Fragmentation of the Albany Thicket Biome: consequences for the biodiversity and health of thicket vegetation
- Authors: Carvalho, Shandon Luke
- Date: 2021-04
- Subjects: Gqeberha (South Africa) , Eastern Cape (South Africa) , Fragmented landscapes
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10948/52344 , vital:43599
- Description: The dense impenetrable vegetation of the Albany Thicket Biome is highly resistant to a wide variety of disturbances but, once disturbed, lacks the regenerative qualities that allow it to return to a stable state. Agricultural development is the main cause of degradation in this biome, creating a landscape consisting of patches of thicket vegetation scattered throughout land cleared for crops or transformed through grazing by domestic livestock. The main objective of this study is to determine the health, status and biodiversity of thicket fragments as it relates to elephant impacts. The level of fragmentation and the remaining extent of intact thicket were investigated as its current status is unknown. The findings suggest that the Thicket Biome is highly fragmented as almost 50% of solid thicket has been cleared, transformed or degraded by agricultural or urban development. For Arid Thicket, the level of fragmentation and the remaining extent of intact thicket could not be determined and both could potentially be greater. For the intact thicket of Dune, Mesic and Valley Thicket types, patch sizes ranged between almost 6 and 876 km2 while the weighted mean was between 2 and 251 km2 . Remote sensing methods (NDVI) were used to determine whether the health of thicket could be remotely assessed. The thicket within and beyond the extent of piospheres around watering holes is subjected to different levels of herbivory. These different levels were compared to corresponding NDVI values with the latter accurately measuring the impact of herbivores along a gradient and providing a method to assess the health of thicket vegetation. Ground surveys of the edge effect, along thicket fragments adjacent to open pastures and separated by cut lines, were conducted. Based on these surveys, the extent of the edge effect was established at a distance of 7 m into thicket fragments separated by cut lines but could not be determined for thicket fragments adjacent to open pastures. Ground surveys were also conducted to assess the health of thicket vegetation exposed to different levels of herbivory, including the impact of elephants (Loxodonta africana). Results showed that different elephant densities produced different levels of impact that could be described in terms of changes in species richness, species diversity, plant height and cover, and growth form composition. Lastly, the findings of the health-based assessments were combined with elephant densities to develop a model that could assess the health of thicket vegetation using a range of ecological variables and relate it to an ideal range of elephant densities. This assessment method was tested at the Addo Elephant National Park and results showed that an elephant density of 1 elephant/km2 would maintain the appropriate diversity, structure and composition of thicket. , Thesis (MSc) -- Faculty of Science, Department of Botany, 2021
- Full Text: false
- Date Issued: 2021-04
- Authors: Carvalho, Shandon Luke
- Date: 2021-04
- Subjects: Gqeberha (South Africa) , Eastern Cape (South Africa) , Fragmented landscapes
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10948/52344 , vital:43599
- Description: The dense impenetrable vegetation of the Albany Thicket Biome is highly resistant to a wide variety of disturbances but, once disturbed, lacks the regenerative qualities that allow it to return to a stable state. Agricultural development is the main cause of degradation in this biome, creating a landscape consisting of patches of thicket vegetation scattered throughout land cleared for crops or transformed through grazing by domestic livestock. The main objective of this study is to determine the health, status and biodiversity of thicket fragments as it relates to elephant impacts. The level of fragmentation and the remaining extent of intact thicket were investigated as its current status is unknown. The findings suggest that the Thicket Biome is highly fragmented as almost 50% of solid thicket has been cleared, transformed or degraded by agricultural or urban development. For Arid Thicket, the level of fragmentation and the remaining extent of intact thicket could not be determined and both could potentially be greater. For the intact thicket of Dune, Mesic and Valley Thicket types, patch sizes ranged between almost 6 and 876 km2 while the weighted mean was between 2 and 251 km2 . Remote sensing methods (NDVI) were used to determine whether the health of thicket could be remotely assessed. The thicket within and beyond the extent of piospheres around watering holes is subjected to different levels of herbivory. These different levels were compared to corresponding NDVI values with the latter accurately measuring the impact of herbivores along a gradient and providing a method to assess the health of thicket vegetation. Ground surveys of the edge effect, along thicket fragments adjacent to open pastures and separated by cut lines, were conducted. Based on these surveys, the extent of the edge effect was established at a distance of 7 m into thicket fragments separated by cut lines but could not be determined for thicket fragments adjacent to open pastures. Ground surveys were also conducted to assess the health of thicket vegetation exposed to different levels of herbivory, including the impact of elephants (Loxodonta africana). Results showed that different elephant densities produced different levels of impact that could be described in terms of changes in species richness, species diversity, plant height and cover, and growth form composition. Lastly, the findings of the health-based assessments were combined with elephant densities to develop a model that could assess the health of thicket vegetation using a range of ecological variables and relate it to an ideal range of elephant densities. This assessment method was tested at the Addo Elephant National Park and results showed that an elephant density of 1 elephant/km2 would maintain the appropriate diversity, structure and composition of thicket. , Thesis (MSc) -- Faculty of Science, Department of Botany, 2021
- Full Text: false
- Date Issued: 2021-04
The association of the bushclumps of Calcrete Bontveld with adjacent thicket
- Authors: Carvalho, Shandon Luke
- Date: 2018
- Subjects: Plant ecology -- South Africa -- Eastern Cape , Biodiversity conservation Landscape ecology -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/21949 , vital:29806
- Description: 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.
- Full Text:
- Date Issued: 2018
- Authors: Carvalho, Shandon Luke
- Date: 2018
- Subjects: Plant ecology -- South Africa -- Eastern Cape , Biodiversity conservation Landscape ecology -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/21949 , vital:29806
- Description: 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.
- Full Text:
- Date Issued: 2018
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