Web Ecology 8: 84–93. Diversity of a semi-arid, intact Mediterranean ecosystem in southwest Australia Simon Judd, James E. M. Watson and Alexander W. T. Watson Judd, S., Watson, J. E. M. and Watson, A. W. T. 2008. Diversity of a semi-arid, intact Mediterranean ecosystem in southwest Australia. – Web Ecol. 8: 84–93. The drier parts of the Mediterranean biome of southwest Australia contain the larg- est remaining Mediterranean woodlands and shrublands on Earth. Despite this, there has been no formal, comprehensive assessment of their biodiversity. The region abuts the southwest Australian floristic region which has received much scientific attention. The aim of this paper is to provide the first general overview of the biodiversity of part of this intact, yet relatively unknown, Mediterranean ecosystem. We do this by synthesizing data from State Government agencies and published research. We found that, like other parts of southwest Australia, the region has globally significant levels of plant species diversity. More than 2400 plant species, including 291 species considered threatened, have been recorded, representing one-sixth of all Australia’s vascular plant species. Eleven of Australia’s 23 major vegetation groups are represented even though the region covers less than 1% of continental Australia. We documented 170 vertebrate species, including 31 threatened species, with a particularly high richness of reptile species (n = 46). We highlight how little is known about this region. For example, 116 vertebrate species not recorded in the region probably occur there based on their habitat requirements and known distributions. An examination of plant and vertebrate diversity in the region, using a half degree latitude and longitude grid cells, showed a highly heterogeneous pattern of species richness and vulnerability, with a general de- cline in species richness from southwest to northeast. Conservation strategies that rely on capturing the highest levels of biodiversity in a series of protected areas are unlikely to guarantee protection for all species given these high levels of heterogeneity. Instead, a region-wide conservation plan should involve targeted ecological research, considera- tion of ecological processes and stakeholder consultation. S. Judd ([email protected]), School of Natural Sciences, Edith Cowan Univ., 100 Joondalup Drive, Joondalup, WA 6027, Australia. – J. E. M. Watson, The Ecology Centre, School of Integrative Biology, Univ. of Queensland. QLD 4072, Australia. – A. W. T. Watson, The Wilderness Society, 2 Delhi St, West Perth, WA 6005, Australia. Six of Australia’s ten Mediterranean ecoregions are located ocean, and isolated by arid lands to the north, northeast, in southwest Australia (Wilson et al. 2007). These we refer and east. Topographically it is unique among the world’s to collectively as the southwest Australian Mediterranean five regions of Mediterranean climate as it is a flat, stable, biome (SWAMB). It is an island-like (Hopper 1979), highly-weathered plateau with granite occasionally emer- relatively wet continental refuge bordered on two sides by gent as domed inselbergs (Anand and Paine 2002, Hopper Accepted 10 June 2008 Copyright © EEF ISSN 1399-1183 84 WEB ECOLOGY 8, 2008 and Gioia 2004) (photo 1). The last glacial event occurred munities (Hobbs and Atkins 1991, Saunders et al. 1992, in the Permian so the region is very old, with highly nutri- Saunders and Ingram 1995, Arnold and Weeldenburg ent-deficient soils (Hopper et al. 1996). 1998, Hobbs and O’Connor 1999, Abensperg-Traun et Much of the SWAMB is considered a global biodiver- al. 2000). sity hotspot (Myers et al. 2000) for two reasons; it has high Very little is known about the biodiversity of the less levels of plant species richness and endemism (Hopper disturbed, eastern portion of the SWAMB. Hopper and and Gioia 2004), and a large degree of historical habitat Gioia’s (2004) research on the evolution and distribution modification (Hopper and Muir 1984). Southwest Aus- of plant species in southwest Australia ends at the south- tralian landscapes are among the most heavily utilized on west Australian floristic region (SWAFR) boundary, and the planet with almost 20 million ha of native vegetation not the edge of the Mediterranean climatic zone itself (Fig. replaced or modified for broad-scale agriculture in the sec- 1). The aim of this paper is to provide a framework that ond half of the 20th century (Cody 1986, Greuter 1994, complements Hopper and Gioia’s (2004) paper and syn- Yates et al. 1999, Hopper 2003, 2004). Our knowledge of thesizes the current knowledge of biodiversity in the lesser the biodiversity of the SWAMB is dominated by research known region beyond the SWAFR. undertaken in highly fragmented landscapes located in The fact that this eastern part of the SWAMB has not the western part, most of which has had its original veg- been subject to large broad-scale clearing relative to other etation removed, or extensively modified due to higher Mediterranean ecosystems (Fig. 2), provides an insight annual rainfall and, hence, greater potential agricultural into a system that is primarily influenced by ‘natural’ dis- or timber productivity (Watson et al. 2008; Fig. 2). There turbance regimes which has implications for the manage- is a plethora of research highlighting the detrimental im- ment of both natural areas and adjacent modified areas. pact of habitat loss, degradation and fragmentation on We conclude the paper with a short discussion of the re- a range of threatened, range-restricted taxon and com- quirements for conservation planning in the region. Fig. 1. The location of our study area (gridded) shown in relation to Mediterranean southwest Australia sensu Wilson et al. (2007) (hatched), the southwest Australian floristic region (Beard 1980, Hopper and Gioia 2004) and the southwest interzone (Beard 1980) (bold lines). The climate zones of Beard (1984); moderate Mediterranean (MM), dry Mediterranean (DM), extra-dry Mediterranean (EDM), semi-desert Mediterranean (SDM) desert bixeric (DB) and desert non-seasonal (DNS) are also shown (dotted lines). WEB ECOLOGY 8, 2008 85 Fig. 2. Mediterranean southwestern Australia sensu Wilson et al. (2007) and the location of our study area (grid) shown in relation to categories 0 and I (e.g. intact vegetation) in the VAST framework developed by Thackway and Leslie (2006) (grey). National parks and nature reserves (black), and Kalgoorlie (K) and Hyden (H) are shown. Methods classes 0 and I to represent intact vegetation because they identify areas dominated by native vegetation and where there has been no extensive clearing or fragmentation from Study area land use activities (Fig. 2). The study area covers approximately 5.6 million hec- Given the debate about the boundaries of Mediterranean tares (Fig. 1) within which there are 4.7 million hectares ecosystems and biomes (Cowling et al. 1996), we followed of intact vegetation (Fig. 2). The southern and western Wilson et al.’s (2007) definition of the southwest Medi- boundaries of the study area represent the edge of the terranean biome and Beard’s (1984) climatic gradients of cleared agricultural land. The area experiences an eastward moderate, dry, extra-dry and semi-desert Mediterranean trend of both declining rainfall and decreasing dominance bioclimatic zones (Fig. 1). of winter rainfall (Beard 1984). For example, the average We limited our study area to the relatively unknown, annual rainfall for Hyden (118°55´E, Fig. 2) is 343 mm eastern portion of the SWAMB (Fig. 1, 2). The study area while Kalgoorlie (122°30´E, Fig. 2) receives 265 mm an- straddles the extra dry Mediterranean and semi-desert nual rainfall (Bureau of Meteorology 2008). Mediterranean bioclimatic zones. We stratified our re- search by conducting our assessment in a region with pre- dominately intact native vegetation. We defined vegetation Data collation intactness using the Vegetation Assets, States, and Transi- tions (VAST) framework of Thackway and Lesslie (2006). Initially, we aimed to collate records of all taxa collected or The VAST framework classifies the Australian vegetation observed in the study area. After a review of the literature by degree of human modification from pre-European set- we decided to focus on flowering plants and vertebrates tlement conditions as a series of states using the criteria of because very little data collection had been undertaken on floristic composition, vegetation structure and regenera- the other taxa (e.g. invertebrates, fungi, lichens) and the tive capacity. Seven classes are mapped on a 1 × 1 km grid information available was disparate. This synthesis is pri- across Australia, and these classes range from 0 (unmodi- marily based on publically available data sets from Western fied natural bare ground) and I (unmodified native veg- Australian Government agencies. For flowering plants we etation), to VI (removed, transformed to non-vegetation used the Western Australia’s Department of Conservation land use) (Thackway and Lesslie 2006). We selected VAST and Environment FloraBase (data base, <http://florabase. 86 WEB ECOLOGY 8, 2008 Photo 1. A landscape including the highest point in the study area (Peak Charles). Photo by Charles Roche. calm.wa.gov.au/prod/index.htm>). The Western Australia study area based on latitude and longitude. For floristic Herbarium supplied species lists and the total number of studies in the SWAMB Hopper and Gioia (2004) used records for each of 25 grid cells (Data analysis). These lists quarter-degree cells and Hopper (1992) used one degree were tabulated to produce a matrix of plant taxa and grid grid cells. We present the data in half degree cells because cells. at spatial scales smaller than this we found the number Vertebrate data was extracted from the Western Austral- of samples per cell were too small. At a larger scale than ian Museum’s FaunaBase (<http://www.museum.wa.gov. half degree the number of cells became too small for any au/faunabase>) which is a list of the specimens held by determine meaningful geographic trends.