Assessing the impacts of Lantana camara and opportunities for ecological restoration after its removal: does clearing facilitate both soil and native vegetation recovery?
- Authors: Bolosha, Uviwe
- Date: 2024-10-11
- Subjects: Lantana camara , Restoration and conservation , Restoration ecology , Invasive plants , Physicochemical process , Soil seed banks , Invasion driver
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/466524 , vital:76738 , DOI https://doi.org/10.21504/10962/466524
- Description: Invasive alien plants (IAPs) are one of the major contributing factors to biodiversity loss, and Lantana camara is among the top ten alien invaders worldwide. Lantana camara threatens native biodiversity and human health, prevents natural succession, and has an economic and environmental impact globally. With current climate change and future predictions, these IAPs are anticipated to continue posing huge threats to ecosystem composition, structure, and function. Even though L. camara is a widespread IAP, there is still limited knowledge in South Africa on how it influences soil physicochemical properties at the species level, vegetation communities, and soil seed banks at the community level following its invasion. There is also minimal knowledge on the management and control (i.e., clearing for restoration purposes) of L. camara in South Africa, especially in the Eastern Cape province of South Africa. To address the knowledge gap, this thesis was structured into three main aspects: understanding L. camara invasion mechanisms, evaluating invasion impacts on both the aboveground and belowground communities, and invasion management. The main objectives of this thesis were (i) to examine how L. camara invasion (at a species level) affected soil physicochemical properties across different seasons, (ii) to assess how L. camara influences natural vegetation (at a community level), (iii) to examine the effects of L. camara invasion (at the community level) on belowground soil seed banks and also assess the availability of pioneer native species and IAPs in the soil seed banks, and (iv) to evaluate soil and vegetation responses following L. camara clearing in comparison to invaded and uninvaded conditions. To answer these objectives, different studies were carried out in the Eastern Cape province, South Africa, on various farms within the Albany Thicket Biome. The results (Chapter 3) show that L. camara alters and modifies some soil physical properties, such as soil infiltration rate, repellency, and soil penetration resistance, in the communities it invades. A significant decrease in soil penetration under the L. camara canopy was observed compared to soils from the edge and out position. Moreover, significantly faster infiltration rates were observed in the canopy and edge positions than in the out position. The study also observed that these modifications in soil physical properties vary depending on the season. A seasonal comparison in soil penetration showed that soil was more compact in the dry season than the wet season, and significantly faster infiltration rates were observed in summer than in the other seasons. The soil collected under the invaded sampling positions was mostly wettable (80–100%), and not strongly, severely, or extremely repellent across all the seasons. The changes in soil properties caused by L. camara could create favourable conditions for its growth and invasion. Seasonal changes in soil properties also highlight how environmental conditions, especially temperature and rainfall patterns, can affect soil physical properties. The findings in Chapter 4 observed both the negative and positive impacts of L. camara, where the species did not have negative effects on species richness, diversity, or cover of some native species growth forms (i.e., graminoids and forbs). For all species, both species richness and Shannon-Wiener (H’) were significantly higher in the L. camara invaded condition compared to the uninvaded condition. The Simpson’s (J’) and Pielou’s evenness (D’) indices, however, showed no differences between the invasion conditions. Furthermore, the effects of L. camara on vegetation cover were growth form-dependent, with differences being noted for trees and shrubs but not for graminoids and forbs. Changes in vegetation structure and composition were also noted where L. camara created favourable conditions for some species to co-occur with it, meaning that its known trait of changing soil physicochemical properties could benefit some species. Generally, the results of this study showed that the effects of L. camara on vegetation are varied and do not have a predictable pattern, so they should not be generalised. The findings (Chapter 5) also indicate that the L. camara invasion had a negative impact on seedling abundance and composition but not species diversity and richness. This is evident through the decrease in seedling abundance of forbs and graminoids in the L. camara invaded condition. Lantana camara also acted as a refuge for some plant species, mostly native forbs and grasses, including Aptenia cordifolia, Chamaesyce prostrata, Oxalis spp., and Setaria spp., as well as alien forbs such as Bidens pilosa, Plantago lanceolata, and Taraxacum officinale, suggesting L. camara does not entirely eliminate less competitive plant species but can co-exist with them. Lantana camara also displaced some native species, and this could be associated with their displacement in the standing vegetation. Moreover, the species also displaced the seed banks of some alien species, thus showing its competitive ability. Overall, L. camara invasion negatively influenced soil seed bank seedling abundance and composition of some species, but not diversity and richness. The results in Chapter 6 indicated that clearing L. camara is an effective method for reducing its population. However, our findings suggest that clearing alone may not be enough to re-establish these communities with native species. This is because the results of this study showed varied changes in soil properties and native vegetation (species richness, species diversity, percentage cover, and composition) after L. camara clearing. For example, soil moisture and soil penetration resistance showed no significant differences among the invasion conditions; only monthly variations were observed. This is an indication that seasonality influenced these properties. Significantly lower soil infiltration rates were observed in the cleared condition compared to the other conditions and were influenced by the months and the interaction of the clearing conditions and months. The water droplet penetration time showed no significant difference among the clearing conditions over the three months, and all the soil collected from the three clearing conditions was mostly wettable. Soil chemical properties showed that the L. camara invaded and cleared conditions had significantly lower soil pH compared to the uninvaded condition, and an increase in soil pH was observed after clearing L. camara. Vegetation characteristics showed that both the Shannon-Wiener index (H') and the Simpson’s index (D') were lower in the invaded and cleared conditions compared to the uninvaded condition, and significant differences were observed. A slight increase in the H' and D' indices was also observed after clearing L. camara. The mean percentage cover for trees and shrubs was significantly higher in the invaded condition than in the cleared and uninvaded conditions. However, the mean percentage cover of forbs and graminoids was similar among the invaded, cleared, and uninvaded conditions, and no significant differences were observed. When L. camara was cleared, native species recovery was observed and was more notable in the understory species. Overall, some signs of vegetation recovery were observed, although challenges such as secondary invaders and re-invasion by L. camara were noted in the cleared areas. This chapter then concluded that active restoration interventions should be incorporated during restoration to fast-track soil and vegetation recovery. The findings of this thesis will make several significant contributions to the field of biological invasions and provide baseline information that can be used in future studies. These are discussed in the various research chapters. Overall, the thesis concludes that L. camara invasion has varied impacts on native vegetation and soil, and its clearance, should be prioritised to reduce the negative impacts. However, L. camara cleared areas (by WfW in South Africa) require follow-up and monitoring at an early stage to assess vegetation and soil restoration success. In addition, active management measures after L. camara’s removal should be considered for clearing programmes to yield positive ecosystem recovery. , Thesis (PhD) -- Faculty of Science, Environmental Science, 2024
- Full Text:
- Date Issued: 2024-10-11
- Authors: Bolosha, Uviwe
- Date: 2024-10-11
- Subjects: Lantana camara , Restoration and conservation , Restoration ecology , Invasive plants , Physicochemical process , Soil seed banks , Invasion driver
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/466524 , vital:76738 , DOI https://doi.org/10.21504/10962/466524
- Description: Invasive alien plants (IAPs) are one of the major contributing factors to biodiversity loss, and Lantana camara is among the top ten alien invaders worldwide. Lantana camara threatens native biodiversity and human health, prevents natural succession, and has an economic and environmental impact globally. With current climate change and future predictions, these IAPs are anticipated to continue posing huge threats to ecosystem composition, structure, and function. Even though L. camara is a widespread IAP, there is still limited knowledge in South Africa on how it influences soil physicochemical properties at the species level, vegetation communities, and soil seed banks at the community level following its invasion. There is also minimal knowledge on the management and control (i.e., clearing for restoration purposes) of L. camara in South Africa, especially in the Eastern Cape province of South Africa. To address the knowledge gap, this thesis was structured into three main aspects: understanding L. camara invasion mechanisms, evaluating invasion impacts on both the aboveground and belowground communities, and invasion management. The main objectives of this thesis were (i) to examine how L. camara invasion (at a species level) affected soil physicochemical properties across different seasons, (ii) to assess how L. camara influences natural vegetation (at a community level), (iii) to examine the effects of L. camara invasion (at the community level) on belowground soil seed banks and also assess the availability of pioneer native species and IAPs in the soil seed banks, and (iv) to evaluate soil and vegetation responses following L. camara clearing in comparison to invaded and uninvaded conditions. To answer these objectives, different studies were carried out in the Eastern Cape province, South Africa, on various farms within the Albany Thicket Biome. The results (Chapter 3) show that L. camara alters and modifies some soil physical properties, such as soil infiltration rate, repellency, and soil penetration resistance, in the communities it invades. A significant decrease in soil penetration under the L. camara canopy was observed compared to soils from the edge and out position. Moreover, significantly faster infiltration rates were observed in the canopy and edge positions than in the out position. The study also observed that these modifications in soil physical properties vary depending on the season. A seasonal comparison in soil penetration showed that soil was more compact in the dry season than the wet season, and significantly faster infiltration rates were observed in summer than in the other seasons. The soil collected under the invaded sampling positions was mostly wettable (80–100%), and not strongly, severely, or extremely repellent across all the seasons. The changes in soil properties caused by L. camara could create favourable conditions for its growth and invasion. Seasonal changes in soil properties also highlight how environmental conditions, especially temperature and rainfall patterns, can affect soil physical properties. The findings in Chapter 4 observed both the negative and positive impacts of L. camara, where the species did not have negative effects on species richness, diversity, or cover of some native species growth forms (i.e., graminoids and forbs). For all species, both species richness and Shannon-Wiener (H’) were significantly higher in the L. camara invaded condition compared to the uninvaded condition. The Simpson’s (J’) and Pielou’s evenness (D’) indices, however, showed no differences between the invasion conditions. Furthermore, the effects of L. camara on vegetation cover were growth form-dependent, with differences being noted for trees and shrubs but not for graminoids and forbs. Changes in vegetation structure and composition were also noted where L. camara created favourable conditions for some species to co-occur with it, meaning that its known trait of changing soil physicochemical properties could benefit some species. Generally, the results of this study showed that the effects of L. camara on vegetation are varied and do not have a predictable pattern, so they should not be generalised. The findings (Chapter 5) also indicate that the L. camara invasion had a negative impact on seedling abundance and composition but not species diversity and richness. This is evident through the decrease in seedling abundance of forbs and graminoids in the L. camara invaded condition. Lantana camara also acted as a refuge for some plant species, mostly native forbs and grasses, including Aptenia cordifolia, Chamaesyce prostrata, Oxalis spp., and Setaria spp., as well as alien forbs such as Bidens pilosa, Plantago lanceolata, and Taraxacum officinale, suggesting L. camara does not entirely eliminate less competitive plant species but can co-exist with them. Lantana camara also displaced some native species, and this could be associated with their displacement in the standing vegetation. Moreover, the species also displaced the seed banks of some alien species, thus showing its competitive ability. Overall, L. camara invasion negatively influenced soil seed bank seedling abundance and composition of some species, but not diversity and richness. The results in Chapter 6 indicated that clearing L. camara is an effective method for reducing its population. However, our findings suggest that clearing alone may not be enough to re-establish these communities with native species. This is because the results of this study showed varied changes in soil properties and native vegetation (species richness, species diversity, percentage cover, and composition) after L. camara clearing. For example, soil moisture and soil penetration resistance showed no significant differences among the invasion conditions; only monthly variations were observed. This is an indication that seasonality influenced these properties. Significantly lower soil infiltration rates were observed in the cleared condition compared to the other conditions and were influenced by the months and the interaction of the clearing conditions and months. The water droplet penetration time showed no significant difference among the clearing conditions over the three months, and all the soil collected from the three clearing conditions was mostly wettable. Soil chemical properties showed that the L. camara invaded and cleared conditions had significantly lower soil pH compared to the uninvaded condition, and an increase in soil pH was observed after clearing L. camara. Vegetation characteristics showed that both the Shannon-Wiener index (H') and the Simpson’s index (D') were lower in the invaded and cleared conditions compared to the uninvaded condition, and significant differences were observed. A slight increase in the H' and D' indices was also observed after clearing L. camara. The mean percentage cover for trees and shrubs was significantly higher in the invaded condition than in the cleared and uninvaded conditions. However, the mean percentage cover of forbs and graminoids was similar among the invaded, cleared, and uninvaded conditions, and no significant differences were observed. When L. camara was cleared, native species recovery was observed and was more notable in the understory species. Overall, some signs of vegetation recovery were observed, although challenges such as secondary invaders and re-invasion by L. camara were noted in the cleared areas. This chapter then concluded that active restoration interventions should be incorporated during restoration to fast-track soil and vegetation recovery. The findings of this thesis will make several significant contributions to the field of biological invasions and provide baseline information that can be used in future studies. These are discussed in the various research chapters. Overall, the thesis concludes that L. camara invasion has varied impacts on native vegetation and soil, and its clearance, should be prioritised to reduce the negative impacts. However, L. camara cleared areas (by WfW in South Africa) require follow-up and monitoring at an early stage to assess vegetation and soil restoration success. In addition, active management measures after L. camara’s removal should be considered for clearing programmes to yield positive ecosystem recovery. , Thesis (PhD) -- Faculty of Science, Environmental Science, 2024
- Full Text:
- Date Issued: 2024-10-11
Assessing the local awareness and perception of invasive alien plants: A case study of Port St Johns Local Municipality, Eastern Cape Province, South Africa
- Authors: Somkala, Avela Abongile
- Date: 2021-10
- Subjects: Alien plants , Invasive plants
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10353/22600 , vital:52595
- Description: Invasive alien plants (IAPs) are introduced species that constitute a self-sustaining population, consistently producing offspring in large numbers and at considerable distances from the parent plants with the potential to spread over a large area. Species invasions are one of the main conservation threats today and have caused modification of ecosystems, particularly in coastal areas. Therefore, Port St Johns Local Municipality (PSJ LM) was an appropriate study site to evaluate the local awareness and perceptions of IAPs. The study investigated the local community’s perceptions of invasive alien plants' uses and ecological impacts. Information about the local awareness and perceptions of invasive alien plant species in PSJ LM was gathered through semi-structured interviews, observation and guided field walks with 120 participants between February and April 2021. The participants included 30 people working on the alien plant eradication project in PSJ LM (Wards 1, 2 and 3) and 90 randomly selected community members. The data collected were entered in Microsoft Excel 2016 programme and analyzed for descriptive statistical patterns using Statistical Package for Social Studies (SPSS) version 22.0. Biological invasion by IAPs was ubiquitously perceived, with participants working on invasive alien plant eradication project in the area exhibiting more scientifically based knowledge on IAPs than ordinary community members. Invasive alien plants in the area appear to have adverse environmental and socio-economic impacts, as the participants are not benefiting from these plant species. Similarly, costs of eradicating these species were also acknowledged. The ability of local community members to identify IAPs is vital in effective management of the spread of these species. A total of seven invasive IAPs were recorded. Evaluating the perceptions of local people towards IAPs provides valuable insights for development planning and future management programmes focusing on biological invasions. The study will provide a basis for an enabling policy and institutional environment that provides a coherent framework for the sustainable management of IAPs in the Eastern Cape Province. , Thesis (MPhil) -- Faculty of Science and Agriculture, 2021
- Full Text:
- Date Issued: 2021-10
- Authors: Somkala, Avela Abongile
- Date: 2021-10
- Subjects: Alien plants , Invasive plants
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10353/22600 , vital:52595
- Description: Invasive alien plants (IAPs) are introduced species that constitute a self-sustaining population, consistently producing offspring in large numbers and at considerable distances from the parent plants with the potential to spread over a large area. Species invasions are one of the main conservation threats today and have caused modification of ecosystems, particularly in coastal areas. Therefore, Port St Johns Local Municipality (PSJ LM) was an appropriate study site to evaluate the local awareness and perceptions of IAPs. The study investigated the local community’s perceptions of invasive alien plants' uses and ecological impacts. Information about the local awareness and perceptions of invasive alien plant species in PSJ LM was gathered through semi-structured interviews, observation and guided field walks with 120 participants between February and April 2021. The participants included 30 people working on the alien plant eradication project in PSJ LM (Wards 1, 2 and 3) and 90 randomly selected community members. The data collected were entered in Microsoft Excel 2016 programme and analyzed for descriptive statistical patterns using Statistical Package for Social Studies (SPSS) version 22.0. Biological invasion by IAPs was ubiquitously perceived, with participants working on invasive alien plant eradication project in the area exhibiting more scientifically based knowledge on IAPs than ordinary community members. Invasive alien plants in the area appear to have adverse environmental and socio-economic impacts, as the participants are not benefiting from these plant species. Similarly, costs of eradicating these species were also acknowledged. The ability of local community members to identify IAPs is vital in effective management of the spread of these species. A total of seven invasive IAPs were recorded. Evaluating the perceptions of local people towards IAPs provides valuable insights for development planning and future management programmes focusing on biological invasions. The study will provide a basis for an enabling policy and institutional environment that provides a coherent framework for the sustainable management of IAPs in the Eastern Cape Province. , Thesis (MPhil) -- Faculty of Science and Agriculture, 2021
- Full Text:
- Date Issued: 2021-10
Effects of elevated temperature, rainfall and soil nutrients on acacia mearnsii invasion
- Authors: Kharivha, Tshililo
- Date: 2021-10
- Subjects: Acacia mearnsii , Acacia mearnsii Effect of high temperatures on South Africa , Acacia mearnsii Climatic factors South Africa , Plant invasions South Africa , Invasive plants , Climatic changes South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10962/189997 , vital:44954
- Description: Climate change is associated with the risk of plant invasion hence a better understanding of the effects of elevated temperature, precipitation and soil nutrients on dominant invasive plants is needed for effective ecological planning. This study was set out to: (i) examine how elevated temperature (±2°C increase), (ii) high (above local average) and low (below local average) precipitation, (iii) elevated soil nutrient content (increase in soil N), and (iv) a combination of the above manipulations affects germination and growth of Acacia mearnsii, a dominant invasive plant in South Africa. The study further evaluated how the above-mentioned treatments affect soil chemical properties following A. mearnsii germination and growth. The above-mentioned specific objectives were tested under manipulated greenhouse conditions over six experimental months. The results indicated that the above-mentioned climate change scenarios have the potential to facilitate germination and growth of the invasive species A. mearnsii, and this is likely to proliferate its invasion in future. Results showed that seed germination was significantly high under all climate change manipulation treatments (˃50%) with highest seed germination recorded under high rainfall treatment (64%). Plant height was significantly higher under high temperature and high rainfall treatments throughout all the experimental months, though it was lowest under high nitrogen and combined treatment with high rainfall. The numbers of branches were high under higher temperature and low rainfall treatments than under high rainfall, high nitrogen and both combined treatments of low and high rainfall. Relative to the control, plants grown under climate change scenarios increased their root lengths, but this varied across different treatments. Total dry biomass was relatively high under high temperature treatment (0,7 g). Lower plant dry biomass was observed under low and high rainfall treatments (0,4 g), high nitrogen and combined treatments with both low and high rainfall treatments (0,1 g). Concerning the effects of climate change scenarios on soil chemical properties, soil pH levels were significantly higher after A. mearnsii germination and growth than before the experiment was setup. Soil resistivity was significantly higher in climate change treatments receiving nitrogen and combined treatments of low rainfall than other treatments and the soils before experiment. Soil total P was significantly higher in all the climate change treatments after A. mearnsii germination experiment than the before experiment soils. Soils receiving high temperature, high nitrogen, and combined treatment of low rainfall had significantly higher soil total N than other treatments and the before experiment soils. Soil total C was significantly higher in soils receiving high temperature, high nitrogen, and combined treatment of low rainfall after A. mearnsii germination than other treatments and before experiment soils. The findings suggest that future climate change scenarios of increased temperature and rainfall with soil nutrients could considerably enhance growth and germination success of the invasive plant A. mearnsii. Similarly, climate change scenarios could enhance some soil nutrient properties, which in turn, is likely to give the invasive plant A. mearnsii a germination and growth advantage. These results are the first in South Africa to show that future climate changes have the potential to facilitate A. mearnsii germination and growth, making it more invasive. The findings have implications for invasive plants management, especially action for managing the plant through clearing of the plant in sensitive ecosystems (e.g. riparian systems). , Thesis (MSc) -- Faculty of Science, Environmental Science, 2021
- Full Text:
- Date Issued: 2021-10
- Authors: Kharivha, Tshililo
- Date: 2021-10
- Subjects: Acacia mearnsii , Acacia mearnsii Effect of high temperatures on South Africa , Acacia mearnsii Climatic factors South Africa , Plant invasions South Africa , Invasive plants , Climatic changes South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10962/189997 , vital:44954
- Description: Climate change is associated with the risk of plant invasion hence a better understanding of the effects of elevated temperature, precipitation and soil nutrients on dominant invasive plants is needed for effective ecological planning. This study was set out to: (i) examine how elevated temperature (±2°C increase), (ii) high (above local average) and low (below local average) precipitation, (iii) elevated soil nutrient content (increase in soil N), and (iv) a combination of the above manipulations affects germination and growth of Acacia mearnsii, a dominant invasive plant in South Africa. The study further evaluated how the above-mentioned treatments affect soil chemical properties following A. mearnsii germination and growth. The above-mentioned specific objectives were tested under manipulated greenhouse conditions over six experimental months. The results indicated that the above-mentioned climate change scenarios have the potential to facilitate germination and growth of the invasive species A. mearnsii, and this is likely to proliferate its invasion in future. Results showed that seed germination was significantly high under all climate change manipulation treatments (˃50%) with highest seed germination recorded under high rainfall treatment (64%). Plant height was significantly higher under high temperature and high rainfall treatments throughout all the experimental months, though it was lowest under high nitrogen and combined treatment with high rainfall. The numbers of branches were high under higher temperature and low rainfall treatments than under high rainfall, high nitrogen and both combined treatments of low and high rainfall. Relative to the control, plants grown under climate change scenarios increased their root lengths, but this varied across different treatments. Total dry biomass was relatively high under high temperature treatment (0,7 g). Lower plant dry biomass was observed under low and high rainfall treatments (0,4 g), high nitrogen and combined treatments with both low and high rainfall treatments (0,1 g). Concerning the effects of climate change scenarios on soil chemical properties, soil pH levels were significantly higher after A. mearnsii germination and growth than before the experiment was setup. Soil resistivity was significantly higher in climate change treatments receiving nitrogen and combined treatments of low rainfall than other treatments and the soils before experiment. Soil total P was significantly higher in all the climate change treatments after A. mearnsii germination experiment than the before experiment soils. Soils receiving high temperature, high nitrogen, and combined treatment of low rainfall had significantly higher soil total N than other treatments and the before experiment soils. Soil total C was significantly higher in soils receiving high temperature, high nitrogen, and combined treatment of low rainfall after A. mearnsii germination than other treatments and before experiment soils. The findings suggest that future climate change scenarios of increased temperature and rainfall with soil nutrients could considerably enhance growth and germination success of the invasive plant A. mearnsii. Similarly, climate change scenarios could enhance some soil nutrient properties, which in turn, is likely to give the invasive plant A. mearnsii a germination and growth advantage. These results are the first in South Africa to show that future climate changes have the potential to facilitate A. mearnsii germination and growth, making it more invasive. The findings have implications for invasive plants management, especially action for managing the plant through clearing of the plant in sensitive ecosystems (e.g. riparian systems). , Thesis (MSc) -- Faculty of Science, Environmental Science, 2021
- Full Text:
- Date Issued: 2021-10
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