a biogeographic survey of the southern carnarvon basin, western

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  • Records of the Western AlIstralian MlIsfllm Supplement No. 61: 1-12 (2000).

    A biogeographic survey of the southern Carnarvon Basin,Western Australia: background and methods

    Allan H. Burbidget, N.L. McKenzie1 and Mark S. Harvey2

    1 Department of Conservation and Land Management, PO Box 51,Wanneroo, Western Australia 6065, Australia

    2 Department of Terrestrial Invertebrates, Western Australian Museum,Francis Street, Perth, Western Australia 6000, Australia

    Abstract - This paper describes the setting and aims of a multi-disciplinarystudy to sample the biodiversity of a 75000 km2 region of Western Australia(the southern Carnarvon Basin), and identify biophysical factors related tothe. observed patterns of plant and animal distributions. The study wasdesigned to provide a quantitative biological basis for conservation planningand monitoring.


    Decisions on the management of Australianrangelands (e.g. Harrington et al., 1984; StaffordSmith et al., 1997) have been constrained by the lackof data on patterns in biodiversity over most of theAustralian arid zone. Even the species inventoriesof most phylogenetic groups in our arid bio-regionsare fragmentary. While quantitative surveys ofrange condition have been carried out over largeareas of the pastoral zone in Western Australia inrecent years (e.g. Payne et al., 1987; Pringle, 1991),most have focussed on a sub-set of plants and allhave ignored indigenous animal taxa entirely,thereby providing only a biased first approximationto the patterns in biodiversity. The need to acquiresuch information for long term planning ofrangeland management has led a number ofauthors to recommend that the conservationresources of the Australian arid zone be identifiedand measures taken to ensure that these values areconserved (e.g. Foran et al., 1990; James et al., 1995;Landsberg et al., 1997).

    James et al. (1995) identified four key researchthemes relevant to the Australian arid zone: "(1)identification of spatial and temporal patterns ofdistribution of native biota; (2) quantification of theimpacts of pastoralism on native biota; (3)identification of, and control of, potential non-native pest species; and (4) development ofmethods and technologies to allow regionalconservation planning". We contribute data underthe first (inventory) theme and analyse these data toprovide a basis for improved regional conservationplanning. The existing conservation reservenetwork is highly biased in many parts of theAustralian arid zone (Thackway and Cresswell,1995). In particular, the major conservation reserves

    in the Carnarvon Basin are confined to its peripheryand do not include examples of some prominentland surfaces (Burbidge and McKenzie, 1995; seealso Figure 1). Although there was significantinformation available in the form of opportunisticdata and surveys of restricted areas or relativelynarrow taxonomic groups, there has been nosatisfactory basis for planning a representative, yetcost-effective reserve system. We therefore set outto design and conduct a survey that would samplethe main environments of the region, allow aninterpretation of factors determining the patterns ofplant and animal distributions in the study area,provide an explicit basis for designing aconservation reserve system according to CARcriteria (comprehensiveness, adequacy andrepresentativeness; see, for example, Woinarski andNorton, 1993), and to commence the design of sucha system.

    Stafford Smith et al. (1997) have argued that whileecologists need to provide ecological understandingof arid lands, it is also important that they activelyseek the integration of this understanding in thewider policy debate. We attempt to provide a muchbetter understanding of the biogeography of one partof the Australian arid zone, and a beginning to theintegration of such knowledge into the wider debate.


    The Carnarvon Basin extends from near CapeRange in the Exmouth area, south to the MurchisonRiver and inland to the Kennedy Range. It is one ofthe major sedimentary basins of Western Australiaand has a geological history spanning much of thelast 450 million years (Wyrwoll, Stoneman, Elliottand Sandercock, 2000).

  • 2 A.H. Burbidge, N.L. McKenzie, M.S. Harvey

    CALM Leasehold


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    /fShark Bay World

    Heritage Area

    PnslOrnl Lense

    World Heritage AreaBoundary

    Bemier IslandNllIure Reserve


    Dorre IslandNature Reserve


    Figure 1 The extent of present day pastoral leases and major conservation reserves in the southern Carnarvon Basin.

  • Carnarvon Basin survey - background

    IBRA RegionsThackway and Cresswell (1995) provide an

    Interim Biogeographic Regionalisation of Australia(IBRA) in which the country is divided into 80regions based on various physical and biologicalattributes. Western Australia includes 26 of theseregions, most of which are restricted to the state.The Carnarvon Region, located on the mid-westcoast of Western Australia (Figure 2), extends fromnorth of Exmouth Gulf south to Shark Bay. To thesouth lies the Geraldton Sandplains Region. Theboundary between these two regions is also part ofthe boundary between the South-West Province andEremaean Province of Beard (1990), i.e. theboundary between the arid and southern mesicparts of Western Australia. The present study wascentred on this area.

    Table 1 lists the variety of names for thebiogeographic districts referred to in this andfollowing papers. The Carnarvon Region(Thackway and Cresswell, 1995) has a similarnorthern and eastern boundary to the CarnarvonBasin (see Wyrwoll, Stoneman, Elliott andSandercock, 2000). However, the Carnarvon Regionextends south only to Shark Bay where it adjoinsthe Geraldton Sandplains Region [equivalent toBeard's (1980) Irwin Botanical District], whichincludes the southern edge of Shark Bay and thesouthern end of the Carnarvon Basin.

    Carnarvon RegionThe Carnarvon Region occupies the northern and

    central areas of the non-marine parts of theCarnarvon Basin. Because of its geographicalposition, the region is influenced by both the winterrainfall of the south-west and the summer rainfallof the north. It has an arid to semi-arid climate,with a mean annual rainfall as low as 200millimetres in places. Severe droughts are aprominent element of the climate (see Wyrwoll,Courtney and Sandercock, 2000).

    The Region is dominated by extensive, low-gradient, alluvial plains traversed by the Minilya,Gascoyne and Wooramel Rivers (Figure 2; Wyrwoll,Stoneman, Elliott and Sandercock, 2000). Theserivers flow intermittently. Low, open woodlands ofAcacia species, such as Snakewood (A. xiphophylla)and Bowgada (A. linophylla), over shrubs such as


    Poverty Bush (Eremophila), cassias (Senna) andsaltbush, occur on these plains (Beard 1990 andreferences therein). Shrubs and hummock grassesgrow on the low sand ridges that are scatteredacross the plains. In northern parts, the plains gradeinto red sand dune fields, supporting spinifex andmulga communities that are reminiscent ofAustralia's red centre. In the south, near theboundary with the Geraldton Sandplains Region,the plains support Eucalyptus-Callitris woodlands onyellow sand dunes. Intermittently flooded claypansare common and, close to the coast, birridas(evaporite pans) occur in interdunal depressions.Low-lying areas, such as the birridas, the fringes ofLake MacLeod and the coastal flats, support richsamphire communities. In the east of the study area,erosional uplands such as the Kennedy Rangeprovide a contrast to the surrounding plains.

    Land-use in the area is predominantly for pastoralpurposes, with significant areas on the marginsbeing set aside for nature conservation.

    Geraldton Sandplains RegionThe Geraldton Sandplains Region extends from

    Shark Bay south to the vicinity of Jurien andBadgingarra at about latitude 30 (Beard, 1990). Theclimate is dry warm Mediterranean, with cool wetwinters and hot, dry summers. The region isdominated by heaths and scrub-heaths near thecoast. Extensive areas of coastal limestone, partiallymantled by pale yellow to grey sands, support lowheaths with emergent thickets of Banksia andmallees, such as Illyarrie (Eucalyptus erythrocorys). Aparticularly impressive feature of the area to thesouth of Shark Bay is the Zuytdorp cliffs, which aretopped with windblown, almost prostrateshrubland. Further inland, these are replaced bymallee, Banksia or Actinostrobus scrubs and heaths,with Acacia-Allocasuarina thickets still furtherinland. Small areas of Eucalyptus woodlands occur,mostly in the southern part of the region. The partof the region included in the present survey ismostly covered with sand, with some limestoneoutcropping very near the coast, and extends southto the Murchison River (Figure 2).

    Much of the northern Geraldton SandplainsRegion is used for pastoral purposes, with theremainder mostly being in conservation reserves;

    Table 1 Comparison of the names used by Beard (1980, 1990) and Thackway and Cresswell (1995) for certainbiogeographic entities referred to in the present study.


    Irwin Botanical DistrictCarnarvon Botanical DistrictAustin Botanical DistrictAshburton Botanical District


    Northern SandplainsCarnarvon RegionMurchison RegionGascoyne Region

    Thackway and Cresswell, 1995

    Geraldton Sandplains RegionCarnarvon RegionMurchisonGascoyne

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    there is some vacant Crown land north-east ofKalbarri National Park.

    Study Area BoundariesThe study area for the current

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