Browsing by Author "Moncrieff, Glenn R"

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    Anthropogenic modification of the natural fire landscape and its consequences for vegetation patterns on the Cape Peninsula
    (2017) Rogers, Annabelle J; February, Edmund C; Moncrieff, Glenn R; Slingsby, Jasper A
    Understanding the spatial probability of fire and how urban development may alter natural patterns is particularly important in areas where alternate ecosystem states occur at fine spatial scales. The Cape Peninsula, South Africa, is a one such region where fire-sensitive forest patches occur interspersed in a sea of fire-dependent fynbos. Fire is believed to be an important determinate of forest distribution, with absence or occurrence of fires potentially allowing patch contraction and expansion. In this thesis I use a series of computer models to determine the extent to which anthropogenic development and land transformation have altered the spatial variation in fire likelihood, or the 'burn probability', and its consequence for the distribution of forest on the Cape Peninsula. The two multi-model, fire behaviour simulation systems I use are FlamMap and FARSITE. FARSITE is a deterministic simulation package used globally for discrete event simulation. In an effort to assess the viability of using the FARSITE model for fire prediction in fynbos and the determinants of model accuracy, I predicted fire area for a historical fire on the Cape Peninsula using a variety of fuel models and wind conditions. Following this validation, FlamMap was used to simulate the burn probability of the Cape Peninsula under natural conditions – no urban development present – and transformed conditions – where urban areas mapped as non-burnable fuel models. I then determined changes in forest distribution documented over the last 50 years relative to changes in burn probability as a result of urbanisation. My results show that an increase in urbanisation on the Cape Flats has produced a significant urban shadow effect due to the interruption of natural fire catchments. This urban shadow effect has resulted in an overall increase in area of fire refuges on the Peninsula and expansion of forest, particularly on the more mesic eastern slopes at Kirstenbosch and Newlands. The results strongly support that urban-mediated changes to fire patterns are drivers of forest expansion in this region, and adds further evidence to support the significance of fire in determining biome boundaries in the fynbos.
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    The demographic impacts of browsing on woody plants in savannas : from individual branches to whole populations
    (2010) Moncrieff, Glenn R; Bond, William J
    Browsing ungulates can potentially have drastic impacts on vegetation patterns. This is particularly true in African savannas where many large browsers persist at high densities. Most of the theory and models outlining mechanisms of impact on plants and predicting responses are framed in terms of biomass impacts and responses. However, for trees in African savannas, fitness is more closely linked to height than above ground biomass. I evaluate the demographic impacts of browsing, making explicit contrasts with impacts on biomass. The results highlight under- explored intrinsic aspects of plants and browsers that determine the degree of browser impact on plant demography, aspects that have been under-explored due to an emphasis on biomass responses, and provide novel methods to measure and evaluate large-scale browser impacts, which have proved difficult before.
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    Locating and Dating Land Cover Change Events in the Renosterveld, a Critically Endangered Shrubland Ecosystem
    (2021-02-24) Moncrieff, Glenn R
    Land cover change is the leading cause of global biodiversity decline. New satellite platforms allow for monitoring of habitats in increasingly fine detail, but most applications have been limited to forested ecosystems. I demonstrate the potential for detailed mapping and accurate dating of land cover change events in a highly biodiverse, Critically Endangered, shrubland ecosystem—the Renosterveld of South Africa. Using supervised classification of Sentinel 2 data, and subsequent manual verification with very high resolution imagery, I locate all conversion of Renosterveld to non-natural land cover between 2016 and 2020. Land cover change events are further assigned dates using high temporal frequency data from Planet labs. A total area of 478.6 hectares of Renosterveld loss was observed over this period, accounting for 0.72% of the remaining natural vegetation in the region. In total, 50% of change events were dated to within two weeks of their actual occurrence, and 87% to within two months. The Renosterveld loss identified here is almost entirely attributable to conversion of natural vegetation to cropland through ploughing. Change often preceded the planting and harvesting seasons of rainfed annual grains. These results show the potential for new satellite platforms to accurately map land cover change in non-forest ecosystems, and detect change within days of its occurrence. There is potential to use this and similar datasets to automate the process of change detection and monitor change continuously.