Conservation Science W. Aust. 7 (1) : 89–103 (2008) Flora and vegetation of banded iron formations of the Yilgarn Craton: Jack Hills RACHEL MEISSNER AND YVETTE CARUSO Science Division, Department of Environment and Conservation, PO Box 51, Wanneroo, Western Australia, 6946. Email: [email protected] ABSTRACT A study of the flora and plant communities of Jack Hills, 140 km WNW of Meekatharra, found 208 taxa, with 205 native and 3 weeds. Two priority taxon was found and two new species identified. Fifty quadrats were established to cover the major geographical, geomorphologic and floristic variation across the hills. Data from these quadrats were used to define six community types. Differences in communities were strongly correlated with altitude and soil fertility. Several communities had restricted distributions. None of the plant communities found on the Jack Hills is reserved in conservation estate. INTRODUCTION in isolated showers and strong winds (Curry et al. 1994). The highest maximum temperatures occur during summer, Banded iron formation ranges within the Yilgarn Craton with the January as hottest month (mean maximum are highly prospective for iron ore exploration and mining. temperature 38.9 °C and mean 11.3 days above 40 °C). Previous studies on greenstone and banded ironstone Winters are mild with lowest mean maximum temperatures ranges in the Goldfield have found high plant endemicity recorded for July of 18.9 °C. Temperatures rarely fall and restricted vegetation types. It is hypothesised that these below 2 °C in winter, with mean minimum of 7.4°C in patterns may also be found on the ironstone ranges in the July. Yilgarn (Gibson et al. 1997; Gibson & Lyons 1998a,b; Jack Hills is located in the Murchison geological Gibson & Lyons 2001a,b; Gibson 2004a,b). The current province in the northwest part of the Yilgarn Craton. It knowledge of the flora and vegetation that occur on these differs locally from the Weld Range, 90 km south, although ranges is poor and based primarily on the structural formed during the same tectonic phase, as it mainly description of the dominant vegetation (Speck 1963; contains metasedimentary rock rather than the Beard 1976; Curry et al. 1994) rather than the community metavolcanics of the Weld Range (Elias 1982). Jack Hills composition. is dominated by pelitic and psammitic metasediments such The study area is located approximately 140 km WNW as quartz-mica schists, banded iron formations and chert. of Meekatharra and covers the major extent of Jack Hills, The latter two form units several centimetres to several approximately 40 km from the Berringarra-Cue Road to hundred metres thick as prominent strike ridges within Mount Taylor. The range runs in a prominent NE-SW the range (Elias 1982). direction (Figure 1). The south west part of the range The area surrounding Jack Hills is topographically flat, extends across Berringarra-Cue Road, but this area was with the more erosion resistant range of Banded Ironstone not surveyed. prominent in the landscape. Colluvial deposits are present The climate of the region is arid with mild winters in a valley between a divide in the range, resulting in deeper and hot summers. Mean annual rainfall at Meekatharra is sandier soils, than the colluvial deposits exterior to the 235.9 mm, with much variation in rainfall (112.9mm 1st range. This is probably a result of sheetwash across a larger decile; 368.9 9th decile; recorded 1994 to 2004). Annual area exterior to the hills, rather than the smaller constricted rainfall has a bimodal distribution with summer and winter area between two ridges. Skeletal soils are found on the rainfall. Summer rainfall, peaking in January and February, crests and hill slopes of the range. The shallow soils are is influenced by cyclonic activity off the Pilbara coast of formed when erosion is greater than the weathering Western Australia. Cyclones that cross the coast dissipate process resulting in relatively thin soil profile and extensive and develop into rain bearing depressions which may bring rock outcrop (Gray & Murphy 2002) rain inland. In addition, thunderstorm may develop from Jack Hills occurs in the Murchison IBRA region, which convectional activity (Curry et al. 1994). Winter rainfall is characterised by open mulga (Acacia aneura) woodlands is often the result of cold frontal activity associated with and a rich diversity in ephemerals (Environment Australia low pressure systems in the south west of Western Australia. 2000). Beard (1976) describes the dominant cover of These systems often weaken as they move inland and result Acacia aneura and A. grasbyi. 90 R. Meissner & Y. Caruso Figure 1. Location of the study area and distribution of the 50 quadrats (¶) along the Jack Hills. Mount Matthew and Mount Hale are the highest peaks (D) on the range. The 340m contour is shown. Speck (1963) and later Curry et al. (1994) mapped geomorphologic and floristic variation found on the hills land systems at a similar scale. Jack Hills is in the Weld in the study area. Each quadrat was permanently marked land system, which covers the Weld Range to the south. with four steel fence droppers and their positions The vegetation consists of rocky hills with mixed determined using a GPS unit. All vascular plants within shrubland, minor areas of stony soils with mulga mixed the quadrat were recorded. Data on topographical shrubland, and shrublands on valley floors. position, disturbance, abundance, size and shape of coarse The aim of this work was to undertake a detailed fragments on surface, the amount of exposed bedrock, floristic survey of the Jack Hills and to identify the plant cover of leaf litter and bare ground were recorded communities that occur on the range. This was achieved following McDonald et al. (1990). Additionally, growth by detailed flora list, and description of plant communities form, height and cover were recorded for dominant taxa based on a series of permanently established quadrats. The in each strata (tallest, mid- and lower). survey of the Jack Hills will be part of a larger regional Twenty soil samples were collected from the upper 10 study of flora and plant communities of banded ironstone cm of the soil profile within each quadrat. The soil was formations of Yilgarn Craton. bulked and the 2mm fraction analysed for B, Ca, Cd, Co, Cu, Fe, K, Mg, Mn, Mo, Na, Ni, P, Pb, S and Zn using the Mehlich No. 3 procedure (Mehlich 1984). The METHODS extracted samples were then analysed using Inductively Coupled Plasma – Atomic Emission Spectrometer (ICP- Fifty 20 x 20 m quadrats were established on Jack Hills in AES). This procedure is an effective and cost efficient August 2005 (Figure 1). The location of quadrats alternative to traditional methods for evaluating soil attempted to cover the major geographical, fertility and has been calibrated for Western Australian Flora and vegetation of Jack Hills 91 soils (Walton & Allen 2004). pH was measured in 0.01M • Gunniopsis propinqua (P3) is a small prostrate CaCl2 at soil to solution ratio of 1:5. Effective cation succulent herb growing on low outwash areas or flats. exchange capacity (eCEC) was calculated from the sum Only one collection was made from an open drainage of exchangeable Ca, Mg, Na and K (Rengasamy & channel in a valley. Churchman 1999). Exchangeable Ca, Mg, Na and K were • Homalocalyx echinulatus (P3) is a low growing obtained by multiplying the values of Ca, Mg, Na and K myrtaceous shrub to 1m, growing on breakaways, obtained from ICP-AES by a standard constant. sandstone hills and laterite in the northern area of Quadrats were classified on the basis of similarity in the Murchison IBRA region. A single collection was species composition on perennial species only, to be made from a colluvial outwash. consistent with other analyses of banded ironstone ranges (see Gibson 2004 b). Taxa identified to species level and New taxa occurring in more than one quadrat were used in the floristic analysis. Life form followed Paczknowska and Three new taxa, Prostanthera ferricola, Lobelia heterophylla Chapman (2000), where perennial is defined as a plant subsp. Pilbara (R.Meissner & Y.Caruso 1), and Acacia whose life span extends over 2 or more growing seasons. sp. Jack Hills (R. Meissner & Y. Caruso 4) were collected The quadrat and species classifications were undertaken during the Jack Hills survey. using the Bray and Curtis coefficient and Flexible UPGMA • Prostanthera ferricola is a highly aromatic shrub to (Unweighted pair-group mean average; â = - 0.1; Belbin 1 m with purple mauve flowers. The shrubs are highly 1989). Indicator species and species assemblages palatable and were heavily grazed by feral goats. characterising each community were determined following Initially, the collections at Jack Hills were matched Dufrene and Legendre (1997) using INDVAL routine in to a specimen collected by G. Byrne from Doolgunna PC-ORD (McCune & Mefford 1999). Quadrats were station in 2003, approximately 100 km north of ordinated using SSH (semi-strong hybrid Meekatharra. Subsequent taxonomic work identified multidimensional scaling), correlations of environmental the Doolgunna specimen as a distinct new species, variables were determined using the PCC (Principal P. ferricola. Its taxonomic affinities remain unclear, Component Correlation) routine and significance but it is morphologically similar to P. centralis, but determined by the MCAO (monte-carlo attributes in differs significantly by having smaller leaves and short, ordination) permutation test in PATN (Belbin 1989). patent indumentum (Conn & Shepherd 2007). PCC is a routine that runs multiple linear regressions on • Lobelia heterophylla subsp. Pilbara (R.Meissner & the variables and the ordination coordinates, resulting in Y.Caruso 1) was identified as a subspecies of a vector for each variable within the ordination plot. The L. heterophylla, previously collected in the Pilbara. MCAO is a monte-carlo test determining the robustness This taxon is a small herb to 20 cm with bright blue of the PCC results by randomly assigning values of variables flowers, and serrated leaves.