Location and General Description
Tasmanian Central Highland Forests are found on Tasmania’s large Central Plateau, a cool, high surface underlain by Jurassic dolerite and Tertiary basalts. To the east of the Plateau, this ecoregion extends down into the Midlands, a subhumid, cool, inland plain, also with a substrate of Jurassic dolerite and Tertiary basalt. Areas of high elevation were repeatedly glaciated; during the last glaciation the western portion of the Central Plateau was covered by an ice sheet up to 600 m thick (Jackson 1999b). Lake St. Clair on the Central Plateau is the headwater of the Derwent River and the deepest lake in Australia, carved out by glaciers over 2 million years. Ice cap action has resulted in a landscape of small lakes, pools, and tarns on the western portion of the Central Plateau. Rich humus soils are found here, in direct contrast to the low-nutrient soils of the older mountains in western Tasmania (Crowden 1999).
Rainfall is highest in the west, averaging up to 2,000 mm per annum and decreases as one moves down into the Midlands and into the rain shadow of the western highlands and the central plateau. The Central Plateau is the coldest region of Tasmania, with mean annual minimum temperatures less than 5°C . There is also great diurnal variation, so that a summer day temperature of 30?C may fall to 0?C at night. Although winter temperatures may remain near freezing for 3 to 4 months, soil under plant cover does not freeze for any appreciable length of time (Crowden 1999). Severe and prolonged frost is common in winter on the Central Plateau, but due to the maritime aspect of the climate, snow rarely lies longer than three months. Snow can fall at any season, but is more common in spring (Jackson 1999b).
Vegetation on the Central Plateau is a mix of wet and dry sclerophyll woodland at lower elevations, grading into alpine and coniferous forest communities at higher elevations. Dry sclerophyll forest is found in the subalpine habitat of the southeastern Central Highlands, dominated by eucalypts more than 5 m in height (Bryant and Jackson 1999). Eucalyptus coccifera and E. vernicosa may grow up to 1,200 m as low trees or shrubs. Limited rainforest elements extend to higher elevations, as an understory below alpine conifers and eucalypts. Woody plants from the Proteaceae, Epacridaceae, and Myrtaceae combine with some gymnosperms to form evergreen shrub communities at high altitudes. Alpine conifers include the pencil pine (Athrotaxis cupressoides) and other Athrotaxis spp., growing with shrubs such as Diselma spp. and Microstrobos spp. (Jackson 1999a). Treeless, high-altitude alpine vegetation is found above elevations of 1,000 m, but may be found at lower elevations where localized climate conditions permit. Alpine vegetation is usually dominated by shrubs under 2 m in height, but grasses, cushion plants, mosses, and aquatic plants are all found here as well (Bryant and Jackson 1999). Wet communities of bog, sedgeland, and bolster moor increase at higher altitudes where bolster plants impede drainage patterns with their aggressive growth (Jackson 1999a). Montane grasslands are found above 600 m in elevation, often on dolerite substrates, with Poa labillardierei and P. gunnii dominant. Grassy eucalypt woodlands and grasslands are also found at lower elevations in the Midlands (Bryant and Jackson 1999).
The predominant share of Australia’s alpine and subalpine habitats is located in Tasmania and the greatest unbroken extent of these is found on the Central Plateau (Jackson 1999a). Tasmania’s alpine communities are of special interest for a number of reasons. Unlike mainland Australia and New Zealand, snow cover is short-lived, and the grassy herbland element is weakly developed here. Herbs comprise 69 to 76 percent of the mainland alpine flora, but make up only 44 to 64 percent of the alpine Tasmanian flora (Crowden 1999). Instead woody vegetation is found at nearly all elevations with adequate drainage and soil aeration, and there is no clearly defined tree line. When fire disturbance is minimal, dense low thickets of Nothofagus cunninghamii and N. gunnii can grow up to 1,400 m. Although endemism decreases as one moves east from the western mountains, the Central Plateau still contains a highly endemic flora with a rich Gondwanan heritage including Nothofagus spp. and Podocarpaceae. Cushion plant species from five families are also found in Tasmania. Endemic to Tasmania, the pandani (Richea pandanifolia) Epacridaceae is the world’s largest heath plant, found in both sub-alpine communities as well as rainforests (Wildlife and Parks Service Tasmania 1998).
The alpine habitat has an unique fauna, especially adapted to the harsh climate. For example, a number of viviparous skinks are found in this ecoregion: mountain skink (Niveoscincus orocryptus), tussock skink (Pseudemoia pagenstecheri), and glossy grass skink (Pseudemoia rawlinsoni)). The pencil pine moth (Dirce aesiodora) (Archaearinae) is restricted to alpine habitat, found in close association with the pencil pine and believed to be a primitive Gondwanan relic. Over 30 geometrid moths of the genus Chrysolarentia are found only in alpine areas, demonstrating rapid speciation over a small geographical area (Bryant and Jackson 1999). The Ptunarra brown butterfly (Oreixenica ptunarra) is a Tasmanian endemic, dependent on Poa tussocks in high elevation grassland, woodland, and sedgeland. The endemic frog Crinia tasmaniensis is found throughout the island, at high elevations.
A range of other species is found throughout this ecoregion, utilizing dry woodlands at low elevations as well as alpine areas. The Tasmanian devil (Sacrophilus harrisii) is widespread throughout all of Tasmania, and the extinct Tasmanian thylacine (Thylacinus cynocephalus) once ranged throughout Tasmania as well, in low densities. Both the eastern barred bandicoot (Perameles gunnii) and the eastern quoll (Dasyurus viverrinus) are nearly extinct on mainland Australia but still found throughout the Tasmanian Central Highland Forests. The range of the endangered swift parrot (Lathamus discolor) extends into this ecoregion, as it migrates to dry eucalpytus woodland along the coast to breed each autumn (Hilton-Taylor 2000). The following birds utilize a variety of habitats, including eucalypt woodlands: a subspecies of wedge-tailed eagle (Aquila audax fleayi), Tasmanian native hen (Gallinula mortierii), Tasmanian thornbill (Acanthiza ewingii), and yellow wattlebird (Anthochaera paradoxa) (Stattersfield et al. 1998).
The Tasmanian Central Highland Forests are the source of a variety of resources. The Central Plateau region is used for forestry, grazing, and water catchment. Lower elevation grasslands have largely been converted for grazing, with some forestry occurring in the Midlands as well (Bryant and Jackson 1999). The high-elevation, western half of this ecoregion is better-preserved than the eastern portion. Both the Walls of Jerusalem National Park and the Cradle Mountain-Lake St. Clair National Park are part of the Tasmanian Wilderness World Heritage Area and fall within the western half of this ecoregion. These parks preserve mostly alpine vegetation; the dry eucalypt forest and grasslands of this ecoregion are not well-conserved at present (Brown and Podger 1999). However, subalpine eucalypt vegetation has survived largely intact since the 1800s (Kirkpatrick 1999). In contrast, highland silver tussock grassland has largely been converted to pasture over the last few decades. Although a large proportion of native grassland vegetation survives, most is heavily invaded by exotic species, or replaced by native shrubs when disturbed. The Midlands have been heavily impacted by human use so that vegetation there is largely modified grassland and woodland. Silver tussock grasslands are especially prized in the Midlands for stock grazing (Bryant and Jackson 1999).
Types and Severity of Threats
Fire is the biggest threat to alpine vegetation. Shrub communities are especially flammable and alpine vegetation does not regenerate quickly after a fire, if it regenerates at all. Delicate alpine vegetation is also susceptible to trampling from recreational users and a recently discovered cold-tolerant species of Phytophthora, a root-rotting pathogen. Climatic warming also poses a serious threat to alpine ecosystems. Exotic plants are a significant threat to both alpine and grassland ecosystems. Overgrazing and further degradation are threats in grassy woodlands and grasslands. Introduced predators are a threat on Tasmania, although not nearly as problematic as they are on the Australian mainland.
Justification of Ecoregion Delineation
The Tasmanian Central Highlands Forests ecoregion encompasses two IBRA’s, the ‘Central Highlands’ and the ‘Tasmanian Midlands’ (Thackway and Cresswell 1995).
Brown, M. J. and F. D. Podger. 1999. Conservation of Tasmania’s Natural Vegetation. Pages 381 – 400 in J.B. Reid, R. S. Hill, M. J. Brown, and M. J. Hovendon, editors. Vegatation of Tasmania. Flora of Australia Supplementary Series. No. 8. Australian Biological Resources Study, Environment Australia, Canberra.
Bryant, S. and J. Jackson. 1999. Tasmania’s Threatened Fauna Handbook: what, where, and how to protect Tasmania’s threatened animals. Threatened Species Unit, Parks and Wildlife Service, Hobart, Tasmania.
Crowden, R. 1999. Alpine vegetation. Pages 333 – 356 in J.B. Reid, R. S. Hill, M. J. Brown, and M. J. Hovendon, editors. Vegatation of Tasmania. Flora of Australia Supplementary Series. No. 8. Australian Biological Resources Study, Environment Australia, Canberra.
Jackson, W. D. 1999a. Vegetation Types. Pages 1-10 in J.B. Reid, R. S. Hill, M. J. Brown, and M. J. Hovendon, editors. Vegatation of Tasmania. Flora of Australia Supplementary Series. No. 8. Australian Biological Resources Study, Environment Australia, Canberra.
Jackson, W. D. 1999b. The Tasmanian Environment. Pages 11-38 in J.B. Reid, R. S. Hill, M. J. Brown, and M. J. Hovendon, editors. Vegatation of Tasmania. Flora of Australia Supplementary Series. No. 8. Australian Biological Resources Study, Environment Australia, Canberra.
Hilton-Taylor, C. 2000. 1998. The IUCN 2000 Red List of Threatened Species. IUCN, Gland, Switzerland and Cambridge, United Kingdom.
Kirkpatrick, J. 1999. Grassy vegetation and subalpine eucalypt communities. Pages 265 – 285 in J.B. Reid, R. S. Hill, M. J. Brown, and M. J. Hovendon, editors. Vegatation of Tasmania. Flora of Australia Supplementary Series. No. 8. Australian Biological Resources Study, Environment Australia, Canberra.
Parks and Wildlife Service Tasmania. 1998. Plant species of the cool temperate rainforest. http://www.parks.tas.gov.au/veg/rainspp.html. Viewed on August 20, 2001.
Stattersfield, A. J., M. J. Crosby, A. J. Long, and D. C. Wedge. 1998. Endemic Bird Areas of the World. Priorities for biodiversity conservation. BirdLife Conservation Series No. 7. BirdLife International, Cambridge, United Kingdom.
Thackway, R. and I. D. Cresswell. editors. 1995. An Interim Biogeographic Regionalisation for Australia: a framework for establishing the national system of reserves, Version 4.0. Australian Nature Conservation Agency, Canberra.
Prepared by: Miranda Mockrin
Reviewed by: Roger Kitching