The anatomy and ecophysiology of Mariscus congestus from three different habitats in the Albany and Bathurst districts of the Eastern Cape, investigated under field and laboratory conditions
- Authors: Sonnenberg, Bernd Jürgen
- Date: 1992
- Subjects: Cyperaceae -- South Africa , Plant anatomy , Plant physiology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4229 , http://hdl.handle.net/10962/d1003798 , Cyperaceae -- South Africa , Plant anatomy , Plant physiology
- Description: An investigation of the anatomy and gas exchange characteristics of Mariscus congestus in three different habitats was undertaken in order to establish whether M. congestus from the three different habitats displayed any ecotypic responses when placed in a new similar environment. It was hoped that the results of this investigation would yield evidence that would support the ecotype concept similar to the investigations of Milner and Hiesey (1964), Green (1969) and Slayter and Ferrar (1977). On the basis of the site leaf anatomy, M. congestus investigated at the coast (site 1) differed in many respects from the inland plants (sites 2 and 3). These differences suggest that the coastal plants may have undergone a slight ecotypic divergence from the inland plants. The anatomical investigation also suggested that the leaves of M. congestus from all three sites may either be C₄ NADP-ME or PCK and that all had typical Chlorocyperiod anatomy. The habitat microclimates at sites 1-3 had different light and water regimes. There were no significant differences between the 12 month temperature environments of the three sites. There was however, a minor difference between the coastal (high temperature) and the inland (lower temperature) sites. M. congestus at the three sites had significantly different CO₂ assimilation rates, transpiration and stomatal conductance in response to the differing habitat microclimates. The water use efficiency of the sites were however, similar. Site 1 attained the highest CO₂ assimilation rates, transpiration, stomatal conductance, and water use efficiency and site 3 the lowest. Under similar conditions the gas exchange data for the potted plants indicated that M. congestus from the different sites was typically C₄. The optimal photosynthetic temperatures of all the sites was above 30°C and they did not show significant inhibition of CO₂ assimilation by different oxygen concentrations. The results of the laboratory investigation of the potted plants suggested that the only site-specific (ecotypic) response of M. eongestus was the light intensity at which the plants from the different sites were light saturated. The light and temperature response of field plants under field conditions was not comparable to the light and temperature response of potted plants under laboratory conditions. This may have been due to the field results being obtained under differing water and soil nutrient regimes. The potted plants may also have had a reduced root mass compared to their field counterparts and the potted plants may have also have become root bound. Under field conditions the plants had differing light saturation points and optimal photosynthetic temperatures compared to the potted plants. This investigation thus did not support the hypothesis stated in this thesis. The data in this investigation thus may indicate that plants with as diverse habitats as Mariscus congestus that are removed from their natural habitats display rapid changes in gas exchange characteristics in response to their new microclimates, with few ecotypic physiological characteristics of the old habitat being retained.
- Full Text:
- Date Issued: 1992
The conservation status of subtropical transitional thicket, and regeneration through seeding of shrubs in the Xeric succulent thicket of the Eastern Cape
- Authors: La Cock, Graeme Dennis
- Date: 1992
- Subjects: Plant conservation -- South Africa -- Eastern Cape , Woody plants -- South Africa -- Eastern Cape , Shrubs -- South Africa -- Eastern Cape , Succulent plants -- South Africa -- Eastern Cape , Plant conservation -- South Africa -- Western Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4208 , http://hdl.handle.net/10962/d1003777 , Plant conservation -- South Africa -- Eastern Cape , Woody plants -- South Africa -- Eastern Cape , Shrubs -- South Africa -- Eastern Cape , Succulent plants -- South Africa -- Eastern Cape , Plant conservation -- South Africa -- Western Cape
- Description: The historically poorly conserved subtropical transitional thicket (STT) of the Eastern Cape is overutilised by domestic stock and game in the more xeric areas, and has shown no signs of recovery from this grazing pressure. It has been postulated that no regeneration through seeding occurs. This project was undertaken to determine: 1) how much STT has disappeared between 1950 and present, and what the current conservation status is; and 2) whether regeneration of the xeric succulent thicket is taking place through seeding, and if so, where. The study was conducted at the Andries Vosloo Kudu Reserve near Grahamstown. Approximately one-third less STT was mapped in this study, based on 1981 Landsat images, than was mapped in 1950. Approximately 10 % of all remaining STT is conserved. The order Kaffrarian thicket is poorly conserved. Newly germinated seedlings of a wide range of shrub species occurred under the canopies of a wide range of shrubs which served as nurse plants, throughout a gradient of veld condition. Seedlings of Portulacaria afra, the dominant shrub in xeric succulent thicket, were most common. Similarly all saplings recorded in a survey of saplings were associated with bushclumps. One-third of all saplings have the potential to contribute to the spread of bushclumps. Regeneration of xeric succulent thicket through seeding probably does occur, contrary to current ideas. Ptareoxylon obliquum was the most common sapling, despite mature trees now being scarce following earlier heavier utilisation . P. obliquum was also the nurse plant which supported the highest density of newly germinated seedlings. The possible role of P. obliquum in the functioning of xeric succulent thicket is discussed. The confinement of seedlings and saplings to areas under the canopies of trees and shrubs implies that the xeric succulent thicket will not recover rapidly if allowed to rest. Active management techniques will be necessary if rapid recovery is required. Bare areas between bushclumps may no longer be suitable germination habitats because of high Al concentrations. There was no evidence to support the idea that germination and establishment of shrubs in clear areas is linked to episodic climatic events. Dung middens of recently reintroduced black rhinoceros may however aid in germination of seeds and establishment of seedlings under certain climatic conditions. Recommendations for further studies, based on the findings of this project, are made. Possible management techniques aimed at the rapid recovery of this veld are suggested, and management proposals for the Sam Knott Nature Reserve/Andries Vosloo Kudu Reserve complex are made.
- Full Text:
- Date Issued: 1992
The interactive effects of light, temperature and CO₂/O₂ ratios in photosynthesis of Coix lachryma-jobi L
- Authors: Mjwara, Jabulani Michael
- Date: 1992
- Subjects: Coix , Plants -- Effect of light on , Plants -- Effect of oxygen on , Plants -- Effect of carbon dioxide on , Photosynthesis , Plants -- Effect of temperature on
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4216 , http://hdl.handle.net/10962/d1003785
- Description: A portable infra red gas analyzer was used to investigate the interactive effects of light, temperature, and CO,jO, ratios under controlled environmental conditions in an attempt to model gas exchange characteristics of Coix Iachryma-jobi L. Plotting light response curves as a function of temperature (20, 25 30 and 35°C) revealed no sign of light saturation even at a photosynthetic photon flux density (PPFD) close to 2000 !Lmol m-' sol. High net assimilation rates (A) of approximately 24 !Lmol CO, m"s'! were realized at 30-35°C. Assimilation (A) versus internal CO, partial pressure (C,) curves showed a steep rise with increase in C, but saturated at approximately 150 (JLII-!) and all the results, either in the absence or presence of 0" showed a similar response under all temperature regimes. C. Iachryma-jobi exhibited low CO, compensation points cr ) between 0 and 10 JLlI-! under similar experimental temperatures and either at 0 or 21%0,. The slopes of double reciprocal plots of llA versus llCi, were nearly identical and crossed the yintercept at almost identical points under all 0, concentrations. These data indicate first; that there was no apparent 0, inhibition and second; indicated that the apparent inhIbitor constant (K,) for 0, at the site of carboxylation did not change with increase in [OJ from 0 to 21% oxygen. These observations were further confirmed by results obtained from the analysis of apparent carboxylation efficiency (CE, as defined as the slope of response of A to increasing CO,), as no inhibition of A with increase of [OJ occurred. These characteristics were consistent with typical features of C,photosynthesis. The absence of 0, inhibition and low r values indicated that an efficient CO, concentrating mechanism which eliminates photorespiration exists in C. Iachryma-jobi. At the light microscope level, leaf anatomy exhibited typical C, structure viz. bundle sheath with large chloroplasts and this sheath is further surrounded by a radiate Kranz mesophyU cells. Furthermore the anatomical features suggested that C. wchryma-jobi was an NADP-ME species. Stomatal conductance (g,) to assimilation (g,/A) indicated an increase in A with decrease in g" an essential feature of improving water use efficiency (WUE), but one which drastically reduces CO, diffusion rate. The physical lintitation (stomatal lintitation, t) to CO, diffusion under various [0,] and temperatures, but constant PPFD, did not exhibit statistically significant change in t values at either 0 or 21% a, within each temperature regime, however there was a marked decrease in t as the plant approached its optimum photosynthetic temperature.
- Full Text:
- Date Issued: 1992
Coastal dune ecology and management in the Eastern Cape
- Authors: Avis, Anthony Mark
- Date: 1993
- Subjects: Sand dune ecology -- South Africa Shore protection -- South Africa Coastal zone management -- South Africa Sand dunes -- South Africa Sand dune plants -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4185 , http://hdl.handle.net/10962/d1003753
- Description: The importance of understanding the ecological functioning of coastal dune systems is emphasized as being fundamental to the correct management of the dune landscape. Dune vegetation along the Eastern Cape coastline, from Cape St Francis in the west to Kei Mouth in the east was described in terms of the distribution and phytochorological affinities of the taxa. At a regional scale species distribution was strongly influenced by both the climate, particularly rainfall, and the phytochorological affinities of the taxa. Seven communities were defined using TWINSPAN, and the interrelationships between these communities in anyone area appeared to be linked to a successional gradient. Dune Slacks are thought to play a key role in this successional sequence, and a temporal study of this community led to a conceptual model of plant succession in these dunefields. Climate, particularly rainfall and wind, are major factors influencing plant succession. Wind-borne sand causes the slacks to migrate in an easterly direction under the influence of the predominantly westerly winds, although easterly winds, mainly in summer months may reverse these trends. Autogenic changes appeared to be important in this succession, and a comparative study of a good example of a primary succession at Mtunzini in Natal was undertaken to elucidate the main mechanism of change. Eight communities that were identified here were concluded to be distnbuted along a gradient of increasing age, with successional changes predictable, linear and directional. Species were grouped in distinct zones along the continuum and edaphic changes (decrease in soil pH, increase in organic matter and exchangeable bases) were related to the community based changes in species composition. The mechanism of change supported the facilitation model of plant succession which is a modification of the original Clementsian concept. Similar results were found in the Eastern Cape, but due to the harsh environment, multiple pathways of succession exist. Data from this study lent support to the model of plant succession developed earlier, and confinned that the dune slacks played an important role in this facilitation by acting as centres of diversity. The foredunes were found to have an indirect role in protecting these slacks from salt spray and sand movement. The central theme of the management studies was to investigate the ecological consequences of recreational pressure within the dune environment. Current levels of beach utilization at East London were lower than other beaches in South Africa, but a general trend of increasing utilization due to sociopolitical changes can be expected. The suitability of questionnaire surveys to assess aspects such as the adequacy of facilities, perceptual carrying capacity and the beach users opinion of natural vegetation and preference for particular beaches was demonstrated. The dune vegetation was found to be sensitive to human trampling, but at current levels, the ecological carrying capacity will not be exceeded since results of the aerial census counts and questionnaire survey revealed that few people entered sensitive zones such as the coastal forest. More detailed long term studies on the susceptibility of dune vegetation to both trampling and off-road vehicle impacts revealed a low resilience of dune plant communities to these effects. Although susceptibility differed between the three communities tested, generally the greatest amount of damage occurred after the first few passages, and vehicles caused a more significant decrease in height when compared to trampling. Recovery rates were slow and low levels of repeated damage were sufficient to retard or prevent the recovery of the plants. Stricter control of vehicle use on beaches is therefore required, and in high use zones the ecological carrying capacity should be increased by providing access tracks if possible, or if not possible, by restricting access. A historical account of the process of dune stabilization showed that although first initiated in 1845, indigenous species were only used in the past three decades. The use of alien species has resulted in problems such as a reduction in the ecological integrity and aesthetic appeal of coastal systems. The techniques applied in the stabilization of drift sands with indigenous vegetation have been successful, as revealed by a quantitative survey of 17 sites in the Eastern Cape. Sites were grouped by multivariate analysis on the basis of their species composition, and variability between sites was dependent on the types of species planted. Selection of suitable species is therefore important and is discussed with respect to their natural distribution along the coast. The long term objective of stabilization should be the creation of functional, diverse, aesthetic ecosystems, since the intrinsic and economic value of the dune landscape for tourism lies therein. However, detailed studies should be undertaken prior to implementing a manipulative process such as dune stabilization, since ecological processes may be disrupted. An understanding of such processes is therefore important if one wishes to effectively manage the dune landscape.
- Full Text:
- Date Issued: 1993
Contemporary pollen spectra from the Natal Drakensberg and their relation to associated vegetation communities
- Authors: Hill, Trevor Raymond
- Date: 1993
- Subjects: Pollen -- South Africa -- KwaZulu-Natal Palynology -- South Africa -- KwaZulu-Natal
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4199 , http://hdl.handle.net/10962/d1003768
- Description: The research focuses on the contemporary pollen rain-vegetation relationship for vegetation communities within the Natal Drakensberg, a region which is recognized as having the potential for extensive palynological investigations. The objective was to investigate the fundamental assumption underlying palynology, viz: that the pollen rain of a particular region is indicative or representative of the existing vegetation of that region. If the modern pollen rain is indicative of and/or distinctive for a particular vegetation community then the principle of methodological uniformitarianism can be applied, which states that the present day patterns and relationships can provide a factual basis for the reconstruction of the past through the extrapolation of modern analogues backwards in time. A vegetation survey was conducted in thirteen communities identified as pertinent to the research and a two-year modern pollen rain sampling programme was carried out, using both surface soil and pollen trap samples as a means of recording and quantifying the pollen rain. Once the necessary sample preparation and pollen counts had been performed, descriptive and numerical/statistical methods were employed to determine and describe the existing pollen-vegetation relationship. Descriptive analysis of the data sets was carried out with the aid of spectra depicted as rotated bar graphs and representing the relative percentage frequencies of the collected/counted taxa. Annual and seasonal pollen influx values were calculated and presented. Analysis of variance was applied to test various hypotheses related to sampling strategy and pollen influx variation. Statistical methods employed were two-way indicator species analysis (a classification analysis technique), detrended correspondence analysis and principal components analysis (ordination techniques), canonical correlation analysis (for data set association) and multiple discriminant analysis (for determination of vegetation zonal indices). The latter technique allowed for the probability of modern analogues to be assessed which are necessary for accurate interpretation of fossil pollen assemblages if the assumption under investigation is correct. The findings of the study were that the modern pollen rain-vegetation assumption holds true. Recommendations are put forward regarding future contemporary pollen studies with regards to the number of soil and pollen trap samples required, the magnitude of the pollen count and the numerical/statistical techniques most appropriate to clearly interpret the results. The conclusions are that future fossil pollen spectra can be expected to provide a good indication of former regional vegetation patterns for the study region. The study has extended the limited understanding of the contemporary pollen rain-vegetation relationship in South Africa and enables the interpretation of fossil pollen spectra to be carried out with greater confidence. This in turn lends greater credibility to possible Quaternary environmental change models required to help understand present and possible future environmental change.
- Full Text:
- Date Issued: 1993
Studies on dune rehabilitation techniques for mined areas at Richards Bay, Natal
- Authors: Moll, John Bingham
- Date: 1993
- Subjects: Restoration ecology -- South Africa -- KwaZulu-Natal -- Richards Bay , Sand dune ecology -- South Africa -- KwaZulu-Natal -- Richards Bay , Sand dunes -- South Africa -- KwaZulu-Natal -- Richards Bay , Mineral industries -- Environmental aspects -- South Africa -- KwaZulu-Natal -- Richards Bay
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4235 , http://hdl.handle.net/10962/d1003841
- Description: Rehabilitation is a dynamic process influenced by factors related to more than one field of ecology. It is therefore necessary to consider all these components when assessing the rehabilitation, although in the initial stages the successful revegetation of the disturbed areas is the most important criterion. Richards Bay Minerals, on whose mining site this project was carried out, is dredge mining heavy minerals on the north coast of Natal, where they have rehabilitated mined areas since 1978. This project has been carried out to establish: 1) The success of their dune forest rehabilitation using quantitative techniques. 2) The available seed bank in their rehabilitation stands. 3) The similarities in the succession taking place in rehabilitation stands compared to the revegetated stands in the vicinity of Richards Bay. 4) The best methods for creating alternative vegetation communities, especially grasslands, with a high species diversity on the mined tailings. This study reviews only the success of rehabilitation of the natural vegetation but other studies focusing on the insect, reptile, mammal and bird populations are also being undertaken by other researchers. No particular method of determining the success of vegetation rehabilitation has been chosen by restoration ecologists. Therefore in this study a broad range of quantitative techniques were used to show whether successional changes are occurring in the vegetation and physical environment. The results obtained from sampling the rehabilitated vegetation have shown that both the species richness and diversity are increasing as the returned vegetation matures. Levels of soil properties such as Sodium, Phosphate, Calcium and percentage organic matter have also risen with increasing stand age. Community complexity is also increasing with stand age, and TWINSPAN and DECORANA plots have separated out the differently aged stands based on their differences. A "pilot" study was done on the seed bank present in the rehabilitation stands. This has shown the presence of large amounts of early successional, mostly herbaceous species. Seeds of later successional and woody species were scarce which may be a result of the sampling intensity used. However seeds of late successional ground cover species were found in the older stands. Comparisons between the natural revegetation of disturbed areas in the vicinity of Richards Bay and the rehabilitation stands revealed similarities in both species composition and complexity. Species richness and diversity values are comparatively similar for the younger revegetated and older rehabilitation stands, and lWlNSPAN and DECORANA analysis techniques clustered the samples recorded from these areas in close proximity on their relative plots. The oldest revegetated sites contain a number of species found in the rehabilitated vegetation but as Acacia karroo has thinned-out in these stands many of these other species are now mature individuals. Attempts at rehabilitating an area of grassland at Richards Bay Minerals has not produced satisfactory species diversity and experimental manipulations were used to try and increase the diversity of the existing Eragrostis curvula dominated community. Of the several treatments used for the manipulation, a combination of burning and further topsoiling was the most successful in reducing Eragrostis importance and in increasing the species richness. Grassland topsoil spread directly onto the bare tailings produced an extensive vegetation covering over a short period but species richness was not significantly greater than for the existing Eragrostis dominated grassland, and further treatments and management needs to continue if this technique is to be employed. Only a limited amount of alien infestation of the rehabilitated areas was evident from the sampling undertaken during this research. As the removal of alien plants is an ongoing process and the rehabilitation stands are continuously monitored to identify any new invaders, this is not expected to become a problem. From the results of work done overseas and the rehabilitation carried out in South Africa it appears that it is possible to return natural vegetation communities on mined areas. That this is a lengthy process is to be expected but by manipulating the vegetation and continuously monitoring the process it may be possible to speed up development. Areas in need of further research have been identified based on the findings of this project. This will help to reinforce the undertaking of management proposals that will enhance the vegetation recovery and the success of the rehabilitation programme.
- Full Text:
- Date Issued: 1993
Constituent processes of leaf senescence in Hordeum vulgare cv. Dyan
- Authors: Afitlhile, Meshack Mosimanegape
- Date: 1994
- Subjects: Leaves , Leaves -- Development
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4184 , http://hdl.handle.net/10962/d1003752
- Description: Changes in chlorophyll content, carotenoid content and composition, abscisic acid and phaseic acid levels, hydrolytic enzyme activity and polypeptide pattern were monitored during senescence of the primary attached leaves of Hordeum vulgare L. cv. Dyan. Senescence occurred due to the normal course of leaf development or was induced by incubation of leaves in darkness. Loss of chlorophyll and total leaf protein was retarded in light whereas it continued rapidly in leaves from dark-incubated seedlings. Chlorophyll alb ratio increased with the progression of senescence, suggesting that chlorophyll b was referentially degraded during this process. Loss of total protein coincided with enhanced activity of acid and neutral proteases. In contrast, loss of chlorophyll was not accompanied by an increase in· peroxidase activity, suggesting that this enzyme was not responsible for initiating chlorophyll breakdown. Carotenoid and abscisic acid levels were monitored in the same tissue extracts. The results obtained show that the increase in endogenous levels of abscisic acid, induced by senescence, correlated with enhanced epoxidation of the xanthophyll cycle, ie., increased conversion of zeaxanthin to antheraxanthin and all-trans-violaxanthin. In addition, an increase in abscisic acid levels occurred concomitant with a decrease in all-trans-violaxanthin and 9'-cis-neoxanthin, suggesting an apparent 1:1 relationship on a molar basis. It is therefore proposed that enhanced abscisic acid production, due to foliar senescence, arises from fluctuations in carotenoid turnover. Polypeptide patterns in isolated chloroplasts, purified thylakoid and stromal fractions were very similar for leaves incubated in either light or darkness. A decrease in intensity of bands was observed in isolated chloroplasts and stromal fractions. Intensity of bands in thylakoids remained unchanged with the progression of senescence. Protein standards of peroxidase and lipoxygenase co-migrated with proteins of the isolated chloroplast. Although tentative, some proteins of the chloroplast may be representative of precursors of hydrolytic enzymes which are known to increase during senescence.
- Full Text:
- Date Issued: 1994
The influence of the composition of mixed Karoo vegetation on the grazing habits of Merino and Dorper wethers
- Authors: Roux, Francis Augustus
- Date: 1994
- Subjects: Grazing -- South Africa -- Karoo , Sheep -- Feeding and feeds , Dorper sheep -- South Africa , Merino sheep -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4223 , http://hdl.handle.net/10962/d1003792 , Grazing -- South Africa -- Karoo , Sheep -- Feeding and feeds , Dorper sheep -- South Africa , Merino sheep -- South Africa
- Description: The primary objective of this research project was to determine whether area-selective grazing, by Dorper and Merino wethers, took place in small grazing camps as governed by differences in vegetal cover. The main research techniques employed were the descending-point method for the determination of botanical composition, sub-division of the camps into gridblocks to trace sheep movement in relation to vegetation patterning, fistulated animals to determine diet selection, the electronic theodolite for micro-topography, and few minor techniques. The result have shown that area- patch- and species selective grazing are prevalent in small grazing camps under "normal" stocking densities, and that different breeds of stock (Merino and Dorper sheep) have different grazing patterns and diet selection . Climax and sub-climax areas were those primarily select ed for grazing. There is little or no correlation between botanical composition and diet selected as per fistula ted animal. The average distances travelled by Dorpers and Merinos was 2 km / day and 3.1 km/day respectively. Plant phenology did not have a detectable influence in the choice of diet.
- Full Text:
- Date Issued: 1994
A comparison of the reproductive strategies of key species of a prograding dune system in the Mlalazi Nature Reserve, Natal
- Authors: Todd, Colleen Barbara
- Date: 1995
- Subjects: Sand dune plants -- South Africa -- KwaZulu-Natal -- Mlalazi Nature Reserve , Sand dune plants Comparative studies
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4231 , http://hdl.handle.net/10962/d1003800 , Sand dune plants -- South Africa -- KwaZulu-Natal -- Mlalazi Nature Reserve , Sand dune plants Comparative studies
- Description: The succession on the dunes of the Mlalazi Nature Reserve represents a classical example of primary succession. The reproductive strategies of eight key species were compared to determine some of the mechanisms affecting the community dynamics, at the population level, in the early stages of succession. There is a temporal separation in the flowering and fruiting phenologies. Passerina rigida, Stipagrostis zeyheri and Imperata cylindrica produced small seeds with a low fruit/seed mass ratio within a short cycle. The seeds are suitable for wind-dispersal. The animal-dispersed species; Eugenia capensis, Mimusops caffra and Scaevola plumieri, produced large fleshy seeds with a high fruit/seed mass ratio within cycles of six months and more. Chrysanthemoides monilifera, also an animal-dispersed species, produced a large quantity of small fleshy seeds throughout the year. The fern, Microsorium scolopendrium produced spores throughout the year. The staggered fruiting and flowering phenology ensures a year-round availability of fruit in the dunefield. The key species formed less than half of the species composition of the soil seed bank. The size and range of the soil seed bank differed between the species. P. rigida and S. plumieri formed a high proportion of the seeds in the soil with a wide distribution along the successional gradient. The other species had low soil seed densities with short distribution ranges, or were not present. P. rigida and S. plumieri are easily dispersed species, whereas the other species may have a more restricted and clumped distribution due to the effect of foragers. A high density of P. rigida and E. capensis seeds were found under the parent trees. Only seeds of P. rigida and S. zeyheri were found in the soil in the open. Seeds of P. rigida, S. zeyheri, E. capensis and M. caffra were found under the canopies of P. rigida, E. capensis and M. caffra. No seeds of C. monilifera and I. cylindrica were found in the soil, possibly due to predation. The period of the study (September 1991 to November 1992) was in a dry or drought cycle with only 56.8% of the mean annual rainfall falling. Seed germination and seedling survival of all the species were affected by these dry, warm climatic conditions. The species had seedling densities of less than 4 seeds/m². The environmental conditions along the successional gradient also had an effect on seed germination and seedling survival. Environmental factors of soil pH, light intensity and surface soil temperatures were higher in the open than under canopy. Soil pH and the understorey cover decreased as the light intensity decreased from under the canopy of P. rigida to M. caffra . Litter cover and plant height increased. E. capensis had measurements intermediate to the two species, but had higher surface soil temperatures and plant height than P. rigida. Seedlings of P. rigida in the open and under the canopy of the parent plants had died by the end of the monitoring period. 50% of the seedlings of S. zeyheri under the canopy of P. rigida and M. caffra died. The mortality rate of the seedlings of E. capensis was lower under M. caffra than under the parent plants. I. cylindrica may be propagated vegetatively. However, the mortality of the propagules was greater under the canopy of E. capensis than under P. rigida. M. caffra only germinated under the canopy of E. capensis with a 100% mortality of the seedlings. M. scolopendrium only produced propagules through vegetative propagation under the canopy of E. capensis and M. caffra. The mortality of the young ferns was less than 50% and less under M. caffra than under E. capensis. No seedlings of C. monilifera or S. plumieri were found. The seed distribution range, seed germination requirements and the effect of the environmental conditions on the germination of the seeds and seedling establishment of the species appear to important factors of the reproductive strategies regulating the size of the species populations along the successional gradient.
- Full Text:
- Date Issued: 1995
A taxonomic study of Senecio speciosus, Senecio macrocephalus and possible hybrid populations using morphological data, toxicty tests and chromatography
- Authors: Lewis, Gillian Elizabeth
- Date: 1995
- Subjects: Senecio , Senecio -- Analysis , Shrimps , Artemia
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4209 , http://hdl.handle.net/10962/d1003778
- Description: The variation between populations of Senecio speciosus Willd., Senecio macrocephalus DC. and intermediate plants was investigated in a comparative study of morphological characters, toxicity of plant extracts to brine shrimps (Artemia salina) and chromatography of plant extracts. Specimens were collected at 18 localities in the Eastern Cape Province. All these specimens were examined morphologically and chemical extracts were tested for toxicity and by comparative chromatography. The collection of Senecio speciosus and Senecio macrocephalus specimens in the Selmar Schonland Herbarium (GRA) was also examined morphologically. Six geographical areas were represented in the combined collections. Analysis of morphological data separated typical Senecio speciosus and Senecio macrocephalus at either end of hybrid index histograms and principal components analysis diagrams. The intermediate populations displayed morphological characters of both Senecio speciosus and Senecio macrocephalus. Some specimens were intermediate between these two species, falling within the range of variation of these species while others fell outside this range. The Brine Shrimp Assay was used to test for toxicity and to investigate the possibility of using toxicity data as a genetic marker in taxonomic studies. As Senecio speciosus extracts were less than 1% toxic and Senecio macrocephalus extracts were at least 95% toxic to the brine shrimps it is suggested that in this case toxicity can be used as a genetic marker. Toxicity can even be described as a good taxonomic character as discontinuity is very sudden and complete. The intermediate plants in the Grahamstown area were at least 92% toxic to the brine shrimps linking them to Senecio macrocephalus. Thin layer and paper chromatography were used as comparative techniques to study the chemical profiles of the specimens. Alkaloids, terpenoids and flavonoids were studied. Thin layer chromatography to separate the alkaloid components of the plant extracts showed Senecio speciosus and Senecio macrocephalus to have distinct chemical profiles suggesting that they are separate species. The intermediate plants- were found to contain chemical compounds matching either or both Senecio speciosus and Senecio macrocephalus suggesting that they may have arisen by hybridisation. In a preliminary investigation Senecio speciosus extracts showed a complete lack of terpenoid compounds whereas extracts from Senecio macrocephalus and the intermediate specimens tested gave a terpenoid colour reaction in the basal spot only. This links the intermediate populations with Senecio macrocephalus. Paper chromatography to separate the flavonoid constituents of the plant extracts also showed typical Senecio speciosus and Senecio macrocephalus to be distinct. The intermediate populations contained flavonoid compounds from one or both of these species. The populations in the Grahamstown area show morphological features close to and in some cases indistinguishable from Senecio speciosus. Chemically these specimens show some similarities with Senecio macrocephalus. In the East London area specimens show a similar mixture of characters but appear morphologically to be closer to Senecio macrocephalus. However, in the Amatole Mountains, despite both species being present in the same locality it appears that no hybridisation has occurred. It is therefore suggested that at some of the localities where the geographical ranges of Senecio speciosus and Senecio macrocephalus overlap in the Eastern Cape Province hybridisation between these two species occurs.
- Full Text:
- Date Issued: 1995
An integrated approach to aspects of coastal dune planning and management along a portion of the Eastern Cape coastal zone
- Authors: Hellström, Gavin B
- Date: 1995
- Subjects: Coastal zone management -- South Africa , Sand dune ecology -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4197 , http://hdl.handle.net/10962/d1003766 , Coastal zone management -- South Africa , Sand dune ecology -- South Africa
- Description: Ecological evaluation techniques have been used to classify or evaluate the relative conservation worthiness of a portion of the Eastern Cape coastal zone from Cannon Rocks to Port Alfred. A system-based approach, using a basic GIS, was used to compare three aspects of the coastal zone. Two existing planning documents (EMATEK/s Coastal Vegetation Importance Rating plan and CPA's Cape Coastal Conservation plan) were statistically compared - based primarily on the size and number of the landscape fragments (environmental criteria polygons). The resultant plan, an Intermediate Sensitivity Class map, was further integrated with the biophysical aspect of the coastal zone - coastal dunes. The final map is the product of these overlays to be used as a-working overlay for coastal zone decision-making. This is an Environmental Sensitivity map, which has no particular direct reference to any particular biophysical criteria, which categorizes the coastal zone according to the environmental sensitivity or conservation worthiness of the site. The categories are listed according to a sliding-scale of sensitivity or worthiness. There is, however, it strong association between the final map and the vegetation status of the coastline, as a direct result of the vegetation rating map and indirectly from the perception based coastal conservation plan. The formation of most assessment or evaluation plans are based on the vegetation status of the area. This map can be overlayed over the particular stretch of the coastline which it covers and the particular conservation status noted. There are numerous techniques available for assessment and evaluation each having their own specific merits and advantages. This plan, however, is a first attempt at integrating other specific plans into a single working document for the coastal zone manager.
- Full Text:
- Date Issued: 1995
Cell-free biosynthesis of abscisic acid (ABA) in extracts of flavedo from Citrus sinensis (L.) osbeck
- Authors: Richardson, Gaynor Rose-Marie
- Date: 1996
- Subjects: Biosynthesis Abscisic acid Citrus fruits
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4221 , http://hdl.handle.net/10962/d1003790
- Description: The biosynthetic origin of the plant growth regulator abscisic acid remains equivocal and almost nothing is known about the enzymes involved in this process. The present research programme describes the development of a cell-free system, capable of synthesizing abscisic acid and attempts to provide further information about the biochemistry and enzymology of this important biosynthetic pathway. Cell-free extracts were prepared either directly from the flavedo (crude) or from an acetone powder derived from flavedo, of mature coloured fruits of Citrus sinensis L. cv. Midknight and incubated with mevalonic acid, isopentenyl pyrophosphate, famesylpyrophosphate, geranylgeranyl pyrophosphate, ß-carotene and 1',4'-trans-abscisic acid diol. The neutral and acidic products formed were purified by thin-layer chromatography and high performance liquid chromatography, and quantified by high performance liquid chromatography, gas chromatography-electron capture and unequivocally identified by combined gas chromatography-mass spectrometry. Abscisic acid, 1',4'-trans-abscisic acid diol and phaseic acid were unequivocally identified as the major acidic products formed in this cell-free system. The acid fraction also contained xanthoxin acid. Labelled and unlabelled ß-carotene was converted into the neutral compounds xanthoxin and xanthoxin alcohol. In addition. high performance liquid chromatography-photodiode array analYSis of the oxy-carotenoid fraction revealed the complete spectrum of ß, ß-carotenoids induding zeaxanthin, antheraxanthin and violaxanthin with accumulation of an oxygenated carotenoid tentatively identified as 9- cis-violaxanthin. Identification of putative C₁₅ intermediates was achieved by either UV spectrophotometry and combined capillary gas chromatography-mass spectrometry or microchemical analYSis and co-chromatography. Refeeding studies using (±)-[2-¹⁴C]_ abscisic acid diol as substrate revealed that abscisic acid was not metabolized to abscisic acid diol, suggesting that it was/is produced as an intermediate rather than as a catabolite of ABA in this system. Stigmasterol, and to a lesser extent cholesterol reduced conversion of ß-carotene to abscisic acid but did not influence transformation of 1',4'-trans-abscisic acid diol to abscisic acid. AM01618 stimulated fonnation of abscisic acid and appeared to exert its effect at the level of conversion of 1' ,4'-trans-abscisic acid diol. Zeatin and the cytokinin analogue, ancymidol inhibited the biosynthesis of abscisic acid whereas dithiothreitol increased incorporation of label from ß-carotene into abscisic acid suggesting involvement of a cytochrome P450-type mixed function oxidase in this reaction sequence. Sodium dodecylsulphate polyacrylamide gel electrophoresis of the enzyme extract derived from Citrus flavedo revealed the presence of a 53 kD protein with peroxidase activity characteristic of a cytochrome P-450. Abscisic acid biosynthesizing activity was always greater in extracts from acetone powder and abscisic acid biosynthesis was enhanced in the presence of AMO 1618, NAD+, NADH, NADPH, MgCI₂ and Molybdate but was inhibited by FAD. Activity was further enhanced by the addition of (R,S)-abscisic acid as a cold-pool trap and by induding 0.1% w/v of either Tween 20 or Triton X 100 in the extraction buffer. When cis-ß-carotene was used as substrate, no abscisic acid was produced. Conversely when either all-trans-ß-carotene or a mixture of the two isomers was used, incorporation into abscisic acid occurred. Upoxygenase activity in cell-free extracts of Citrus flavedo increased with increasing protein concentration. As the ability of lipoxygenase to make xanthoxin from violaxanthin, had been reported, increased activity in the cell-free system implied that carotenoid deavage was being brought about by a non-haem oxygenase with lipoxygenase-like properties. Reports had implicated phoshorylation in the activation of many catalytic enzymes (Hanks et aI., 1985). Phosphorylation of the enzymes in this cell-free system proved unsuccessful. Further, it had been reported that in vitro phosphorylation of several membrane polypeptides and soluble polypeptides from com, had been promoted by the addition of Ca²₊ In this cell-free system Ca + did not have a stimulatory effect on protein phosphorylation. Dioxygenases generally occur as soluble enzymes, where they catalyse many oxygenation reactions in metabolic pathways. The addition of 2-oxo-glutarate, a requirement of most soluble oxidases, did not affect the activity of the cell-free system.
- Full Text:
- Date Issued: 1996
Production ecology of bryophyte vegetation at Marion Island (Sub-Antarctic)
- Authors: Russell, Shaun
- Date: 1996
- Subjects: Bryophytes -- marion island (Prince edward islands) -- Ecology
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4224 , http://hdl.handle.net/10962/d1003793
- Description: The world's tundra regions can be considered as the last unexploited terrestrial biome on the earth's surface. Bryophytes contribute significantly to primary production and nutrient cycling in tundra habitats but received considerably less attention than the vascular plants during research for the Tundra Biome Project of the International Biological Programme in the 1970s. The IBP synthesis recognised this and called for more bryophyte production data and improved methodology in future studies. The synthesis also identitied the need for more information on within-site variability, energy/chlorophyll relationships and mineral nutrient studies where tundra bryophyte production patterns are concerned. Marion Island in the sub-Antarctic has an oceanic "tundra" type of vegetation, and the island offers the characteristics of an ideal "natural laboratory" for conducting fundamental ecological research particularly in the field of primary production and energy flow. Studies at Marion Island paralleled those of the IBP but also concentrated on the vascular component of the vegetation. Bryophytes contribute up to 60% of the biomass and 90% of plant cover in the mires that dominate the well-vegetated coastal plain of Marion Island. Following the termination of IBP research therefore it was decided to extend these studies during the 1980s by measuring growth and characterising the major factors influencing growth patterns in Marion Island bryophytes. In this thesis information is given on the physical and biotic environment of Marion Island. Data is presented on the cover, biomass, seasonal and annual production values, and turn-over rates (decomposition) of 15 bryophyte species found across the full range of habit at types at Marion Island. An analysis is also made of growth-associated variables viz. soils, climate, plant energy, chlorophyll. water and mineral nutrient contents. Production was found to be related broadly to moisture-related variables, overlain by nutrient factors in some instances. Higher absolute production figures were obtained than at other tundra sites and interesting phenological data are discussed. The results suggest that decomposition is controlled mainly by tissue degradability factors and that decomposition is more significant than production in controlling biomass accumulation. A model is given for production/decomposition patterns across the range of habitat conditions at Marion Island. Several growth measurement techniques were tested and recommendations are made concerning methodology for future bryophyte production studies. By reference to ecological data collected during the study.
- Full Text:
- Date Issued: 1996
Effects of sustained elevated CO₂ concentration on two cultivars of barley (Hordeum vulgare L.)
- Authors: Siphugu, Mashudu Victor
- Date: 1997
- Subjects: Barley Barley -- Growth Photosynthesis -- Research Plants -- Effect of carbon dioxide on
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4226 , http://hdl.handle.net/10962/d1003795
- Description: The enormous burning of fossil fuel and deforestation have caused an increase in the atmospheric CO₂ concentration ([CO₂]) during the last century. This will invariably have profound direct and indirect effects on plant carbon metabolism. The majority of research on the effects of CO₂ enrichment on plants are short-term and are done on other crops, but very little have been done on barley. This project aimed to determine the effects of long-term CO₂ enrichment on photosynthesis, growth and grain yield on barley. Hordeum vulgare L. cvs Stirling and Schooner plants were grown from seeds in controlled environment chambers at ambient (350) and elevated (600) μmol molˉ¹ [CO₂]. Measurements of net assimilation rate (NAR), photosynthetic pigments content and growth parameters were started 7 days after germination (DAG) and continued until senescence. The anatomy of matured fully developed leaves was also monitored. Elevated [CO₂l resulted in an increase in NAR in the two cultivars from days 7 until 14, after which the stimulation of NAR of CO₂-enriched plants started to decrease. At the onset of senescence, NAR was almost equal in plants grown under both ambient and elevated [CO₂]. The response of assimilation as a function of internal [CO₂l (C₁) at the end of the experimental period showed a significant decrease in both the initial slope of the A/C₁ curves and the CO₂-saturated photosynthetic rates in the two cultivars. Stirling showed no significant changes in the content of chlorophyll α,chlorophyll б or in total carotenoids. However, Schooner showed a stimulation in chlorophyll α content at day 7, but decreased at day 28. Chlorophyll б and total carotenoids content were not affected by CO₂ enrichment. While total above-ground biomass was not affected by elevated [CO₂] in the two cultivars, total plant height decreased significantly after 14 days in Stirling whereas no significant change occurred in Schooner throughout the experimental period. Leaf area was not significantly affected by CO₂ enrichment in the two cultivars although the leaves in CO₂ enriched plants were slightly shorter. Anatomical studies reveal that leaf thickness was significantly increased by CO₂ enrichment in Stirling, but the increase was not significant in Schooner. Both cultivars did not show any significant effect on chloroplast morphology and ultrastructure as a consequence of elevated CO₂ exposure. No signs of starch accumulation were evident in variety Schooner, but Stirling showed some form of starch accumulation, under increased atmospheric [CO₂]. Elevated CO₂ resulted in a significant reduction by more than 50 % in the number of grain yield per plant in both Stirling and Schooner. Results from this study therefore indicate that CO₂ enrichment will not be beneficial in terms of growth and yield in this important crop.
- Full Text:
- Date Issued: 1997
The effect of elevated CO₂ on Phaseolus vulgaris L. cv Contender
- Authors: Mjwara, Jabulani Michael
- Date: 1997
- Subjects: Plants -- Effect of carbon dioxide on Kidney bean
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4215 , http://hdl.handle.net/10962/d1003784
- Description: The response of Phaseolus vulgaris L. cv. Contender grown in controlled environmental conditions, at either ambient or elevated (360 and 700 μmol mol ̄¹, respectively) CO₂ concentrations ([CO₂]), was monitored from 10 days after germination (DAG) until the onset of senescence. Elevated CO₂ had a pronounced effect on total plant height (TPH), leaf area (LA), dry weight (DW) accumulation and specific leaf area (SLA). All of these were significantly increased by elevated [CO₂] with the exception of SLA, which was significantly reduced. Except for higher initial relative growth rates (RGR) in CO₂-enriched plants, RGR did not differ significantly between the two CO₂ treatments throughout the remainder of growth period. While growth parameters clearly differed between CO₂ treatments, the effects of CO₂ on many physiological processes including net assimilation rate (NAR), Rubisco activity, and some foliar nutrient concentrations were largely transient. For example, CO₂ enrichment significantly increased NAR, but from 20 DAG onward, NAR declined to levels measured on plants grown under ambient CO₂. Similarly, the decline in both foliar N concentration and Rubisco activity in CO₂-enriched plants after 20 DAG was significantly greater than the decline observed for ambient CO₂ plants. Soluble leaf protein and total chlorophylls (a+b) were also significantly reduced in plants grown under elevated CO₂. Chlorophyll (a/b) ratios increased with time underelevated CO₂, indicating that the rate of decline of chlorophyll b was higher than that of chorophyll α. No significant changes in total carotenoid (x+c) levels were observed in either CO₂ treatment. Under enhanced CO₂, the foliar concentrations of K and Mn were increased significantly, while P, Ca, Fe and Zn were reduced significantly. However, changes in Mg and Cu concentrations were not significant. High CO₂-grown plants also exhibited pronounced leaf discoloration or chlorosis, coupled with a significant reduction in leaf longevity. The levels of non-structural carbohydrates (sucrose, glucose, fructose and starch) and nitrogenous compounds (nitrogen, total soluble proteins and free amino acids) were determined for leaves and developing seeds of P. vulgaris. Leaf tissue of elevated CO₂-grown plants accumulated significantly higher levels of both soluble sugars and starch. Leaf ultrastructure revealed considerable erilargement of starch grain sizes with surface areas more than five times larger compared to those of control plants. No apparent differences in structure and membrane integrity of chloroplasts in both CO₂ treatments were noted. Although ambient CO₂-grown plants had comparatively low levels of non-structural carbohydrates (NSC), they accumulated significantly higher levels of nitrogenous compounds. The levels of NSC were consistently higher in seeds of plants grown under elevated CO₂. In comparison to plants grown at elevated [CO₂], pods and seeds of ambient CO₂-grown plants had significantly larger pools of free amino compounds and N. Stomatal conductance (gs) declined significantly, as expected for plants grown under elevated CO₂. This was accompanied by a decline in transpiration rates (E). Reduced gs and E led to high AlE ratio, which meant improved water use efficiency (WUE) values for CO₂-enriched bean plants. Leaf carbon isotope discrimination (∆) against the heavier isotope of carbon (¹³C), has been used to select for high WUE in C₃ plants. In plants grown at elevated CO₂ concentration, ,1 was significantly reduced. Although ∆ was negatively correlated with WUE in both CO₂ treatments, the correlation was steeper and highly negative for CO₂-enriched plants. These results indicate underlying differences in gas-exchange physiology, including stomatal responses between ambient and elevated CO₂-grown plants. Photosynthetic acclimation was investigated using the response of assimilation to internal carbon dioxide concentration (A/C₁ curves). At early stages of growth, the initial slope of the A/C₁ response curve did not differ with CO₂ treatment. In contrast, CO₂-saturated photosynthetic rate (Amax) was significantly higher in plants grown under elevated versus ambient CO₂ at 15 DAG. However, at subsequent stages of growth both the initial slope and Amax declined in bean plants grown in elevated CO₂. Apparent carboxylation efficiency (ACE, estimated from the initial slope of A/C₁ response) values followed a similar trend and were significantly reduced in CO₂-enriched plants. These results indicate that acclimation or negative adjustment of photosynthesis may have been caused by a combination of both stomatal and biochemical limitations. Bean plants grown under conditions of elevated atmospheric CO₂ flowered 3 to 4 days earlier, and produced significantly more flowers and pods than plants grown at ambient conditions. Plants grown at elevated CO₂ aborted 22 and 20% more flowers and pods, respectively, than plants grown at ambient CO₂. Elevated CO₂ also significantly increased the number of tillers or lateral branches produced by plants, which contributed to a significant increase in pod number and seed yield in these plants. Although plants grown at elevated CO₂ produced on average 8 seeds per pod, while plants grown under ambient CO2 conditions produced 5 seeds per pod, the greater number of seeds was offset by lower seed weights in plants grown under _ elevated CO₂. Thus, despite high seed yield in beans grown under elevated CO₂, the harvest index (HI) did not change significantly between CO₂ treatments.
- Full Text:
- Date Issued: 1997
Ammophila arenaria (L.) Link (marram grass) in South Africa and its potential invasiveness
- Authors: Hertling, Ursula Margret
- Date: 1998
- Subjects: Grasses -- South Africa Alien plants -- South Africa Sand dune plants -- South Africa Grasses -- Ecology -- South Africa Sand dune ecology -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4198 , http://hdl.handle.net/10962/d1003767
- Description: Ammophila arenaria (L.) Link is a European sand binding plant which was introduced to South Africa in the 1870's for the purpose of dune stabilisation. Because of its known invasiveness along the west coast of North America, and the problems South African ecosystems experience with alien invader plants, it was deemed necessary to study the biology and ecology of this species in South Africa. The aim of this thesis is to establish the potential invasiveness of A. arenaria on Cape coastal dunes and assess whether its use for dune stabilisation is still justifiable. A. arenaria occurs nowadays between the Langebaan area on the west coast and Gonubie in the Eastern Cape. Although widespread, the grass appears to occur only in areas where it has been planted. Its unaided spread may be prevented by adverse climatic conditions. Studies on the community biology of South African A. arenaria communities as compared to indigenous dune plant communities and natural A. arenaria communities in Europe cannot confirm the aggressive behaviour that A. arenaria shows in California and Oregon. In South Africa, A. arenaria does not exert strong floristic control over other species or outcompete and replace them, neither does it alter the topography of South African beaches and dunes. It forms weaker species associations and tends to develop communities of little species variability along the coast, thereby proving its alienness in South Africa, but this does not imply its invasiveness. Studies on succession of A. arenaria stabilisation areas show that monospecific A. arenaria plantings can be succeeded by a species-rich indigenous dune scrub or dune fynbos within a few decades. Plant-parasitic nematodes have been recorded, which may play an important role in the succession of A. arenaria stands in South Africa as was observed in Europe. Monitoring of A. arenaria communities and indigenous communities over nearly three years shows that A. arenaria is not spreading and replacing indigenous plants but in fact rather being replaced by the latter. A. arenaria profits from a superior sand burial tolerance but is affected by adverse climatic factors, mostly the lack of rainfall and strong radiation. In comparison to the indigenous dune grasses Thinopyrum distichum and Ehrharta villosa, it does not show any superior demographic traits such as an unusually high growth rate or large aboveground biomass production. Although A. arenaria produces viable seed in South Africa, the indigenous grasses show better germination and seedling establishment in the field. This study indicates that A. arenaria is not invasive in South Africa, nor likely to become an invader species in the near future. However, more research is required to confirm these results and more caution recommended regarding the further use of this alien grass for dune stabilisation.
- Full Text:
- Date Issued: 1998
Natural resources and local management in the Hewu District of the Eastern Cape : limitations to achieving sustainability
- Authors: Nkansa-Dwamena, Yaw
- Date: 1998
- Subjects: Natural resources -- South Africa -- Management , Natural resources -- South Africa -- Eastern Cape -- Management
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4218 , http://hdl.handle.net/10962/d1003787 , Natural resources -- South Africa -- Management , Natural resources -- South Africa -- Eastern Cape -- Management
- Description: The Mceula Commonage Land in the Hewu district lies due northwest of Whittle sea and west of Queenstown in the Eastern Cape. This thesis has two main objectives. Firstly, to survey and analyse the condition of the natural resource. base in the Hewu district with particular reference to water, soil, vegetation and land use. Secondly, to investigate the relationship between scientific approaches to assessing land use degradation and to compare these to the results obtained using a participatory approach of the rural environment of the Hewu district of the Eastern Cape. Random quadrats (4m2) were sampled and corresponding line transects were done with increasing distances from the villages. The Braun-Blanquet method was used to find the cover and abundance of the various species of plants. Data obtained from point sampling along 100 metre line transects was used to assess the condition of the veld using Trollope's technique. Six communities were defined using TWINSP AN, and grazing capacities and veld condition scores of the respective sites were calculated. It was concluded that the six communities were distributed along a gradient of palatable to non palatable grass and grasslike species. Rangelands close to the villages had low veld condition scores and percentage plant cover as opposed to those farther away from the villages. The null hypothesis of no significant difference between the percentage plant cover and condition of the veld close to the villages and farther away from the villages was rejected. Whilst it is urgent to resolve political disputes around land through land distribution, a key issue for the future is sustainability of the natural resource base of South Africa. To attain this, the old traditional methods of research must be supplemented with the participatory method, where the local community becomes fully involved. The central theme of the participatory approach was to investigate the possibility of promoting local management of the natural resources. Workshops were conducted to involve the local community in the project. The community formed six discussion groups that met regularly to discuss environmental issues. The six groups that were formed were: Firewood or woodlot collectors, shepherds / livestock raisers, crop fanners / agriculturists, water collectors, building material / soil collectors and medicinal plant users. The results obtained from the meeting of the discussion groups were used to compare the scientific results obtained from Braun-Blanquet method. Perceptions about their environment, which came out of the results of the discussion groups showed that the local knowledge of the rural community of Mceula was sufficient to train them to manage their environment sustainably.
- Full Text:
- Date Issued: 1998
Vulnerability, irreplaceability and reserve selection for the elephant-impacted flora of the Addo National Elephant Park, Eastern Cape, South Africa
- Authors: Johnson, Catherine Fiona
- Date: 1998
- Subjects: Addo Elephant National Park (South Africa) , Veld plants -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4202 , http://hdl.handle.net/10962/d1003771 , Addo Elephant National Park (South Africa) , Veld plants -- South Africa -- Eastern Cape
- Description: The Addo Elephant National Park (AENP) is the only existing national park situated in succulent thicket. This unique veld type is endemic to the Eastern Cape, and forms an important centre of endemism for small succulents and geophytes which comprise the subdominant component of the vegetation. It is regarded as the most threatened vegetation type in the Eastern Cape, as much of it has been severely degraded by farming activities and its rate of regeneration is very low. Thus the AENP represents an important sanctuary for certain species. However, large herbivores, particularly elephants, pose a further threat to the vegetation, and areas from which elephants have been excluded in the park (botanical reserves) have been shown to be more speciesrich than the surrounding vegetation. Most elephant-impact studies have focussed on the large shrub component of the vegetation, and only preliminary studies have been done in AENP to date. As the elephant population continues to grow, there is pressure to utilise the botanical reserves to increase the amount of available grazing. It is thus important that the botanical reserve system be highly effective and efficient in terms of area. Existing botanical reserves were established ad hoc and are therefore not necessarily optimal in this regard. An iterative reserve-selection algorithm was used to maximise plant species conservation in the most efficient area.
- Full Text:
- Date Issued: 1998
The coastal grasslands of the Eastern Cape west of the Kei River
- Authors: Judd, Rachel Anne
- Date: 1999
- Subjects: Grassland ecology -- South Africa -- Eastern Cape Grasslands -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4203 , http://hdl.handle.net/10962/d1003772
- Description: The grasslands of South Africa are the foundation of commercial and subsistence agriculture yet they are being degraded at an alanning rate. The coastal grasslands of the Eastern Cape are no exception and they suffer added pressure of coastal resort development because of their proximity to an attractive coastline. In order to determine the degree of conservation necessary for any area it is essential to know what species occur there in order to determine if protection from habitat destruction is required. Four aims were defined for this studv. The initial aim was a phytogeographical classification of the grasslands in the coastal region west of the Kei River. This was done by vegetation sampling followed by computer based analysis with TWINSPAN. This analysis defined ten grassland associations. five being located in the area west of the Keiskamma River and five occurring east of it. The associations in the eastern half are termed mesic while those in the western balf are xeric. The second aim was to determine the presence of any underlying ecological gradients affecting the distribution of tbe associations. Indirect gradient analysis was carried out where samples are analysed irrespective of environmental factors. Direct gradient analysis was then carried out using scores per sample of various environmental factors. Environmental factors whicb migbt produce such gradients are both naturally-ocurring and man-induced. Natural factors which were recorded in the field include depth of soil at sample site, soil family, aspect and distance from the shore. An important factor is the land / sea interface. Natural factors analysed in the laboratory include soil pH. conductivity. percent organic matter, calcium, magnesium, phosphate and potassium. Man-induced factors are land use history e.g. Ploughing and grazing. Both direct and indirect gradient analysis were carried out with the computer based programme CANOCO. The third aim of the study was to determine the presence of any successional trends between the ten defined associations. This was done using several characteristics of the associations. Alpha and beta diversity were the first factors compared between associations. The percentage contribution of the Cyperaceae, Fabaceae, Asteraceae and Poaceae to each association was assessed and compared. The presence of various life forms of the species occurring in each association was determined together with the cover abundance of different classes of grass species. These results were then combined and analysed in the light of the results from CANOCO analvsis. They show that the mesic Themeda Iriandra - Anthospermum herhoceum, association which occurs closest to the shore and with the least disturbance is a depauperate form of the mesic climax Themeda triandra association. The mesic Hyparrhenia hirta - Dtheteropogon amplectens association may be a secondary grassland on account of phosphate and potassiun poor soils and land-use. The mesic Hyparrhenia hirta - Themedo triandra association is a slightly degraded form of the climax association due to grazing. The severely disturbed Stenotaphrum secundatum - C'entella coriacea association, which is located close to the shore, is a secondary grassland. Analysis of the xeric associations indicates a clearly defined ordination of associations on the basis of land-use. The Cynodon daclylon - Helictolrichon hirtulum and Sporobolis africanus - Setaria sphacelata associations which occur where ploughed lands have been left to lie fallow are secondary in nature. The Themeda triandra - Ehrharta calycina association is thought to be the closest representati ve of a climax xeric association but the presence of E. calycina indicates that some disturbance has occurred. The vegetation is subject to moderate grazing. The Cynodon dactylon - Ehrharla calycina and Diheleropogon filifolius - Ehrharla calycina associations are subject to varying intensities of trampling and grazing and are degraded forms of the Themeda triandra - Ehrharla calycina association. Because of tbe overriding influence of the land-use gradient separation along gradients of the remaining eight factors was limited. The effect of fire and temporal change in the mesic Themeda triandra and Hyparrhenia hirta - Themeeia trianda associations was assessed via long-term studies at Potter's Pass outside East London. The results show a quick response to burning with a return to 100% cover within six months by both associations. During spring the two associations could not be separated by either TWINSPAN or DECORANA. indicating a temporal shift from the Hyparrhenia hirta - Themeda triandra association to the Themeda triandra association. The fourth and final aim was to identify plants requiring protection from habitat destruction and to make recommendations for further conservation areas and management of the coastal grasslands. Through the collection and identification of as many plants as possible a species checklist was prepared and the status of each was determined through reference to the Red Data Book of threatened and endangered species. Kniphofia rooperi is vulnerable in the Cape and Euphorbia hupleuroides is considered rare in kwazulu-Natal. Ten species are endemic to the Cape and / or South Africa. The richness of the vegetation lies in the presence of species representative of the four major floras which converge in the eastern Cape. i.e. The Cape, NamaKarroo, Tongoland-Pondolaod floras and the Kalahari Highveld Regional Transitional Zone. Suggestions are made for the conservation of the grassland associations at various sites within the study area based on the present area conserved. Less than 2% of the coastline in the study area is conserved and it is felt that the area under conservation should be increased. Management suggestions based on the available literature are given for both farmed and conserved areas. There is a great potential for further studies on grassland dmamics within the areas surveyed. In terms of management, the grasslands require careful examination to determine the most effective season in which to burn if at all. As with most agricultural systems in South Africa. grazing strategies will benefit from further research. Any additional research on the dynamics of these grasslands can only be of benefit to the sustained utilisation of this vital resource.
- Full Text:
- Date Issued: 1999
Effects of sustained elevated CO2 concentration and Nitrogen nutrition on wheat (Triticum aestivum L. cv Gamtoos)
- Authors: Kgope, Barney Stephen
- Date: 2000
- Subjects: Wheat -- Growth , Wheat -- Nutrition , Nitrogen fertilizers , Nitrogen in agriculture
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4205 , http://hdl.handle.net/10962/d1003774 , Wheat -- Growth , Wheat -- Nutrition , Nitrogen fertilizers , Nitrogen in agriculture
- Description: There is consensus that high CO2 results in enhanced growth and yield for most crop plants. However, most of these studies were carried out in the presence of adequate nutrients, which is also the case in agricultural systems (managed ecosystems). About 20% of the earth’s land mass have sufficiently low levels of nutrients to cause some kind of stress to plants. On the other hand, elevated [CO2] decreases foliar nutrient elements in plants and as a result partitioning of certain nutrient elements in plants is altered. Little data is available on the partitioning of most nutrient elements in plants, and this will definitely impact on growth and yield. To investigate this, wheat (Triticum aestivum L. c.v. Gamtoos) was grown in controlled environment cabinets at 360 and 700 µmol mol -1 CO2. The full Long-Ashton nutrient solution comprising of three-nitrogen concentrations ([N]) viz. (4,6 and 12 mM) was used to water plants everyday. The measurement of net assimilation rate (NAR), stomatal conductance (gs), transpiration rate (E), water use efficiency (WUE), foliar [N], nitrogen use efficiency (NUE) and growth parameters (total plant biomass (TPB), total plant height (TPH), leaf area (LA), shoot and root dry weight) were made 7 days after germination (7 DAG) till the onset of flowering. The increase in nitrogen supply in the order of 4, 6 and 12mM resulted in an increase in NAR, g_s_ , WUE and a decline in E under elevated [CO2]. Under elevated [CO2] NAR was observed to increase during the first two weeks reaching its maximum at 14 DAG, thereafter followed by a decline reaching its maximum at 28 DAG. This was later followed by an increase at 35 DAG onwards. Under elevated [CO2], NAR was increased significantly between the nitrogen regimes during the first (7-14 DAG) and the last two (35-42 DAG) weeks. The response of assimilation as a function of internal [CO2] (Ci), showed a decrease with age at ages 14, 28 and 35 DAG. This negatively affected the initial slope and the CO2 saturated photosynthetic rates under all treatments. This suggest that acclimation may have been as a result of both stomatal and biochemical limitations. All the photosynthetic pigment levels (chl_a_, chl_b_, chl_(a+b)_, and C_(x+c)_ ) increased with an increase in nitrogen supply from 4 to 6mM [N]. A 12mM [N] resulted in a significant decline in the photosynthetic pigment levels compared to a 6mM [N]. Chla remained higher than chlb under all treatments. Also, NAR was seen to increase and decrease concomitantly with the photosynthetic pigment levels. Foliar [N] was seen to decrease with an increase in nitrogen supply from 4 to 6 mM [N] under elevated [CO2] and the effects were adverse under the 4mM [N]. Under the 6mM N regime foliar [N] was positively correlated to NAR for elevated [CO2] grown plants. Similarly, E was positively correlated to foliar [N] under the same conditions. Elevated CO2 and increase in nitrogen supply had a pronounced effect on total plant height (TPH), total plant biomass (TPB), leaf area (LA), shoot and root dry weight and nitrogen use efficiency (NUE). The effects were more pronounced under a 6mM [N] as a result of high NUE. However, under 12mM [N] growth was not as expected as a result of lower NUE. Under all treatments shoot dry weight (SDW) was positively correlated to NUE. Anatomical studies revealed that total leaf and midrib thickness was significantly increased with an increase in nitrogen supply under elevated CO2 to support the larger leaf areas. There were no significant changes in the chloroplast ultrastructure as a result of the increase in nitrogen supply and CO2 enrichment. Starch grain surface area was seen to decline with an increase in nitrogen under both ambient and elevated CO2. Elevated CO2 and increase in nitrogen supply significantly increased total grain dry weight per plant by 47 and 46% respectively under 6 and 12mM [N]. In contrast, the increase was by about 21, 61 and 67% respectively under 4, 6 and 12mM [N] between the CO2 regimes.
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- Date Issued: 2000