Ord Victoria Plains 1 Ord Victoria Plains 1 (OVP1 – Ord subregion) GORDON GRAHAM AUGUST 2001 Information from Western Australia and the Northern Territory has been listed separately in this synopsis as a result of different vegetation mapping protocols that have been used in the two jurisdictions and the associated difficulties in combining that information. Subregional description and biodiversity bitextura (curly spinifex) hummock grassland wooded with Eucalyptus spp or Bauhinia values cunninghamii (bauhinia) low trees. • Eucalyptus pruinosa (silver box) +/- Bauhinia Description and area cunninghamii (bauhinia) low open-woodland +/- a shrub layer and tussock grasses or Triodia spp. Western Australia: (spinifex) • The bioregion shows level to gently undulating plains Eucalyptus spp. grassy woodland • with scattered hills on Cambrian volcanics and Eucalyptus terminalis (desert bloodwood) low open- Proterozoic sedimentary rocks; vertosols on plains and woodland with Sehima nervosum (white grass) and predominantly skeletal soils on hills. The overall Chrysopogon fallax (golden beard grass) tussock vegetation is grassland with scattered bloodwoods grasses +/- Triodia spp. (spinifex). • (Eucalyptus spp.) and snappy gum (Eucalyptus brevifolia) Eucalyptus opaca (plains bloodwood) and Eucalyptus with spinifex and annual grasses. The climate is dry hot chlorophylla (shiny-leaved box) sparse low-open tropical, semi-arid with summer rainfall. The subregional woodland with tussock grasses or a Triodia pungens area is 2, 282, 600ha. (soft spinifex), Triodia intermedia (winged spinifex) hummock grassland wooded with Eucalyptus The lithological mosaic has three main components: brevifolia. (1) Abrupt Proterozoic and Phanerozoic ranges and • Triodia wiseana (limestone spinifex) open-hummock scattered hills mantled by shallow sand and loam grassland wooded with low trees of Terminalia spp. soils supporting Triodia hummock grasslands with or Adansonia gregorii (boab). sparse low trees. • Astrebla lappacea (curly Mitchell grass) and/or (2) Cambrian volcanics and limestone form extensive Astrebla pectinata (barley Mitchell grass) tussock plains with short grass (Enneapogon spp.) on dry grassland sparsely wooded with Acacia spp. low calcareous soils and medium-height grassland trees. communities (Astrebla spp. and Dichanthium spp.) • Enneapogon purpurascens (nine-awn grass) tussock on cracking clays. Riparian forests of red river gum grassland. (Eucalyptus camaldulensis) fringe drainage lines. • Eucalyptus spp., Eucalyptus miniata (Northern (3) In the southwest, Phanerozoic strata expressed as woollybutt) +/- Eucalyptus tetrodonta (Darwin often lateritised upland sand plains with sparse trees. stringybark) open-woodland with Triodia bitextura This component recurs as the Sturt Plateau Region (curly spinifex) and Sorghum spp. (sorghum) grasses. in central Northern Territory. • Eucalyptus dampieri (pindan bloodwood) low open- woodland with Triodia pungens (soft spinifex) The Ord subregion is comprised of a major river system and/or Triodia intermedia (winged spinifex) draining low-lying plains and hilly tracts northwards via hummock grasses. the Ord River. The average annual rainfall is between 500 • Triodia pungens (soft spinifex) and/or Triodia and 800 mm. Phanerozoic strata of the Ord Basin strata intermedia (winged spinifex) hummock grassland have been well exposed, including sandstones, limestone sparsely wooded with low trees. and volcanics. • Eucalyptus brevifolia (snappy gum) low open- woodland with Triodia pungens (soft spinifex) Broad scale vegetation mapping of the area describes the and/or Triodia bitextura (curly spinifex) hummock following components: grasses and/or tussock grasses. • Eucalyptus microtheca (coolibah) and/or Eucalyptus • Triodia wiseana (limestone spinifex) and Triodia spp. +/- Excoecaria parvifolia (gutta percha) grassy intermedia (winged spinifex) hummock grassland low woodland. sparsely wooded with Eucalyptus brevifolia (snappy • Astrebla pectinata (barley Mitchell grass) closed- gum) low trees. tussock grassland +/- low trees. • Eucalyptus brevifolia (snappy gum) low open- • Dichanthium fecundum (curly bluegrass) and woodland with Triodia bitextura (curly spinifex) Chrysopogon fallax (golden beard grass) tussock hummock grasses +/- Enneapogon spp. (nine-awn grassland sparsely wooded with low trees. grass) short-tussock grasses or sometimes a grassland • Eucalyptus brevifolia (snappy gum) low open- without trees. woodland with Triodia spp. (spinifex) hummock grasses or sometimes a hummock grassland without Northern Territory: trees. The Ord subregion lies between the Victoria River • Triodia pungens (soft spinifex) and/or Triodia District and the Ord River catchment, containing intermedia (winged spinifex) and/or Triodia drainage for both catchments. It contains Cambrian 526 The Department of Conservation and Land Management Ord Victoria Plains 1 volcanics and sedimentary rocks from the Wiso and Ord the extent to which various islands of vegetation such as Basins respectively. The climate is monsoonal with annual springs function as refuges. average rainfall varying from 400 to 800mm south to north. Elevation varies between 100 and 450m, with a High Species and Ecosystem Diversity: minor range up to 400m separating the Victoria and Ord Rainforests are defined by their vegetation associations River catchments. Major drainage includes the West and are resource centres for a variety of faunal taxa that Baines and Negri Rivers and Stirling, Mistake and are either directly linked to rainforests or are more widely Blackfellow Creeks. Vegetation includes a variety of ranging species that are dependent on them. Examples grassland (Triodia spp., Enneapogon purpurascens, include fruit pigeons and flying foxes. Chrysopogon fallax, and Dichanthium fecundum) and low open woodland (Eucalyptus terminalis and E. Northern Territory: chlorophylla) with grass understorey. Soils in the Endemism: subregion are predominantly shallow loams, clays, and Some endemism is associated with Bungle Bungle sands, with some deep loams covering the Ord Basin. sandstone massif (e.g. Lerista bunglebunglensis and several plant species) (Woinarski 1992). Dominant land use Rare Features: Western Australia: Many localised rare species are associated with Bungle The dominant landuses are (ix) Grazing – Native pastures Bungle ranges (Woinarski 1992). (see Appendix B, key b), (xi) UCL and Crown reserves, and (vii) Mining. Refugia: The Bungle Bungle massif is considered a significant Northern Territory: refuge (Morton et al. 1995). No information supplied. Existing subregional or bioregional plans and/or Continental Stress Class systematic reviews of biodiversity and threats The Continental Stress Class for both the West Australian Western Australia: and Northern Territory components of OVP1 is 6. The CTRC report in 1974 (System 7) formed the basis of the Department’s publication “Nature Conservation Known special values in relation to landscape, Reserves in the Kimberley” (Burbidge et al. 1991) which has itself been incorporated in a Departmental Draft ecosystem, species and genetic values Regional Management Plan (Portlock et al. 2001). These reports were focused on non-production lands and those Western Australia: areas not likely to be prospective for minerals. Action statements and strategies in the draft regional Rare Features: management plan do not go to the scale of subregion or • The structure of the Bungle Bungle range within the even bioregion. There have been specific flora and fauna Purnululu National Park. • studies of the Purnululu National Park and associated The Osmand Ranges and the springs within them Conservation Park. Previous rainforest studies are • The enormous, man-made freshwater Lake Argyle. applicable (McKenzie et al. 1991). The islands within this lake have been previously described as providing an outdoor laboratory to There has been no systematic review of biodiversity but it investigate evolutionary processes and other changes is apparent that there are on-going changes to the status over time. This has also been acknowledged with its of fauna (particularly mammals) and plant taxa. There is Ramsar listing. reasonable evidence about continuing loss of species and • Geology of interest associated with the Halls Creek changes to assemblages at the landscape level which are Fault. affecting vegetation structure (e.g. loss of shrub layer), composition (e.g. perennial vs. annual grasses), Centres of Endemism: vegetation cover, leaf litter, and organics in the upper soil • A species of skink Lerista bunglebungle has been horizon. Flow-on effects and other factors (e.g. exotic described within this subregion. predators) affect fauna. Work to date has been of a • Rainforest patches are particularly important to general nature. invertebrates such as Camaenid land snails and annelids. Camaenid land snails have a large number Northern Territory: of endemic species and some endemic genera Management Issues Paper Completed for NT - showing strongly localised patterns of endemism. All General description of issues, and summary of the rainforest patches studied to date have endemic information, but not a strategy for implementation of earthworm species associated with them. enhanced conservation management (Kraatz 2000). Refugia: Reservation priorities identified for WA portion of ‘Dry’ rainforest patches provide dry season refuges. bioregion (Burbidge et al. 1991) Riparian zones, whilst degraded, are important. Lake Argyle itself, with