Thesis (MScConsEcol (Conservation Ecology and Entomology))--Stellenbosch University, 2008. / The widespread ecological impacts of overgrazing by livestock within the Succulent Karoo have received considerable attention. Literature shows communal and commercial rangelands have been thoroughly studied, and vegetation responses have been investigated in an attempt to understand the effects of overgrazing. Regarding animal species, literature is in short supply. In a one-year study of small mammal assemblages, the effect of the rangelands, and subsequently vegetation, on small mammal assemblages was examined, as well as the effects on number of occupied, unoccupied and collapsed burrows. This study shows that vegetation composition differs between rangelands, with a greater perennial shrub cover on the communal rangelands and a greater perennial succulent cover on commercial rangelands, consequently creating different habitats for animal assemblages. This study supports the notion of small mammal composition relating to vegetation structure, with certain species being impacted by heavy grazing. Four small mammal species were found in greater abundances on commercial rangelands, with one being exclusive, while communal rangelands were exclusively occupied by three nocturnal species. Diet and habitat requirements are the most important factors regarding species occurrence. With small mammal species composition differing between rangelands, and species richness not being affected by rangeland type, this study illustrates that the disappearance of certain species may arise without these different rangelands. This could result in reduced species richness, and thus diversity being lost. Regarding species present on both rangelands, no differences were observed in body mass, body size or body condition. Despite no differences found in body condition, calculating a body condition index is a good method for investigating how a species is coping within an environment. The proportion and number of occupied and collapsed burrows can be seen as a measure of trampling effect. It was expected for grazing intensity, as well as vegetation changes, to affect the occurrence of such burrows. This study showed differences between the communal and commercial rangelands as negligible. As expected, numbers of burrowing small mammal species were negatively correlated with numbers of collapsed burrows. However, a lack of consistency deemed this result unimportant. Results show that the effects of overgrazing on small mammal populations are complex and require more attention if to be fully explained. This study provides insights into the effects of land use on small mammals and burrow numbers, which have implications for the conservation of these species within arid regions.

Gethyllis multifolia L. Bolus and G. villosa Thunb. are winter-growing, summerblooming, deciduous and bulbous geophytes that grow naturally in the semi-arid succulent Karoo biome of South Africa. Both species grow under full sun conditions and have four distinctive growth phases: a winter (cold and wet) growing phase, leaf senescence phase towards spring, flowering phase during the hot and dry summer months, and fruit and leaf formation phase in autumn. The medicinal uses of this genus (including G. multifolia “Kukumakranka” and G. villosa “hairy kukumakranka”) range from cures for colic, digestive disturbances, teething problems, fatigue, boils, bruises and insect bites, to being used as an aphrodisiac. Gethyllis multifolia is threatened in its natural habitat and is listed in the ‘Vulnerable’ category of the ‘Red Data List of Southern African Plants’ and the ‘IUCN-World Conservation Union List of Plants’. The literature indicate that the habitats of both species are being exposed to drier conditions and is further threatened by the encroachment of invasive indigenous plant species. It is not known to which extent these factors may pose a threat to the existence of both species. The first objective of this investigation was to determine the costs of vegetative and reproductive growth during the seasonal life cycle of the plant, using carbon (C) and nitrogen (N) as a physiological currency. The second objective was to elucidate a functional basis to explain the difference in the conservation status of both species in their natural habitat. Both species were subjected to drought and shading as environmental stresses and the plant physiological performance was investigated via photosynthetic gas exchange. The third objective of the study was to evaluate the antioxidant content (total polyphenol, flavonol/flavone and flavanone content) and antioxidant capacity [ferric reducing antioxidant power (FRAP), oxygen radical absorbance capacity (ORAC) and 2,2'-azino-di-3- ethylbenzthiazoline sulphonate (ABTS) radical cation scavenging ability] of natural populations and plant samples that were exposed to photo- and -drought environmental stresses. This study was done to elucidate the antioxidant profile of plant parts of natural populations as well as providing farmers, traditional healers and pharmaceutical companies with cultivation environmental conditions to enhance the antioxidant properties of the species. This investigation also attempted to isolate and characterize, by means of thin-layer chromatography (TLC) and column chromatography (CC), natural compounds from both species to lend support to the purported antioxidant benefit of both species and to further lend support to claims made by traditional healers of the medicinal potential of the genus. This study, however, did not engage in any in vivo studies or human trials to support published literature of the medicinal benefits of the genus. The photosynthetic adaptation studies indicated that G. villosa had a better photosynthetic performance than G. multifolia during both drought and low light conditions because of the inability of G. multifolia to adapt to a wider range of environmental extremes. The C and N cost of growth and reproduction studies revealed that G. villosa had a more efficient resource utilisation strategy for both growth and reproduction. These physiological responses suggest that G. villosa, in general, has a more efficient survival strategy and that G. multifolia will struggle to adapt to drier environmental conditions, as well as growing in the shade of encroaching invasive plant species. To conclude, this could be a contributing factor as to why G. multifolia is threatened in its natural habitat and G. villosa not. The antioxidant content-and -capacity study on natural populations of both species revealed the highest total polyphenol content, FRAP and ORAC values for the flowers and fruits of G. multifolia and G. villosa compared to other plant parts. These values were found to be in line with and in some cases higher than most commercial fruits and vegetables. The antioxidant activity during drought and photo-stress of the leaves, bulbs and roots was found to be highest in the roots of both species during drought stress. Gethyllis multifolia, in general, exhibited higher total polyphenol content than G. villosa, with the highest content measured during drought stress in the roots of G. multifolia. Phytochemical investigation of the leaves, bulbs and roots of G. multifolia and G. villosa revealed the presence of tannins, flavonoids, phenolics, saponins, glycosides as well as essential oils, while alkaloids were absent. The chromatographic profiles of the leaves, bulbs and roots of both species further indicated that the roots of G. multifolia contained the highest concentration of natural products, compared to G. villosa and other plant parts. Further in-depth studies on the roots of G. multifolia led to the isolation and characterization of three known flavonoids, of which one was also isolated as its endogenously acetylated derivative. In contrast to the fact that both species had a high polyphenol content and exhibited high antioxidant activity, the isolated compounds in this study revealed very low antioxidant activity. However, the literature revealed that some of these isolated compounds exhibit antifungal, antibacterial, antiangiogenic and anticarcinogenic properties in vitro, which could be ascribed to the medicinal applications of plant parts of certain species belonging to this genus. Furthermore, this study suggests that further chemistry and pharmaceutical research on the genus, Gethyllis, in specific the flowers and fruit of these two species, be pursued. / Philosophiae Doctor - PhD

Philosophiae Doctor - PhD / Gethyllis multifolia L. Bolus and G. villosa Thunb. are winter-growing, summer blooming, deciduous and bulbous geophytes that grow naturally in the semi-arid succulent Karoo biome of South Africa. Both species grow under full sun conditions and have four distinctive growth phases: a winter (cold and wet) growing phase, leaf senescence phase towards spring, flowering phase during the hot and dry summer months, and fruit and leaf formation phase in autumn. The medicinal uses of this genus (including G. multifolia "Kukumakranka" and G. villosa "hairy kukumakranka") range from cures for colic, digestive disturbances, teething problems, fatigue, boils, bruises and insect bites, to being used as an aphrodisiac. Gethyllis multifolia is threatened in its natural habitat and is listed in the 'Vulnerable' category of the 'Red Data List of Southern African Plants' and the 'IUCN-World Conservation Union List of Plants'. The literature indicate that the habitats of both species are being exposed to drier conditions and is further threatened by the encroachment of invasive indigenous plant species. It is not known to which extent these factors may pose a threat to the existence of both species. The first objective of this investigation was to determine the costs of vegetative and reproductive growth during the seasonal life cycle of the plant, using carbon (C) and nitrogen (N) as a physiological currency. The second objective was to elucidate a functional basis to explain the difference in the conservation status of both species in their natural habitat. Both species were subjected to drought and shading as environmental stresses and the plant physiological performance was investigated via photosynthetic gas exchange. The third objective of the study was to evaluate the antioxidant content (total polyphenol, flavonol/flavone and flavanone content) and antioxidant capacity [ferric reducing antioxidant power (FRAP), oxygen radical absorbance capacity (ORAC) and 2,2'-azino-di-3- ethylbenzthiazoline sulphonate (ABTS) radical cation scavenging ability] of natural populations and plant samples that were exposed to photo- and -drought environmental stresses. This study was done to elucidate the antioxidant profile of plant parts of natural populations as well as providing farmers, traditional healers and pharmaceutical companies with cultivation environmental conditions to enhance the antioxidant properties of the species. This investigation also attempted to isolate and characterize, by means of thin-layer chromatography (TLC) and column chromatography (CC), natural compounds from both species to lend support to the purported antioxidant benefit of both species and to further lend support to claims made by traditional healers of the medicinal potential of the genus. This study, however, did not engage in any in viva studies or human trials to support published literature of the medicinal benefits of the genus. The photosynthetic adaptation studies indicated that G. villosa had a better photosynthetic performance than G. multifolia during both drought and low light conditions because of the inability of G. multifolia to adapt to a wider range of environmental extremes. The C and N cost of growth and reproduction studies revealed that G. villosa had a more efficient resource utilisation strategy for both growth and reproduction. These physiological responses suggest that G. villosa, in general, has a more efficient survival strategy and that G. multifolia will struggle to adapt to drier environmental conditions, as well as growing in the shade of encroaching invasive plant species. To conclude, this could be a contributing factor as to why G. multifolia is threatened in its natural habitat and G. villosa not. The antioxidant content-and -capacity study on natural populations of both species revealed the highest total polyphenol content, FRAP and ORAC values for the flowers and fruits of G. multifolia and G. villosa compared to other plant parts. These values were found to be in line with and in some cases higher than most commercial fruits and vegetables. The antioxidant activity during drought and photo-stress of the leaves, bulbs and roots was found to be highest in the roots of both species during drought stress. Gethyllis multifolia, in general, exhibited higher total polyphenol content than G. villosa, with the highest content measured during drought stress in the roots of G. multifolia. Phytochemical investigation of the leaves, bulbs and roots of G. multifolia and G. villosa revealed the presence of tannins, flavonoids, phenolics, saponins, glycosides as well as essential oils, while alkaloids were absent. The chromatographic profiles of the leaves, bulbs and roots of both species further indicated that the roots of G. multifolia contained the highest concentration of natural products, compared to G. villosa and other plant parts. Further in-depth studies on the roots of G. multifolia led to the isolation and characterization of three known flavonoids, of which one was also isolated as its endogenously acetylated derivative. In contrast to the fact that both species had a high polyphenol content and exhibited high antioxidant activity, the isolated compounds in this study revealed very low antioxidant activity. However, the literature revealed that some of these isolated compounds exhibit antifungal, antibacterial, anti angiogenic and anti carcinogenic properties in vitro, which could be ascribed to the medicinal applications of plant parts of certain species belonging to this genus. Furthermore, this study suggests that further chemistry and pharmaceutical research on the genus, Gethyllis, in specific the flowers and fruit of these two species, be pursued.

Thesis (MSc (Botany and Zoology))--University of Stellenbosch, 2006. / Global circulation models predict that the Cape Floristic Region (CFR), a biodiversity hotspot, in the near future will be subjected to rising temperatures and widespread droughts as a result of rising atmospheric CO2 causing global climate change. It is predicted that climate change will lead to a southward shift of the Succulent Karoo, a neighbouring more drought tolerant biome, and a possible invasion of Fynbos, the main vegetation type of the CFR, by succulent species. In this research project, the effects of climate change on Fynbos, and the likelihood of Succulent Karoo invading Fynbos are assessed by means of various monitoring and experimental studies on an altitudinal gradient spanning a natural transition between fynbos and succulent karoo vegetation. An analysis of plant species diversity and turnover on the gradient revealed high species turnover between succulent karoo and the rest of the gradient, associated with a boundary between two soil types: shale (associated with succulent karoo) and sandstone (associated with fynbos). Phenological monitoring of fynbos species across the gradient showed how growth of fynbos species is affected negatively by high temperatures, and that low but regular rainfall is required to sustain growth during the dry Mediterranean summer. Retrospective growth analysis of Proteaceae species pairs with contrasting range sizes revealed that small geographic ranges do not signify low tolerance of climate variation, but rather that faster growing species are more sensitive to interannual climate variation than slow growing species. Exposing fynbos species to experimental drought confirmed that faster growing species will be more severely affected by climate change than slow growing species with conservative water use strategies. This experiment also confirmed the importance of rainfall reliability for growth in fynbos species when a naturally occurring prolonged dry period affected some species more severely than the drought treatment of an average reduction in rainfall. A reciprocal transplant experiment exposed fynbos seedlings to both warmer and drier conditions when they were planted outside of their natural ranges in the succulent karoo. Soil type as a barrier to invasion of fynbos by succulent karoo was also tested. Soil type was found to be not limiting to succulent karoo species and competition and disturbance was revealed to be more important in determining the fynbos-succulent karoo boundary than climate. It was concluded that productivity in fynbos will be adversely affected by rising temperatures and that differing responses to climate change between slow and fast growing species will lead to shifts in dominance among species, and consequently altered community structures and vegetation dynamics. Fires are likely to facilitate invasions of marginal habitats by succulent karoo because of sensitivity of fynbos regeneration stages to high temperatures and drought.

Thesis (MSc (Conservation Ecology and Entomology)--University of Stellenbosch, 2006. / A pilot study was conducted at the Namakwa Sands Mineral Separation Plant, to investigate the effects of acidic gaseous emissions from the Mineral Separation Plant on the adjacent Succulent Karoo vegetation. Sulphuric acid fumes, a major gaseous emission of the mineral processing, was the subject of investigation of the present study, due to the potential high negative impact of elevated concentrations thereof on vegetation in the ecosystem. Permanent sample plots along three transects radiating from the Mineral Separation Plant were laid out in the eastern, south-eastern and southern directions following the prevailing wind directions and practical consideration of land accessibility. The ecological components assessed as indicators of possible pollution levels in the environment included percentage plant mortality, foliar sulphur content of selected plant species, chemical composition of solubles in mist and dust samples, and soil pH. In addition, the vegetation was screened for plant species suitable to be used as potential bioindicators. Potential bioindicator plant species were selected on the basis of their relatively wide distribution in the study area and apparent sensitivity to the ambient air pollutants. The percentage of dead plants of each species that occurred on the sample plots was used as a criterion of the possible sensitivity of the plant species towards air pollution. The bioindicator plant species selected for potential monitoring purposes were: Galenia fruticosa, Lampranthus suavissimus, Lycium ferocissimum and a Ruschia sp. (SP 9). Plant mortality was greater nearer the emission source, with 28 + 5 % dead plants at 400 m, 19 + 6 % at 800 m and only 10 + 4 % at 1,200 m from the Mineral Separation Plant. Data summed for all species recorded and pooled for all three transects per sampling distance. With the methods used in this study, in the case of all sample plots on the three transects, no significant difference was found between the mean pH values of soil samples collected from open spaces without plant cover (8.01 + 0.46) and those collected underneath shrubs (8.91 + 0.96). Subsequently only the pH values of soil samples collected on open spaces were used to investigate the variation in soil acidity with distance and direction from the emission source. The means represent total number of samples from open space versus those collected from underneath shrubs. The pH of soil samples increased with distance from the emission source along the transects to the south and south-east of the emission source. Eastward of the emission source, soil pH values remained relatively low at all sample distances. This pilot study could not determine whether the continuous acidity of the soil along the eastern transect in the direction of the prevailing wind, was caused by increased deposition of gaseous emissions on the higher lying hilly terrain in this area, or by the underlying geology. Ion chromatographic analysis of mist and dust samples collected on each sample plot indicated the presence of several chemicals that had probably originated from the gaseous emissions from the Mineral Separation Plant as well as wind blown constituents from the adjacent surroundings of the sample plots. Of these chemicals, only the sulphate concentrations of the mist and dust samples were further evaluated, since that could be related to the emission of sulphuric acid fumes by the Mineral Separation Plant. Results indicated that the mean sulphate concentration of mist and dust samples collected from sample plots relatively close to the Mineral Separation Plant, 118.8 + 31.6 mg/litre (400 m), were higher than further afield, decreasing to 57 + 30.1 mg/litre at 800 m and 43.1 + 19.6 mg/litre at 1,200 m. These values, representing the mean sulphate concentrations of mist and dust samples at each sampling distance (data of the three transects pooled), differ significantly at the 85 % confidence level. Statistical evaluation of the data of the mist and dust pH measurements, pooled for the three transects on the basis of distance, indicated a gradual increase of the mean values from 400 m (7.3 + 0.26), through 800 m (7.7 + 0.34), to 1,200 m (8.2 + 0.83), although these values were not significantly different. A decreasing trend in accordance with that in the case of the sulphate concentrations of mist and dust samples with distance from the mineral processing plant, was also observed in the sulphur content of the leaves of selected plant species, with mean sulphur content higher at 400 m sampling distance (0.29 + 0.091 %) than at 800 m (0.264 + 0.086 %) and a further decline at 1,200 m (0.232 + 0.079 %), data of the three transects pooled. However, these values were also not significantly different. Although not significantly so, the decreasing trend in the results of the sulphate concentration of mist and dust samples, the sulphur content of plant leaf samples as well as plant mortality observed, and increasing soil pH values with distance from the Mineral Separation Plant, suggest that the gaseous emissions from the Mineral Separation Plant could probably have had a detrimental effect on the adjacent Succulent Karoo vegetation. A more detailed study is necessary to confirm this trend. In addition it is recommended that in order to clarify the soil pH measurements outcome along the eastern transect that were contradicted by the results of the mist and dust pH measurements, a more intensive survey over a greater distance (at least further than 1.2 km from the Mineral Separation Plant), be conducted to quantify vegetation damage and acid deposition to the east of the emission source.

Thesis (MSc) -- University of Stellenbosch, 2004. / ENGLISH ABSTRACT: This thesis focuses on the effects of vegetation resting on biodiversity and community dynamics at Rocherpan Nature Reserve (320 36'S, 180 18'E) in the semi-arid coastal strip of the Succulent Karoo known as Strandveld. As a whole, the Succulent Karoo has an extraordinary high level of phyto diversity with high levels of endemism. This is particularly true for succulent shrubs belonging to the groups Mesembryanthemaceae, Crassulaceae and Asteraceae. The thesis begins with an investigation into effects that vegetation resting has on plant diversity. The aim was to determine if resting affected biodiversity levels and if so, which plant groups are affected and why. Through a numerical approach, it was determined that with resting overall species richness remained the same. However, different plant life forms responded to resting differently. With increased resting, abundance of succulent shrubs decreased, while richness of annuals increased. The second aspect under investigation was to determine how resting the vegetation affected community dynamics. The aim was to understand how vegetation structure and interspecific associations changed with resting and to apply these findings to known community models. Through an autocorrelation approach, it was found that horizontal patterning of long-lived woody species, that formed distinctive vegetation clumps, did not change with resting, while differences were found in woody matrix species and succulent species. These changes in structure were investigated further through a study on the demography of specific species. Demography of woody species associated with vegetation clumps did not change with vegetation resting, while significant changes were observed for woody matrix species and succulent species. In longer rested vegetation, woody matrix species showed a greater range in size class distribution (i.e. had both very large and smaller plants) with the tendency towards larger plant sizes. Succulents on the other hand, had a smaller range in size class distribution with a tendency towards larger plants. For all species investigated there were low seedlings counts. It was concluded that succulent shrub populations were 'mature' and continued resting could result in local extinction of some species due to the lack of regeneration. The overall lack of seedlings was attributed to a saturated establishment environment. Implications for conservation management were discussed. / AFRIKAANSE OPSOMMING: Hierdie tesis fokus op die gevolge van plantegroeirus op biodiversiteit en gemeenskapsdinamika by die Roeherpan Natuurreservaat (320 36'S, 180 18"0) in die halfdor kusstrook van die Sukkulente Karoo, bekend as die Sandveld. In die geheel gesien het die Sukkulente Karoo 'n buitengewone hoë vlak plantdiversiteit met hoë vlakke endemie. Dit is veral waar vir sukkulente struike wat tot die groepe Mesembryanthemaceae, Crassulaceae en Asteraceae behoort. Hierdie tesis ondersoek eerstens die gevolge wat plantegroeirus op plantdiversiteit het. Die doel was om te bepaal of rus die biodiversiteitsvlakke beïnvloed het en indien wel, watter plantgroepe en waarom. Deur middel van 'n numeriese benadering is bepaal dat die algehele diversiteit, numeries gesproke, met plantegroeirus dieselfde gebly het. Verskillende plantlewensvorme het egter verskillend gereageer. Met toenemende rus het die diversiteit van sukkulente struike afgeneem, terwyl die diversiteit van jaarplante verhoog het. Die tweede aspek wat ondersoek is, was om te bepaal hoe die plantegroeirus die dinamika van die omgewingsgemeenskap beïnvloed het. Die doel was om te verstaan hoe die struktuur van die plantegroei en die interspesifieke assosiasies verander het met rus en om dan hierdie bevindinge toe te pas op bekende gemeenskapsmodelle. Deur middel van 'n outokorrelasiebenadering is gevind dat die horisontale patrone van meerjarige houtagtige spesies wat in duidelik-uitkenbare plantegroeigroeperings voorkom, nie met rus verander het nie. Veranderinge is egter wel in die houtagtige matriksspesies en die sukkulente spesies waargeneem. Hierdie veranderinge in struktuur is verder ondersoek deur 'n studie te maak van die demografie van spesifieke spesies. Daar is gevind dat die demografie van houtagtige spesies geassosieer met plantegroeigroeperings nie met plantegroeirus verander het nie, maar beduidende veranderinge is waargeneem in die geval van houtagtige matriksspesies en sukkulente spesies. By plantegroei wat langer gerus het, het die houtagtige matriksspesies 'n wyer verspreiding in klasgroottes vertoon (d.i. daar was baie groot plante én kleiner plante) met 'n gemiddelde afname in plantgrootte. Sukkulente, aan die ander kant, het 'n kleiner verspreiding in klasgroottes vertoon met 'n neiging tot groter plante. Vir al die spesies wat ondersoek is, was daar lae saailingtellings. As gevolg van die "volwassenheid" van die populasies van sukkulente struike, sou voortdurende rus, weens die gebrek aan regenerasie, kon lei tot die plaaslike uitwissing van sommige spesies. Die algemene gebrek aan saailinge is toegeskryf aan die versadigde vestigingsomgewing. Die implikasies VIr natuurbewaringsbestuur word bespreek. v

The semi-arid forms of subtropical thicket in the Eastern and Western Cape have been heavily degraded through unsustainable pastoralism over the last century or more. The degraded areas exhibit a significant loss of above-ground and belowground carbon stocks, and consequently provide an opportunity for restoration through the formal and informal carbon markets. A prerequisite for the attainment of carbon credits is to ensure sound carbon stock baselines prior to effecting restoration. I report on the carbon stocks (including sub-pools) for a number of intact subtropical thicket types, as well as the differentials between the intact and degraded states (including the sub-pools). Total carbon stocks (TCS in t C ha⁻¹) for intact vegetation (to a soil depth 0–25 cm), ranged from 87.73±6.51 to 70.64±17.24. For degraded vegetation (including old lands), TCS (t C ha⁻¹) ranged from 34.05±3.61 to 21.03±2.70. For all vegetation types, the differentials in TCS along the degradation gradient (0–25 cm) are highly significant and strengthen the possibility for carbon credit financing to catalyse the restoration of the degraded semi-arid subtropical thickets. This study has shown a mean loss of 57.23 t C ha⁻¹ in Baviaanskloof spekboom thickets, when measured to a soil depth of 25 cm. Portulacaria afra is a key species within the semi-arid subtropical thickets, being a canopy dominant and a driver of soil nutrient status, but has been largely lost from the degraded landscapes. Degraded semi-arid subtropical thicket vegetation lacks regeneration via seedling recruitment; restoration therefore requires the manual replanting of P. afra using cut truncheons. Survivorship trials were undertaken infield in 2005 to establish restoration protocols for P. afra, with survivorship being recorded in 2006 and 2008. Overall survivorship for all treatments was found to be 43.2±2.8% in 2006, dropping to 35.8±2.7% in 2008. Planting posture (flat or upright) showed the most significant results of all the factors tested in 2006 and 2008. Micro-damming also influenced survivorship in that micro-damming was associated with marginally higher survivorship (47.4 ±2.0% with damming vs. 39.1±1.5% without damming in 2006, and 39.3±1.9% vs. 32.3±1.5% in 2008). Higher planting density only showed a significant positive impact on survivorship in 2008. Neither stem diameter nor clumping significantly affected degree of survival. A key finding in the study has been the non-static nature of P. afra truncheon survivorship, even after being well established (three years since planting). The results from the study will guide the restoration protocols for the restoration of degraded subtropical thickets, where P. afra requires replanting.

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.

Crassulacean acid metabolism (CAM) provides desert plants with distinct advantages over the C3 and C4 photosynthetic pathways in harsh climates where water is scarce. CAM is, however more metabolically costly than C3 or C4 photosynthesis, and some plants, such as Mesembryanthemum crystallinum, facultatively utilize CAM when water is abundant, and water conservation unnecessary. In such situations, these plants behave akin to a C3 plant when photosynthesizing. CAM is divided into four phases, with each phase displaying unique metabolic processes. Certain changes, including changes in the timing of CO2 fixation, stable carbon isotope ratios, and tissue malic acid content accumulation patterns can indicate that a plant has shifted from CAM to C3 photosynthesis. Such shifts have been observed to be regulated primarily by water availability and ontogenic development. While facultative CAM is well documented in species like Mesembryanthemum crystallinum, and it has not been studied extensively in Agave with the exception of Agave deserti, and Agave angustifolia. A better understanding of this phenomenon would apply to the agricultural growth of this genus. This study aimed to trigger C3 to CAM shifts in Agave sensu lato species, in order to expand upon the findings of previous studies, and better understand the prevalence of facultative CAM expression in the genus. Gas exchange and stable carbon isotope measurements were taken from 2-month-old, 10-month-old, and mature agaves grown in controlled ocnditions. Tissue acid content measurements were taken from mature plants. Despite the Agave sensu lato species in this study being subjected to moisture applications ranging from dry to saturated, we were unable to observe any distinct shifts from CAM to C3 photosynthesis in any of the species tested for both seedlings and mature plants. Diel net CO2 fixation rates also increased with age, and water applications for seedlings, and decreased with heavy irrigation in mature plants. Stable carbon isotope ratios revealed that some carbon in the plant tissues was fixed by rubisco, and that some species (Polianthes tuberosa, Prochnyanthes mexicana) had carbon isotope ratios of a C3 plant, but these ratios did not change with different irrigation treatments. Malic acid accumulation remained typical of CAM plants for the species tested as well, with one exception in Polianthes tuberosa. As such, we conclude that the Agave sensu stricto species tested in this study are obligate CAM plants, and that they perform poorly mature individuals are over-watered. Additionally, the Agave sensu lato species P. mexicana, and P. tuberosa appear to be C3 plants given the results of this study.

There are many factors that have been proposed to contribute to plant invasiveness in nonnative ecosystems. Traits of invading species are one of them. It has been proposed that successful species at a certain invasion stage share particular traits, which could be used to predict the behaviour of potentially invasive plants at the respective stage. Three main stages of invasion are distinguished: introduction, naturalization, and invasion. I conducted a stageand trait-based analysis of available data for the invasion of New Zealand by the flora of southern Africa. Using 3076 southern African native vascular plant species introduced into New Zealand, generalised linear mixed model analysis was conducted to assess association of several species traits with the three invasion stages. The results showed that plant traits were significantly associated with introduction but fewer traits were associated with naturalization or invasion, suggesting that introduction can be predicted better using plant traits. It has been also hypothesized that species may become invasive in non-native ecosystems because they are removed from the regulatory effects of coevolved natural enemies (Enemy Release hypothesis). A detailed field study of the succulent plant Cotyledon orbiculata var. orbiculata L. (Crassulaceae) was conducted in the non-native New Zealand and native Namibian habitats to compare the extent of damage by herbivores and pathogens. C. orbiculata is a southern African species that is currently thriving in New Zealand in areas seemingly beyond the climatic conditions in its native range (occurring in higher rainfall areas in New Zealand than are represented in its native range). As hypothesised, C. orbiculata was less damaged by herbivores in New Zealand but, contrary to expectation, more infected by pathogens. Consequently, the plant was overall not any less damaged by natural enemies in the non-native habitat than in its native habitat, although the fitness impacts of the enemy damage in the native and invaded ranges were not assessed. The results suggest that climatic conditions may counteract enemy release, especially in situations where pathogens are more prevalent in areas of higher rainfall and humidity. To forecast plant invasions, it is concluded that species traits offer some potential, particularly at the early stage of invasion. Predicting which introduced plants will become weeds is more difficult. Enemy release may explain some invasions, but climatic factors may offset the predictability of release from natural enemies.