Browsing by Author "Midgley, Alison"

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    The many forms of thirst : investigating forest constraints in the Cape Floristic Region
    (2013) Midgley, Alison
    Identifying the primary determinants of forest distribution has been a considerable challenge for ecologists. Although focus was traditionally directed towards climatological variables, predictive models showed that suitable forest conditions were far more extensive than the actual forest distribution. This study investigated the primary constraints of forests in the Cape Floristic Region (CFR), in South Africa. Based on a study by Lehmann et al. (2011) on savanna ecosystems, it was hypothesised that seasonal drought and moisture balance were more likely to limit forest distribution than broader rainfall patterns. The biomes of the CFR were mapped using Mucina & Rutherford’s (2006) vegetation map. Environmental data was extracted from Schulze (2007) and analysed using various statistical methods and the effective rainfall during the wet and dry seasons was examined in relation to vegetation patterns. As a complementary analysis, high resolution spatial data was extracted from the Worldclim database (www.worldclim.org) and run in the program Maximum Entropy. The presence of forest was shown to be constrained by soil moisture deficits in the driest half of the year. However there was considerable overlap of climactic and edaphic conditions across the different biomes. It was suggested that seasonal drought may play an indirect rather than direct role in shaping vegetation type. As the length of the dry season correlated with the length of the dry season, it was determined that seasonal drought may effect vegetation by promoting landscape-shaping fires. These findings have implications for predicting and understanding historical and future ecosystem shifts and their relationship with global and local climate change.
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    Plant community patterns and diversity in sites impacted by Eucalyptus camuldulensis Dehnh. : insights from the Berg River, Western Cape / Alison Midgley
    (2013) Midgley, Alison; Muasya, Muthama
    Alien Eucalyptus and Acacia species are amongst the most prolific invaders of the Berg River catchment, in the Western Cape. This study assessed the effects of invasive species and the potential for passive successional restoration in a heavily invaded riparian site (>80% aerial cover), a cleared riparian site and a pristine reference site. Three plots were demarcated per site, and transects were taken perpendicular to the river on the lower, middle and upper bank. Three 2m2 quadrats were intensively sampled per transect. Species diversity and community composition of indigenous and alien species were compared by measuring herbaceous, shrub and tree cover. Soil conditions, such as texture, salinity, acidity and moisture, were also compared. Distinctly different plant communities were found in each site, although cleared and invaded sites were more similar to each other. Cleared sites showed >45% cover by invasive successional species and grasses atypical of natural succession patterns. It was proposed that restoration constraints (e.g. method of clearance, intensity of prior invasion, land-use) were encouraging alien re-colonisation. However, there was evidence that the overall the trajectory of successional was favourable for indigenous trees and species. It was suggested that active re-vegetation of indigenous tree species, and adherence to correct clearance methods would aid site restoration.