The influence of Acacia Mearnsii invasion on soil properties in the Kouga Mountains, Eastern Cape, South Africa
- Van der Waal, Benjamin Wentsel
- Authors: Van der Waal, Benjamin Wentsel
- Date: 2010
- Subjects: Acacia mearnsii -- South Africa , Wattles (Plants) -- South Africa , Soil erosion -- South Africa -- Eastern Cape , Conservation of natural resources -- South Africa , Biological invasions -- South Africa -- Eastern Cape , Alien plants -- South Africa -- Eastern Cape , Invasive plants -- South Africa -- Eastern Cape , Biogeography -- South Africa -- Eastern Cape , Soil management -- South Africa -- Eastern Cape , Soil moisture -- South Africa -- Eastern Cape , Soils -- Sodium content -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4839 , http://hdl.handle.net/10962/d1005515 , Acacia mearnsii -- South Africa , Wattles (Plants) -- South Africa , Soil erosion -- South Africa -- Eastern Cape , Conservation of natural resources -- South Africa , Biological invasions -- South Africa -- Eastern Cape , Alien plants -- South Africa -- Eastern Cape , Invasive plants -- South Africa -- Eastern Cape , Biogeography -- South Africa -- Eastern Cape , Soil management -- South Africa -- Eastern Cape , Soil moisture -- South Africa -- Eastern Cape , Soils -- Sodium content -- South Africa -- Eastern Cape
- Description: The invasion of Acacia mearnsii in the Kouga catchment, Eastern Cape, South Africa, has various negative impacts on the ecosystem. These impacts include: reduced species richness, increased water use, increased nutrients and increased N cycling rates. The native shrubby fynbos vegetation has adapted to the acidic nutrient poor soils and Mediterranean climate of the Kouga Mountains. Fynbos, however, is currently being out competed by the much taller Acacia mearnsii trees, due to their competitive nature and ability to fix nitrogen, thereby enriching the soil. The invaded sections of the valley bottoms and lower hill slopes are characterised by an almost complete monoculture of Acacia mearnsii, with very few fynbos species still present. The Department of Water and Environmental Affairs sponsored Working for Water programme started clearing Acacia mearnsii in 1996 in the Kouga Mountains. Cleared sites have remained bare for long periods, indicating that soil properties are not favourable for indigenous propagule re-establishment. The aim of this research was to assess how A. mearnsii invasion and clearing affect fynbos recovery through its impact on soils. This was done by characterising vegetation and soil properties on fynbos, infested and cleared slopes. Vegetation cover for various growth forms was determined and a species list was compiled for each plot. The slope angle, surface hardness, litter cover, bare ground cover and soil depth were measured in the field, whereas water repellency, particle size and the chemical composition were measured in the laboratory. Furthermore, the plant establishment capacity of soils from fynbos, infested and cleared slopes was calculated. This was done by germinating fynbos seeds and growing fynbos plants in soils from the various slopes. The effect that invasion and clearing has on soil erosion was quantified using erosion plots on fynbos, infested and cleared slopes. The invasion and clearing of Acacia mearnsii led to an increase in soil nutrients, especially nitrogen, phosphorus, potassium, carbon and manganese. Furthermore, soils became more acidic, with increased water repellency and reduced surface hardness. The vegetation changed to a tree-dominated structure, replacing the native species. Native plant germination was relatively unaffected by invasion and clearing, with an increase in germination just after clearing. Plant growth of a native grass, Themeda triandra, and herb, Helichrysum umbraculigerum, has increased on soils from cleared slopes. This study showed that soil movement increased on slopes which are invaded and cleared of Acacia mearnsii, with erosion rates doubling on invaded slopes
- Full Text:
- Date Issued: 2010
- Authors: Van der Waal, Benjamin Wentsel
- Date: 2010
- Subjects: Acacia mearnsii -- South Africa , Wattles (Plants) -- South Africa , Soil erosion -- South Africa -- Eastern Cape , Conservation of natural resources -- South Africa , Biological invasions -- South Africa -- Eastern Cape , Alien plants -- South Africa -- Eastern Cape , Invasive plants -- South Africa -- Eastern Cape , Biogeography -- South Africa -- Eastern Cape , Soil management -- South Africa -- Eastern Cape , Soil moisture -- South Africa -- Eastern Cape , Soils -- Sodium content -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4839 , http://hdl.handle.net/10962/d1005515 , Acacia mearnsii -- South Africa , Wattles (Plants) -- South Africa , Soil erosion -- South Africa -- Eastern Cape , Conservation of natural resources -- South Africa , Biological invasions -- South Africa -- Eastern Cape , Alien plants -- South Africa -- Eastern Cape , Invasive plants -- South Africa -- Eastern Cape , Biogeography -- South Africa -- Eastern Cape , Soil management -- South Africa -- Eastern Cape , Soil moisture -- South Africa -- Eastern Cape , Soils -- Sodium content -- South Africa -- Eastern Cape
- Description: The invasion of Acacia mearnsii in the Kouga catchment, Eastern Cape, South Africa, has various negative impacts on the ecosystem. These impacts include: reduced species richness, increased water use, increased nutrients and increased N cycling rates. The native shrubby fynbos vegetation has adapted to the acidic nutrient poor soils and Mediterranean climate of the Kouga Mountains. Fynbos, however, is currently being out competed by the much taller Acacia mearnsii trees, due to their competitive nature and ability to fix nitrogen, thereby enriching the soil. The invaded sections of the valley bottoms and lower hill slopes are characterised by an almost complete monoculture of Acacia mearnsii, with very few fynbos species still present. The Department of Water and Environmental Affairs sponsored Working for Water programme started clearing Acacia mearnsii in 1996 in the Kouga Mountains. Cleared sites have remained bare for long periods, indicating that soil properties are not favourable for indigenous propagule re-establishment. The aim of this research was to assess how A. mearnsii invasion and clearing affect fynbos recovery through its impact on soils. This was done by characterising vegetation and soil properties on fynbos, infested and cleared slopes. Vegetation cover for various growth forms was determined and a species list was compiled for each plot. The slope angle, surface hardness, litter cover, bare ground cover and soil depth were measured in the field, whereas water repellency, particle size and the chemical composition were measured in the laboratory. Furthermore, the plant establishment capacity of soils from fynbos, infested and cleared slopes was calculated. This was done by germinating fynbos seeds and growing fynbos plants in soils from the various slopes. The effect that invasion and clearing has on soil erosion was quantified using erosion plots on fynbos, infested and cleared slopes. The invasion and clearing of Acacia mearnsii led to an increase in soil nutrients, especially nitrogen, phosphorus, potassium, carbon and manganese. Furthermore, soils became more acidic, with increased water repellency and reduced surface hardness. The vegetation changed to a tree-dominated structure, replacing the native species. Native plant germination was relatively unaffected by invasion and clearing, with an increase in germination just after clearing. Plant growth of a native grass, Themeda triandra, and herb, Helichrysum umbraculigerum, has increased on soils from cleared slopes. This study showed that soil movement increased on slopes which are invaded and cleared of Acacia mearnsii, with erosion rates doubling on invaded slopes
- Full Text:
- Date Issued: 2010
The invasion of pteronia incana (blue bush) along a range of gradients in the Eastern Cape Province : it's spectral chacteristics and implications for soil moisture
- Authors: Odindi, John Odhiambo
- Date: 2009
- Subjects: Invasive plants -- South Africa -- Eastern Cape , Alien plants -- South Africa -- Eastern Cape , Soil moisture -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10650 , http://hdl.handle.net/10948/1052 , Invasive plants -- South Africa -- Eastern Cape , Alien plants -- South Africa -- Eastern Cape , Soil moisture -- South Africa -- Eastern Cape
- Description: Extensive areas of the Eastern Cape Province have been invaded by Pteronia incana (Blue bush), a non-palatable patchy invader shrub that is associated with soil degradation. This study sought to establish the relationship between the invasion and a range of eco-physical and land use gradients. The impact of the invader on soil moisture flux was investigated by comparing soil moisture variations under grass, bare and P. incana invaded surfaces. Field based and laboratory spectroscopy was used to validate P. incana spectral characteristics identified from multi-temporal High Resolution Imagery (HRI). A belt transect was surveyed to gain an understanding of the occurrence of the invasion across land use, isohyetic, geologic, vegetation, pedologic and altitudinal gradients. Soil moisture sensors were calibrated and installed under the respective surfaces in order to determine soil moisture trends over a period of six months. To classify the surfaces using HRI, the pixel and sub-pixel based Perpendicular Vegetation Index (PVI) and Spectral Mixture Analysis (SMA) respectively were used. There was no clear trend established between the underlying geology and P. incana invasion. Land disturbance in general was strongly associated with the invasion, as the endemic zone for the invasion mainly comprised abandoned cultivated and overgrazed land. Isohyetic gradients emerged as the major limiting factor of the invasion; a distinct zone below 619mm of mean annual rainfall was identified as the apparent boundary for the invasion. Low organic matter content identified under invaded areas was attributed to the patchy nature of the invader, leading to loss of the top soil in the bare inter-patch areas. The area covered by grass had consistently higher moisture values than P. incana and bare surfaces. The difference in post-rainfall moisture retention between grass and P. incana surfaces was significant up to about six days, after which a near parallel trend was noticed towards the ensuing rainfall episode. Whereas a higher amount of moisture was recorded on grass, the surface experienced moisture loss faster than the invaded and bare surfaces after each rainfall episode. ii There was consistency in multi-temporal Digital Number (DN) values for the surfaces investigated. The typically low P. incana reflectance in the Near Infrared band, identified from the multi-temporal HRI was validated by field and laboratory spectroscopy. The PVI showed clear spectral separability between all the land surfaces in the respective multi-temporal HRI. The consistence of the PVI with the unmixed surface image fractions from the SMA illustrates that using HRI, the effectiveness of the PVI is not impeded by the mixed pixel problem. Results of the laboratory spectroscopy that validated HRI analyses showed that P. incana’s typically low reflectance is a function of its leaf canopy, as higher proportions of leaves gave a higher reflectance. Future research directions could focus on comparisons between P. incana and typical green vegetation internal leaf structures as potential causes of spectral differences. Collection of spectra for P incana and other invader vegetation types, some of which have similar characteristics, with a view to assembling a spectral library for delineating invaded environments using imagery, is another research direction.
- Full Text:
- Date Issued: 2009
- Authors: Odindi, John Odhiambo
- Date: 2009
- Subjects: Invasive plants -- South Africa -- Eastern Cape , Alien plants -- South Africa -- Eastern Cape , Soil moisture -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10650 , http://hdl.handle.net/10948/1052 , Invasive plants -- South Africa -- Eastern Cape , Alien plants -- South Africa -- Eastern Cape , Soil moisture -- South Africa -- Eastern Cape
- Description: Extensive areas of the Eastern Cape Province have been invaded by Pteronia incana (Blue bush), a non-palatable patchy invader shrub that is associated with soil degradation. This study sought to establish the relationship between the invasion and a range of eco-physical and land use gradients. The impact of the invader on soil moisture flux was investigated by comparing soil moisture variations under grass, bare and P. incana invaded surfaces. Field based and laboratory spectroscopy was used to validate P. incana spectral characteristics identified from multi-temporal High Resolution Imagery (HRI). A belt transect was surveyed to gain an understanding of the occurrence of the invasion across land use, isohyetic, geologic, vegetation, pedologic and altitudinal gradients. Soil moisture sensors were calibrated and installed under the respective surfaces in order to determine soil moisture trends over a period of six months. To classify the surfaces using HRI, the pixel and sub-pixel based Perpendicular Vegetation Index (PVI) and Spectral Mixture Analysis (SMA) respectively were used. There was no clear trend established between the underlying geology and P. incana invasion. Land disturbance in general was strongly associated with the invasion, as the endemic zone for the invasion mainly comprised abandoned cultivated and overgrazed land. Isohyetic gradients emerged as the major limiting factor of the invasion; a distinct zone below 619mm of mean annual rainfall was identified as the apparent boundary for the invasion. Low organic matter content identified under invaded areas was attributed to the patchy nature of the invader, leading to loss of the top soil in the bare inter-patch areas. The area covered by grass had consistently higher moisture values than P. incana and bare surfaces. The difference in post-rainfall moisture retention between grass and P. incana surfaces was significant up to about six days, after which a near parallel trend was noticed towards the ensuing rainfall episode. Whereas a higher amount of moisture was recorded on grass, the surface experienced moisture loss faster than the invaded and bare surfaces after each rainfall episode. ii There was consistency in multi-temporal Digital Number (DN) values for the surfaces investigated. The typically low P. incana reflectance in the Near Infrared band, identified from the multi-temporal HRI was validated by field and laboratory spectroscopy. The PVI showed clear spectral separability between all the land surfaces in the respective multi-temporal HRI. The consistence of the PVI with the unmixed surface image fractions from the SMA illustrates that using HRI, the effectiveness of the PVI is not impeded by the mixed pixel problem. Results of the laboratory spectroscopy that validated HRI analyses showed that P. incana’s typically low reflectance is a function of its leaf canopy, as higher proportions of leaves gave a higher reflectance. Future research directions could focus on comparisons between P. incana and typical green vegetation internal leaf structures as potential causes of spectral differences. Collection of spectra for P incana and other invader vegetation types, some of which have similar characteristics, with a view to assembling a spectral library for delineating invaded environments using imagery, is another research direction.
- Full Text:
- Date Issued: 2009
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