Browsing by Author "Milton, Suzanne Jane"

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    Modelling the current and potential distribution of woody plants, with special emphasis on the importance of spatial scale and environmental factors
    (2002) Rouget, Mathieu; Richardson, Dave; Cowling, Richard M; Lavorel, Sandra; Milton, Suzanne Jane
    The relationship between species distribution and environment has always been a central issue in ecology. The primary aim of this thesis is to explore the role of abiotic and biotic factors in mediating the distribution of woody plants, particularly invasive alien species. Predictions of the future distribution of invasive species are required for management, conservation actions, and legislation. Using predictive geographical modelling, this thesis assesses the role of spatial scale in understanding the determinants of species distribution, modelling invasion spread, and taking conservation decisions. The species distribution databases were collated in a Geographic Information System from various sources (from field mapping to remote-sensing data), and at various spatial scales (from local to sub-continental). Classification and regression trees, a flexible non-parametric statistical technique, were developed for each case study. I show that static modelling approaches, such as classification trees, are appropriate for modelling species distribution at regional to sub-continental scales. More mechanistic approaches, which include biological attributes, are required for accurate modelling of species abundance at local scale. A hierarchy of environmental factors was observed. Abiotic factors such as climate were more important for modelling species distribution at broad scales, whereas biotic factors were the fine-scale drivers of species distribution and abundance. This highlights the scale- dependence of prediction accuracy and of environmental drivers. Predictive habitat modelling was also applied to modelling future land use changes (including invasive alien species) in the context of conservation planning for the Cape Floristic Region. Effective conservation planning requires a detailed assessment of current land use patterns and future land use scenarios. Conservation planning is generally derived at regional scale but implementation takes place at finer scales. I investigated the transition from broad-scale planning to fine-scale implementation. This work emphasises the importance of diverse and fragmented habitats in measuring conservation value. This thesis concludes by linking predictive habitat modelling, species determinants, and application types to the spatial scale analysed.
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    The short-term effect of rehabilitation on ecosystem services in the semi-arid succulent Karoo lowlands and the Little Karoo, South Africa
    (2011) De Abreu, Petra; Milton, Suzanne Jane; Hoffman, Timm; Le Maitre, David
    This study has shown that using active rehabilitation in combination with improved management strategies (e.g. rest from grazing) may induce recovery of certain ecosystem services within practically relevant time scales. However, these benefits might not be tangible for landowners or society as of yet, due to the small-scale nature of the rehabilitation application along with the relatively high, short-term associated costs. To alleviate financial constraints on farmers and in order to socially and financially enhance local communities, the focus for now should be on sourcing funds from government and private sectors for rehabilitation implementation.
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    Studies of herbivory and vegetation change in Karoo shrublands
    (1993) Milton, Suzanne Jane; Siegfried, W R; Rutherford, MC
    The broad objective of these studies was to view present landuse (extensive small stock ranching) in the Karoo against the background of relationships between indigenous plants and animals and to indicate how modification of herbivore regimes might affect this arid environment. Specific objectives were to determine how grazing by domestic livestock brings about vegetation change, why such changes are sometimes irreversible, and whether existing conceptual models of vegetation dynamics adequately explain the impact of domestic livestock on Karoo vegetation. Three interrelated aspects of plant-animal interactions were considered: the influence of herbivores on the evolution of Karoo plants, food selection by indigenotis and introduced herbivores and the effects of herbivory, competition and rainfall on plant reproduction and recruitment. The results of these investigations are presented as 14 papers. The first three papers interpret plant morphology and biogeography to provide information on past spatial and temporal use of the landscape by herbivores, and the next seven provide new information on food selection by invertebrates, indigenous vertebrates and by domestic sheep. Three papers examine the hypothesis that the reproductive output, survival and abundance of some Karoo plant species are influenced by herbivory. The possible consequences of various land management options on diversity and productivity of Karoo rangelands are discussed in the concluding paper. It was inferred, from biogeographic trends in the relative abundance of plants with thorns or propagules adapted for epizoochoric dispersal, that densities of large mammalian herbivores decreased from the north eastern to the southwestern Karoo. Within the most arid parts of the Karoo, mammalian herbivory appears to have been concentrated along drainage lines and in pans.
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    Studies on Australian acacias in the South Western Cape, South Africa
    (1980) Milton, Suzanne Jane; Hall, A V; Moll, EJ
    The thesis comprises six papers dealing with aspects of the ecology of the exotic Acacias which are considered to be weeds in the South Western Cape. Topics covered are the origins and reasons for success of the Australian Acacias in the Cape, their phenology, reproductive biology, shade tolerance, litterfall and biomass. The implications of these findings for management are discussed in the general conclusion, and the raw data is tabulated in four appendices. The work is illustrated with 37 figures.