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Nelson Mandela University (2018)

The association of the bushclumps of Calcrete Bontveld with adjacent thicket

Carvalho, Shandon Luke

Titre : The association of the bushclumps of Calcrete Bontveld with adjacent thicket

Auteur : Carvalho, Shandon Luke

Université de soutenance : Nelson Mandela University

Grade : Magister Scientiae 2018

Résumé
The thicket mosaic vegetation type known as Calcrete Bontveld is now only found at three sites within the Eastern Cape Province. Consisting of thicket-like bushclumps scattered among grassy dwarf shrubland, this vegetation is isolated from other systems due to its unique geographical location and the surrounding Valley Thicket. A strong similarity between the bushclumps of Calcrete Bontveld and the adjacent Valley Thicket has led to the aim of this study, which was to demonstrate that an association exists between these two vegetation types. To investigate this, two sites, namely Grassridge (natural vegetation on a mine) and Shamwari (natural due to its status as a reserve), were selected. This provided a unique comparison of the functionality of the two vegetation types and identified key processes responsible for the existence of this association. In terms of edaphic variables, soil organic content and field capacity, values were similar between bushclumps and thicket while soil depth was the greatest in thicket at both sites. At both sites, life forms, diversity and similarity indices were similar for bushclumps and thicket. By utilizing the Island Biogeography Theory, these bushclumps show an island-type origin and the distance between them and the adjacent Valley Thicket (mainland-type), as well as their size, influenced the association between the two vegetation types. Commonality of species between thicket and bushclumps are postulated to be tied to their dispersal mechanisms and fruit types. Bushclump isolation on flat-topped ridges excluded thicket species dispersed by autochory and anemochory. Zoochorous dispersal (by birds and mammals) was the common factor in the transfer of species between thicket and bushclumps as the latter is a large resource patch for fauna. The size of the bushclumps and their distance from the thicket influenced zoochorous dispersal. Larger and closer bushclumps attracted more birds and mammals than the small or more distant ones. These effects differ at the two sites due to the complex animal interaction that occurs in the Shamwari Game Reserve as opposed to the reduced animal interaction at Grassridge. This study suggests that an association exists between the bushclumps of Calcrete Bontveld and the adjacent Valley Thicket, and is reliant on the natural zoochory that occurs at each site.

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