Browsing by Author "Withers, Melanie Jane"
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- ItemA river health assessment of selected Southwestern Cape rivers : riparian vegetation index (RVI) application, evaluation and alternatives(Stellenbosch : Stellenbosch University, 2003-12) Withers, Melanie Jane; Boucher, C.; Esler, Karen J.; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.ENGLISH ABSTRACT: This study focuses on riparian vegetation condition at sites along three nvers within the southwestern Cape, South Africa namely the Lourens, Hout Bay and Palmiet Rivers. The Riparian Vegetation Index (RVI) is used as a tool to assess riparian vegetation condition. Data from this study will be used in State of Rivers reporting for the River Health Programme in South Africa. This study highlights sites of high conservation status with regards to vegetation condition and indicates sites of concern due to poor vegetation condition. Deviations from expected vegetation condition scores at certain sites along the rivers have highlighted certain flaws in the RVI method. Further, the repeatability and validity of the RVI method is tested. The method is tested for variability and validity across disturbance gradients at sites along the Eerste River. Results indicate that the RVI method produces repeatable results. The sub-index, Recruitment of Indigenous Riparian Species (RIRS), is the most variable in terms of assessor scores, while Structural Intactness (SI) is the most reproducible sub-index. This has important implications for the future development of the method, which should place more emphasis on reproducible sub-indices within the final RVI formula and should standardise those sub-indices that are highly variable. Statistical analysis indicates that the method does not reflect the perceived biological status of the vegetation. This may be due to the specified sampling duration, which should be increased in order to reflect more meaningful results. Criticisms of and difficulties with the RVI method as well as suggestions to improve the method are dealt with and an alternative method to the Riparian Vegetation Index is explored. The Floristic Quality Assessment (FQA) method, used to determine vegetation integrity in Illinois USA, is adapted to assess riparian vegetation condition at sites along the Lourens, Hout Bay and Palmiet Rivers. Coefficients of conservatism, determined for the flora observed in the assessment, attempt to categorise species according to their response to levels of habitat degradation. These values are incorporated into the Floristic Quality Index (FQI) formula, which yields the final floristic quality assessment results. Correlation analyses indicate that RVI and FQA results are strongly correlated although the RVI at this stage best represents the perceived biological status of vegetation at sites. The FQA method, or a statistically modified alternative, may be a suitable and more objective alternative to the RVI method.