Browsing by Author "Blanchard, Ryan"

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    Alien plant invasion on the Agulhas Plain : a detailed description of invasion patterns
    (2004) Blanchard, Ryan; Richardson, David Mark; Rouget, Mathieu
    Invasive alien species occur within several biodiverse regions of South Africa. It is not yet fully understood the extent to which invasive alien species affect natural vegetation. It is important to classify such species based on abundance and distribution in order to determine invasion patterns and set priorities for management within a region. Such a study was adapted for the Agulhas Plain of South Africa in the Cape Floristic Region. Eucalyptus lehmannii was recognised as the top invasive alien species, occupying both natural and transformed landscapes at high densities, >130% canopy cover. Acacia saligna and Acacia cyclops are the most widely distributed species, covering 41 % and 53% of the total area. Effectively determining invasive alien species richness required the use different variables to those used in this study. Invasive alien species invasion pattern was classified into two groups, namely coastal invasion and interior invasion. These characteristics differed with regards to vegetation types and species composition. Natural vegetation within the Mountain fynbos (100% invaded), Dune fynbos (91 % invaded) and Mountain top fynbos (99% invaded) vegetation types were largely threatened by invasive alien species. Vegetation types largely affected by transformation include Elim asteraceous fynbos (89% transformed) and Renoster fynbos. The invasion patterns described could be used in prioritisation of manageable land.
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    An investigation of riparian vegetation recovery following invasive alien tree clearing in the Western Cape
    (2008) Blanchard, Ryan; Holmes, P M; Richardson, D M
    Riparian zones are dynamic, as a result of varying levels of disturbance from natural flooding regimes, and this makes them particularly susceptible habitats to invasion by alien plants. In South Africa, particularly the Fynbos Biome, closed-stand invasions by alien Acacia and Eucalyptus species have been able to develop within riparian areas. Their impacts on water resources and biodiversity have been countered by manual clearing in order to protect the valuable ecosystem services provided by intact riparian zones, as well as the biodiversity of indigenous communities. The Working for Water programme is tasked with the important role of controlling invasive alien plants with an assumption that indigenous vegetation will recover naturally. Current management objectives are to reduce above ground biomass of invasive alien plants by labour intensive means, after which indigenous vegetation is usually left to recover without further intervention. However, it is unclear to what extent natural recovery can be achieved. The main aims of this study were to ascertain the nature of riparian vegetation recovery, as well as determine which clearing treatment was most successful in promoting recovery. This was achieved by focusing on: 1) the recovery of species composition and biodiversity, 2) recovery of vegetation structure (assumed to be a surrogate for ecosystem function) and 3) whether a particular clearing treatment best promoted indigenous riparian vegetation recovery. Reference sites (control), as determined by Prins et aI., (2004), were compared to alien impacted sites in order to analyse variation among vegetation variables. Three initial clearing treatments were identified, namely: Fell Only (trees are felled and slash left on site), Fell & Remove (slash is removed from the riparian zone) and Fell & Bum (the slash is left for six months to a year before it is burnt).