Exploitation of botanical resources has resulted in significant decreases in the sizes of some plant populations, especially for species that have a high commercial value and are important to the lives and livelihoods of rural communities. Medicinal plant resources are used and traded commercially in both rural areas and urban centres, and over-exploitation has become a deterministic factor in the extinction risks to certain species. The main aim of the study was to design a risk assessment model to determine the impact of the medicinal plant trade on the Witwatersrand (centred around Johannesburg) on indigenous plant resources. The goal was to incorporate trade variables correlated with harvesting risks together with biological characteristics of the harvested species to predict which species are most threatened by the trade and are thus high on the list for conservation priority. The study required semi-quantitative surveys of the medicinal plants sold by traders in the Witwatersrand to be conducted. In 1994 and 2001, the plants sold in 50 muti shops and by 100 vendors in the Faraday Street market respectively were inventoried. Quantitative trade data were also captured, including volume, pricing structures and plant size (e.g. bark thickness and bulb diameter). A scientific sampling strategy was adhered to throughout the study to add statistical validity to the results. In a novel approach to analysing ethnobotanical data, the frequency of plant occurrences in the markets was analysed using measures (analysed by EstimateS) of species diversity traditionally used in ecology. The measures allowed for sampling strategies and sizes to be compared between data sets and for the number of species likely to be sold in the region to be estimated. Furthermore, data sets could be compared in terms of species richness, diversity, evenness and complimentarity. Another novel approach taken in the thesis was to estimate the number of individual plants harvested annually by gatherers, specifically the number of trees that are debarked and the number of whole bulbs that are removed. In order to estimate the number of trees debarked, a study was conducted to determine the relationship between bark thickness and stem diameter for six species. The results made it possible to estimate the condition of the resource in the wild from market records (i.e. bark thicknesses) and to see how the availability of larger trees has declined for species such as Warburgia salutaris between 1994 and 2001. Results for bulbs showed that there has been a significant decrease in the diameter of Eucomis autumnalis bulbs present in the markets in the same period, suggesting significant levels of resource depletion. The thesis explored the use of a multivariate methodology for assessing the extinction risks of species and assigning species harvested for the medicinal plant trade to various hierarchies of risk and conservation priority. Hierarchical and non-hierarchical cluster analysis (Ward’s and K-means respectively) methods were found to be effective in assigning species to clusters of similar risk and conservation priority. From a combined list of 392 ethnospecies recorded in the muti shops and Faraday market, a short-list of 119 higher risk species was identified using four to five trade variables. This list was further reduced to 87 species to ascertain conservation priorities based on the additional inclusion of seven biological variables in the assessment. From this list, approximately 31 species were identified as having higher conservation priority and would be candidates for further research, management and protection within the ambit of conservation and sustainable utilisation programmes. These species would further benefit from Orange Listing or having their IUCN Red List status re-evaluated. The methods developed in this study are recommended for other ethnobotanical studies. Furthermore, the risk assessment method could be applied to the assessment of species similarly traded in other medicinal plant markets or applied to the assessment of species under threat from other stressors at a regional, provincial and/or national level using the appropriate variables.

The study evaluated the extent and threat of bark harvesting of plant species for medicinal purposes in the Venda region and investigated possibilities of the sustainability of these practices. Approximately 30% of the woody plant species in Venda were found to have medicinal properties in their bark, but only about 12% of these species are commonly traded in muthi shops in the region. Fifty-eight medicinal plant species are commonly harvested for medicinal properties in their bark and found in muthi shops in the region. These 58 species were scored for the possible threat of bark harvesting to the species’ survival using 20 ecologically relevant plant population traits. The most vulnerable species were Adansonia digitata, Adenia spinosa, Albizia adianthifolia, Albizia versicolor, Brackenridgea zanguebarica, Croton megalobotrys, and Warburgia salutaris. Of these species Brackenridgea zanguebarica and Warburgia salutaris are amongst the ten most traded medicinal plant species in Venda region. Elaeodendron transvaalense and Brackenridgea zanguebarica, the two species investigated in detail in this study, were amongst the most commonly traded medicinal plant species in Venda region. Analysis of size class distributions showed that both species had growing and healthy populations, exhibiting J-shaped population curves, centroids left-skewed from the midpoint of the size class distribution, and a fine-grained status. However, size-class distributions in both species revealed certain classes that needed monitoring since they were negatively affected by bark harvesting. Adult individuals of B. zanguebarica showed a high degree of bark regeneration as a response to bark removal from medicine men. The crown health status of E. transvaalense was generally good although some individuals, contributing 9% of the sample, had dead crowns. A linear relationship was noticed between areas harvested and stem circumference, which is understandable considering the large surface area of harvestable bark on bigger individuals. Matrix modeling of E. transvaalense revealed that the vegetative stage should be targeted for management action. An assessment of the adequacy of the Brackenridgea Nature Reserve, an initiative aimed at protecting Brackenridgea zanguebarica, revealed that the reserve size is not enough for conservation of a viable population. The method flagged out potential growth habitat for B. zanguebarica around the current reserve, which could be incorporated to enlarge the conservation area, which could be incorporated to enlarge the conservation area. Four different scenarios were analysed on how best to conserve the species. Assuming a 50% reduction in human-related activities, such as cultivation, harvesting and livestock grazing, it is recommended that the reserve be enlarged from its current 110 ha to 366 ha to maintain a viable population into the future. Finally, the study recommended the adoption of an integrated approach to achieve sustainability of bark harvesting in the Venda region. Only by selecting best practices from both indigenous and conventional conservation techniques will the conservation of natural resources that are of important to local communities, be successful. An action plan that will involve the formation of an association by all stakeholders interested in the sustainable utilization of natural resources must be developed. The association must be governed by a constitution with a clear mission statement and the harvesting of natural resources should be done in line with a collection policy. / Thesis (PhD)--University of Pretoria, 2012. / Plant Science / unrestricted

In South Africa, there is a growing concern regarding the sustainability of bark harvesting due to the reduced availability of medicinal trees in natural areas and the slow growing and slow-reproducing nature of South Africa’s indigenous trees, of which some have specific habitat requirements and a limited distribution. With an estimated 80% of all Africans in South Africa still relying on plant material for their basic healthcare needs, approximately 200 000 traditional healers and an estimated 63 000 commercial harvesters, medicinal plants are being exploited to extinction. The aim of the study was to determine whether bridge-grafting could be used to restore growth in girdled Ocotea bullata and Curtisia dentata trees as these two medicinal tree species are listed on the South African Red List as ‘endangered’ and ‘near threatened’ due to overexploitation. These trees were also historically used in furniture production and general carpentry, which increased these trees’ vulnerability to extinction. Bridge-grafting is a technique widely described in horticultural literature but has not been used to restore growth in medicinal tree species with extensive harvesting damage. Metabolomics as analytical method is a relatively new science, but it is very useful, accurate and repeatable in obtaining knowledge on the metabolites present in a plant, and for determining the concentrations of metabolites. NMR metabolomics is, however, not sensitive enough to quantify metabolites with very low concentrations such as plant hormones. The results achieved showed that O. bullata and C. dentata responded differently to girdling and bridge-grafting regarding location of callus initiation, callus development, rate of callus development, basal shoot initiation and development and their sucrose source-sink relationships. NMR metabolomics showed that seasonality was an important factor affecting metabolite responses in both species. NMR metabolomics also showed that after one year, there were no differences in responses above and below the girdle wounds, nor were there differences between the grafted trees and the normal control trees. iv Although the method of bridge-grafting was successful in restoring the growth of O. bullata and C. dentata with this study, much more research needs to be conducted to prevent endangered girdled medicinal trees from becoming extinct, to maintain tree species diversity, genetic diversity and biodiversity. / School of Environmental Sciences / M. Sc. (Nature Conservation)