White box and stringybarks can be additional components of the ironbark/cypress pine communities, and in localised areas form associations with mugga ironbark (Eucalyptus sideroxylon), an important habitat resource for fauna.
At mid to high elevations in mountainous terrain, forests of silver-top stringybark (Eucalyptus laevopinea), manna gum (Eucalyptus viminalis) and mountain gum (Eucalyptus dalrympleana subsp. heptantha) occur. Montane woodlands and sub-alpine forests of snow gum (Eucalyptus pauciflora), mountain gum, manna gum and rough-barked mountain gum (Eucalyptus volcanica) occur at high elevation on Mt Kaputar.
Riparian forests of river oak (Casuarina cunninghamiana), sometimes with river red gum (Eucalyptus camaldulensis), occur along the major watercourses, with Blakely's red gum and rough-barked apple (Angophora floribunda) forming the common association along minor drainage lines. Forest and woodlands of northern smooth-barked apple (Angophora leiocarpa) and dirty gum (Eucalyptus chloroclada) are associated with sandstone parent material on the north-western edge of the bioregion.
Basalt-derived soils around Inverell support vegetation dominated by white box and silver-leaved ironbark grading to yellow box, rough-barked apple, Blakely's red gum and white cypress pine on lower slopes. Manna gum can occur in the valleys with river oak along the streams.
Vegetation communities on limestone and serpentinite sites are usually floristically distinct from adjacent areas. Large grass trees (Xanthorrhoea sp.) can be a prominent feature of such sites. Serpentinite areas are botanically important as they support endemic flora and currently undescribed species, including a red stringybark, which together with spinifex hummock-grass dominates several sites.
The Nandewar Bioregion also supports small patches of dry rainforest vegetation including the endangered ecological communities - semi-evergreen vine thicket and ooline. Other endangered ecological communities in the bioregion include the much depleted white box/yellow box/Blakely's red gum and brigalow woodlands, Howell shrublands, McKie's stringybark open forest and minor occurrences of native grasslands on cracking clays in the bioregions southwest.
At least two-thirds of the original cover of woody vegetation in the bioregion has been cleared and less than 2 per cent is protected in conservation reserves. Vegetation clearance remains a significant threat to biodiversity across the bioregion. Coolatai Grass (Hyparrhenia hirta), an invasive species, is threatening to displace the indigenous ground flora of large tracts of grassy box woodlands, derived native grasslands and granite woodlands.
More than 60 rare or threatened species have been recorded from the Nandewar Bioregion. This includes 18 species listed under the NSW TSC Act 1995, 9 of which are considered as endangered and 9 vulnerable. The remainder are rated as rare or threatened at a national scale (Briggs and Leigh 1995). Two of these, Euphrasia arguata and Euphrasia ruptura, are now thought to be extinct.
The major threats to these species continue to be vegetation clearance and habitat fragmentation and disturbance. Species such as Digitaria porrecta, and Cadellia penstalylis, are seriously threatened by weed invasion and pasture improvement of native grasslands.
The Nandewar Bioregion supports many other plant species of conservation significance such as the serpentinite endemics and presently undescribed taxa, for example members of the Macrozamia and Homoranthus genera.
Four hundred and sixty seven vertebrate species are known to occur in the bioregion. Of these, 134 species, or almost one-third, are considered to be of conservation significance and 51 of these are listed as extinct, endangered or vulnerable in the TSC Act. Protection of the remnant vegetation of the Nandewar Bioregion is critical to the survival of these species.
Several frogs are considered to be of extremely high conservation significance in the bioregion, having declined in distribution. These include Litoria booroolongensis and Adelotus brevis, both of which are now extremely rare in the bioregion.
One turtle species, Elseya bellii, is listed as a threatened species and found on the upper reaches of the Gwydir, Namoi and Macdonald rivers. It is considered to be of high conservation significance in the Nandewar Bioregion. Very little is known about turtle distribution in the bioregion in general, including that of Chelodina expansa, which has secretive habits and is usually found in muddy water (Cann and Ward 1998).
Twelve lizard species are considered to be of conservation significance, including Anomalopus mackay and Underwoodisaurus sphyrurus. Two-thirds of the records for the latter occur in the Nandewar Bioregion.
Half of the 26 snake species of the bioregion are considered to be of conservation significance. This may be partly due to the lack of data for the bioregion. Among these, Holocephalus bitoquatus is known from historical records in the bioregion but there have been no records of recent sightings.
There is a high diversity of woodland birds in the Nandewar Bioregion, including significant populations of a number of threatened species, such as the turquoise parrot (Neophema pulchella), brown treecreeper (Climacteris picumnus), speckled warbler (Chthonicola sagittatus), diamond firetail (Emblema guttata), grey-crowned babbler (Pomatostomus temporalis) and hooded robin (Melanodryus cucullata). Of the 252 diurnal bird species of the bioregion, 45 are of conservation significance and 18 of these are listed in the TSC Act.
The Nandewar Bioregion, together with the New England Tableland Bioregion, supports a significant proportion of the NSW population of the regent honeyeater (Xanthomyza phrygia). Declines in the numbers of ground-feeding insectivores, grassland and freshwater birds and some temperate woodland birds are evident in the bioregion.
Populations of musk lorikeets (Glossopsitta concinna) have increased in this and the New England Tableland Bioregion, as have little corella (Cacatua sanguinea) populations (Australian Terrestrial Biodiversity Assessment 2002), while 6 of the 11 nocturnal birds of the bioregion, including several owls and the bush stone-curlew (Burhinus grallarius), are considered to be of conservation significance.
Six of the 9 native arboreal mammals of the bioregion are of conservation significance, including the koala (Phascolarctos cinereus) which although widespread relies on remnant forest in the bioregion. The bioregion also supports high density populations of squirrel glider (Petaurus norfolcensis). The greater glider (Petauroides volans) is an example of the disjunct faunal populations found in Mt Kaputar National Park.
Fourteen of 27 bats in the bioregion are also of conservation significance, including some of the rarest bats in north-eastern NSW such as Vespadelus troughtoni and Chalinolobus dwyeri, which are known from several locations in the bioregion.
There were no significant wetlands recorded for this bioregion (Australian Terrestrial Biodiversity Assessment 2002).
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Page last updated: 27 February 2011