The interactions between sand, aeolianite and vegetation in a large coastal transgressive dune sheet
Bate, G.C.; Dobkins, G.S. (1992). The interactions between sand, aeolianite and vegetation in a large coastal transgressive dune sheet, in: Carter, R.W.G. et al. Coastal dunes: geomorphology, ecology and management for conservation: Proceedings of the 3rd European Dune Congress Galway, Ireland, 17-21 June 1992. pp. 139-152
In: Carter, R.W.G.; Curtis, T.G.F.; Sheehy-Skeffington, M.J. (Ed.) (1992). Coastal dunes: Geomorphology, ecology and management for conservation: Proceedings of the 3rd European Dune Congress Galway, Ireland, 17-21 June 1992. A.A. Balkema [etc.]: Rotterdam. ISBN 90-5410-058-3. 533 pp., more
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| Abstract |
The Alexandria dunefield is the largest coastal sand sea in South Africa, running for more than 50 km along the coast in Algoa Bay situated on the south east of the country. Vegetation cover is continuous on the landward slipface which is estimated to be moving inland at 0.25 m per year. Within the dunefield, however, the mostly moist sand is largely devoid of vegetation except for a number of bushpockets of different types. Some of these bushpockets are mobile, moving before the advancing slipfaces of transgressive dunes at approximately 1 m per year, while others are fixed, being associated with knolls of aeolianite. Distinctive plant species are associated with these different bushpockets. One plant species, Myrica cordifolia, forms calcareous nodules around its roots. This plant forms a large part of the vegetation which grows before the advancing slipfaces in dell bushpockets and these nodules form an important part of the aeolianite in the dunefield. Other plant species in the dell pockets (Chrysanthemoides monilifera and Rhus crenata) occasionally manage to grow up an advancing slipface and establish themselves at the top of the stoss face. The arrangement of these vegetated patches is very similar to exposed knolls of aeolianite, giving rise to the suggestion that dune aeolianite might be formed in response to plant growth under the conditions which prevail in this dunefield. Evidence for this hypothesis, together with evidence of early habitation of the area by Stone-age Man and their possible involvement in the destabilization of an otherwise moist dunefield, is presented. |
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