Browsing by Author "Aston, Tim"

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    A study of bush encroachment in Hluhluwe National Park, using aerial photographs within a GIS framework
    (2003) Aston, Tim
    Bush encroachment has been an ongoing process since the proclamation of the Hluhluwe Reserve. In this paper, I assess both the total extent of bush encroachment over the last 40 years for a section of the reserve (9.1 %}, as well as which landscape factors pre-dispose areas to encroachment in that section. Aerial photographs from 1960 were linked together and aligned to an orthorectified Image from 2000, which had been georeferenced and aligned to the GIS database that exists for the area. Areas of closed canopy vegetation were converted into polygons, and the physical attributes of the areas that had been encroached Upon were extracted from the GIS database that exists for the area. Classification trees were used for the analysis of landscape correlates of encroachment. Fire frequency and the area of forest within 200m of a point in? 1960 were Identified as being the main factors determining which areas had been encroached upon
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    CO₂ responsiveness of different plant functional types
    (2003) Aston, Tim
    Atmospheric CO₂ levels have increased by 30 % since the onset of the industrial revolution and are likely to continue to rise in the future. Whilst growth of plants is typically enhanced under elevated CO₂ concentrations, the degree of the response varies from species. In this study 4 species were exposed to 6 different CO₂ levels across a range from sub ambient to super ambient conceliltrations.
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    Geohydrological characteristics of Table Mountain Group aquifer-fed seeps and the plant ecophysiological consequences
    (2007) Aston, Tim; Bond, William J; February, Edmund C; Midgley, Jeremy J
    Fynbos, the native vegetation of the Western Cape of Southern Africa experiences a mild, Mediterranean type climate with hot dry summers and cool wet winters. In terms of climate, fynbos is comparable with other Mediterranean systems found around the Mediterranean in Europe, in parts of Chile, south-western Australia and in the Chaparral in California (Aschmann, 1973). The Cape Floristic Region, of which fynbos is part, is one of the world's most botanically diverse regions, home to an estimated 9030 vascular species (Goldblatt, 1978; Goldblatt and Manning, 2002). The region has exceptionally high levels of endemism. Almost 69% of its 8920 species of flowering plants are endemic (Goldblatt and Manning, 2002), and, despite its small area, it is regarded as one of the six global plant kingdoms (Takhtajan, 1986). Ericaceae, Iridaceae, Proteaceae and the Restionaceae are well represented and there are a number of families that are endemic or nearly so (Goldblatt and Manning, 2002). The largest is the Penaeaceae, followed by Grubbiaceae, Roridulaceae and Geissolomataceae, which together contain 15 endemic genera (Goldblatt and Manning, 2002). These families are almost without exception evergreen sclerophyllous shrubs and are thought to be palaeoendemic remnants from an ancient temperate flora, when conditions were cooler and wetter (February et al., 2004). As a result, many of these species are restricted to wetter areas such as wetlands and mountain seeps (February et al., 2004). Many of these seeps, as well as other groundwater-fed ecosystems, are likely to be connected to the Table Mountain Group (TMG) aquifer from which the city of Cape Town may begin to abstract water.