Landscape planning for biodiversity conservation in agricultural regions: A case study from the Wheatbelt of Western Australia
Biodiversity Technical Paper, No. 2
Robert J. Lambeck, CSIRO Division of Wildlife and Ecology
Commonwealth of Australia, 1999
ISBN 0 6422 1423 9
Chapter 1 - Introduction and background
Land-management strategies in Australia have generally focused on maximising economic returns through specialisation on a single product. While such approaches have generated substantial wealth in many regions they have also created significant problems. Land degradation, loss of biological diversity and vulnerability to the vagaries of international markets are all manifestations of the problems that can arise from single-objective management. Declines in the productive capacity of substantial portions of the landscape, together with the impoverishment of Australia's unique flora and fauna (Saunders and Curry 1990; Saunders et al. 1991; Morton et al. 1995) have led to the realisation that land management strategies based on short term profitability are not sustainable in the longer term.
Diversification of productive landscapes, combined with multiple objective management, is seen as one means of simultaneously retaining production, conservation, social and amenity values. While the need for integrated management of more diverse landscapes is increasingly being acknowledged (Fry 1991; Hobbs & Saunders 1991; Hobbs et al. 1993), little progress has been made towards developing procedures for achieving this. In fact, much of the theoretical debate has contributed little towards practical application (Saunders et al. 1991).
If we are to successfully combine non-productive land uses, such as the conservation of biodiversity, with other land uses, we must accomplish four essential tasks. The first of these is to set clear objectives for the region to be managed. Secondly, it is necessary to specify what is required in a landscape to meet those objectives. This requires definition of the composition, the amount and the configuration of essential landscape elements. The third task is to identify how (or if) the landscape elements required for meeting different land-use objectives can be combined in a landscape. Finally, it is necessary to assess the economic implications of the different scenarios that may be adopted in order to meet the identified objectives.
This report addresses the first three of these tasks with an emphasis on meeting nature conservation objectives and integrating these with production goals. An assessment of the economic implications of the conservation scenarios developed was beyond the scope of this project. The procedures used to address these tasks are illustrated by a case study from the central wheatbelt of Western Australia.
A brief review of the issues affecting the region and a description of the study area are presented initially to provide some background to the report. Chapter 2 examines a range of alternative nature conservation objectives and explores the consequences of pursuing each of these objectives. On the basis of this assessment, the most appropriate objective for the purpose of this study is selected and landscape designs and management recommendations are developed to meet that objective. The extent to which the results derived from this study can be applied to other regions is then examined. Chapter 3 presents an approach to developing land use plans which integrate the requirements for meeting nature conservation objectives with production and land conservation objectives. Finally, an Appendix is presented which considers the expansion of the approaches developed in this project to a regional scale.
The wheatbelt of Western Australia covers an area of about 18 million ha extending in a broad band from Geraldton in the north-west to Esperence in the south-east (Figure 1). Annual rainfall ranges from 600mm in areas closer to the coast to 280mm on the eastern boundary. This climatic region represents a transitional zone between the more mesic Bassean region of the south-west.
The original vegetation consisted of a mosaic of plant communities including tall, open woodland, dense shrubland, and low heathland which reflected an underlying mosaic of landforms and soil types (Beard 1983). The region supports an important agricultural industry, based primarily on cereal cropping and sheep grazing, which generates an estimated $4.5 billion annually (Government of Western Australia 1996).
The case study was based on the Wallatin Creek sub-catchment which occurs to the north of the central wheatbelt town of Kellerberrin about 200 km east of Perth. The catchment covers an area of 26015 ha and contains 19 properties. The property owners have formed an incorporated company which they have called Wallatin Wildlife and Land Care Inc., reflecting the multiple management objectives that they have for the catchment.
The area has an average annual rainfall of 339 mm which falls predominantly in winter. Unpredictable rainfall may also occur in some years during the hot summer months (Hobbs 1992b).
The gently undulating topography of the region has resulted from the erosion of lateritic sand plains which comprised part of the Great Plateau of Western Australia (McArthur 1993). The landscape has been subject to weathering since at least the Palaeozoic era when Australia was part of Gondwana. Differential erosion has resulted in different strata being exposed at different positions in the landscape. A typical catenary sequence resulting from this variable weathering process is shown in Figure 2. The higher parts of the landscape (Ulva) which form the drainage divides consist of sandy soils with laterite capping. The exposed slopes (Booraan and Collgar), which have resulted from the dissection of the sand plain, are characterised by outcrops of weathered granite (Danberrin) and duplex soils which vary in composition with position on the slope. Below these weathered slopes lie broad alluvial flats of heavier soils (Belka and Merredin). The lowest positions in the landscape are occupied by predominantly saline lakes, swamps and playas (Nangeenan and Belka). A more detailed description of the geomorphology and topography of the region can be found in McArthur (1993).
Source: Lantzke (1992)
The variations in soil and landform types described above are associated with characteristic vegetation types (Figure 3). The sandy uplands or Ulva, support Kwongan heath vegetation characterised by high levels of endemism and species richness (Lamont et al. 1984). The upper slopes (Booraan) support a dense shrub layer dominated by a variety of Melaleuca species and Allocasuarina campestris as well as eucalypt woodland communities in some locations.
The gentle lower weathered slopes (Collgar) support diverse mallee (multi-stemmed eucalypt) communities some of which are associated with dense thickets of Melaleuca cardiophylla.
The broad flat alluvial portions of the landscape (Belka, Nangeenan and Merredin landforms) are dominated by woodland communities, predominantlyWheatbelt Wandoo (Eucalyptus capillosa), Salmon Gum (E. salmonophloia) and Gimlet (E. salubris).
Areas of weathered granite rock outcrops (Danberrin) are associated with York Gum (E. loxophleba) and Jam Wattle (Acacia acuminata) but there may also be dense stands of Casuarina (Allocasuarina huegeliana) woodland around the margins of the rock. The lowest positions in the landscape support Samphire communities on very saline soils and Atriplex species in less saline areas.
Source: Beard 1990
Initial clearing of the native vegetation in the wheatbelt commenced in the mid 1800s but progressed relatively slowly until the early 1900s when machinery which enabled more rapid and widespread removal of vegetation became available. In the central wheatbelt the process of extensive clearing continued until the 1960s by which time the limits of suitability for agriculture had largely been reached (Figure 4).
Subsequent removal of vegetation has taken the form of the sporadic removal of remnants that were passed over in the first wave of clearing. In most areas of the wheatbelt today less than 10% of the original vegetation remains, the majority of which occurs in small remnants and roadside verges (Wallace & Moore 1987).
Source: Arnold and Weeldenberg 1991
Source: McFarlane et al. 1993
While the extensive clearing of native vegetation for agriculture has generated significant wealth for the nation, it has also created substantial problems. The replacement of perennial vegetation with annual crops has significantly reduced rates of evapotranspiration and altered patterns of water flow through the soil (McFarlane et al. 1993). As a consequence, the naturally saline water table has risen (and is continuing to rise) over much of the wheatbelt. Currently 1.8 million hectares of formerly productive land, or approximately 10% of the agricultural region, has been affected by salinity at an estimated cost of $1445 million (Government of Western Australia 1996). This trend can be clearly seen in the Kellerberrin shire (Figure 5). It is estimated that up to 30% of the wheatbelt has the potential to be salt affected if no action is taken (Government of Western Australia 1996). Similarly the area affected by waterlogging is increasing, causing losses of millions of dollars through lost production in the Kellerberrin area alone (McFarlane & Wheaton 1990). In addition, wind and water erosion affects 2 million ha and 0.75 million ha of the wheatbelt respectively (Nulsen 1993). Soil structure decline and soil acidification are also significantly reducing agricultural productivity.
Changes in land cover have had a major impact on the natural ecosystems of these regions. Numerous plant and animal species have been lost and there have been significant changes in the distribution and abundance of those which remain. These changes to the biota have, in turn, modified the ecosystem processes in which the various plant and animal species participated. Because it is these changes to natural ecosystems that are the main focus of this project, they are explored in greater detail in the next chapter.
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