Some properties of a model F1 layer of the ionosphere
- Authors: De Jager, Gerhard
- Date: 1963
- Subjects: Ionosphere , Ionospheric electron density
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5515 , http://hdl.handle.net/10962/d1011046 , Ionosphere , Ionospheric electron density
- Description: The present work was initially aimed at providing an explanation for some of the phenomena that occur in the ionosphere at sunrise. The approach that was taken was to determine the changes that take place on a theoretical model of the ionosphere and then to compare these with observations. A prerequisite for this approach was a theoretical model that would show, among other things, a bifurcation of the F layer during daytime without making unjustified arbitrary assumptions. The absence of such a model, particularly as far as non-equilibrium conditions are concerned, resulted in the present attempt to provide such a model for the F1 region.
- Full Text:
- Date Issued: 1963
- Authors: De Jager, Gerhard
- Date: 1963
- Subjects: Ionosphere , Ionospheric electron density
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5515 , http://hdl.handle.net/10962/d1011046 , Ionosphere , Ionospheric electron density
- Description: The present work was initially aimed at providing an explanation for some of the phenomena that occur in the ionosphere at sunrise. The approach that was taken was to determine the changes that take place on a theoretical model of the ionosphere and then to compare these with observations. A prerequisite for this approach was a theoretical model that would show, among other things, a bifurcation of the F layer during daytime without making unjustified arbitrary assumptions. The absence of such a model, particularly as far as non-equilibrium conditions are concerned, resulted in the present attempt to provide such a model for the F1 region.
- Full Text:
- Date Issued: 1963
Photosynthetic and growth responses of C3 and C4 grasses to short- duration sunflecks and resultant consequences for their performance in understory environments
- Authors: Adams, Claire Elizabeth
- Date: 2017
- Subjects: Understory plants -- Effect of light on , Grasses -- Effect of light on -- South Africa , Erharta -- Effect of light on , Brachiara -- Effect of light on
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/5016 , vital:20753
- Description: Low C4 grass species abundance in understory environments is thought to be as a result of their high-light requirements, lack of photosynthetic advantage relative to C3 species in cooler environments, and an inability to adequately utilise sunflecks. This study sets out to investigate this theory, hypothesizing that C3 grass species outperform C4 grass species under the canopy, not as a result of quantum efficiency temperature effects, but as a result of C4 species inability to utilize short-duration sunflecks. Short sunflecks could result in a breakdown in assimilate movement between the mesophyll (MSC) and bundle sheath (BSC) cells. The role of BSC leakiness, stomata and PSII efficiency on the ability of C3 and C4 Alloteropsis semialata to utilize short-duration sunflecks was investigated using gaseous exchange and chlorophyll fluorescence techniques, while the growth of both subspecies under a simulated flecking-light environment tested whether these measured responses translated into effects on growth. As C3 grasses are known to possess higher levels of stomatal conductance in relation to C4 species, results showed that C3 A. semialata was able to utilize short-duration sunflecks as a result of increased stomatal conductance and an ability to induce photosynthesis under various light flecking conditions. In contrast, C4 A. semialata was unable to utilize sunflecks possibly as a result of energetic limitations of the carboxylation mechanism (PSII) and not because of increased bundle sheath leakiness. These photosynthetic responses translated into growth differences when both types were grown in an artificially flecking light environment. The photosynthetic differences noted for C3 and C4 A.semialata were also evident in shade adapted understory grasses; Erharta erecta (C3), Dactylotenium australe (C4) and Brachiaria chusqueoides (C4). As photosynthetic induction was marginally more rapid in all species relative to A. semialata it suggests some degree of adaptation in shade grasses, however the inability of the C4 species to utilise short sunflecks remained. As a result, it was hypothesized that C3 shade adapted E. erecta and C4 B. chusqueoides, co-inhabiting the same forest understory, are able to do so because of differences in light micro-environments associated with each species. However, canopy openness and light profiles determined for theses micro-climates showed no differences and that both species have persisted within a relatively stable understory environment. The coexistence was possible as the understory was supplied with a significant proportion of its daily light in flecks sufficiently long as to not compromise C4 productivity. A survey of 10 species of grasses under various canopy densities and in the open showed a strong negative linear relationship between canopy openness and the rate at which photosynthesis was induced by flecking light, which has not been shown before. This did not result from the phylogenetic relationship between species and could be shown for a single species (E. erecta) growing in a range of light environments. This demonstrates that C4 grasses, despite adaptation, would be limited from sunfleck environments if a significant proportion of the daily light available consists of flecks of short-duration. The generation of such environments may occur as a result of woody thickening and could help explain the observed decline in C4 grasses under these conditions.
- Full Text:
- Date Issued: 2017
- Authors: Adams, Claire Elizabeth
- Date: 2017
- Subjects: Understory plants -- Effect of light on , Grasses -- Effect of light on -- South Africa , Erharta -- Effect of light on , Brachiara -- Effect of light on
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/5016 , vital:20753
- Description: Low C4 grass species abundance in understory environments is thought to be as a result of their high-light requirements, lack of photosynthetic advantage relative to C3 species in cooler environments, and an inability to adequately utilise sunflecks. This study sets out to investigate this theory, hypothesizing that C3 grass species outperform C4 grass species under the canopy, not as a result of quantum efficiency temperature effects, but as a result of C4 species inability to utilize short-duration sunflecks. Short sunflecks could result in a breakdown in assimilate movement between the mesophyll (MSC) and bundle sheath (BSC) cells. The role of BSC leakiness, stomata and PSII efficiency on the ability of C3 and C4 Alloteropsis semialata to utilize short-duration sunflecks was investigated using gaseous exchange and chlorophyll fluorescence techniques, while the growth of both subspecies under a simulated flecking-light environment tested whether these measured responses translated into effects on growth. As C3 grasses are known to possess higher levels of stomatal conductance in relation to C4 species, results showed that C3 A. semialata was able to utilize short-duration sunflecks as a result of increased stomatal conductance and an ability to induce photosynthesis under various light flecking conditions. In contrast, C4 A. semialata was unable to utilize sunflecks possibly as a result of energetic limitations of the carboxylation mechanism (PSII) and not because of increased bundle sheath leakiness. These photosynthetic responses translated into growth differences when both types were grown in an artificially flecking light environment. The photosynthetic differences noted for C3 and C4 A.semialata were also evident in shade adapted understory grasses; Erharta erecta (C3), Dactylotenium australe (C4) and Brachiaria chusqueoides (C4). As photosynthetic induction was marginally more rapid in all species relative to A. semialata it suggests some degree of adaptation in shade grasses, however the inability of the C4 species to utilise short sunflecks remained. As a result, it was hypothesized that C3 shade adapted E. erecta and C4 B. chusqueoides, co-inhabiting the same forest understory, are able to do so because of differences in light micro-environments associated with each species. However, canopy openness and light profiles determined for theses micro-climates showed no differences and that both species have persisted within a relatively stable understory environment. The coexistence was possible as the understory was supplied with a significant proportion of its daily light in flecks sufficiently long as to not compromise C4 productivity. A survey of 10 species of grasses under various canopy densities and in the open showed a strong negative linear relationship between canopy openness and the rate at which photosynthesis was induced by flecking light, which has not been shown before. This did not result from the phylogenetic relationship between species and could be shown for a single species (E. erecta) growing in a range of light environments. This demonstrates that C4 grasses, despite adaptation, would be limited from sunfleck environments if a significant proportion of the daily light available consists of flecks of short-duration. The generation of such environments may occur as a result of woody thickening and could help explain the observed decline in C4 grasses under these conditions.
- Full Text:
- Date Issued: 2017
Developing a citizen technician based approach to suspended sediment monitoring in the Tsitsa River catchment, Eastern Cape, South Africa
- Authors: Bannatyne, Laura Joan
- Date: 2018
- Subjects: Sediments (Geology) -- Management , Sediments (Geology) -- South Africa -- Eastern Cape , Watersheds -- South Africa -- Eastern Cape , Suspended sediments -- South Africa -- Eastern Cape , Suspended sediments -- Monitoring -- Citizen participation , Tsitsa River
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/62593 , vital:28211
- Description: Suspended sediment (SS) in channels is spatiotemporally heterogeneous and, over the long term, is known to be moved predominantly by flood flows with return periods of ~1 - 1.5 years. Flood flows in the Tsitsa catchment (Eastern Cape Province, South Africa) are unpredictable, and display a wide range of discharges. Direct, flood-focused SS sampling at sub-catchment scale was required to provide a SS baseline against which to monitor the impact on SS of catchment rehabilitation interventions, to determine the relative contributions of sub-catchments to SS loads and yields at the site of the proposed Ntabelanga Dam wall, and to verify modelled SS baselines, loads and yields. Approaches to SS sampling relying on researcher presence and/or installed equipment to adequately monitor SS through flood flows were precluded by cost, and the physical and socioeconomic conditions in the project area. A citizen technician (CT)-based flood-focused approach to direct SS sampling was developed and implemented. It was assessed in terms of its efficiency and effectiveness, the proficiency of the laboratory analysis methods, and the accuracy of the resulting SS data. A basic laboratory protocol for SSC analysis was developed, but is not the focus of this thesis. Using basic sampling equipment and smartphone-based reporting protocols, local residents at eleven points on the Tsitsa River and its major tributaries were employed as CTs. They were paid to take water samples during daylight hours at sub-daily timestep, with the emphasis on sampling through flood flows. The method was innovative in that it opted for manual sampling against a global trend towards instrumentation. Whilst the management of CTs formed a significant project component, the CTs benefitted directly through remuneration and work experience opportunities. The sampling method was evaluated at four sites from December 2015 - May 2016. The CTs were found to have efficiently and effectively sampled SS through a range of water levels, particularly in the main Tsitsa channel. An acceptable level of proficiency and accuracy was achieved, and many flood events were successfully defined by multiple data points. The method was chiefly limited by the inability of CTs to sample overnight rises and peaks occurring as a result of afternoon thunderstorms, particularly in small tributaries. The laboratory process was responsible for some losses in proficiency and accuracy. Improved laboratory quality control was therefore recommended. The CT-based approach can be adapted to other spatial and temporal scales in other areas, and to other environmental monitoring applications.
- Full Text:
- Date Issued: 2018
- Authors: Bannatyne, Laura Joan
- Date: 2018
- Subjects: Sediments (Geology) -- Management , Sediments (Geology) -- South Africa -- Eastern Cape , Watersheds -- South Africa -- Eastern Cape , Suspended sediments -- South Africa -- Eastern Cape , Suspended sediments -- Monitoring -- Citizen participation , Tsitsa River
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/62593 , vital:28211
- Description: Suspended sediment (SS) in channels is spatiotemporally heterogeneous and, over the long term, is known to be moved predominantly by flood flows with return periods of ~1 - 1.5 years. Flood flows in the Tsitsa catchment (Eastern Cape Province, South Africa) are unpredictable, and display a wide range of discharges. Direct, flood-focused SS sampling at sub-catchment scale was required to provide a SS baseline against which to monitor the impact on SS of catchment rehabilitation interventions, to determine the relative contributions of sub-catchments to SS loads and yields at the site of the proposed Ntabelanga Dam wall, and to verify modelled SS baselines, loads and yields. Approaches to SS sampling relying on researcher presence and/or installed equipment to adequately monitor SS through flood flows were precluded by cost, and the physical and socioeconomic conditions in the project area. A citizen technician (CT)-based flood-focused approach to direct SS sampling was developed and implemented. It was assessed in terms of its efficiency and effectiveness, the proficiency of the laboratory analysis methods, and the accuracy of the resulting SS data. A basic laboratory protocol for SSC analysis was developed, but is not the focus of this thesis. Using basic sampling equipment and smartphone-based reporting protocols, local residents at eleven points on the Tsitsa River and its major tributaries were employed as CTs. They were paid to take water samples during daylight hours at sub-daily timestep, with the emphasis on sampling through flood flows. The method was innovative in that it opted for manual sampling against a global trend towards instrumentation. Whilst the management of CTs formed a significant project component, the CTs benefitted directly through remuneration and work experience opportunities. The sampling method was evaluated at four sites from December 2015 - May 2016. The CTs were found to have efficiently and effectively sampled SS through a range of water levels, particularly in the main Tsitsa channel. An acceptable level of proficiency and accuracy was achieved, and many flood events were successfully defined by multiple data points. The method was chiefly limited by the inability of CTs to sample overnight rises and peaks occurring as a result of afternoon thunderstorms, particularly in small tributaries. The laboratory process was responsible for some losses in proficiency and accuracy. Improved laboratory quality control was therefore recommended. The CT-based approach can be adapted to other spatial and temporal scales in other areas, and to other environmental monitoring applications.
- Full Text:
- Date Issued: 2018
How do urban dwellers identify with features within urban green spaces in the Eastern Cape?
- Authors: Manyani, Amanda
- Date: 2019
- Subjects: Land use, Urban -- South Africa , Greenbelts -- South Africa , City planning -- South Africa
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/95596 , vital:31174
- Description: Public urban green spaces contain natural and artificial features which play crucial roles in supporting urban social-ecological systems, a fact now recognized globally. The various natural and artificial features contained in public urban green spaces are said to be key contributors to the quality of life and well-being of urban dwellers. Nevertheless, this has been largely ignored in urban design in South Africa, especially in the poorer township and Reconstruction Development Program (RDP) areas. At the individual household and community levels within the poorer communities, the provision of green spaces and trees, as well as recreation facilities, is well below world standards, and much less than what is available in the more affluent areas of South African towns. Additionally, most research on the links between nature and human well-being in urban contexts comes from developed world contexts which adopt a westernized view of the relationship. Yet, in many societies of the Global South, including South Africa, worldviews and experiences of nature in green spaces and use of other recreational features takes on different meanings to those of the Global North. To show these differences, a combination of methods was used in this study, different types of green spaces were assessed and evaluated by structured observations so as to record the features present within the spaces. A survey of 360 households was conducted by targeting green space users and households within 100 metres from a green space. Results indicated that, across all the green space types, formal green spaces had a low cover of shrubs, trees and herbs whilst having high lawn cover. Furthermore, vegetation had poor rating across all the green spaces since the vegetation was either overgrown herbs, dense thickets of shrubs and mostly alien trees that were either diseased or forked. Similar to the disparity in the composition and structure of vegetation within the green spaces, there was a wide variability in the composition of recreational features and amenities across the green spaces. The formal green spaces had the most amenities like play equipment, shelter and seating. Informal green spaces and commonages had little or no recreational features available. The attributes of these spaces therefore influenced the reasons for visiting as more than 90 % of the respondents simply used the spaces for transit. With regards to attitudes and preferences towards particular features, they were emerging sense of strong negative feelings towards natural features. Most respondents emphasized the need for green spaces that are well laid out with maintained lawns, recreational facilities and open vegetation. Thus, the current design and available features within the studied urban green spaces do not meet local needs and aspirations and thus do not contribute to better well-being and quality of life as much as they could. Specifically, the various health benefits linked with being in contact with nature in the public green spaces were not evident in this study. The South African specific context in green space use, perception and people’s preferences is thus crucial for urban planning and sustainability.
- Full Text:
- Date Issued: 2019
- Authors: Manyani, Amanda
- Date: 2019
- Subjects: Land use, Urban -- South Africa , Greenbelts -- South Africa , City planning -- South Africa
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/95596 , vital:31174
- Description: Public urban green spaces contain natural and artificial features which play crucial roles in supporting urban social-ecological systems, a fact now recognized globally. The various natural and artificial features contained in public urban green spaces are said to be key contributors to the quality of life and well-being of urban dwellers. Nevertheless, this has been largely ignored in urban design in South Africa, especially in the poorer township and Reconstruction Development Program (RDP) areas. At the individual household and community levels within the poorer communities, the provision of green spaces and trees, as well as recreation facilities, is well below world standards, and much less than what is available in the more affluent areas of South African towns. Additionally, most research on the links between nature and human well-being in urban contexts comes from developed world contexts which adopt a westernized view of the relationship. Yet, in many societies of the Global South, including South Africa, worldviews and experiences of nature in green spaces and use of other recreational features takes on different meanings to those of the Global North. To show these differences, a combination of methods was used in this study, different types of green spaces were assessed and evaluated by structured observations so as to record the features present within the spaces. A survey of 360 households was conducted by targeting green space users and households within 100 metres from a green space. Results indicated that, across all the green space types, formal green spaces had a low cover of shrubs, trees and herbs whilst having high lawn cover. Furthermore, vegetation had poor rating across all the green spaces since the vegetation was either overgrown herbs, dense thickets of shrubs and mostly alien trees that were either diseased or forked. Similar to the disparity in the composition and structure of vegetation within the green spaces, there was a wide variability in the composition of recreational features and amenities across the green spaces. The formal green spaces had the most amenities like play equipment, shelter and seating. Informal green spaces and commonages had little or no recreational features available. The attributes of these spaces therefore influenced the reasons for visiting as more than 90 % of the respondents simply used the spaces for transit. With regards to attitudes and preferences towards particular features, they were emerging sense of strong negative feelings towards natural features. Most respondents emphasized the need for green spaces that are well laid out with maintained lawns, recreational facilities and open vegetation. Thus, the current design and available features within the studied urban green spaces do not meet local needs and aspirations and thus do not contribute to better well-being and quality of life as much as they could. Specifically, the various health benefits linked with being in contact with nature in the public green spaces were not evident in this study. The South African specific context in green space use, perception and people’s preferences is thus crucial for urban planning and sustainability.
- Full Text:
- Date Issued: 2019
Post-release evaluation of Megamelus scutellaris Berg. (hemiptera: delphacidae): a biological control agent of water hyacinth Eichhornia crassipes (Mart.) Solms-Laub (Pontederiaceae) in South Africa
- Authors: Miller, Benjamin Erich
- Date: 2019
- Subjects: Megamelus scutellaris Berg. , Delphacidae , Noxious weeds -- Biological control -- South Africa , Aquatic weeds -- Biological control -- South Africa , Water hyacinth -- Biological control -- South Africa , Biological pest control agents
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/92330 , vital:30710
- Description: Water hyacinth, Eichhornia crassipes (Mart.) Solms-Laub. (Pontederiaceae) is a free-floating aquatic macrophyte from South America that was introduced to South Africa in the 1900s for its attractive ornamental flowers. The plant was classified as a serious invader in the country in the 1970s, eventually becoming the worst invasive aquatic plant in South Africa. Biological control is widely regarded as the most effective method of managing water hyacinth, as it is ecologically safe, cost-effective, and self-sustaining. To date, nine biological control agents have been released in South Africa against water hyacinth, including eight arthropods and a pathogen. Due to the cumulative effects of highly eutrophic waterbodies, which mitigate the damage caused by biological control, and the cold winters which inhibit the rate of biological control agent population build up, South Africa currently has more biological control agents released on water hyacinth than anywhere else in the world. The need for a cold-tolerant agent that can reproduce and develop quickly, while still being damaging to water hyacinth in eutrophic systems, led to the introduction of the most recently released water hyacinth biological control agent, the planthopper Megamelus scutellaris Berg (Hemiptera: Delphacidae), which was initially collected from Argentina. This thesis formed the first post-release evaluation of M. scutellaris since its release in South Africa in 2013. It included a greenhouse experiment to measure the agent’s feeding damage in relation to different nutrient levels and stocking rates, as well as a field component to evaluate both the post-winter recovery of M. scutellaris, and a nationwide survey to measure the establishment of the agent around the country in relation to climate, water quality, and plant health. In the greenhouse experiment, the feeding damage was quantified using measurements of plant growth parameters and chlorophyll fluorometry. It was found that, like other biological control agents of water hyacinth, M. scutellaris was most damaging when released in high numbers on plants grown at medium nutrient levels, and less effective on plants grown at elevated nutrient levels. A water hyacinth infestation on the Kubusi River was selected for the evaluation of the post-winter recovery of M. scutellaris. The Kubusi River is both the first site where M. scutellaris was released, and the coldest site where water hyacinth biological control agents have established successfully in South Africa. Monthly visits tracking seasonal plant health characteristics and agent population densities indicated that the populations of M. scutellaris were impacted most significantly by the season. Low temperatures led to the water hyacinth plants being of poor quality during the winter, which had a subsequent negative effect on the agent populations. The agents could only fully recover by late summer, which meant that the plants were without any significant biological control through the initial phases of the growing season, when they were most vulnerable, and a significant lag-phase occurred between the recovery of the plants and the recovery of the agent population after the winter bottleneck. A survey of all sites where M. scutellaris had been released in South Africa yielded 16 sites where the agents had successfully established, having survived at least one full winter. Among these sites were four sites where the agents were found without them having been released, indicating that they can disperse unaided to new sites. The temperature was a major factor responsible for the success or failure of establishment, with very few agents surviving in the hot areas of South Africa or in areas with a high frost incidence. The density of M. scutellaris was higher in nutrient-rich water, and on plants with more leaves, suggesting that the quality of the plants also contributed to establishment. The results of this thesis showed that M. scutellaris is able to establish successfully in South Africa, and that the agents are capable of causing significant damage to water hyacinth, making it a promising addition to the biological control programme. Novel methods of measuring subtle insect feeding damage in plants and quantifying agent populations are also discussed, along with suggestions for the future implementation of M. scutellaris in South Africa.
- Full Text:
- Date Issued: 2019
- Authors: Miller, Benjamin Erich
- Date: 2019
- Subjects: Megamelus scutellaris Berg. , Delphacidae , Noxious weeds -- Biological control -- South Africa , Aquatic weeds -- Biological control -- South Africa , Water hyacinth -- Biological control -- South Africa , Biological pest control agents
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/92330 , vital:30710
- Description: Water hyacinth, Eichhornia crassipes (Mart.) Solms-Laub. (Pontederiaceae) is a free-floating aquatic macrophyte from South America that was introduced to South Africa in the 1900s for its attractive ornamental flowers. The plant was classified as a serious invader in the country in the 1970s, eventually becoming the worst invasive aquatic plant in South Africa. Biological control is widely regarded as the most effective method of managing water hyacinth, as it is ecologically safe, cost-effective, and self-sustaining. To date, nine biological control agents have been released in South Africa against water hyacinth, including eight arthropods and a pathogen. Due to the cumulative effects of highly eutrophic waterbodies, which mitigate the damage caused by biological control, and the cold winters which inhibit the rate of biological control agent population build up, South Africa currently has more biological control agents released on water hyacinth than anywhere else in the world. The need for a cold-tolerant agent that can reproduce and develop quickly, while still being damaging to water hyacinth in eutrophic systems, led to the introduction of the most recently released water hyacinth biological control agent, the planthopper Megamelus scutellaris Berg (Hemiptera: Delphacidae), which was initially collected from Argentina. This thesis formed the first post-release evaluation of M. scutellaris since its release in South Africa in 2013. It included a greenhouse experiment to measure the agent’s feeding damage in relation to different nutrient levels and stocking rates, as well as a field component to evaluate both the post-winter recovery of M. scutellaris, and a nationwide survey to measure the establishment of the agent around the country in relation to climate, water quality, and plant health. In the greenhouse experiment, the feeding damage was quantified using measurements of plant growth parameters and chlorophyll fluorometry. It was found that, like other biological control agents of water hyacinth, M. scutellaris was most damaging when released in high numbers on plants grown at medium nutrient levels, and less effective on plants grown at elevated nutrient levels. A water hyacinth infestation on the Kubusi River was selected for the evaluation of the post-winter recovery of M. scutellaris. The Kubusi River is both the first site where M. scutellaris was released, and the coldest site where water hyacinth biological control agents have established successfully in South Africa. Monthly visits tracking seasonal plant health characteristics and agent population densities indicated that the populations of M. scutellaris were impacted most significantly by the season. Low temperatures led to the water hyacinth plants being of poor quality during the winter, which had a subsequent negative effect on the agent populations. The agents could only fully recover by late summer, which meant that the plants were without any significant biological control through the initial phases of the growing season, when they were most vulnerable, and a significant lag-phase occurred between the recovery of the plants and the recovery of the agent population after the winter bottleneck. A survey of all sites where M. scutellaris had been released in South Africa yielded 16 sites where the agents had successfully established, having survived at least one full winter. Among these sites were four sites where the agents were found without them having been released, indicating that they can disperse unaided to new sites. The temperature was a major factor responsible for the success or failure of establishment, with very few agents surviving in the hot areas of South Africa or in areas with a high frost incidence. The density of M. scutellaris was higher in nutrient-rich water, and on plants with more leaves, suggesting that the quality of the plants also contributed to establishment. The results of this thesis showed that M. scutellaris is able to establish successfully in South Africa, and that the agents are capable of causing significant damage to water hyacinth, making it a promising addition to the biological control programme. Novel methods of measuring subtle insect feeding damage in plants and quantifying agent populations are also discussed, along with suggestions for the future implementation of M. scutellaris in South Africa.
- Full Text:
- Date Issued: 2019
The remote sensing of fires and their effects on soil properties in the uKhahlamba Drakensberg Park
- Authors: Moore, Natasha Jade
- Date: 2019
- Subjects: Remote sensing -- South Africa -- KwaZulu-Natal , Soil ecology -- South Africa -- KwaZulu-Natal , Grassland fires -- South Africa -- KwaZulu-Natal , Grassland fires -- Remote sensing -- South Africa -- KwaZulu-Natal , Soils -- Effect of fires on -- South Africa -- KwaZulu-Natal , uKhalamba Drakensberg Park (South Africa)
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/94400 , vital:31042
- Description: Fires are a common and natural occurrence globally and specifically on the African continent. The Drakensberg Mountains are home to southern Africa’s high-altitude fire-climax grasslands, where fire is the dominant management tool. Fire is used to maintain the grasslands in the uKhahlamba Drakensberg Park (UDP) World Heritage Site, located on the eastern escarpment of the KwaZulu-Natal Drakensberg. This study aimed to investigate the spatial and temporal frequency of fires using remote sensing, and to investigate the effect of fire frequency on soil properties in the UDP. Remote sensing offers a set of supportive tools for the management of this sensitive vegetation and specifically to assess the frequency and spatial extent of fires. Field assessments can then be used to assess the impact of fires. Remotely sensed data were used to determine fire frequency and the spatial extent of fires in the UDP. The Moderate Resolution Imaging Spectroradiometer (MODIS) and Visible Infrared Imaging Radiometer Suite (VIIRS) active fire detection point data were processed to investigate the temporal resolution of fires. Landsat 5 and 8 imagery were utilised for conducting Normalised Burn Ratios (NBR) to determine the spatial extent of the burn scars of fires. The results from the remotely sensed data were used to select study sites for accessing the effects of fire frequency on soil properties. The remote sensing results showed the main fire season in the UDP was from May to October, and annual burn scars from the available Landsat data for 1998 to 2017 ranged from 22.5% to 57.67% of the UDP. Remote sensing was shown to be an effective tool for monitoring fires in the UDP, with a combination of satellite data producing the best results. Soil properties were highly varied across the UDP. Environmental factors were shown to have a more significant influence on soil properties than fire frequency. This study highlighted the complex nature and diversity of fires and soils across the UDP.
- Full Text:
- Date Issued: 2019
- Authors: Moore, Natasha Jade
- Date: 2019
- Subjects: Remote sensing -- South Africa -- KwaZulu-Natal , Soil ecology -- South Africa -- KwaZulu-Natal , Grassland fires -- South Africa -- KwaZulu-Natal , Grassland fires -- Remote sensing -- South Africa -- KwaZulu-Natal , Soils -- Effect of fires on -- South Africa -- KwaZulu-Natal , uKhalamba Drakensberg Park (South Africa)
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/94400 , vital:31042
- Description: Fires are a common and natural occurrence globally and specifically on the African continent. The Drakensberg Mountains are home to southern Africa’s high-altitude fire-climax grasslands, where fire is the dominant management tool. Fire is used to maintain the grasslands in the uKhahlamba Drakensberg Park (UDP) World Heritage Site, located on the eastern escarpment of the KwaZulu-Natal Drakensberg. This study aimed to investigate the spatial and temporal frequency of fires using remote sensing, and to investigate the effect of fire frequency on soil properties in the UDP. Remote sensing offers a set of supportive tools for the management of this sensitive vegetation and specifically to assess the frequency and spatial extent of fires. Field assessments can then be used to assess the impact of fires. Remotely sensed data were used to determine fire frequency and the spatial extent of fires in the UDP. The Moderate Resolution Imaging Spectroradiometer (MODIS) and Visible Infrared Imaging Radiometer Suite (VIIRS) active fire detection point data were processed to investigate the temporal resolution of fires. Landsat 5 and 8 imagery were utilised for conducting Normalised Burn Ratios (NBR) to determine the spatial extent of the burn scars of fires. The results from the remotely sensed data were used to select study sites for accessing the effects of fire frequency on soil properties. The remote sensing results showed the main fire season in the UDP was from May to October, and annual burn scars from the available Landsat data for 1998 to 2017 ranged from 22.5% to 57.67% of the UDP. Remote sensing was shown to be an effective tool for monitoring fires in the UDP, with a combination of satellite data producing the best results. Soil properties were highly varied across the UDP. Environmental factors were shown to have a more significant influence on soil properties than fire frequency. This study highlighted the complex nature and diversity of fires and soils across the UDP.
- Full Text:
- Date Issued: 2019
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