Browsing by Author "Chimphango, Samson"
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- ItemOpen AccessConserving living landscapes: investigating the impacts of livestock grazing and assessing rangeland restoration potential in Overberg Renosterveld, South Africa(2021) Poulsen, Zoë Chapman; Chimphango, Samson; Hoffman, Michael Timm; Anderson, Pippin; Muasya, A MuthamaBiodiversity is declining faster than at any other time in the Earth's history, driven mostly by land use change and degradation. Overberg Renosterveld, some of the most species diverse mediterranean type shrublands, are no exception with about 95% of their original extent lost to agriculture. Historically, large herds of indigenous grazing mammals roamed these landscapes. Today the Overberg's agricultural lands are fragmented by land cover change and divided by fences. In the contemporary landscape animals, largely domestic livestock, and plant resources are closely coupled, and overgrazing of remaining renosterveld fragments a significant threat, with potential to cause irreversible damage. The Conservation of Agricultural Resources Act (CARA) (Act 43 of 1983) states that farmers must not exceed the grazing capacity of the veld unless it is protected against deterioration and destruction, and that any land that is degraded or denuded must be effectively restored or reclaimed. Despite this legislation, there is little empirical research on the impacts of livestock grazing on renosterveld, as well as on restoration of overgrazed areas. It was the aim of this thesis to contribute to this gap in understanding. The thesis assessed the role of grazing by different livestock types, namely cattle and sheep, on biodiversity, the soil seed bank, and the restoration potential of renosterveld vegetation from resting the veld. The effect of livestock grazing by sheep and cattle on plant species richness and diversity and growth form diversity was assessed using Modified Whittaker plots and presented in Chapter 3. It was hypothesised that livestock grazing by cattle would have less effect on species richness and diversity and growth form diversity than sheep grazing and that both cattle and sheep grazing would lead to a reduction in species richness and diversity in comparison to renosterveld sites with a treatment of no grazing. Thirty sites where either no grazing has taken place or that have been grazed by cattle or sheep were selected with sites being evenly distributed between Eastern, Central and Western Rûens Shale Renosterveld. At each of the thirty sites, vegetation data were collected from a series of nested subplots of ten 1 m2 , two 10 m2 and one 100 m2 subplots nested within a 1 000 m2 plot. One soil sample was also collected from each 1 000 m2 plot to a depth of 10 cm for nutrient analysis. Findings revealed that sites grazed by sheep had significantly lower plant species richness (median richness = 29 species, mean Shannon-Weiner = 3.39) and diversity when compared to sites with a treatment of no grazing (median richness = 49 species, mean Shannon Weiner = 3.83). Sites with a treatment of no grazing had significantly higher richness of geophyte species (mean = 14.7) than sites grazed by cattle (mean = 7.0) and sheep (mean = 7.1) during the study. The results obtained were in line with the hypothesis that livestock grazing by sheep resulted in a reduction in species richness and diversity and vegetation cover in Overberg Renosterveld in comparison to sites where no grazing has taken place. Sites with a treatment of no grazing showed higher species richness and vegetation cover of non-succulent shrubs, annual forbs and perennial forbs than sites grazed by sheep. It was concluded that livestock grazing of Overberg Renosterveld by sheep needs to be done with care. This can be done by adopting a passive adaptive management approach. Here one set of management protocols can be developed and implemented and through science-based monitoring to inform management, these can be adapted as needed based on the key findings. Chapter 4 investigated ecosystem resilience and the restoration potential of Overberg Renosterveld through an exploration of its soil seed bank as a source for potential recovery. A glasshouse germination experiment investigated the effect of livestock grazing by cattle and by sheep in comparison with a grazing treatment of no grazing on the soil seed bank in Overberg Renosterveld, as well as the similarity between the standing vegetation and the soil seed bank. It was hypothesised that cattle and sheep grazing would reduce species richness, species diversity and growth form diversity in the soil seed bank in comparison with sites with a treatment of no grazing. Soil samples were collected from 30 sites that were also used in Chapter 3. The soil was then spread on top of a 6 cm layer of compost in seed trays, and smoke treated to enhance germination. Seedlings were assigned to growth form categories including forbs, geophytes, annuals, graminoids, succulent shrubs and nonsucculent shrubs and then identified to family, genus or species level. The results of the soil seed bank study were correlated with the vegetation results from Chapter 3 to examine the relationship between the standing vegetation and the soil seed bank. A total of 48% of taxa in the standing vegetation had seed present in the germinable seed bank. However, there were no differences in species richness, species diversity or number of individuals between grazing treatments. The results indicated that livestock grazing has a far less significant impact on the composition, species diversity and growth form diversity of the soil seed bank in Overberg Renosterveld than hypothesised. Instead, the results showed that there was a well-developed seed bank comprising mainly indigenous species with a variety of different growth forms including palatable grasses and shrubs. This indicates that Overberg Renosterveld vegetation has high restoration potential. Chapter 5 showed results on the effects of livestock grazing by cattle and sheep over time on plant species richness, diversity and growth form diversity in comparison with sites protected from grazing. Following collection of a baseline dataset, four years of follow up data were collected. A total of 22 fenced plots across Western, Central and Eastern Rûens Shale Renosterveld had a baseline dataset collected prior to being monitored on an annual basis over four years in grazed/ungrazed paired plots. Results on vegetation recovery from the fenced exclosures showed a significant increase in plant cover over time at sites that were not grazed. Mean species richness increased from 20.6 species to 25.4 species at sites with no grazing. Mean vegetation cover increased from 71% at T0 (the baseline time step) to 120% at T4 (the final time step) at the end of the study. Sites grazed by sheep had a decrease in vegetation cover over time each year from T0 to T4 from 75% to 50%. Results from a linear mixed model revealed that species richness between grazing treatments was significantly different at all time steps in the study. However, the significant differences were primarily due to comparisons between grazed sites and sites with a treatment of no grazing. Therefore, livestock grazing by sheep has a significant effect on renosterveld vegetation over time. Findings from this component of the study indicates that Overberg Renosterveld degraded by continuous heavy grazing has significant passive restoration potential by fencing renosterveld patches to facilitate more effective grazing management. Most of the renosterveld of the Overberg has been lost through habitat transformation for agriculture, and the future of that which remains is uncertain. This thesis affirms concerns around the impact of livestock grazing and shows the importance of improved ecological understanding around grazing management. Grazing by sheep was shown to cause greater impacts on renosterveld than other domestic livestock studied and is therefore a threat to renosterveld. These findings warrant closer attention to management practices around sheep grazing. However, the state of renosterveld soil seed banks offer considerable hope. Findings revealed a diverse indigenous seed bank, showing that renosterveld degraded by overgrazing has high restoration potential. Furthermore, fencing renosterveld to exclude livestock improves species richness and diversity over time. These findings highlight the need for caution when grazing renosterveld. However, where the damage has been done, the potential for recovery is high. Harnessing the soil seed bank in combination with excluding livestock grazing by fencing are effective tools in this critically endangered vegetation for achieving restoration and conservation goals.
- ItemOpen AccessEffects of ultraviolet-B radiation on plant growth, symbiotic function and concentration of metabolites in legumes and an assessment of F1 generation for carryover effects(2003) Chimphango, Samson; Dakora, Felix DReduction in ozone layer thickness in the stratosphere and the resultant increase in ground level of biologically active ultraviolet-B (UV-B) radiation prompted research into the effect of UV-B on growth and metabolism of terrestrial plants. In this study, eight legume species including three tropical food grain legumes [Vigna unguiculata (L.) Walp. (cowpea), Glycine max (L.) Merr (soybean), and Phaseolus vulgaris (L.) (common bean)], two temperate pasture legumes [Lupinus luteus (lupin) and Vicia atropurpurea (vetch)], a tree [Virgilia oroboides (Bergius T.M. Salter] and two shrub legumes [Cyclopia maculata (L.) Vent (honey bush) and Podalyria calyptrata Willd] indigenous to Southern Africa were exposed to UV-B radiation at above and below-ambient levels, and assessed for its effects on plant growth, symbiotic function and root concentration of metabolites.
- ItemOpen AccessPhosphorous uptake and utilization efficiency in cluster root and non-cluster root forming species of the Core Cape Subregion, South Africa(2015) Basic, Dunja; Chimphango, Samson; Muasya, MuthamaThe Core Cape Subregion (CCR) is made up of a mosaic of highly weathered and nutrient leached soil substrates in the Western Cape. Plant available phosphorus (P) in these soils is very low, generally ranging from 0.4-3.7 µg P g-1 soil and as a result plants have evolved a number of traits to enhance P-acquisition, such as increased root surface area (SA) and specific root length (SRL), cluster root and root hair proliferation and exudation of organic acids and acid phosphatases (APase) from the roots. Crop yield is limited worldwide due to the unavailability of P and P-fertilization is showing limited success due to soil retention. Sustainable management of this would include exploiting plants with natural adaptations for enhanced P acquisition and utilization. The aim of this study was to discover whether cluster root forming species are more efficient at P acquisition than non-cluster root species. This was achieved by focusing on two objectives: (1) to characterize root traits for increased P acquisition in different soils of the CCR and (2) comparing P-uptake and utilization efficiencies of cluster root species to non-cluster root species under glasshouse and natural conditions. Plants from Fabaceae, Polygalaceae, Proteaceae, Cyperaceae, and Juncaceae were grown in two different glasshouse experiments and observed in a field study.
- ItemOpen AccessRelationship between Aspalathus linearis (Burm. F.) R. Dahlgren (rooibos) growth and soil moisture in a glasshouse and in the DSSAT-CSM crop model(2021) Adaramola, Rhoda Fiyinfoluwa; Chimphango, Samson; Abiodun, BabatundeClimate change and drought pose a major threat to agriculture and water resources globally and for rooibos (Aspalathus linearis (Burm. F.) R. Dahlgren) production in the Western Cape province of South Africa. Rooibos is adapted to the coarse, nutrient poor, acidic, well-drained, deep sandy soil of the Fynbos biome. The region has a Mediterranean climate, which is characterised by wet cold winters, with an average annual rainfall of about 375 mm, and dry summers. The growth of rooibos peaks in the summer months, implying a reliance on soil moisture. The current study aims to investigate the relationship between rooibos growth and soil moisture. The objectives of the study were: 1) to determine the effect of soil moisture on growth and evapotranspiration in rooibos under glasshouse conditions, 2) to adapt the CROPGRO model in DSSAT to simulate the shoot biomass yield of rooibos, using the rooibos CROPGRO model, 3) to investigate the effect of rooibos growth on soil moisture, and 4) to determine the effect of different levels of mulching and irrigation on rooibos yield and soil moisture. Some of the results obtained in the glasshouse study in Objective 1 and observational field data from the literature were used in the adaptation of the CROPGRO model. The glasshouse study was carried out at the University of Cape Town, using soils from Clanwilliam and Citrusdal sites to grow rooibos seedling for 16 weeks in pots before exposing them to drought treatments. The pots were arranged on trays in the glasshouse using a completely randomized design. Two drought treatments were used: moderate drought stress (MDS), set at 20% FC, and severe drought stress (SDS), during which watering was completely withdrawn, were applied to 10 pots per treatment per site. Data on plant growth, root morphology, evapotranspiration, soil moisture, chlorophyll fluorescence and leaves to determine chlorophyll and carotenoid concentration were collected from the plants in the glasshouse after 10 days of these drought treatments. The SDS plants were re-watered for 8 weeks for recovery, and together with the MDS and control plants were transferred into a growth chamber for measurement of gas exchange parameters and biomass. The CROPGRO model in DSSAT was adapted for rooibos by changing some parameters in a pigeon pea (Cajanus cajan L. Millspaugh) CROPGRO model. The adapted rooibos model was used to set up an experiment that compared the cumulative evapotranspiration and soil moisture from the rooibos field and bare soil under rainfed conditions. Also, in a simulation experiments, the model was used to determine the effect of three levels of mulching by means of wheat residue at 8000 kg/ha, 4000 kg/ ha and 2000 kg/ha and drip irrigation at 25.4mm and at 12.5mm once a week from December to March, both separately and in combination, on rooibos shoot biomass and soil moisture. The results from the glasshouse study showed a 40% decrease in biomass under MDS conditions for 12 weeks, while SDS plants could not survive beyond 10 days in the glasshouse. Root morphological features changed under severe drought stress, resulting in longer and thinner roots relative to the control plants. The reduced biomass accumulation under drought conditions was followed by reduced photosynthesis, stomata conductance, transpiration, and concentration of chlorophyll and carotenoids. Changes in both maximum quantum efficiency of photosystem II (Fv/Fm) and fluorescence quantum yield (Fq'/Fm') were observed in the later stages of the SDS plants (days 9 and 10) compared to the control plants but were unaltered in the MDS plants. The soil moisture correlated negatively with evapotranspiration and stomata conductance in control plants, while these relationships were absent in MDS plants. Changes in temperature in the glasshouse correlated positively with stomata conductance and transpiration in the control plants, but these correlations were also absent in MDS plants. However, changes in temperature correlated negatively with soil moisture in both the control plants and the MDS treated plants. The CROPGRO model in DSSAT was successfully adapted to simulate shoot biomass in rooibos under field conditions and the rooibos model had an agreement of 94% with observational shoot biomass under field conditions. Furthermore, the model simulated cumulative evapotranspiration in rooibos plants in the field, with an agreement of 56%. The simulated experiments showed that cumulative evapotranspiration from the rooibos field was 33% higher than that of bare soil, and showed that rooibos plants extract moisture from deep soil layers to a depth of about 2 m. Furthermore, rooibos growth in deep soil, and in mulched or irrigated treatments, produced higher shoot biomass than control plants. In deep soil, the simulated irrigated rooibos plants, which received 25.4 mm water weekly from December to March, produced a higher biomass yield than only rainfed or mulched plants. However, the combined treatments of mulching at 8000 or 4000 kg/ha and irrigation at 12.5 mm was similar to irrigation at 25.4mm. The average extractable soil moisture was greater in deep soil for all the treatments and control plants compared to shallow soil. Overall, the rooibos crop model shows that an increased supply of soil moisture enhances the production of biomass yield in rooibos in the field. Also, rooibos extracts moisture from a deeper soil layer, which enables it to hydrate its leaves and to transpire during the summer period for better growth and biomass production. Water loss through evapotranspiration was high in rooibos fields, and thus mulching of the plants would be beneficial for increased biomass production. However, even better rooibos yields were obtained when mulching was combined with irrigation. The glasshouse experiments showed a yield decrease of rooibos biomass by about 40% when the moisture supply was reduced by about 50% of the adequate conditions. The thinner and longer roots of rooibos, among other drought tolerance traits, most likely enable it to cope with low rainfall and drought conditions, which are prevalent in the Cederberg region of the Western Cape. The production of rooibos in the farms is prone to water loss through evapotranspiration, and thus soil moisture conservation technologies such as mulching would greatly enhance its biomass yield.
- ItemOpen AccessA systematic study of the South African genus Prionium (Thurniaceae)(2013) Munyai,Rabelani; Muasya, Muthama; Chimphango, SamsonThe South African monocotyledonous plant genus Prionium E. Mey (Thurniaceae; Cyperid clade) is an old, species-poor lineage which split from its sister genus Thurnia about 33 - 43 million years ago. It is a clonal shrubby macrophyte, widespread within the Fynbos biome in the Cape Floristic Region (CFR) with scattered populations into the Maputaland-Pondoland Region (MPR). This study of the systematics of the genus Prionium investigates whether this old lineage comprising of a single extant species P. serratum, is morphologically, genetically and ecologically impoverished, and identifies apomorphic floral developmental traits in relation to its phylogenetic position as sister to the Cyperid families, Juncaceae and Cyperaceae. Sampling for morphological, molecular and ecological studies was done to obtain representatives from its entire distribution range, falling within the phytogeographic regions of the CFR (North West, NW; South West, SW; Agulhas Plain, AP; Langeberg, LB) and extending into Eastern Cape (South East, SE) and KwaZulu Natal (KZN). Samples for the floral ontogenetic study were collected to obtain representatives of the Cyperid clade families: Cyperaceae (Eriophorum, Scirpus), Juncaceae (Juncus, Luzula) and Thurniaceae (Prionium).