Exploring the role of herbivory in Albany Subtropical Thicket restoration
- Authors: Hunt, Kristen Louise
- Date: 2024-04
- Subjects: Shrubs -- South Africa , Portulacaria afra -- South Africa , Grasslands -- South Africa , Plant communities -- South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/64060 , vital:73647
- Description: This dissertation attempted to investigate the influence of herbivory on the success of thicket restoration, addressing a critical gap in the current knowledge within the restoration initiative. Despite two decades of thicket restoration practices, the role of herbivory in influencing restoration success has been assumed and not yet quantified. This research aimed to observe and identify herbivore species and their interactions that may affect the survival of Portulacaria afra Jacq. material planted in thicket restoration contexts. This research took place on three game farms serving as case studies within the Albany Subtropical Thicket (Eastern Cape, South Africa). Multiple experiments were conducted to assess how the concept of different “natural refugia” might impact herbivore interactions with planted material, incorporating factors such as planting around rainfall, within open and semi-intact vegetation patches, and in proximity to water sources. Trail cameras were used for real-time monitoring of herbivore interactions within planted sites to understand and quantify herbivore interactions with P. afra cuttings and how they may impact plant survival. Results from the trail camera monitoring (Chapter 2) indicate varied herbivore interactions occurring on planted material, with the primary herbivore responsible for these interactions varying among farms. Species interactions were not consistent across farms, and herbivore interactions exhibited spatial and temporal variability. Notably, interactions declined soon after the start of the wet phase when surrounding vegetation could recover, indicating the influences of alternative forage availability on herbivore foraging choices. Different herbivore interactions were identified and quantified through trail camera images, ranging from minor biomass removal (estimated at <5 cm of stem and leaf material) to more detrimental actions such as uprooting and leaf stripping. Consistently, planted P. afra survival rates (Chapter 3) were significantly higher for protected material than those exposed to herbivores, regardless of whether planted in a dry or wet phase. Moreover, when exposed to herbivores, rooted material had significantly higher survival rates than unrooted material, indicating the potential advantage of a well-developed root system in faster recovery after a herbivory event. This research explored the influence of various factors, including rainfall, rooting state, protection, surrounding vegetation, and proximity to water, on P. afra survival and how some of these factors may affect P. afra survival in relation to herbivore interactions (Chapter 3). Significant differences in cutting survival were observed between dry and wet phases, rooted and unrooted material, and material protected vs exposed to herbivores. While survival was not significantly different in experiments involving surrounding vegetation and proximity to water, potential patterns were identified, warranting further investigation. A clipping and defoliation experiment under simulated seasonal conditions emphasised the significance of , Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 2024
- Full Text:
- Date Issued: 2024-04
- Authors: Hunt, Kristen Louise
- Date: 2024-04
- Subjects: Shrubs -- South Africa , Portulacaria afra -- South Africa , Grasslands -- South Africa , Plant communities -- South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/64060 , vital:73647
- Description: This dissertation attempted to investigate the influence of herbivory on the success of thicket restoration, addressing a critical gap in the current knowledge within the restoration initiative. Despite two decades of thicket restoration practices, the role of herbivory in influencing restoration success has been assumed and not yet quantified. This research aimed to observe and identify herbivore species and their interactions that may affect the survival of Portulacaria afra Jacq. material planted in thicket restoration contexts. This research took place on three game farms serving as case studies within the Albany Subtropical Thicket (Eastern Cape, South Africa). Multiple experiments were conducted to assess how the concept of different “natural refugia” might impact herbivore interactions with planted material, incorporating factors such as planting around rainfall, within open and semi-intact vegetation patches, and in proximity to water sources. Trail cameras were used for real-time monitoring of herbivore interactions within planted sites to understand and quantify herbivore interactions with P. afra cuttings and how they may impact plant survival. Results from the trail camera monitoring (Chapter 2) indicate varied herbivore interactions occurring on planted material, with the primary herbivore responsible for these interactions varying among farms. Species interactions were not consistent across farms, and herbivore interactions exhibited spatial and temporal variability. Notably, interactions declined soon after the start of the wet phase when surrounding vegetation could recover, indicating the influences of alternative forage availability on herbivore foraging choices. Different herbivore interactions were identified and quantified through trail camera images, ranging from minor biomass removal (estimated at <5 cm of stem and leaf material) to more detrimental actions such as uprooting and leaf stripping. Consistently, planted P. afra survival rates (Chapter 3) were significantly higher for protected material than those exposed to herbivores, regardless of whether planted in a dry or wet phase. Moreover, when exposed to herbivores, rooted material had significantly higher survival rates than unrooted material, indicating the potential advantage of a well-developed root system in faster recovery after a herbivory event. This research explored the influence of various factors, including rainfall, rooting state, protection, surrounding vegetation, and proximity to water, on P. afra survival and how some of these factors may affect P. afra survival in relation to herbivore interactions (Chapter 3). Significant differences in cutting survival were observed between dry and wet phases, rooted and unrooted material, and material protected vs exposed to herbivores. While survival was not significantly different in experiments involving surrounding vegetation and proximity to water, potential patterns were identified, warranting further investigation. A clipping and defoliation experiment under simulated seasonal conditions emphasised the significance of , Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 2024
- Full Text:
- Date Issued: 2024-04
The influence of soil properties on the growth and distribution of Portulacaria Afra in subtropical thicket, South Africa
- Authors: Becker, Carina Helene
- Date: 2013
- Subjects: Portulacaria afra -- South Africa , Plant conservation -- South Africa , Shrubs -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10753 , http://hdl.handle.net/10948/d1013046
- Description: Subtropical Thicket is the dominant vegetation biome in the Eastern Cape, and extends through to parts of the Western Cape. It is dominated by Portulacaria afra (spekboom), a woody succulent plant recognised for its importance as an ecosystem engineer and its carbon sequestration potential. Due to excessive grazing from domestic stock, spekboom has been completely removed from some areas. The Subtropical Thicket Restoration Programme (STRP) initiated a large scale restoration programme of planting spekboom cuttings in these degraded areas. Their efforts have been met with varying levels of success and improvement of the programme relies on continuous monitoring and scientific evaluation. I investigated the influence of selected soil properties on spekboom growth, mortality and landscape distribution, at both restoration sites and natural intact areas, and through experiments. Site or location was the most important factor influencing spekboom success at restoration plots, whereby sites in the eastern end of spekboom distribution perform better. Moving westwards slope orientation emerged as an important factor, whereby north facing slopes are preferred by spekboom. Although high levels of soil salinity (NaCl) restricted spekboom growth and affected its health, it could tolerate the levels it was exposed too. Soil pH, above 7, and phosphorous concentration, above 70 mg.kg-1, were the only limiting factors to spekboom survival found in the restoration sites. This preference for acidic soils was mirrored in intact Thicket. However in general, soil is not a major factor influencing spekboom growth and distribution, and spekboom is tolerant of a wide range of soil conditions. Spekbooms constraint is most likely a function of climate, which varies greatly across the biome. This study answered some vital questions regarding the possible influence of soil in spekboom growth and distribution. It disapproved the theory that a catena effect may be responsible for the lack of spekboom growing in bottomland areas. The study also indicates and supports the versatility of spekboom as a plant for restoring degraded lands across a range of different geologies and soil types. To maximise spekboom survival rates, restoration efforts should be focussed towards the eastern end of its distribution and to avoid planting in soils with pH levels higher than 7.
- Full Text:
- Date Issued: 2013
- Authors: Becker, Carina Helene
- Date: 2013
- Subjects: Portulacaria afra -- South Africa , Plant conservation -- South Africa , Shrubs -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10753 , http://hdl.handle.net/10948/d1013046
- Description: Subtropical Thicket is the dominant vegetation biome in the Eastern Cape, and extends through to parts of the Western Cape. It is dominated by Portulacaria afra (spekboom), a woody succulent plant recognised for its importance as an ecosystem engineer and its carbon sequestration potential. Due to excessive grazing from domestic stock, spekboom has been completely removed from some areas. The Subtropical Thicket Restoration Programme (STRP) initiated a large scale restoration programme of planting spekboom cuttings in these degraded areas. Their efforts have been met with varying levels of success and improvement of the programme relies on continuous monitoring and scientific evaluation. I investigated the influence of selected soil properties on spekboom growth, mortality and landscape distribution, at both restoration sites and natural intact areas, and through experiments. Site or location was the most important factor influencing spekboom success at restoration plots, whereby sites in the eastern end of spekboom distribution perform better. Moving westwards slope orientation emerged as an important factor, whereby north facing slopes are preferred by spekboom. Although high levels of soil salinity (NaCl) restricted spekboom growth and affected its health, it could tolerate the levels it was exposed too. Soil pH, above 7, and phosphorous concentration, above 70 mg.kg-1, were the only limiting factors to spekboom survival found in the restoration sites. This preference for acidic soils was mirrored in intact Thicket. However in general, soil is not a major factor influencing spekboom growth and distribution, and spekboom is tolerant of a wide range of soil conditions. Spekbooms constraint is most likely a function of climate, which varies greatly across the biome. This study answered some vital questions regarding the possible influence of soil in spekboom growth and distribution. It disapproved the theory that a catena effect may be responsible for the lack of spekboom growing in bottomland areas. The study also indicates and supports the versatility of spekboom as a plant for restoring degraded lands across a range of different geologies and soil types. To maximise spekboom survival rates, restoration efforts should be focussed towards the eastern end of its distribution and to avoid planting in soils with pH levels higher than 7.
- Full Text:
- Date Issued: 2013
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