498 South African Journal of Science 97, November/December 2001 Serpentine Ecology tine flora is a response to the toxicity of particular metals, in particular Ni1,5 and Mg.2,11 In this study the occurrence of a large number of endemic species at upland xeric sites with high surface soil Ni (>0.3%) supports the Ni and drought hypothesis (Table 1, Fig. 2). Kruckeberg7 states that high Ni concentration in soils reduces species richness through biotype depletion. The reduction in species richness with the increased Ni in Central Queensland soils support this rationale. For example, Soil Group 3 with the highest Ni concentrations recorded on average 11 fewer plant species than the lower Ni (<0.3%) soils of groups 1, 2, 4, 5 and 6. The predominance of serpentine endemic shrubs (13 of 19 taxa) in this study agrees with Borhidi’s2 hypothesis that such life forms are more frequent as initial colonizers of primary Fig. 4. Comparison of species richness of open-forest strata between upland (in in situ serpentine soils. situ soils) and lowland (depositional soils) serpentine landforms of Central The total number of endemics found in the uplands (23 spp.) is Queensland. substantially greater than that found in the lowlands (15 spp.). This suggests that the predominant evolutionary processes lead- 30% of the total serpentine flora by covering <0.1% of the study ing to speciation are most likely to occur in upland, older in situ area. However, no serpentine endemic plants have yet been re- soils. The features of upland landforms that potentially promote corded from this community.11 the evolution of serpentine endemics include low fertility, high Ni, high Mg, a predominance of shallow soils magnifying physi- Discussion ological aridity, and a long period of landform evolution. Some Serpentine landforms in Central Queensland are character- endemic taxa that presumably originated on the uplands may ized by endemic open-forest communities in both the uplands have migrated with the movement of younger depositional soils and lowlands (Appendix 1). The distinctiveness of these land- down to the lowlands (e.g. Bursaria reevesii, Capparis thozetiana, forms has been attributed to abiotic influences such as high soil Pimelea leptospermoides, Stackhousia tryonii). Mg and Ni as well as biotic responses including physiological There is greater structural diversity, particularly in canopy drought and the evolution of an unique flora and vegeta- height, within upland plant communities than lowland plant tion.11,18–23 For example, Stackhousia tryonii and Pimelea lepto- communities (Appendix 1). Figure 5 summarizes upland envi- spermoides have evolved a specific physiological condition of ronmental conditions that are due to landform factors such as accumulating Ni.18–20 topography, aspect and elevation. Variability in soil chemistry, Brooks and others1,2,5,26 have suggested that serpentine floras water availability and fire regimes within the uplands may are subjected to two dominant selective pressures: (i) selection contribute to the greater structural diversity of these plant for Ni tolerance and (ii) selection for drought tolerance. Proctor4 communities. The abundance of heathy, sclerophyllous and others1,5,8 argue that a major force in the evolution of serpen- understorey in the uplands appears to be associated with high Fig. 5. Illustration of four plant communities along a north–south gradient on serpentine soils at Mt Fairview, Central Queensland. Serpentine Ecology South African Journal of Science 97, November/December 2001 499 soil Ni concentrations (Figs 2, 4, 5). However,open forests in both alien and endemic herbs on serpentine. Ecology 80, 70–80. the uplands and lowlands have a localized abundance of heathy 7. Kruckeberg A.R. (1954). The ecology of serpentine soils. III. Plant species in relation to serpentine soils. Ecology 35, 267–274. understorey of species such as Leucopogon spp., Macrozamia sp. 8. Rune O. (1953). Plant life on serpentine and related rocks in the north of nov., Melaleuca bracteata, Pimelea leptospermoides and Xanthorrhoea Sweden. Acta Phytogeogr. Suec. 36, 1–139. spp. (Appendix 1). The abundance of shrubby species may re- 9. Whittaker R.H. (1954). The vegetation response to serpentine soils. Ecology 35, flect a more general nature of serpentine landform.11,19–22 275–288. The total species richness of lowland open forests is greater 10. Wild H. (1965). The flora of the Great Dyke of Southern Rhodesia with special than that of upland open forests, mainly because of a higher references to the serpentine soils. Kirkia 5, 49–86. 11. Batianoff G N., Neldner V.J. and Singh S. (2000). Vascular plant census and number of herbaceous species (Table 1, Fig. 4). The reduction in floristic analysis of serpentine landscapes in Central Queensland. Proc. R.. Soc. total serpentine herb diversity in uplands relative to lowlands Qld. 109, 1–30. corresponds to previous reports on the effect of elevation on 12. Cole M.M. (1973). Geobotanical and biogeochemical investigations in the serpentine flora.6 In Central Queensland11,19–22 and other areas of sclerophyllous woodland and shrub associations of the eastern goldfields area of Western Australia, with particular reference to the role of Hybanthus 12,14–16,19 Australia, the abundance of grasses (particularly Triodia floribundus (Lindl.) F.Muell. as a nickel indicator and accumulator plant. J. appl. spp.) and other species of herbs is possibly due to their tolerance Ecol. 10, 269–320. of high Mg and/or lower Ca concentrations at serpentine 13. Severne B.C. and Brooks R.R. (1972). A nickel-accumulating plant from West- sites.6,10,26 Harrison6 found that soils low in Ca (and high in Mg) ern Australia. Planta 103, 91–94. 14. Lyons M.T., Brooks R.R. and Craig D.C. (1974). The influence of soil composi- harbour a larger number of native herbs. In addition to herba- tion on the vegetation of the Coolac Serpentine Belt in New South Wales. J. R. ceous plants, two serpentine woody endemic species, Neoroepera Soc. N.S. W. 107, 67–75. buxifolia and Callistemon sp. nov., are also reported to tolerate 15. Davie H. and Benson J.S. (1997). The serpentine vegetation of the soils with high Mg concentrations and/or a high Mg:Ca ratio.11 Woko-Glenrock region, New South Wales,Australia. In The Ecology of Ultramafic and Metalliferous Areas, eds T. Jaffré, R.D. Reeves and T. Becquer, pp. 155–162. Studies of plant–soil associations suggest that soil Ni and Mg Centre ORSTOM. Nouméa, New Caledonia. concentrations influence species composition and vegetation 16. Specht A., Forth F.and Steenbeeke G. (2001). The effect of serpentine on vegeta- structure on serpentine soils. This study has demonstrated that tion structure, composition and endemism in northern NSW,Australia. S. Afr. J. the differences between upland and lowland endemism and Sci. 97, 521–529. 17. Gibson N., Brown M.J., Williams K. and Brown A. V.(1992). Flora and vegeta- species richness are directly associated with soil chemistry.How- tion of ultramafic areas in Tasmania. Aust. J. Ecol. 17, 297–303. ever, serpentine species composition may also be influenced by 18. Batianoff G.N., Reeves R.D. and Specht R.L. (1990). Stackhousia tryonii Bailey. A other abiotic conditions. Collaboration between soil scientists, nickel-accumulating serpentinite endemic species of central Queensland. Aust. plant physiologists and ecologists is needed to examine further J. Bot. 38, 121–130. the links between endemism, species richness and soil-landform 19. Batianoff G.N. and Specht R.L. (1992). Queensland (Australia) serpentine vege- tation. In The Vegetation of Ultramafic (Serpentine) Soils, eds A.J.M. Baker, J. Proc- characteristics. tor and R.D. Reeves, pp. 109–128. Intercept, Andover, Hants. Queensland Herbarium staff, particularly John Neldner, are acknowledged for 20. Batianoff G.N., Reeves R.D. and Specht R.L. (1997). The effects of serpentine supporting this project. Taxonomic guidance was provided by Anthony Bean and on vegetation structure, species diversity and endemism in Central Queensland. In The Ecology of Ultramafic and Metalliferous Areas, eds T. Jaffré, Paul Forster and soil descriptions by Bruce A. Forster. Will Smith drafted Figs 1 R.D. Reeves and T. Becquer, pp. 147–154. Centre ORSTOM, Nouméa, New and 5. G.N.B. is grateful to Ray Specht for valuable scientific advice in early stages of Caledonia. writing the paper. The constructive critique provided by Ailsa Holland, Andrew 21. Batianoff G.N., Specht R.L. and Reeves R.D. (1991). The serpentinite flora of the Franks and anonymous referees considerably improved this document. humid subtropics of eastern Australia. Proc. R. Soc. Qld. 101, 137–157. 22. Forster B.A. and Baker D.E. (1997). Characterisation of the serpentine soils of 1. Arianoutsou M., Rundel P.W. and Berry W.L. (1993). Serpentine endemics as Central Queensland, Australia. In The Ecology of Ultramafic and Metalliferous biological indicators of soil elemental concentrations. In Plants as Biomonitors: Areas, eds T. Jaffré, R.D. Reeves and T. Becquer, pp. 27–37. Centre ORSTOM, Indicators for Heavy Metals in the Terrestrial Environment, ed. B. Markert, Nouméa, New Caledonia. pp. 179–189. VCH, Weinheim. 23. Plowman K. (2000). Capricornia (Central Queensland) Serpentinite Landscape 2. Borhidi A. (1991). Phytogeography and Vegetation Ecology of Cuba. Akademiai Nomination. 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