Browsing by Author "Rogers, Annabelle J"
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- ItemOpen AccessAnthropogenic 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 AUnderstanding 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.
- ItemOpen AccessExploration of climate mediated decline in a critically endangered southern hemisphere conifer over the last 40 years / Annabelle J. Rogers(2013) Rogers, Annabelle J; February, Edmund C; Verboom, TonyWiddringtonia cedarbergensis is a critically endangered conifer restricted entirely to the Cederberg Mountain range in the Western Cape of South Africa. This study aimed to assess whether contemporary climate change could be a driver in the recently documented tenfold decline of W. cedarbergensis in the last 40 years. By building distribution models using Maxent bioclimatic modelling for pre- and post- 1970’s point occurrence data, the distribution of the species pre- and post-1970’s were compared and assessed for significant change. Models predicted a clear range contraction in W. cedarbergensis from pre- to post- 1970. The present model predictions of suitability occur in a tight altitudinal band on the mid to upper slopes of the middle Cederberg (minimum of 1048m to a maximum of 1530m). However, the climatic predictions associate the present model distribution with relatively warmer and drier areas compared to that of the pre- 1970 model, suggesting a shift down slope rather than upslope. This is possibly due to the exaggeration of the upper limit of distribution for the pre-1970’s model that predicts W. cedarbergensis to occur as high as 1850m. This is unlikely due to the high prevalence of frost at this elevation. Though any climatic signal was complicated due to historical data error, high confidence in the present model prediction adds a valuable contribution to a body of literature that documents the decline of W. cedarbergensis and has important implications for conservation management of the species.
- ItemOpen AccessOccult moisture inputs in the fynbos : Foliar moisure uptake in Ericaceae, Restionaceae and Proteaceae / Annabelle J. Rogers(2013) Rogers, Annabelle J; West, Adam G'Occult' precipitation may be an important moisture source that can impact specific plant responses to water stress in certain ecosystems. Species in many ecosystems have been shown to use this moisture source via foliar moisture uptake. The Cape Peninsula and the surrounding southern coast experience high altitude mountain cloud cover in the summer dry period. Previous work on species that exist exclusively in the cloud belt found that species from the Erica and Restionaceae family were able to absorb water through their leaf surfaces, while members of the Proteaceae were unable to do so (Gibson, 2012). Adding to the body of research, this study explores whether foliar uptake occurs in species that do not exist in the cloud belt of the Cape Peninsula and the relative importance of this method of uptake in positively impacting a plants water balance during a cloud event. Direct foliar uptake was assessed at the leaf level using two methods; submersion and mist exposure. The importance of foliar uptake was measured at the whole plant level by exposing whole plants to cloud in a mist chamber. By covering the soil in a subset of plants, we were able to isolate the importance of foliar uptake relative to uptake via drip. Results found that the restios and ericas showed a stronger ability to take up moisture via their leaves than protea species, which showed little ability to do so. In contrast to this, the mist exposure method showed no significant uptake in any species except E. quadrangularis. This disparity is possibly due to specific leaf morphology. All species showed significant hydration in response to a whole plant cloud event in both the covered and uncovered treatments. The significant hydration in response to an occult event suggests that certain low land species are capable of utilizing small occult inputs despite the lack of regular summer cloud events as seen in the cloud belt species. As family patterns of foliar moisture uptake seen in cloud belt species (Gibson 2012) are conserved in the surveyed low land species, it can be concluded that moisture uptake is not a trait specific to cloud belt species, and represents a family level pattern of ability.