Doctoral Degrees (Plant Sciences)

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Browsing Doctoral Degrees (Plant Sciences) by Subject "Acacia -- Africa, Southern"

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    Interpretation of the Acacia karroo class, southern Africa
    (University of the Free State, 2008-05) Dingaan, Mamokete Nthabiseng Vivian; Du Preez, P. J.; Bredenkamp, G. J.
    English: Acacia karroo is an ecologically important and one of the most widespread species in South Africa. There has been an opinion that Acacia karroo-dominated vegetation, especially that along river banks, should be classified under one class, and that a comprehensive syntaxonomic review of Acacia karroo-dominated syntaxa is needed. The present study was hence initiated with the aim of providing more insight into the syntaxonomic status of all the previously described Acacia karroo syntaxa. A total of 1 553 relevés and 2 006 species from 60 phytosociological studies were hierarchically classified according to Braun-Blanquet procedures. TURBOVEG was used for the input, processing, and presentation of phytosociological data. MEGATAB was used to first construct the phytosociological and synoptic tables. TWINSPAN was applied to the floristic data as a first approximation, after which Braun-Blanquet procedures were used to refine the classification. The result of the classification process was a suggested Acacia karroo Class differentiated into the following six orders: i) Cyperus longus – Asparagus laricinus Order associated with rivers and streams in the northern Free State. The species composition of this vegetation type indicates that it could represent a transformed Hemarthria altissima Class (Du Prezz & Bredenkamp 1991) brought about by degradation and disturbance, and the subsequent encroachment by Acacia karroo. ii) Achyranthes aspera – Diospyros lycioides Order represents riparian vegetation of the northern, central, and southern Free State. It mostly occurs on the well developed banks along the rivers, streams, and drainage lines, but can also be found on clayey soils on the floodplains adjacent to the rivers. iii) Felicia filifolia – Tragus koelerioides Order represents false karoid vegetation of the mountains, hills, ridges and valleys of the Graaff-Reinet and Cradock areas in the Eastern Cape, and Beaufort West in the Western Cape. iv) Rhus ciliata – Rhus lancea Order represents false karroid vegetation of the southern Free State and is mainly associated with undulating plains and gentle slopes. v) Acacia mellifera - Eragrostis lehmanniana Order represents vegetation of the Kalahari thornveld found in northwestern Free State, northeastern Northern Cape, as well as southern and central North-West. vi) Teucrium trifidum – Themeda triandra Order is found in northern Free State, in the eastern part of North-West, and also in eastern and western Gauteng, as well as in western Mpumalanga. It occurs in kloofs and sheltered valleys, and also on mountain slopes It is also encountered on bottomlands and footslopes with deep clayey soils. vii) Acacietalia karroo (Eckhardt, Van Rooyen & Bredenkamp 1997) represents vegetation of the crests, slopes and footslopes of hills in central-northern KwaZulu-Natal but it is also encountered in the incised river valleys in southern KwaZulu-Natal. The Acacia karroo Class is further differentiated into ten sub-orders, forty alliances, 110 associations, and 39 sub-associations. All communities were described and ecologically interpreted.