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[?ecords of the Western Austrn/iall Museum Supplement No. 67: 39-89 Wetland flora and vegetation of the Western Australian wheatbelt M.N. Lyons, N. Gibson, G.]. Keighery and 5.0. Lyons Department of Conservation and Land Management, Science Division, PO Box 51 Wanneroo, Western Australia 6946, Australia Abstract - Eight hundred and thirteen quadrats were surveyed to sample wetland vegetation throughout the wheatbelt and adjacent south coast of 2 Western Australia, an area of ca. 220 000 km . Two hundred and fourteen wetlands were intensively sampled with between one and ten quadrats placed at each wetland to capture the major vegetation zonation. A further 100 quadrats were scattered through the study area to sample particular examples of wetland vegetation. Sampling spanned the full range of elevations at wetlands from inundated basins to the adjacent landforms such as lunettes. A total of 1436 taxa of vascular plants from 109 families were recorded. Naturalized taxa were 11.8% of the flora. Four hundred and twenty-eight taxa (29.7%) were categorized as restricted to wetland habitats. These included both aquatic (53 taxa) and amphibious plants (89 taxa). The wetlands of the study area represent the world centre of diversity for annual Juncaginaceae and the subfamily Salicornioideae (Chenopodiaceae). Species richness of quadrats (100 012) ranged from 1-72 taxa, with a mean of 20.5 taxa per quadrat. Thirty-one per cent of taxa only occurred at a single quadrat (singletons) and 59.3% occurred at less than five quadrats. Eight previously unrecognized taxa were collected for the first time and the habitats and distributions of several undescribed taxa with few previous collections were clarified. Collections were made of 78 taxa listed on the Department of Conservation and Land Management's priority flora list. Eight of these were gazetted as Declared Rare Flora (Wildlife Conservation Act, 1950) with two (Frnnkenia conferta and F. parvL/la) regarded as extinct prior to the current survey. Detailed cluster analysis was conducted on a reduced dataset (980 taxa by 760 quadrats) that excluded singleton species and some species-poor quadrats. A classification of 26 quadrat groups was defined. The primary division in the quadrat classification separated quadrats of inland largely naturally saline wetlands from quadrats at non-saline wetlands and at various wetland types with coastal and southwestern distributions. Lower levels in the classification were strongly related to local elevation and edaphic attributes of quadrats. Thirty-four assemblages were defined from species cluster analysis and 29 were regarded as coherent species groups. The richness patterns of assemblages were modeled against 34 environmental attributes. Models explained between 26% and 74'Yo of total deviance. Modeling was complicated by some assemblages having few members. Of the parameters used in the modeling, elevation at wetlands, substrate, electrical conductivity and pH were the dominant variables of models with the greatest decrease in deviance. Most assemblages were geographically well defined with annual precipitation and annual temperature range being important regional scalars. Fifteen plant assemblages containing 472 native taxa are identified as being at particular risk from secondary salinisation. They include assemblages of both non-saline and naturally saline wetlands. INTRODUCTION and largely flat (Hopper et aI., 1996; Beard et ai, The wetlands of the Southwest Botanical Province 2000). (SWBP) of Western Australia occur in an area The wheatbelt of Western Australia, within the recognised as one of 25 global biodiversity hotspots SWBP, has seen some of the most rapid and (Myers et aI., 2000), largely because of the diversity extensive clearing of native vegetation on earth of the flora. This diverse and highly endemic flora (Hobbs et al, 1993; Beresford et al., 2001). Mostly occurs in a landscape that is old, highly weathered since the beginning of the 20 th century much of the 40 M. N. Lyons, N. Gibson, G. J. Keighery, S. D. Lyons native vegetation has been removed and replaced documented the flora and vegetation of wetlands by annual crops and pasture (Hobbs et al., 1993). In on the extremities of the current survey area the most cleared bioregion within the wheatbelt, the (Gibson et al., 2000; Keighery et at 2002). Most Avon Wheatbelt, over 90% of the native vegetation studies have focused on individual wetlands, has been removed (Thackaway and Cresswell, 1995; predominantly in terms of vegetation responses to Sheppard et aI., 2002). changes in hydrology and salinity (Froend et aI., The dominant drainage systems of the wheatbelt 1987; Froend and McComb, 1991; Froend and van are characterised by chains of salt lakes following der Moezel, 1994). The general pattern of change of the courses of Tertiary palaeo-rivers (Beard, 1999; fresh or brackish plant communities to rising saline 2000). These systems of salt lake chains extend well ground waters is an initial collapse of the into the arid interior of Western Australia. Only overstorey species followed later by a death of along the western and southern margins of the understorey species as the water table rises to the ancient Yilgarn Craton has drainage been surface. Salt tolerant species such as Halosarcia spp. rejuvenated by marginal uplift during thf' then replace the original vegetation. The responses Cretaceous (Beard, 1999). Drainage east of the of the vegetation to hydrologic changes without Meckering line (Mulchay, 1967) and north of the salinisation can be as dramatic (Froend and van der Ravensthorpe Ramp (Cope, 1975) is effectively Moezel, 1994). internal except in years of extreme rainfall. Specific aims of the wetland vegetation survey Subdued drainage, coupled with the gradual were to: deposition of salt from marine aerosols, has led to • Document the flora of the wetlands of the study the slow accumulation of salt in wheatbelt soils and area. groundwater. Removal of native perennial • Provide a classification of wetland vegetation vegetation altered the hydrological balance such based on species composition and identify the that increased groundwater recharge and surface primary environmental correlates of the flow led to saline groundwater rise and the biogeographic patterns. mobilization of salt stored in the soil profile (Teakle • Evaluate whether wetland plant assemblages and Burvill, 1938). This secondary salinisation has can be modeled in terms of edaphic, climatic had major impacts on wetlands and vegetation of and geomorphic variables. valley floors (Wood, 1924; Teakle and Burvill, 1938; • Provide a summary of the species assemblages Froend et aI., 1987; Halse et al., 1993; George et al., most at risk from secondary salinisation. 1995). Predictions as to the area of wheatbelt shires that will eventually be impacted by shallow Study area watertables range from between 22% and 34% The study area extends from the Murchison River (Short and McConnel, 2001; George and Coleman, in the north to Cape Arid in the south-east (Figure 2002). Dryland salinity is also predicted to alter the 1). Surveyed wetlands fell within an area of ca. 220 2 behaviour of wheatbelt catchments, increasing 000 km , an area that included all of the Avon flooding frequency and amplitude (George and Wheatbelt and parts of the Mallee, Geraldton Coleman, 2002). Sandplains, Esperance Sandplains, Jarrah Forest In response to the threat to biodiversity posed by and Swan Coastal Plain bioregions as defined by secondary salinisation the Government of Western Environment Australia (2000). With a few Australia initiated a comprehensive biological exceptions in the Coolgardie and Yalgoo bioregions, survey of the wheatbelt under the Salinity Action the eastern boundary of the study area follows the Plan (Anonymous, 1996). The survey aimed to extent of agricultural clearing (Figure 1). document the biodiversity patterns for a range of Within the study area, rainfall ranges from ca. 300 biota of the agricultural zone and select a number mm to 600 mm. The only permanently filled of Natural Diversity Recovery Catchments for wetlands occur in the high rainfall extreme south focused actions to prevent/ameliorate biodiversity west of the study area and even these may losses from secondary salinisation. The biodiversity occasionally dry. All the remaining wetlands patterns of wetland biota as a whole are reported surveyed dry-out in most years, or only fill by Halse et al. (2004). This paper provides more episodically. Active rivers only occur in the zones detailed information about the wetland flora and of rejuvenated drainage west of the Meckering line vegetation of the study area. and along the south coast (Figure 2). Both the Very few detailed studies of wetland flora and naturally saline south flowing streams and rivers vegetation have been undertaken within the study along the south coast and most of originally fresh to area. Halse et al. (1993) surveyed 106 wetlands brackish west flowing streams have seen varying located in an area broadly corresponding to the levels of salinisation (Schofield et aI., 1988). current study area (but including the Swan Coastal Freshwater streams persist within intact Jarrah Plain) and described basic dominants and provided Forest catchments. All streams cease to flow during structural vegetation maps. A few studies have summer, with larger streams and rivers reduced to WetIand flora and vegetation 41 , Q Biogeographical regions and subregions ofthe outh West Botanical Province GS Geraldton Sandplain von M Mallee ES Esperence JF Jarrah Forest W Warren SCP Swan Coastal Plain Eastern extent of clearing o 100 kilometres Figure 1 Map showing the distribution of quadrats within the South West Botanical Province (Beard, 1980). The bioregions and sub-regions shown (!BRA regions) are those defined by Environment Australia (2000). Seventeen quadrats occurred beyond the eastern boundary of the province, within the adjacent Yalgoo and Coolgardie bioregions. The study area broadly corresponds to the area between the 600mm-rainfall isohyet and the eastern extent of broadscale clearing. a series of very isolated pools (Lane and McComb, beds of coarse material are also common in braided 1988).

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