ETD Collection

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    Impact of charcoal production on populations of selected Savanna tree species on clay soils in Catuane, southern Mozambique
    (2007-02-21T13:39:28Z) Manjate, Nelson Belecuane
    The impact of charcoal production on populations of selected savanna tree species was investigated on clay soils in Catuane, southern Mozambique. The study focused on answering questions related to the contribution of charcoal production to the local economy, the way populations of selected species were changed by the activity and the way in which they recover. Acacia nigrescens, Acacia nilotica and Ziziphus mucronata were identified as being amongst the most utilised species for charcoal production due to their hard wood quality. The charcoal production is being done by individuals from outside the local community. They are able to generate relatively high revenues from their product, which they sell to external markets, notably Maputo. The local community do not share in the benefits of the production. Interviews with members of the local community, indicated that they would prefer the activity to be stopped or more rigourously controlled. A comparison was made between adjacent harvested and un-harvested areas to assess the effects of charcoal production on the tree populations. Population structure by stem circumference classes were broadly similar in all three study species being characterised by a high frequency in the smallest circumference class. All other classes had considerably lower frequencies. With regards density, Acacia nigrescens and Acacia nilotica showed significantly lower densities in the harvested area. Ziziphus mucronata showed no significant difference. The frequency of stump circumference classes of Acacia nigrescens and Acacia nilotica were normally distributed with the class 81-90 cm being the most common. Ziziphus mucronata data were skewed to the left, with most stumps in the class 52-60 cm. Stump heights were mostly in the region of 20 cm. Circumferences of stumps were similar across the study species, being in the region of 90 cm. Coppicing in stumps was relatively poorly developed, with the majority of stumps having no successful coppice shoots. Kilns had an average density of two kilns per hectare. There was an inverse relationship between species abundance and mean harvesting radius. The results of the study indicate that harvesting has had an effect on species abundance and population structures. With decreases in density and a shift in age distribution towards a predominance of juvenile trees. However, the results are not unequivocal, since the area is not pristine and may have been subjected to other activities before harvesting for charcoal. The charcoal producers appear to harvest all sizes of tree. Their production data, approximately 1300 kg of charcoal produced per hectare, indicate the potential for over utilisation of the woodland resource. Futhermore their practice of cutting at low height subjects the stumps to growth retarding elements such as herbivory and fire, possibly contributing towards relatively unsuccessful coppicing and exacerbating the sustainability issue. To address these issues, along with the socio-economics issues, appropriate structures need to be implemented by government, in consultation with communities.
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    Elucidation of the aerobic respiratory chains in mycobacteria
    (2006-10-27T07:51:11Z) Matsoso, Limenako
    The aerobic respiratory chain of mycobacteria consists of at least two branches, a cytochrome c branch terminating in an aa3-type cytochrome c oxidase, and a quinol branch terminating in cytochrome bd oxidase. The structure and function of the former branch, leading from the menaquinone-menaquinol pool to the cytochrome bc1 complex and terminating in the aa3-type cytochrome c oxidase, was characterized in Mycobacterium smegmatis. Allelic exchange mutants of M. smegmatis in the bc1 complex (ΔqcrCAB::hyg) and in subunit II of the aa3-type cytochome c oxidase (ΔctaC::hyg) were constructed and analyzed for growth, and gene expression using lacZ reporter assays and genome expression profiling by DNA microarray. Both mutants were found to be profoundly growth impaired. Disruption of this pathway resulted in an adaptation of the respiratory network that is characterized by a marked up-regulation of cydAB, which encodes the bioenergetically less-efficient and microaerobically induced cytochrome bd-type menaquinol oxidase that is required for the growth of M. smegmatis under O2-limiting conditions. Other adaptations to re-routing of the electron flux through the branch terminating in the bd-type oxidase were revealed by comparative expression profiling of the bc1-deficient mutant and its parental wild type strain using a partialgenome microarray of M. smegmatis that is enriched in essential genes. The majority of the genes up-regulated in the mutant are involved in intermediary metabolism and respiration. Also induced were several genes including, uspL and a homologue of Rv1592c, which were previously shown to be up-regulated by hypoxia in M. smegmatis (uspL) and M. tuberculosis (uspL and Rv1592). The cytochrome bc1-aa3 branch is required for growth of M. smegmatis under aerobic conditions and its disruption results in growth attenuation and up-regulation of cytochrome bd oxidase.