Conservation Science W. Aust. 7 (3) : 557–570 (2010) Flora and vegetation of banded iron formations of the Yilgarn Craton: Barloweerie and Twin Peaks Greenstone Belts RACHEL MEISSNER AND JESSICA WRIGHT Science Division, Department of Environment and Conservation, PO Box 51, Wanneroo, Western Australia, 6946. Email: Rachel [email protected] ABSTRACT The Twin Peaks and Barloweerie Greenstone Belts are located within the Youanmi Terrane and are represented by two ranges, separated by 24km. This paper describes the flora and vegetation of these ranges and their relationship with environmental attributes. One hundred and ninety nine taxa, including 90 ephemerals and four introduced taxa, were recorded from the hills. Seven priority taxa, including one endemic, Baeckea sp. Mount Barloweerie (J.Z. Weber 5079), were recorded from the ranges. Hierarchical classification identified three floristic communities on the ranges. Geomorphology differentiated the communities into upland and lowland communities. Significant differences were found between soil depth, rock outcrops and surface fragments as well as some difference in trace elements. No representative areas of the Twin Peaks and Barloweerie Greenstone Belts are within Western Australian conservation estate. Keywords: BIF, banded ironstone, ranges, floristic communities, Yilgarn INTRODUCTION often have unique and rare flora (Markey & Dillon 2008a,b; Meissner & Caruso 2008 a,b,c). The objective Banded iron formations (BIF) are ancient sedimentary of this study is to describe the flora and plant communities rocks formed in the Archaean period approximately 3.8 of the banded ironstone ranges on the Twin Peaks and to 2.5 billion years ago. Within the Yilgarn Craton, BIFs Barloweerie Greenstone Belts and their relationships with occur as relatively thin deposits associated with Archaean environmental variables, and to provide baseline greenstone belts (Page 2001) and as they are more resistant information for future management. to erosion, BIF form distinct ranges and hills within the region. Geology The Twin Peaks and Barloweerie Greenstone Belts are located in the Murchison Interim Biogeographic The ironstone ranges surveyed are part of two greenstone Regionalisation for Australia (IBRA) (Department of the belts, Twin Peaks and Barloweerie and occur within the Environment and Water Resources 2004), which is Youanmi Terrane of the Yilgarn Craton (Watkins 1990). characterised by Acacia aneura low woodlands and The BIF occur within the Windaning Formation, which abundant ephemerals. Within the Murchison region, the is defined as a succession of jaspilite BIF and grey-white primary land use is pastoralism and the greenstone belts chert units interlayered with felsic volcanic, volcaniclastic, occur across Wooleen, Billabalong and Boolardy Stations. and volcanogenic rocks, and minor amounts of basalt Wooleen and Billabalong Stations were part of the first (Watkins & Hickman 1990). The Windaning formation blocks settled by 1874 and 1880, respectively, in the region occurs throughout the Youanmi Terrane and is a distinct along the Murchison River (Curry et al. 1994). The stratigraphic marker (Watkins & Hickman 1990). Barloweerie Greenstone Belt occurs largely within the Pia The main exposure of BIF in the Twin Peak Greenstone Wadjarri aboriginal reserve. Belt is represented by a range approximately 8km along a Previous vegetation surveys of ironstone ranges on the relatively low strike ridge along a northeast bearing (Fig. Yilgarn Craton have shown that each range supports plant 1). South of this range, the exposure near Mount Hope is communities distinct from other ironstone ranges and poor and very weathered (Baxter 1974). Within the Barloweerie Greenstone Belt, 24km to the east of the Twin Peaks belt, the ironstone is exposed in a narrow fold that forms the dominant ridge of Mount Barloweerie, the © The Government of Western Australia, 2010 highest peak in the area (Fig. 1). 558 R. Meissner & J. Wright Figure 1. Location of the 51 plots () established on the Twin Peaks and Mount Barloweerie Greenstone Belts. The 300 m contour is shown with the highest peaks of Mount Hope (330m) and Mount Barloweerie (428m). Shaded grey represent banded iron formation of the Windaning formation. Climate The highest maximum temperatures occur during summer, with the January as hottest month (mean The climate of the region is classified as arid and maximum temperature 39.2 °C and mean 14.4 days above characterised by hot, dry summers and mild winters. 4 0 °C). Winters are mild with lowest mean maximum Rainfall is bimodal, with significant rainfall events temperature of 20.9 °C recorded for July. Temperatures occurring in winter and summer (Beard 1976). The two rarely fall below 2 °C in winter and there is a mean highest mean monthly rainfalls at Murchison Settlement minimum of 6.1 °C in July. (ca. 50km north of Mount Hope) occur in January and June (31.2mm and 30.5mm respectively), with highest Vegetation recorded daily rainfall of 143.8mm in January 1963. Mean annual rainfall at Murchison Settlement is 245.1mm, with Beard (1976 ) mapped the ranges of the Twin Peaks and large variation (139.2mm 1st decile; 402.5mm 9th decile; Barloweerie Greenstone Belts as several vegetation recorded 1989 to 2009). associations. The lower and colluvial slopes were mapped Summer rainfall is influenced by cyclonic activity off as A. aneura shrublands over Eremophila spathulata and the north west coast of Western Australia with convectional Eremophila sp. aff. compacta shrublands. The BIF activity bringing either isolated thunderstorms in localised vegetation on the Twin Peaks Greenstone Belt was mapped areas, or widespread rainfall (Curry et al. 1994). In as A. aneura and Acacia quadrimarginea open shrublands, contrast, winter rainfall is associated with low pressure while the vegetation on Mount Barloweerie was mapped systems originating in the Southern Ocean. The cold fronts as A. aneura and Acacia spp. (A. ramulosa var. linophylla, arising from the south west systems often weaken as they A. effusifolia) shrublands over Thryptomene johnsonii, move inland and result in isolated showers and strong Eremophila forrestii, Solanum lasiophyllum, Maireana winds (Curry et al. 1994). Flora and vegetation of Barloweerie and Twin Peaks 559 convexa, Eremophila sp. over Myriocephalus guerinae and Mehlich No. 3 procedure (Mehlich 1984). The extracted Brachyscome sp. samples were analysed for B, Ca, Cd, Co, Cu, Fe, K, Mg, In a more recent rangeland condition survey, the BIF Mn, Mo, Na, Ni, P, Pb, S and Zn using an Inductively of the Twin Peaks and Mount Barloweerie Greenstone Belt Coupled Plasma - Atomic Emission Spectrometer (ICP- are characterised by the Gabanintha land system (Curry AES). This procedure is an effective and cost-efficient et al. 1994). Land systems are used to assess rangeland alternative to traditional methods for evaluating soil resources and describe recurring patterns of fertility and has been calibrated for Western Australian geomorphology, vegetation and soils (Curry et al. 1994). soils (Walton & Allen 2004). The soil pH was measured The Gabanintha land system is characterised as ridges, in 0.01M CaCl2 at soil to solution ratio of 1:5. Effective hills and footslopes of various greenstones, supporting cation exchange capacity (eCEC) was calculated from the sparse Acacia and other mainly non-halophytic shrublands. sum of exchangeable Ca, Mg, Na and K (Rengasamy & Typically, the crests and upper slopes of the ranges were Churchman 1999). Exchangeable Ca, Mg, Na and K were characterised by either Rocky Hill Mixed Shrublands or obtained by multiplying the values of Ca, Mg, Na and K Stony Mulga Mixed Shrublands vegetation types, with obtained from ICP-AES by a standard constant. Organic the latter characterising the lower slopes and stony plains carbon was measured on soil that was ground to less than (Curry et al. 1994). The Rocky Hill Mixed Shrublands 0.15mm using Metson’s colorimetric modification of the are dominated by A. aneura, Eremophila macmillaniana Walkley and Black method 6A1 (Metson 1956; Walkley and Ptilotus obovatus and several species found only 1947). It involved wet oxidation by a dichromate-sulfuric within this vegetation type, Acacia grasbyi, Eremophila acid mixture, which produced enough heat to induce glutinosa, Solanum ashbyae, Tribulus platypterus, oxidation of the organic carbon (Rayment & Higgenson Cheilanthes austrotenuifolia and Spyridium sp. (Curry et 1992). Total Nitrogen was measured using the Kjeldahl al. 1994). The Stony Mulga Mixed Shrubland on the stony method 7A2 (Rayment & Higgenson 1992). The nitrogen slopes, footslopes and plains was dominated by A. aneura, was measured by automated colorimetry by the A. pruinocarpa, A. grasbyi, Eremophila macmillaniana, nitroprusside/dichloro-S-triazine modification (Blakemore E. spathulata, E. fraseri, E. freelingii, E. spathulata, et al. 1987) of the Berthelot indophenol reaction reviewed Solanum lasiophyllum, Ptilotus rotundifolius, Senna by Searle (1984). Electrical conductivity (EC) was based helmsii, P. obovatus and Ptilotus schwartzii. on a 1:5 soil/deionised water extract and measured by a conductivity meter at 25° C (Rayment & Higgenson 1992). METHODS Quadrats were classified on the basis of similarity in species composition using perennial species only and The methodology employed in this survey follows the excluding singletons. This was to maintain consistency standard procedure used in previous vegetation surveys with previous