Masters Degrees (Conservation Ecology and Entomology)

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Browsing Masters Degrees (Conservation Ecology and Entomology) by Subject "Acacia mearnsii"

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    Impacts of the invasive tree Acacia mearnsii on riparian and instream aquatic environments in the Cape Floristic Region, South Africa
    (Stellenbosch : Stellenbosch University, 2018-03) Railoun, Moegamad Zaid; Jacobs, Shayne Martin; Simaika, John; Stellenbosch University. Faculty of Agrisciences. Dept. of Conservation Ecology and Entomology.
    ENGLISH ABSTRACT: In this study, I compared the notoriously invasive wattle species Acacia mearnsii, to two native woody species in terms of patterns leaf litterfall and nutrient resorption in riparian environments, and the decomposition of the leaf litter in aquatic environments and in stream macroinvertebrate communities in mountain streams in the Fynbos biome of the CFR. More explicitly, the study assessed: (1) leaf litter fall between A. mearnsii and co-occuring native species on an monthly basis (2) the nutrient (N and C) concentrations dropped in leaf litter inputs monthly (3) the amount of nutrients (N and P) resorbed between species before senescence (4) the decomposition rates between A. mearnsii and fynbos species in away and home environments to test the Home Field Advantage (HFA) hypothesis and, finally (5) the macroinvertebrate assemblages in different leaf bags in home and away environments to test macroinvertebrate litter affinity effects instream. The results in the study indicate that A. mearnsii had seven to times times higher leaf litterfall rates in the Wit and Du Toit‟s River compared to co-occuring native species in invaded and near pristine riparian zones. Acacia mearnsii had two peaks in litterfall, one at the end of the dry season in mid-autumn, and the other in mid-summer. A. mearnsii also kept a higher foliar N concentration than co-occuring native species, which gives the wattle species a competitive advantage. Native species exhibited low nitrogen concentrations which are reflected annually. In addition, the results indicated that co-occuring natives efficiently recycles nutrients before leaf abscission, for instance through high P resorption efficiencies. Acacia mearnsii was not as efficient in recycling nutrients, most notably N, but was more efficient in recycling P, suggesting it may require more P than can be readily supplied from the soil. The results indicate that the studied species had high resorption parameters (proficiency, A. mearnsii and efficiency in native species), which indicated a P limited landscape. This can be an important reason in the success of Acacia spp. in South African landscapes and particularly in riparian zones. The results also indicated that A. mearnsii and fynbos species differed locally at all sites in instream decomposition rates, with A. mearnsii decaying at a much faster rate. The difference in decay rates was attributed to differences in litter quality characteristics between native and invasive species (N concentration and C:N ratio). The faster decay rates in A. mearnsii due to leaf litter with high N and P can have a detrimental effect on in stream functionality therefore affect the species diversity of aquatic biota. The macroinvertebrate litter affinity effects were tested and showed no preference to home turf litter or introduced littertype regardless of the local environment at each invasion status. Functional feeding groups increased at both Wit River site, as macroinvertebrates were season-dependent on leaf litter and additionally resources A. mearnsii site may hold. Conversely, at the Du Toit‟s River low invertebrate diversity and abundances and was regulated by stream characteristics and site geomorphology at both reaches. Furthermore, seasonal hydrological regime could have accounted for macroinvertebrate species abundance and diversity at each river as there was a selective pressure on communities to utilize resources. The research contributes to a more comprehensive understanding of nutrient cycling, acquisition and conservation strategies of native compared to invasive species in the Fynbos biome in South Africa. Additionally it also gives insight into how invading species could potentially modify aquatic ecosystems and change macroinvertebrate communities in disturbed environments. Invaders can strongly affect multiple services in an ecosystem therefore it is imperative that these mulitiple roles should be asssed and managed as environmental change (i.e, drought) could cause a long lasting effect on ecosystems holistically (riparian areas, in stream biogeochemistry and aquatic assemblages).