MVG 4 - TROPICAL EUCALYPT OPEN FORESTS Tropical eucalypt savanna forest Kakadu National Park, NT (Photo: D. Keith) Overview Also known as tropical savannas. MVG 4 occurs in high rainfall areas of Cape York in Queensland, on Melville and Bathurst Islands, the Top End in Northern Territory, and in Western Australia close to Kimberley coast. Structurally it is an open forest with a tall grass-dominated groundlayer. Dominated by eucalypts, primarily species of Corymbia and Eucalyptus, notably the subgenera Fibridia and Leprolaena, but the tree canopy also includes a range of tropical non-eucalypt genera. The grassy understorey is dominated by annual and perennial species exclusively with C4 photosynthetic pathways. Closely associated with tropical monsoonal climates with wet summers and dry winters. Regularly fire-prone in dry seasons. Facts and figures Major Vegetation Group MVG 4 – Tropical Eucalypt Open Forests Major Vegetation Subgroups xx. Tropical eucalypt savanna forest NT, QLD, WA (number of NVIS descriptions) Typical NVIS structural formations Low open forest Number of IBRA regions 26 Most extensive in IBRA region Est. pre-1750: Jarrah Forest (WA) (Est. pre-1750 and present) Present: Nandewar (NSW) Estimated pre-1750 extent (km2) 4 726 Present extent (km2) 3 952 Area protected (km2) 1 417 Structure and physiognomy Open forests dominated by eucalypts with tall grass dominated understories. Trees are taller with straighter boles and the canopy cover is greater than in the savanna woodlands of MVG 12. Leaves of the tree canopies are sclerophyllous and vary in size from notophyll (20 – 45 cm2) to mesophyll (45 – 150 cm2). Broad-leaved shrubs, palms and cycads occur in the understorey (Dunlop 2001; Beard et al. 2013) Ground layer is dominated by annual and perennial grasses, all of which have C4 photosynthetic pathways. There are conspicuous variations in the features of the understorey and composition of the herb layer at different seasons (Dunlop 2001). The understorey may have a suite of evergreen and deciduous or semi-deciduous species (Dunlop 2001). Indicative Species Compositionally similar to MVG 12. Eucalyptus tetrodonta, Eucalyptus miniata and Corymbia nesophila are widespread across the tropics. Corymbia megasepala and Eucalyptus crebra occur on Cape York, Corymbia polysciada, Corymbia bleeseri and Eucalyptus ferruginea are common in the Top End (Dunlop 2001; Neldner et al. 2014). Non-eucalypt trees and tall shrubs include Alphitonia excelsa, Callitris intratropica, Erythrophleum chlorostachy and Terminalia species (Dunlop 2001; Beard et al. 2013; Neldner et al. 2014). Other species in the shrub and small tree layer include Acacia oncinocarpa, Alphitonia excelsa, Buchanania obovata, Cochlospermum fraseri, Cycas armstrongii, Livistona eastonii, Livistona humilis, Xanthostemon paradoxus and species of Petalostigma, Gardenia and Grevillea (Dunlop 2001; Beard et al. 2013; Neldner et al. 2014). Grasses of the ground layer include Heteropogon triticeus, Chrysopogon fallax, Sorghum plumosum, Sorghum intrans and numerous other species (Dunlop 2001; Beard et al. 2013; Neldner et al. 2014). A range of forbs, including native legumes (family Fabaceae) occur amongst grass tussocks. Environment Restricted to tropical monsoonal climates receiving approximately 1000 - 1400 mm mean annual rainfall in the summer months, with a dry season during the winter months. Occur on sandy and lateritic plains and rises. Seasonally fire-prone due to curing of annual and perennial grassy ground layers. Geography Principally found across monsoonal and tropical northern Australia on sandy and lateritic plains and rises from the northern Kimberley to Cape York Peninsula. Change Contemporary land use changes associated with development of plantations, irrigated cropping and pastoral intensification involve clearing of tropical open forests and increased stocking rates of cattle. Changed fire regimes associated with pastoral intensification and unplanned ignitions are having significant regional impacts on the biodiversity of savanna ecosystems (Woinarski et al. 2011; Russell-Smith et al. 2012) Introduction of large grazing animals has led to profound changes in vegetation structure, abundance and distribution with flow on effects to native fauna (Kutt and Gordon 2012). Threats include weed invasion, inappropriate fire regimes (e.g. frequent high intensity fires) and overgrazing. There are issues associated with understanding and managing these areas for multiple values. Part of this is providing support to Indigenous groups and developing among these groups an understanding of methods of feral animal and weed control. Tenure Northern Territory: in protected areas Queensland: in protected areas Western Australia: scattered in freehold land, protected areas, state forest and crown land Key values Biodiversity including a unique mixture of biota with arid and wet tropical origins. Globally significant as one of the most extensive continuous tracts of savanna, and the only one dominated by eucalypts. Product of recent global evolutionary processes associated with the spread of C4 grasses. Critical habitat for populations of a wide range of tropical vertebrate and invertebrate species. Ecotourism and scenic landscapes. Globally significant, growing carbon pool. Beef cattle production. List of key management issues Total grazing pressure management. Feral animal impacts e.g. cats, and cane toads, and associated decline in mammal populations (Russell-Smith 2014). Fire management particularly mitigating fire regimes with a high frequency of severe fire brought about by the fuel loads of introduced grasses and ignitions associated with grazing land management practices. Weed control of invasive grasses and other weeds. Expansion and intensification of mining and agriculture. Long term monitoring to inform future management strategies. References Australian Surveying and Land Information Group (1990) Atlas of Australian Resources. Volume 6 Vegetation. AUSMAP, Department of Administrative Services, Canberra, 64pp. & 2 maps. Beadle N.C.W. (1981) The Vegetation of Australia. Cambridge Univ. Press, Cambridge, 690pp. Beard J.S., Beetson, G.R, Harvey J.M. Hopkins A.J.M and Shepherd D.P. (2013) The Vegetation of Western Australia at 1:3,000,000 Scale. Explanatory Memoir. Second Edition. Science Division, Department of Parks and Wildlife, Western Australia Dunlop C.R.(2001) Eucalyptus Communities. In. Native Plants of Northern Australia (ed. Brock J.)pp. 13 - 17. Reed New Holland, Sydney Dyer R., Jacklyn P., Partridge I., Russell-Smith J., Williams R.J. (eds) (2001) Savanna Burning: Understanding and using Fire in northern Australia. Tropical Savanna CRC, Darwin. Kutt A.S., Gordon I.J. (2012) Variation in terrestrial mammal abundance on pastoral and conservation land tenures in north-eastern Australian tropical savannas Animal Conservation 15, 416 – 425. Lehmann C.E.R., Archibald S.A., Hoffmann W.A., Bond W.J. (2001). Deciphering the distribution of the savanna biome. New Phytologist 191, 197 – 209. National Land and Water Resources Audit (2001) Australian Native Vegetation Assessment 2001. National Land and Water Resources Audit, Canberra, 332pp. Neldner, V.J., Niehus, R.E., Wilson, B.A., McDonald, W.J.F. and Ford, A.J. (2014). The Vegetation of Queensland. Descriptions of Broad Vegetation Groups. Version 1.1. Queensland Herbarium, Department of Science, Information Technology, Innovation and the Arts. Russell-Smith J., Edwards A.C., Price O.F. (2012). Simplifying the savanna: the trajectory of fire- sensitive vegetation mosaics in northern Australia. Journal of Biogeography 39, 1303 – 1317. Russell-Smith J., Edwards A., Woinarski J., Fisher A., Murphy B., Lawes M., Crase B. and Thurgate N. (2014) Northern Australian tropical savannas: the Three Parks Savanna Fire Effects Plot Network. In. Biodiversity and Environmental Change Monitoring, Challenges and Direction (ed. Lindenmayer D, Burns E, Thurgate N and Lowe A.) pp. 335 - 378. CSIRO, Victoria. Williams R.J., Griffiths A.D., Allan G.E. (2002). Fire regimes and biodiversity in the wet-dry tropical landscapes of northern Australia. In Flammable Australia. The fire regimes and biodiversity of a continent. (ed Bradstock R.A., Williams J.E and Gill A.M.) pp. 281 - 304. Cambridge University Pres, Cambridge. Woinarski J.C.Z., Fitzsimons J.A., Traill B.J., Burbidge A.A., Fisher A. (2011) The disappearing mammal fauna of Australia: context, cause and response. Conservation Letters 4, 192 – 201. Data sources Interim Biogeographic Regionalisation for Australia (IBRA), Version 6.1. National Vegetation Information System, Version 4.1. 1996/97 Land Use of Australia, Version 2. Collaborative Australian Protected Areas Database – CAPAD 2004 – Terrestrial. Notes This fact sheet should be read in conjunction with MVG 12: Tropical Eucalypt Woodlands See the Introduction to the MVG fact sheets for further background on this series .