Territory Environments
Eucalypt open forests of the top end
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Tall eucalypt open forests, typically dominated by Darwin Stringybark Eucalyptus tetrodonta and Darwin Woollybutt E. miniata, are restricted to the higher rainfall areas of the Top End, and typically occur on deep sandy and loam soils. As soils become shallower, and in areas of lower rainfall, these forests decline in stature and canopy cover, and change in floristic composition, grading into the much more extensive eucalypt woodlands.
From the NT vegetation map (Wilson et al. 1990), the total area of eucalypt open forests in the Northern Territory is 60,921 km2. About half of this area lies on the Tiwi Islands (Bathurst and Melville). In addition to this area of open forests, Eucalyptus tetrodonta and E.miniata also dominates much larger areas of eucalypt woodlands.
A range of other tree species may co-dominate or occur as notable tall understorey species: these include Melville Island Bloodwood Corymbia nesophila, Cooktown Ironwood Erythrophleum chlorostachys, Grey Bloodwood Corymbia porrecta, Northern Cypress-Pine Callitris intratropica and the tall palm Gronophyllum ramsayi. Depending upon fire regimes, there may also be a sparse to dense shrubby understorey, typically including the cycad Cycas armstrongii, Acacia spp., Terminalia spp., the sand palm Livistona humilis, Planchonia careya and Buchanania obovata. There is typically a tall and dense grass layer, usually including Sorghum, Eriachne, Heteropogon and Chrysopogon species.
The eucalypt open forests support a diverse wildlife. Characteristic mammal species include the sugar glider Petaurus breviceps, brush-tailed rabbit-rat Conilurus penicillatus, black-footed tree-rat Mesembriomys gouldii, and northern brush-tailed phascogale Phascogale (tapoatafa) pirata; characteristic birds include northern rosella Platycercus venustus, masked owl Tyto novaehollandiae, partridge pigeon Geophaps smithii, and blue-faced honeyeater Entomyzon cyanotis; characteristic reptiles include the frilled lizard Chlamydosaurus kingii and tree monitor Varanus scalaris. These open forests are home to many threatened species, including the brush-tailed rabbit-rat, northern brush-tailed phascogale, masked owl, butler's dunnart, and red goshawk.
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Eucalypt open forests are reasonably well represented in conservation reserves, particularly at Garig National Park (which includes 1,894 km2 of eucalypt open forest).
A range of conservation management issues affect the eucalypt open forests. Fire is a frequent recurring event, and changes in the fire regime since European settlement have led to some changes in the floristic composition and vegetation structure, and hence to fauna. Exotic grasses, particularly gamba grass and mission grass, have invaded many areas of forest, and the large fuel load that they provide leads to more extensive, more intense, and more destructive fires. Feral animals are also widespread: these include buffalo, pig, banteng, horse, and big-headed ants. The eucalypt open forest typically occur on deep well-drained soils, and these environments are also sought by horticulture and forestry: increasing amounts of eucalypt open forests have been cleared for mango and other fruit crops around Darwin, and for plantation forestry on the Tiwi Islands.
References
- Williams RJ, Duff GA, Bowman DMJS & Cook GD (1996). Variation in the composition and structure of tropical savannas as a function of rainfall and soil texture along a large-scale climatic gradient in the Northern Territory, Australia. Journal of Biogeography 23, 747-756.
- Wilson BA, Brocklehurst PS, Clark MJ & Dickinson KJM (1990). Vegetation Survey of the Northern Territory, Australia. Technical report no. 49, Conservation Commission of the Northern Territory, Darwin.
- Woinarski JCZ, Brennan K, Hempel C, Firth R & Watt F (2000). Biodiversity conservation on the Tiwi Islands: plants, vegetation types and terrestrial vertebrates on Melville Island. PWCNT: Darwin.
