Road Verge and Rangeland Plant Communities in the Southern Karoo: Exploring What Influences Diversity, Dominance and Cover
Article First Online: 17 June 2005 Received: 10 December 2003 Accepted: 31 August 2004 Abstract
Road verges in the Prince Albert district, South Africa were examined to determine whether they are important refugia for plant species in the Karoo biome. Vascular plants at 50 sites on road verges were compared with those plant communities in the adjacent grazed rangelands. Verges were found to support a greater mean number of species, total plant cover, and number of individual plants. Road verges were found to contain 11 unique species compared with 20 unique species in rangelands. Plant community composition varied with more forbs and succulents on the verge and more shrubs in the rangeland. Significantly greater cover of unpalatable plants was found on the ungrazed road verge, and no difference in palatable and highly palatable plant cover was recorded, indicating that herbivory is not a major driver in defining community differences in these environments. No significant differences in soil moisture or texture were found between verge and rangeland. We argue that road maintenance and construction activities have an over-riding controlling influence on road verge community composition. Although it is not possible to discount the possibility that road verges provide an important refuge for certain species, it appears that they are disturbed environments that do not contribute significantly to the plant conservation needs of this biome.
Keywords Herbivory Karoo Plant community Rangeland Road maintenance Road verges Road verge width Soil moisture South Africa References Begon, M., Harper, J.L., Townsend, C.R. 1996Ecology Blackwell Science Ltd. Oxford Google Scholar Bennett, A.F. 1991 Roads, roadsides and wildlife conservation: a review Saunders, D.A. Hobbs, R.J. eds. Nature Conservation 2: The Role of Corridors Surrey Beatty & Sons Chipping Norton, NSW, Australia Google Scholar Dean, W.R.J., Milton, S.J. 1991 Disturbance in semi-arid shrubland and arid grasslands in the KarooSouth Africa: mammal diggings as germination sites Afr. J. Ecol. 29 11 16 Google Scholar Dean, W.R.J., Milton, S.J. 1995 Plant and invertebrate assemblages on old fields in the arid southern KarooSouth Africa Afr. J. Ecol. 33 1 13 Google Scholar du Toit, P.C.V. 1995 The grazing index method of range condition assessment Afr. J. Range For. Sci. 12 61 67 Google Scholar
du Toit P.C.V., Botha W. van D., Blom C.D., Becker H.R., Olivier D.J., Meyer E.M. and Barnard G.Z.J. 1995. Estimating grazing index values for Karoo plants. Department of Agriculture Technical Communication 239, Pretoria.
Google Scholar Esler, K.J., Cowling, R.M. 1995 The comparison of selected life-history characteristics of the Mesembryanthema species occurring on and off Mima-like mounds (heuweltjies) in semi arid southern Africa Vegetatio 116 41 50 Google Scholar Esler, K.J., Phillips, N. 1994 Experimental effects of water stress on semi-arid Karoo seedlings: implications for field seedling survivorship J. Arid Environ. 26 325 337 CrossRef Google Scholar Forman, R.T.T. 2000 Estimate of the area affected ecologically by the road system in the United States Conserv. Biol. 14 31 35 Google Scholar Forman, R.T.T., Alexander, L. 1998 Roads and their major ecological effects Annu. Rev. Ecol. Syst. 29 207 231 CrossRef Google Scholar Gelbard, J.L., Belnap, J. 2003 Roads as conduits for exotic plant invasions in a semiarid landscape Conserv. Biol. 17 420 432 CrossRef Google Scholar
Gwala P.P., Drennan P.M. and van Staden J. 1991. Factors affecting the germination of seeds of
South African Association of Botanists and Phycological Society of Southern Africa. Annual Congress, University of Natal.
Google Scholar Hall, A.V. 1987 Threatened plants in the Fynbos and Karoo Biomes, South Africa Biol. Conserv. 40 29 52 CrossRef Google Scholar Hibberd, J.K., Soutberg, T.L. 1991 Roadside reserve condition 1977–1989 in the Southern Tableands of New South Wales Saunders, D.A. Hobbs, R.J. eds. Nature Conservation 2: The Role of Corridors Surrey Beatty & Sons Chipping Norton, NSW, Australia Google Scholar Hilton-Taylor, C., Moll, E. 1986 The Karoo – A Neglected Biome Veld Flora 72 33 36 Google Scholar Hobbs, R.J., Huenneke, L.F. 1992 Disturbancediversity, and invasion: implications for conservation Conserv. Biol. 6 324 337 CrossRef Google Scholar Hoffman, M.T., Cowling, R.M. 1990 Desertification in the Lower Sundays River Valley, South Africa J. Arid Environ. 19 105 117 Google Scholar Lamont, B.R., Whitten, V.A., Witkowski, E.T.F., Rees, R.G., Enright, N.J. 1994 Regional and local (road verge) effects on size and fecundity in Banksia menziesii Aust. J. Ecol. 19 197 205 Google Scholar Low, A.B., Rebelo, A.G. 1996Vegetation of South AfricaLesotho and Swaziland Department of Environmental Affairs and Tourism Pretoria Google Scholar McCune, B., Grace, J.B. 2002Analysis of Ecological Communities MjM Software Design Oregon Google Scholar Milberg, P., Lamont, B.B. 1995 Fire enhanced weed invasion of roadside vegetation in south-western Australia Biol. Conserv. 73 45 49 CrossRef Google Scholar Milton, S.J. 1992 Effects of rainfall, competition and grazing on flowering of Tripteris sinuatum (Asteraceae) in arid Karoo rangeland J. Grassland Soc. S. Afr. 9 158 164 Google Scholar Milton, S.J. 1995 Effects of rainfall, sheep and tehritid flies on seed production of two arid Karoo shrubs in South Africa J. Appl. Ecol. 32 137 144 Google Scholar Milton, S.J., Dean, W.R.J., Kerley, G.I.H. 1992 Tierberg Karoo Research Centre: history, physical environmentflora and fauna Trans. R. Soc. S. Afr. 48 15 46 Google Scholar Milton, S.J., Wiegand, T. 2001 How grazing turns rare seedling recruitment events to non-events in arid environments Breckle, S.W. Veste, M. Wucherer, W. eds. Sustainable Land-Use in Deserts Springer Heidelberg 197 207 Google Scholar Moloney, K.A., Levin, S.A. 1996 The effects of disturbance architecture on landscape level population dynamics Ecology 77 375 394 Google Scholar O’Connor, T.G. 1995 Transformation of a savanna grassland by drought and grazing Afr. J. Range For. Sci. 12 53 60 Google Scholar Todd, S.W., Hoffmann, M.T. 1998 A fence-line contrast reveals effects of heavy grazing on plant diversity and community composition in NamaqualandSouth Africa J. Plant Ecol. 142 169 178 Google Scholar Trombulak, S.C., Frissell, C.A. 2000 Review of ecological effects of roads on terrestrial and aquatic communities Conserv. Biol. 14 18 30 CrossRef Google Scholar Way, J.W. 1977 Roadside verges and conservation in Britain: a review Biol. Conserv. 12 65 74 CrossRef Google Scholar Werger, M.J.A. 1985 The Karoo and southern Kalahari Evenari, M. Noy-Meir, I. Goodall, D.W. eds. Hot Deserts and Arid Shrublands, Vol. 12B. Ecosystems of the World Elsevier Amsterdam 293 Google Scholar Wilson, M.V., Shmida, A. 1984 Measuring Beta diversity with presence absence data J. Ecol. 72 1055 1064 Google Scholar Zar, J.H. 1984Biostatistical Analysis2 Prentice-Hall New Jersey Google Scholar