Browsing by Author "Ruwanza, S."

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    Effects of Lantana camara invasion on vegetation diversity and composition in the Vhembe Biosphere Reserve, Limpopo Province of South Africa
    (2020) Ruwanza, S.
    Although the effects of invasive alien plants on natural ecosystems are widely acknowledged, the effects of specific plant species can be context dependent. The study examined changes in native vegetation diversity and composition following Lantana camara invasion at different cover conditions in the Vhembe Biosphere Reserve, Limpopo Province of South Africa. Using a comparative approach, native vegetation diversity, cover, and composition were compared in L. camara high and low cover and uninvaded conditions, on three replicated sites, each with five 10 × 10 m plots. Results show that vegetation diversity (species richness, Shannon-Wiener, and evenness index) were significantly higher in the uninvaded condition than in the L. camara high and low invasion conditions. Species relative cover was significantly higher in uninvaded condition than in L. camara high and low invasion conditions, though it decreased gradually along the invasion cover gradient for trees and shrubs as well as forbs. Analysis of similarities showed significant separations in vegetation composition among the three invasion conditions for all the growth forms, with most woody alien plants, e.g. Acacia mearnsii, Rubus rigidus, and Caesalpinia decapetala being associated with L. camara high and low invasion conditions. The study concludes that invasion by L. camara was associated with changes in native vegetation diversity, cover, and composition, with observed changes being more visible under L. camara high as compared to low invasion condition. The presence of L. camara at high cover condition significantly decreased native species diversity and composition, an indication that impacts of L. camara invasion are cover dependent. From a management standpoint, the study suggests the removal of L. camara, however such removal should consider protecting the co-occurring native species. This study offers a baseline for further research to determine mechanisms responsible for native vegetation change associated with L. camara invasion.
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    Medium-term vegetation recovery after removal of invasive Eucalyptus camaldulensis stands along a South African river
    (Elsevier, 2018) Ruwanza, S.; Gaertner, M.; Esler, K. J.; Richardson, D. M.
    Effective ecological restoration requires detailed monitoring to determine the success achieved through different interventions in achieving objectives. In 2017, we resurveyed riparian sites along the Berg River in the Western Cape, South Africa, that have been cleared of invasive stands of Eucalyptus camaldulensis in 2010 using two clearing methods (fell-and-stackburn and fell-and-remove) and two restoration approaches: passive (where vegetation was allowed to recover without intervention) and active (assisted recovery). A significant increase in vegetation cover (P b .001) and diversity (P b .05) of native riparian species was recorded in passive restoration plots, but an increase in the cover of woody invasive alien plants was also observed. Only four of the nine native species that were planted to fast-track restoration were still present in the active restoration plots, but the abundance of these native species was significantly (P b .001) lower in 2017 than in 2011. We conclude that native vegetation recovery following E.camaldulensis removal seven years ago is following a positive recovery trajectory in both passive and active restoration sites, as shown by the increased occurrence of native trees and shrubs, e.g. Maytenus oleoides, Melianthus major and Searsia angustifolia which were not present before clearing. However, the reinvasion of cleared sites by woody invasive alien plants has the potential to slow down and potentially halt the recovery process. Further management interventions, e.g. removal of reinvading woody invasive alien plants, are required, emphasizing the sustained engagement to ensure restoration in these ecosystems.