Soil and vegetation recovery following Acacia dealbata clearing in the Tsitsa catchment, Eastern Cape Province of South Africa: implications for ecological restoration
- Authors: Balintulo, Putuma
- Date: 2022-04-06
- Subjects: Acacia South Africa Eastern Cape , Invasive plants South Africa Eastern Cape , Working for Water Programme , Soil restoration South Africa Eastern Cape , Plant nutrients South Africa Eastern Cape , Restoration ecology South Africa Eastern Cape , Clearing of land South Africa Eastern Cape , Legacy effect
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/290778 , vital:56783
- Description: Invasion by alien plant species in South Africa continues to compromise the stability of ecosystems by causing declines in biodiversity, altering soil nutrients and processes, and subsequently transforming ecosystem functionality. Control of invasive alien plant species has been widely implemented in South Africa to minimize their negative impacts; however, the legacy effects can persist long after the plant has been removed. The impacts of Acacia dealbata clearing on soil properties and native vegetation recovery remains understudied despite their significance in ecological restoration and monitoring. This comparative study determined the impacts of A. dealbata clearing on both soil physicochemical properties and vegetation in the Eastern Cape Province of South Africa. Soils were collected from three different clearing treatments, namely, cleared, invaded, and uninvaded, on 5 m x 5 m plots over three summer months. The plots were replicated four times for each clearing treatment, making a total of 72 sampling plots. Soils were assessed for soil pH, resistivity, P, C, N, and exchangeable cations as well as soil moisture content, penetration resistance, infiltration rate, hydraulic conductivity, and water repellency. Clearing of A. dealbata did not have any significant effects on most soil nutrients, however, there were variations in soil pH, resistance, and Na. Soil pH was significantly higher in the uninvaded treatments than in the cleared and invaded treatments. Soil moisture content was significantly higher in the cleared treatments than the adjacent invaded and uninvaded treatments, but this was observed in the month of December only. Soil penetration resistance and infiltration rates were significantly higher in the month of December in the cleared treatments. For all clearing treatments, no significant differences were recorded for soil hydraulic conductivity. These results on changes in soil properties following A. dealbata clearing are varied, with some soil properties showing decreases, an indication that removal of A. dealbata has the potential to shift soil properties towards a positive recovery trajectory. This study further assessed whether the clearing of A. dealbata facilitates the recovery of native plant species. Vegetation surveys were conducted in the three above-mentioned treatments and plots. Results showed little recruitment of native grasses and forbs, but the persistence of A. dealbata seedlings in the cleared treatments. Species richness and Shannon-Wiener diversity index were significantly (P < 0.05) higher in the cleared and invaded treatments than the uninvaded treatments, and this was more visible for trees and shrubs. Cover for all species was significantly higher (P < 0.05) in the uninvaded than the cleared and invaded treatments. This study observed the recruitment of some native species in the cleared treatments that were not present in the invaded treatments. Therefore, the recruitment and establishment of some native species, mostly grasses, in the cleared treatments gives assurance that passive restoration is on a positive vegetation recovery trajectory that can lead to recovery of native vegetation after A. dealbata clearing. Therefore, the study concludes that investing in ecological restoration after alien plant clearing is a necessity for complete ecosystem recovery to be achieved. Overall, the study concludes that the removal of A. dealbata triggers changes to some soil properties. Similarly, the study observed recruitment of some native grasses in cleared areas, an indication that alien plant clearing facilitates changes in both soil properties and vegetation. However, soil and vegetation recovery are being hampered by the regrowth of A. dealbata and secondary invaders that were observed in the cleared treatments. Two key recommendations of this study are (i) clearing follow-up to remove recruiting seedlings of invasive plant species and secondary invaders should be timeous and well-funded, and (ii) active restoration should be considered to speed-up soil and vegetation recovery processes. , Thesis (MSc) -- Faculty of Science, Environmental Science, 2022
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The assessment of degradation state in Ecological Infrastructure and prioritisation for rehabilitation and drought mitigation in the Tsitsa River Catchment
- Authors: Mahlaba, Bawinile
- Date: 2022-04-06
- Subjects: Environmental degradation South Africa Eastern Cape , Restoration ecology South Africa Eastern Cape , Climate change mitigation South Africa Eastern Cape , Droughts South Africa Eastern Cape , South African National Biodiversity Institute , Sustainable development South Africa Eastern Cape , Watersheds , Ecological Infrastructure (EI) , Tsitsa River Catchment
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10962/202138 , vital:46470
- Description: Ecosystem degradation is a serious concern globally, including in South Africa, because of the potential adverse impacts on food security, livelihoods, climate change, biodiversity, and ecosystem services. Ecosystem degradation can result in flow alteration in the landscape through changes in the hydrological regime. The study adopts the South African National Biodiversity Institute (SANBI) Framework of Investing in Ecological Infrastructure (EI) to prioritise the restoration of degraded ecosystems and maintain ecosystem structures and functions. This study aims to assess how EI (specifically wetlands, grassland, abandoned cultivated fields, and riparian zone) can facilitate drought mitigation: to assess land degradation status and identify priority EI areas that can be restored to improve the drought mitigation capacity. Two assessment methods were used in this study. Firstly, the Trends.Earth tool was used to assess degradation and land cover change from the year 2000-2015 in Tsitsa catchment, through assessment of Sustainable Development Goal degradation indicator (SDG15.3.1) at a resolution of 300 m. The degradation indicator uses information from three sub-indicators: Productivity, Landcover and Soil Organic Carbon to compute degraded areas. The degraded areas need to be restored and rehabilitated to maintain the flow of essential ecosystems services provided by EI. The second assessment used the Analytical Hierarchy Process (AHP), which integrates stakeholder inputs into a multi-criteria decision analysis (MCDA). The AHP is a useful decision support system that considers a range of quantitative and qualitative alternatives in making a final decision to solve complex problems. As part of the AHP analysis, participatory mapping using Participatory Geographic Information System was conducted to obtain stakeholder inputs for prioritising restoration of the key EI categories (wetlands, grassland, abandoned cultivated fields, and riparian zone) in the catchment. During the participatory mapping, communities prioritised the key EI based on three criteria: (1) ecosystem health, (2) water provisioning and (3) social benefits. The AHP method was used in ArcGIS to prioritise suitable key EI restoration areas with high potential to increase water recharge and storage, contribute to drought mitigation and ecosystem services for the catchment. The prioritisation of EI for community livelihoods in the AHP analysis included all three main criteria. In comparison, the prioritisation of suitable key EI restoration areas for flow regulations was based on two criteria: ecosystem health and water provisioning. The land degradation indicator showed that approximately 54% of the catchment is stable, 41% is degraded land, and 5% of the area has improved over the assessment period (15 years). The degradation status in the EI suggests that more than half (>50%) of each EI category is stable, but there are areas showing signs of degradation, including 43% of grasslands degraded and 39% of wetlands, cultivated lands, and riparian zones also degraded. Degradation is dominant in the upper (T35B and T3C) and lower (T35K, T35L and T35M) parts of the catchments. The three criteria used by the stakeholders in the prioritisation process of the key EI were assigned 12 spatial attributes (the catchment characteristics about the study area in relation to the criteria) to indicate relevant information needed for selecting suitable restoration areas to enhance flow regulation. The AHP analysis results identified approximately 63% (17,703 ha) of wetlands, 88% (235,829 ha) of grasslands, 78% (13,608 ha) of abandoned cultivated fields and 93% (3,791 ha) of the riparian zones as suitable areas for restoration to mitigate drought impact through flow regulation. Also, the suitability results showed 63% (17,703 ha) of wetlands, 58% (2,203 ha) of riparian zones, 68% (11,745 ha) of abandoned cultivated fields and 46% (122,285 ha) of grasslands as suitable restoration areas for improving ecosystem services for community livelihoods. The AHP analysis identified more than 39-43% (of the degraded EI indicated by the Trends.Earth analysis) areas that are suitable for restoration, because key EI plays a significant role in flow regulation and people’s livelihoods, especially when they are managed, maintained, and restored to good health conditions. Therefore, the prioritized EI areas should be either maintained, managed, rehabilitated or restored. The major distinct causes of land degradation are woody encroachment in grasslands, invasion of alien plants on abandoned cultivated fields and soil erosion in the catchment. The most suitable EI areas recommended for restoration are those natural resources near local communities, which provide essential ecosystem services to sustain their livelihood. Therefore, degraded EI in the T35 catchments should be restored and maintained to improve livelihood and mitigate drought impacts. The study pointed out how the key selected ecological infrastructure can help mitigate the impacts of droughts and improve human livelihood. The study contributes towards the important concept of investing in ecological infrastructure to improve the social, environmental, and economic benefits. , Thesis (MSc) -- Faculty of Science, Institute for Water Research, 2022
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