Browsing by Author "Slingsby, Jasper A"

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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 diversity of ground bryophyte communities along an altitudinal gradient on La Réunion island
    (2011) Lane, Wade Howard; Hedderson, Terry A; Ah-Peng, Claudine; Slingsby, Jasper A
    Aim: To compare the α, β and phylogenetic diversity of the ground bryophyte communities along a tropical altitudinal gradient in order to determine which processes govern these assemblages. Location: La Réunion island (55°39'E; 21 °00'S), in the western Indian Ocean. Methods: The ground bryophyte communities were surveyed along the eastern slope of Piton des Neiges (350 - 3050 m). α, β and phylogenetic diversity along the altitudinal gradient was determined and graphically presented. Results: The α diversity had two distinct peaks at 1150 - 1350 m and at 2750 m, these corresponded to a dominance in liverwort and moss species, respectively. The phylogenetic diversity along the altitudinal gradient was far greater than is predicted from the null models suggesting that ground bryophyte communities are structured according to "environmental filters". The mid-domain effect and mass effect could not be used to describe the changing diversity along the altitudinal gradient, however a correlation analysis revealed temperature and relative humidity influences the changing a diversity. Main Conclusions: In conclusion both ecological and evolutionary processes structure the ground bryophyte communities.
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    Monitoring the Knysna forest : species, community and forest responses
    (2012) Morris, Thomas; Slingsby, Jasper A; Midgley, Jeremy J
    Forests are valuable ecosystems to society but are greatly threatened by changing factors from habitat conversion to climate change. South Africa's only extent of indigenous forest is predicted to disappear within the next 30 years. Many challenges are currently faced when trying to detect and interpret directional changes in forests which results in an urgent need to understand any effects that these change factors have on forest ecosystems. We investigate evidence for change in the old growth Lilyvlei Nature Reserve by monitoring growth and dynamics at various levels by examining a 20 year record of tree growth and stand dynamics. Through the inclusion of biodiversity measures and ecologically important plant traits, changes in forest dynamics and growth are investigated. Results show no total change in biomass across the 20 year period, although an intensification of extreme climatic events and dynamics indices were recorded for the second period. Significant correlations were found between community diversity measures and forest growth. Trait variables showed insignificant correlations with forest growth and dynamics. These results suggest that the Knysna forest is controlled by climatic variables and that increased diversity within communities result in increased growth. It is believed that changes in the forest may be masked by compositional shifts of just a few dominant species. These results become important, particularly in the light of changing climatic, atmospheric and environmental changes that threaten global ecosystems in the time to come. However, considering the brief 20 year period observed in a forest where the average individual has a life span of over a century, the importance of long term monitoring becomes an important component in the understanding of forest ecosystems.
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    Vegetation change and vegetation type stability in the Cape of Good Hope Nature Reserve 1966 - 2010
    (2010) Hall, Stuart; Midgley, Jeremy J; Slingsby, Jasper A
    Vegetation stability was investigated within the Cape of Good Hope Nature Reserve by incorporating three vegetation surveys spanning a 44 year time period. The goals of this study were to investigate changes in overall species diversity within the reserve, stability of community composition within and between sites, and which factors are influencing stability. A survey was conducted on 26 vegetation plots across the reserve. Data from this survey and two previous surveys was used to compare species diversity between time periods. Vegetation compositional similarity was also compared between sites. I tested for the effect of difference in vegetation age and soil type as predictors of vegetation groups. Results showed an overall decrease in species diversity. Analysis ofvegetation groups showed that vegetation types are mostly stable as current vegetation can be predicted by groups based on 1966 data. Vegetation is influenced significantly by fire history and soil types.