A first formal classification of the Hardeveld vegetation in Namaqualand, South Africa

Questions The Succulent Karoo is a winter-rainfall desert in southern Africa with a highly diverse flora. Which environmental factors differentiate vegetation composition at the plot level: How can compositional pattern be best represented by a formal phytosociological classification. Location Soebatsfontein communal area and surroundings in the Namaqualand Hardeveld Bioregion of the Succulent Karoo Biome, Northern Cape Province, South Africa. Methods We recorded vascular plant species composition, together with a range of structural and soil parameters as well as grazing intensity, in 355 plots of 100 m² size. This sample covered all vegetation types of the study area except those of river beds and anthropogenic sites. Vegetation classification was carried out using modified TWINSPAN followed by manual re-arrangement of a subset of plots with the aim of increasing floristic distinctiveness of the vegetation units. For the final vegetation units, we determined diagnostic species and environmental parameters, according to phi-values and ANOVA, respectively, and translated these into a phytosociological classification. Results The major factor influencing species composition and richness was soil salinity. At a broad scale, the less saline sites could be differentiated into sandy plains and rocky hills, and the saline sites into quartz fields, the centres of heuweltjies (termitaria) and the matrix between. We translated these patterns into two phytosociological classes with four orders, six alliances and 16 associations. Most of the syntaxa are very well defined in floristic terms, and all except the Othonnion cylindricae are new to science. The Hermannio trifurcae-Zygophylletea morgsanae represents the zonal vegetation of marginally saline soils, the Didelto carnosae-Cephalophylletea inaequalis the vegetation of saline soils. The vegetation of the extremely saline quartz patches probably belongs to a third class not described here due to the scarcity of representative plots. Conclusions Our phytosociological approach allowed the various degrees of ecological and floristic similarity to be represented by syntaxa of different ranks. A comparison with previous classifications from the Succulent Karoo revealed a high spatial turnover, with only two of our alliances and none of our associations coinciding with those found in previously studied areas of the Succulent Karoo. Our formal classification has the potential to be a powerful tool for local land use, ecological comparison and conservation, and to contribute to a future national phytosociological classification of South Africa.

[1]  S. Milton,et al.  TIERBERG KAROO RESEARCH CENTRE: HISTORY, PHYSICAL ENVIRONMENT, FLORA AND FAUNA , 1992 .

[2]  G. Bredenkamp,et al.  Analysis of the spontaneous vegetation of intensively managed urban open spaces in the Potchefstroom Municipal Area, North West Province, South Africa , 1999 .

[3]  N. Jürgens,et al.  Community structure on unusual habitat islands: quartz-fields in the Succulent Karoo, South Africa , 1999, Plant Ecology.

[4]  John Phillip Harison. Acocks,et al.  Veld types of South Africa. , 1955 .

[5]  R. H. Westfall,et al.  Biomes of Southern Africa: An objective categorization , 1994 .

[6]  R. Cowling,et al.  Biodiversity, habitat and range-size aspects of a flora from a winter-rainfall desert in north-western Namaqualand, South Africa , 1999, Plant Ecology.

[7]  The vegetation of the Bd and Ea land types in the grassland of the western Transvaal, South Africa , 1993 .

[8]  F. Ellis,et al.  Soils of Namaqualand: Compensations for aridity , 2007 .

[9]  Lubomír Tichý,et al.  JUICE, software for vegetation classification , 2002 .

[10]  B. Bestelmeyer,et al.  Indicator patches: exploiting spatial heterogeneity to improve monitoring systems , 2009 .

[11]  R. Cowling,et al.  Plant functional diversity, species diversity and climate in arid and semi-arid southern Africa , 1994 .

[12]  J. Dengler,et al.  Montane-subalpine tall-herb vegetation (Mulgedio-Aconitetea) in central Europe: large-scale synthesis and comparison with northern Europe. , 2010 .

[13]  Milan Chytrý,et al.  Determination of diagnostic species with statistical fidelity measures , 2002 .

[14]  G. Bredenkamp,et al.  Vegetation ecology of Sekhukhuneland, South Africa: Combretum hereroense-Grewia vernicosa Open Mountain Bushveld , 2002 .

[15]  J. Stol,et al.  Abundance and composition of plant species along grazing gradients in Australian rangelands , 2003 .

[16]  G. Bredenkamp,et al.  Vegetation ecology of the pans (playas) of Soetdoring Nature Reserve, Free State Province , 2003 .

[17]  R. Cowling,et al.  The comparison of selected life-history characteristics of Mesembryanthema species occurring on and off Mima-like mounds (heuweltjies) in semi arid southern Africa , 1995, Vegetatio.

[18]  M. Hoffman,et al.  Density of Microhodotermes viator (Hodotermitidae) mounds in southern Africa in relation to rainfall and vegetative productivity gradients , 2007 .

[19]  J. Midgley,et al.  Heuweltjie age and vegetation change based on δ13C and 14MC analyses : research letter , 2002 .

[20]  W. Wanek,et al.  Nitrogen input by cyanobacterial biofilms of an inselberg into a tropical rainforest in French Guiana , 2007 .

[21]  Jaroslav Moravec,et al.  International Code of Phytosociological Nomenclature. 3rd edition , 2000 .

[22]  G. Hardin,et al.  The Tragedy of the Commons , 1968, Green Planet Blues.

[23]  N. Jürgens.  A new approach to the Namib Region , 1991, Vegetatio.

[24]  R. Mittermeier,et al.  Biodiversity hotspots for conservation priorities , 2000, Nature.

[25]  M. Hoffman,et al.  A fence-line contrast reveals effects of heavy grazing on plant diversity and community composition in Namaqualand, South Africa , 1999, Plant Ecology.

[26]  Jörg Ewald,et al.  A critique for phytosociology , 2003 .

[27]  A national vegetation database for South Africa. , 2012 .

[28]  G. Bredenkamp,et al.  The syntaxonomy and synecology of the forests in the eastern Orange Free State, South Africa. II. The Pittosporetalea viridiflorum , 1991 .

[29]  U. Schmiedel,et al.  Vegetation dynamics of endemic‐rich quartz fields in the Succulent Karoo, South Africa, in response to recent climatic trends , 2012 .

[30]  G. Midgley,et al.  Substrate effects of zoogenic soil mounds on vegetation composition in the Worcester - Robertson valley, Cape Province. , 1990 .

[31]  R. Cowling,et al.  Namaqualand, South Africa – an overview of a unique winter-rainfall desert ecosystem , 1999, Plant Ecology.

[32]  P. Desmet.  Namaqualand—A brief overview of the physical and floristic environment , 2007 .

[33]  M. Hill,et al.  Detrended correspondence analysis: an improved ordination technique , 1980 .

[34]  M. Hoffman,et al.  The impacts of sustained heavy grazing on plant diversity and composition in lowland and upland habitats across the Kamiesberg mountain range in the Succulent Karoo, South Africa , 2007 .

[35]  G. Bredenkamp,et al.  The syntaxonomy and synecology of the forests in the eastern Orange Free State, South Africa. I. The Podocarpetalia latifolii , 1991 .

[36]  A. Rebelo,et al.  Plant assemblages on mima-like earth mounds in the Clanwillian district, South Africa. , 1989 .

[37]  Vegetation analysis of wetlands in the Klerksdorp Municipal Area, North West Province, South Africa. , 2000 .

[38]  I. Noy-Meir,et al.  Desert Ecosystems: Environment and Producers , 1973 .

[39]  M. Chytrý,et al.  Statistical determination of diagnostic species for site groups of unequal size , 2006 .

[40]  R. Cowling,et al.  Extraordinary high regional-scale plant diversity in southern African arid lands: Subcontinental and global comparisons , 1998 .

[41]  Rüdiger Wittig,et al.  The BIOTA Biodiversity Observatories in Africa—a standardized framework for large-scale environmental monitoring , 2011, Environmental Monitoring and Assessment.

[42]  Long-term vegetation change in the Succulent Karoo, South Africa following 67 years of rest from grazing , 2008 .

[43]  M. Hoffman,et al.  Changes in population biology of two succulent shrubs along a grazing gradient , 2003 .

[44]  K. Esler,et al.  Comparative patterns of phenology and growth form diversity in two winter rainfall deserts: the Succulent Karoo and Mojave Desert ecosystems , 1999, Plant Ecology.

[45]  J. Dengler,et al.  NEW IDEAS FOR MODERN PHYTOSOCIOLOGICAL MONOGRAPHS , 2005 .

[46]  C. Laurent,et al.  Environmental perceptions and practices of livestock keepers on the Namaqualand Commons challenge conventional rangeland management , 2007 .

[47]  Milan Chytrý,et al.  Modified TWINSPAN classification in which the hierarchy respects cluster heterogeneity , 2009 .

[48]  J. Oldeland,et al.  The Global Index of Vegetation-Plot Databases (GIVD): a new resource for vegetation science , 2011 .

[49]  U. Schmiedel,et al.  Vegetation of quartz fields in the Little Karoo, Tanqua Karoo and eastern Overberg (Western Cape Province, South Africa) , 2006 .