Doctoral Degrees (Forest and Wood Science)

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Browsing Doctoral Degrees (Forest and Wood Science) by browse.metadata.advisor "Geldenhuys, Coert Johannes"

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    Effect of population size on viable seed output, seed rand and natural regeneration pattern of a tropical conifer Widdringtonia whytei-Rendle in Malawi
    (Stellenbosch : Stellenbosch University, 2013-12) Chanyenga, Tembo Faera; Geldenhuys, Coert Johannes; Sacande, Moctar; Stellenbosch University. Faculty of AgriSciences. Dept. of Forest and Wood Science.
    ENGLISH ABSTRACT: Widdringtonia whytei is a tropical endemic, fire-adapted pioneer coniferous tree species within natural fire-fragmented Afromontane forest patches in a confined area on Mulanje Mountain in Malawi. Natural and anthropogenic fires within the surrounding fire-prone landscape, insect attacks, and uncontrolled harvesting of mature trees for timber threaten the survival of W. whytei. This study investigated the effects of population fragmentation on the reproductive biology of W. whytei, through four specific studies: effects of population size, tree size and crown position on viable seed output; seed rain variation among population sizes; effects of temperature and light on viability and germination of W. whytei seeds; and the influence of population size on natural regeneration patterns. The study was conducted during 2008 and 2009 on three sites using three W. whytei population sizes: small (≤10 reproductively mature cone-bearing W. whytei trees), medium (11-20 cone-bearing trees) and large (>20 cone-bearing trees). Data were collected using field and laboratory experiments and a review of secondary information. The effect of fragment size and crown position on viable seed output and seed rain pattern was tested with a nested linear mixed model. The influence of stem diameter (dbh) on viable seed output was tested using a separate data set. The variation in seed rain was explored with a generalised linear model (GLM) with a negative binomial link function. Variations in seed germination was analysed with a Weibull regression model. The influence of fragment size on seedling regeneration was tested with a GLM (binary logistic regression). Viable seed output from W. whytei cones was very low (23%) and was not affected by population size, tree diameter or crown position. W. whytei population size influenced seed rain with large fragments having higher seed rain densities. Number of dispersed seeds was generally very low and poorly dispersed. W. whytei cones are semiserotinous and depends on moderate to severe fires for heavy seedfall and wider dispersal. Such fires did not occur during the study period. Temperature is a critical factor for seed germination. Seeds germinate between 15 and 25°C with the optimum at ~ 20°C either under light or dark conditions. Regeneration density followed the seed rain pattern indicating that seed availability is a critical factor for regeneration. Regular cool fires outside the forest patches and along the edges during the hot dry season, and the thick litter layer and shady conditions inside forest patches, caused most of the seedling mortality. This study highlighted the difficulties W. whytei experiences with low output of viable seed, limited seed dispersal and low seedling regeneration in and around forest patches, i.e. factors important for conservation management of this species. It is recommended that gaps with diameter equal to canopy height and occasional spot fires would promote seed dispersal onto exposed mineral soil for rapid seedling establishment and subsequent population growth. Such natural fire disturbance events may show the true seed rain and seedling establishment patterns in this species.
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    Knowledge systems and adaptive collaborative management of natural resources in southern Cameroon : decision analysis of agrobiodiversity for forest-agriculture innovations
    (Stellenbosch: University of Stellenbosch, 2009-12) Mala, William Armand; Geldenhuys, Coert Johannes; Prabhu, Ravindhra; University of Stellenbosch. Faculty of Agrisciences. Dept. of Forest and Wood Science.
    ENGLISH ABSTRACT: This study aimed to analyze under which conditions the structure, organization and integration of knowledge systems can provide the implementation of adaptive collaborative management of natural resources under conditions of high biodiversity in the humid forest zone of southern Cameroon. The study specifically did the following: characterized sustainable slash-and-burn agriculture innovations; examined the influences of local perceptions of nature and forest knowledge management systems on adaptive slash-and-burn agriculture practices; analyzed the influences of the social representation of land use patterns and their local indicators on agro-ecological sustainability; characterised the biophysical dimensions of local management of agricultural biodiversity knowledge systems; analyzed how local agricultural biodiversity knowledge is used to adapt and to satisfy household consumption needs, market preferences, and sustainable livelihoods; examined the influences of local perceptions of climate variability for the ability and adaptive capacity of people to use local knowledge to deal with the effect of pests-diseases on crop yield, corrective management actions, and adaptive slash-and-burn agriculture management. The study was conducted in three blocks within the humid forest zone of southern Cameroon along a gradient of natural resource use management intensification and population density. Data were collected via structured and semi-structured interviews, multi-disciplinary landscape assessment and a review of secondary information. Chisquare tests were used to show how local knowledge influences - natural resource management at the forest-agriculture interface, while binary logistic regressions were used to understand the influences of biophysical and socio-economic factors on farmers’ decisions to domesticate tree species and to cultivate several crop cultivars. Fourteen research and development (R&D) themes were identified and found to be equally distributed among blocks but unequally distributed across technical, marketing and socio-organisational types of innovation. There was a gap between social demand and innovation offer. Innovations offered covered more technical issues, such as crop variety development, indicating their agricultural focus rather than the integration of forest and agriculture issues. The local perceptions of nature and forest resources are based on social representation of the vital space into components having a specific function for the social, physical and spiritual life of people. Needs of the human world determine the role of local forest knowledge systems in the interpretation and responses of the natural environment, and guide the trajectories of natural resource management practices. The management of agro-ecological sustainability is based on the local definition of well-being, social representation of space and on a multi-criteria approach combining bio-indicators such as plants, earthworm activities, age of vegetation or forest cover, soil colour and quality but it is also positively influenced by land use history, the use value of wild plant and crop species, the knowledge of crop qualities, the knowledge of interactions between crops, and between crops and other wild plant species, the tree size of tree species used, the future use of a current land use, the estimated land use for own use and market access.