Doctoral Degrees (Forestry)

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    Assessing the compaction susceptibility of South African forestry soils.
    (1995) Smith, Colin William.; Johnston, M. A.; Lorentz, Simon Antony.
    The widespread use of heavy machinery during harvesting and extraction operations in South African timber plantations has led to concern that soil compaction is causing long term site productivity declines and environmental damage. This study was conducted with the intention of establishing a framework for the routine prediction of compaction susceptibility of South African forestry soils. Principal facets of compaction behaviour were established for a wide range of soils and these were related to changes in soil physical conditions resulting from compaction. Soils were chosen from a broad range of geological and climatic regions and varied greatly in texture (8 to 66% clay) and organic matter content (0.26 and 5.77% organic carbon). A quantitative description of compaction behaviour was obtained using a simple uniaxial compression technique. Bulk density was related to applied pressure, water content and initial bulk density as independent variables. Statistical analysis of the coefficients in the model enabled the relative importance of applied pressure and water content during the compaction process to be evaluated and related to commonly measured soil physical properties. Compressibility was strongly correlated with clay plus silt content and to a lesser extent with clay content and organic carbon determined by loss-on-ignition (LOI). Though significant correlations were obtained between maximum bulk density (MBD) and clay plus silt content, MBD was more strongly correlated with organic carbon (LOI). A classification system for compaction risk assessment is presented, based on the relationship between compactibility (MBD) and organic carbon (LOI), and between clay plus silt and compressibility. The effect of soil compaction on soil physical quality was assessed by examining changes in penetrometer soil strength (PSS) and water retentivity curves of compacted soils. Clay content strongly influenced the relationship between PSS, bulk density and water content. The PSS at wilting point (-1500 kPa) increased with increasing clay content whereas PSS at a matric potential of -10 kPa and was most strongly related to organic carbon (LOI) and increased with increasing organic carbon content. Compaction generally resulted in an increase in field capacity and wilting point on a volumetric basis and a flattening of the water retentivity curves. However, no simple effects of compaction on available water capacity were observed. Changes in PSS, aeration porosity and water retention following compaction allowed the definition of a single parameter, the non-limiting water range (NLWR), to describe more precisely the changes taking place in the air-soil-water matrix following compaction. "Compaction envelopes" were constructed to illustrate these complex inter-relationships and to relate changes in NLWR to compactive effort and relative bulk density. The use of NLWR is recommended as a sensitive parameter for assessing compaction risk of forestry soils.
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    The impact of change in climate, human demography, and other social factors on the fire regime of the Kogelberg Nature Reserve.
    (2011) Gumbi, Duma Petros.; Kirkman, Kevin Peter.
    Background. Fire is a dominant ecological factor in the Fynbos Biome in the Western Cape, and changes in the fire regime have important consequences for the biodiversity conservation of the landscape. Fire regimes in the Western Cape are known to have changed over the past decades due to factors such as changing climate, resources for fighting fires, sources of ignition and human demography. Fire regimes at any given site are never fixed, occurring at varying intervals, in different seasons and at different intensities. Each event is therefore unique and the ecological consequences will depend on both the burn parameters and the nature of the fires that preceded it. Over time, it has been difficult to accurately and consistently quantify fynbos fire regimes and the impact of change in climate, human demography and other social factors because of the unavailability of accurate fire data and records. An understanding of the trends in fire regime and the impact of changes in climate, human demography and other social factors is important to maintain biodiversity and the co-existence of species. There is an urgent need to find effective approaches for assessment of fire regime conditions that balance scientific credibility, spatial continuity and quick delivery. This study seeks to determine the trends in the fire regime (frequencies, return interval, veld age and seasonality) of the Kogelberg Nature Reserve and the impact of changes in climatic patterns, fire-fighting resources, sources of ignition and population increase. Methods. The study site was the Kogelberg Nature Reserve in the Western Cape Province because of its exceptional conservation significance. It is regarded as the floristic heart of the globally unique Cape Floral Kingdom since it appears to have the highest levels of plant species richness and endemism in the Fynbos Biome. Fifty-four years of fire data records were analysed to determine the trends in the fire regime. The study period was divided into two management periods; 1952-1980 and 1981-April 2006 for analysis of the historical fire regime, with the former being a period when there was less pressure of human settlement and before the reserve was proclaimed a mountain catchment area. The latter period was when the reserve had been declared a nature reserve and more people were settling in the neighbouring towns, the fire risk was increasing and allegations of climate change were being made. To test for the impact of climate change on the fire regime of the Kogelberg Nature Reserve, weather data (temperature, wind speed, relative humidity and rainfall) from a weather station in the vicinity of the nature reserve were analysed to determine fire danger indices for a period of 33 years. The United States of America National Fire Danger Rating System as adapted for South African conditions was used to formulate burning indices from the weather data. A relationship between the fire days and the fire data was established. To test for the impact of the changes in fire fighting resources and sources of ignition, data were obtained from the fire records. To investigate the impact caused by population increase on the fire regime of the Kogelberg Nature Reserve population, data were obtained from Statistics South Africa. Available records for each factor were analysed to test for changes in that factor, and each factor was compared with the trends in fire frequency in the study site. Logistic regression was used to test for the relationships in the changes in fynbos fire regimes and its adaptation to changes in climate and social factors. A multivariate analysis was done to tie the four causing variables namely; fire numbers, fires sizes with population density and burning indices. Results. Analysis of data indicated a significant increase in the frequency and size of fires during the period 1981-2006 compared to the period 1952-1980. There has been an increase in the burning of veld younger than 6 years, and the total area burnt has increased significantly in the period 1981-2006 coupled with an increase in the number of fires. However, the size per individual fire has decreased significantly in the period 1981-2006. This study found that the conditions for starting fires improved significantly during the period 1989-2005, due to burning indices increasing from the period 1989-2005 which resulted in conditions for starting fires becoming more conducive than the previous era although fires in the reserve started under all environmental conditions. The population size of people staying in the neighbouring towns and villages has more than doubled during the period 1996-2006. Multivariate analysis showed that there was a significant correlation between number of days when fires burnt and area burnt and population with numbers of fires. Finally, since 1988 Cape Nature has not been able to comply with the minimum requirements for fire prevention due to lack of capacity and resources. Conclusions. The Kogelberg Nature Reserve has been negatively impacted by the increased conditions of ignitions associated with climate change, increased unplanned fires associated with increase in population growth and lack of capacity and resources to prevent and control veld fires. These results could negatively impact biodiversity of the Kogelberg Biosphere Reserve if no actions are taken to address these shortfalls.
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    Ecotourism for sustainable development : economic valuation of recreational potentials of protected areas in the Congo Basin.
    (2008) Tieguhong, Julius Chupezi.; Zwolinski, Janusz.
    This study was designed to capture the complexity of man-to-forest relationships in the endangered, world-renowned tropical rain forests of the Congo Basin in Africa. Their biological complexity and integrity have been challenged by human development and new knowledge is urgently needed to save these forests and the people dependent on them. The scope of the study was enormous because of the complexity of the resource, the diversity of forest-dependent people and actors. The major benefit of this research was in accessing and exposing new and quantitative information in remote settlements of the region by applying innovative methodologies and analytical techniques. These included: 1. The definition of forest-dependency based on detailed annual inventories of sources of households’ incomes, their statistical ranking and interpretation with logistic regressions, and the Kuznets ratio and Gini coefficients as introduced by the World Bank; 2. critical appraisal of the international parks in the region based on auto-financing principles and tested with contingent valuation and tax maximization techniques, such as Laffer’s curves, and leading to the development of new conservation models of financial self-sufficiency and a new formula for practical park management; 3. the critique of poaching by explaining and exposing food insecurities, especially deficient supplies of animal protein and associated malnutrition among the rural poor; 4. assessment of housing inadequacy among forest dwellers and its impact on forest regeneration and resources; 5. clarification of the impacts of timber logging by accessing detailed unpublished information from timber companies; 6. the introduction of survey-based valuation techniques as essential prerequisites to policy formulation and the sustainable management of forests; 7. proposing a flow chart that embraced the resources and stakeholders through the flow of market values and services for further exploration. Contrary to traditional beliefs; the results showed that both poor and wealthy households are equally dependent on forest resources for their livelihoods with no significant difference in consumed forest products between the 25% higher income earners and the 25% lower income households. Forests contribute over 57% of wage income in the region and forest-derived income is of a higher total value than any other source, including agriculture. Among forest foods, wild fruit and bushmeat are by far the most important. Therefore, the clearing of forests for agriculture or instituting conservation policies that completely keep local people away from forests will result in constrained access to resources of immense importance to local livelihoods. However, the findings contradict the commonly propagated views that timber harvesting in the region is directly responsible for deforestation, the loss of forest structure and biodiversity. It was shown that the harvesting of saplings and poles for housing may endanger forest regeneration and species composition of forests neighbouring the villages. The desired financing of national parks should be through internally generated revenues, requiring deliberate investments in facilities and infrastructure. The necessity to satisfy the basic needs of the forest-dependent people remains urgent. The complexity of man-to-forest relationships is beyond one study and needs to be further expanded on, in our quest to sustainable forest management based on participatory principles. Such management needs to provide for and be supported by various stakeholders including the local communities, state agencies, donors, NGOs, and commercial conglomerates. Moreover, the need to understand forest values beyond market principles is required in order to translate the concept of sustainable forest management from a theoretical concept in the Congo Basin to one that can reduce conflicts, deforestation, poverty and famine.