Cunninghamia Date of Publication: 24/10/2012 A journal of plant ecology for eastern Australia ISSN 0727- 9620 (print) • ISSN 2200 - 405X (Online) Vegetation structure and floristics of granite landforms in the South-west Slopes of New South Wales Damian R. Michael* and David B. Lindenmayer Fenner School of Environment and Society, The Australian National University, Canberra, ACT. 0200 AUSTRALIA. *Corresponding author: [email protected] Abstract: We describe the natural vegetation structure and floristics of 44 small-sized granite outcrops (inselbergs) in agricultural landscapes in the South-west Slopes (SWS) bioregion of New South Wales (35º 26’ S, 147º 23’ E to 35º 58’ S, 146º 59’E) and their relationships with geomorphology. We provide a list of 196 species (117 natives and 79 exotics). We found that structurally complex outcrops supported a greater diversity of native ground cover species and fewer exotic species than structurally simple outcrops. Tor landforms lacked vegetation structural complexity and were deficient in native shrubs, mid-storey and over-storey species but typically supported exotic grasses and broad- leaved exotic weeds. Floristic composition differed among landforms and cluster analysis revealed highly dissimilar native plant communities among outcrops. Our study highlights the need to rehabilitate tor landforms and manage a broad spectrum of outcrops to conserve floristic diversity in agricultural landscapes. Selecting genetically diverse species for replanting, considering the density and spatial arrangement of plantings, and controlling invasive plants and feral herbivorous animals are fundamental issues in restoring granite outcrop vegetation in the SWS bioregion. Cunninghamia (2012) 12 (4):309–323 doi: 10.7751/cunninghamia.2012.12.022 Introduction 2008, Michael et al. 2008). However, in many parts of the world, agricultural development and the associated impacts Inselbergs are granite outcrops that rise abruptly from flat of habitat fragmentation is threatening the natural insularity landscapes (Twidale 1982) providing a broad range of of inselbergs by creating smaller habitat isolates, and micro-climatic conditions that contrast with surrounding increasing isolation by reduced vegetation connectivity. This landscapes (Campbell 1997) and supporting biologically process has serious implications for the long-term viability diverse communities (Porembski & Barthlott 2000). For of plant populations in modified landscapes (Broadhurst & these reasons, the biota of inselbergs have fascinated Young 2006, Broadhurst et al. 2008). scientists from around the world for over 200 years (Walters An important aspect of inselberg ecology is their role in 1982), not least because these environs are rich in endemic providing refugia for endemic and fire sensitive flora. Fires taxa (Porembski & Barthlott 2000), but also because they on granite outcrops are generally rare due to the buffering provide a model framework for examining patterns of effect of rock (Burke 2003), and in the absence of fire, floristic diversity and species composition in the context of fire-sensitive and mesic-adapted plants such as ferns grow island biogeography theory (Burke 2003, Butler & Fensham in sheltered locations (Hopper et al. 1997). Many outcrops Cunninghamia: a journal of plant ecology for eastern Australia © 2012 Royal Botanic Gardens and Domain Trust www.rbgsyd.nsw.gov.au/science/Scientific_publications/cunninghamia 310 Cunninghamia 12(4): 2012 Michael & Lindenmayer, Floristics of granite landforms support obligate seeders (Hopper 2000, Hunter 2003) Methods such as Callitris spp., Acacia spp., Pultenaea spp. and Dodonaea spp. which germinate following fire, in contrast to sprouters which regenerate primarily from epicormic Study area buds or underground rhizomes, such as many Eucalyptus This study area was in the southern half of the South-west spieces (Clarke 2002). In sclerophyllous vegetation, frequent Slopes (SWS) bioregion of New South Wales, bordered by high-intensity fires promote sprouters whereas intermediate Big Springs in the north (35º 19’ S, 147º 25’ E), Albury in low-intensity fires promote obligate seeders (Keith 1996). the south (36º 00’ S, 146º 53’E), Kyeamba in the east (35º Frequent fires can therefore alter plant species composition, 26’ S, 147º 37’E) and Goombargana in the west (35º 44’ a process which can threaten the integrity and long-term S, 146º 34’E). Annual average rainfall in the region ranges persistence of outcrop flora (Bradstock et al. 2002). from approximately 450 mm at Walbundrie to 550 mm The grassy box woodlands of temperate south-eastern near Tarcutta (Bureau of Meterology 2012). Due to drought Australia represent a broad bio-climatic region that has conditions the average monthly precipitation during the been extensively modified (Beadle 1981) and continues study period, Oct 2006 – Feb 2007, was generally below to be threatened by agricultural intensification and urban average for each month (2006 Oct– 2.4 mm, Nov– 46.2 mm, development (Yates & Hobbs 1997, Lindenmayer et al. Dec– 1.6 mm; 2007 Jan– 36.5 mm, Feb– 40.8 mm, Bureau 2010). It is estimated that less than 5% of the original grassy of Meterology 2012). The vegetation type is temperate box woodland remains intact (Prober 1996), with much of woodland (sensu Hobbs & Yates 2000), dominated by the the remaining vegetation occurring on skeletal soils and endangered ecological vegetation community – White box rocky outcrops. The South-west Slopes (SWS) botanical (Eucalyptus albens), Yellow box (Eucalyptus melliodora), region of New South Wales is one of the most heavily cleared Blakely’s red gum (Eucalyptus blakelyi) woodland (www. bioregions in New South Wales (Benson 2008). Grassy box environment.gov.au 2012). woodlands are significantly fragmented; improvements to Granitoid formations associated with the Southern Highlands the condition and extent of remnant vegetation are a priority Fold Belt (Wagga Metamorphic Belt) are one of the main conservation action of natural resource management agencies lithologies in the SWS (Packham & Day 1969). Soils derived (Murray Catchment Management Authority 2007). If it were from surface weathering of granite produces a shallow layer not for an archipelago of rocky outcrops in the SWS, the of sandy loam that overlays sandy clay (Norris & Thomas majority of which are granite, grassy box woodland may 1991). Four geomorphologically distinct granite landforms have been more extensively cleared than current vegetation (sensu Campbell 1997; see Michael et al. 2008 for images) patterns suggest. occur in the region. These are: In Western Australia, inselberg vegetation has been the (1) Bornhardt / Dome (6 outcrops) – large, steep-sided subject of considerable research (Smith 1962, Burgman dome-shaped hills arising abruptly from the 1987, Ornduff 1987, Hopper et al. 1997, Ohlemuller 1997, surrounding landscape characterized by large expanses Porembski et al. 1997, Pigott 2000, Porembski 2000), of bare rock. Shallow and elliptical bornhardts are whereas inselbergs in eastern Australia have received far less called ‘whalebacks’ or ‘turtlebacks’. attention (Ashton & Webb 1977, Norris & Thomas 1991, Hunter & Clarke 1998). The value of granite outcrops in (2) Nubbin (13 outcrops) – small, conical hills rising supporting rock-dwelling reptiles in agricultural landscapes gently from the surrounding landscape, characterized has been reported recently in the SWS (Michael et al. 2008, by small boulder-strewn rock piles. Michael et al. 2010a), and specific management actions have (3) Castle koppie (8 outcrops) – small, steep-sided been proposed to enhance habitat for this group (Michael et hills arising abruptly from the surrounding landscape al. 2010b). Given the paucity of vegetation studies in the SWS characterized by large orthogonally fractured boulder (Burrows 1999), additional studies are required which may stacks. help inform restoration activities in the region. The main aim of this study was to examine vegetation patterns and floristic (4) Tors (17 outcrops) – sparsely aggregated rocks in flat composition of relatively small granite outcrops in relation to or gently undulating landscapes characterized by different landforms. It is widely recognized that vegetation individual, block-shaped pillars of various sizes. communities change in response to lithology (Norris & Thomas 1991, Burrows 1999). However, the influence of Sampling protocol geological landform on patterns of vegetation is less well understood (Kruckenburg 2002). We frame our study by Between October 2006 and February 2007, one of the proposing three main questions. 1) Do current patterns of authors (DM) assessed vegetation on 44 privately owned vegetation structure differ among landforms of the same granite outcrops located within agricultural landscapes. geology? 2) Is floristic composition influenced by granite Subsets of all four landforms were surveyed each month landform? 3) Can these findings help guide conservation and over the assessment period. With the exception of three restoration activities in the SWS bioregion? outcrops where livestock had been excluded prior to the study, grazing pressure included set stocking rates (N = 25 outcrops) or rotational grazing regimes (N = 16 outcrops). On each outcrop, we established a 1 hectare (100 m x 100 Cunninghamia 12(4): 2012 Michael & Lindenmayer, Floristics of granite landforms 311 Table 1. Summary of geological and floristic attributes for each granite landform in the SWS bioregion