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University of Namibia (2008)

The distribution, abundance and reproductive status of the invasive alien plant, Datura Innoxia Mill., in the city of Windhoek, Namibia

Katjirua Joyce

Titre : The distribution, abundance and reproductive status of the invasive alien plant, Datura Innoxia Mill., in the city of Windhoek, Namibia

Auteur : Katjirua Joyce

Université de soutenance : University of Namibia

Grade : Master of Science in Biodiversity Management and Research 2008

Résumé
Invasive alien species (IAS) are non-native species that cause, or have the potential to cause, harm to the environment, economies, or human health. The threat to biodiversity due to invasive alien species is considered second to that of habitat loss. The focus of the study was on one of the invasive alien plant Datura innoxia. The study was conducted in the City of Windhoek, the capital of Namibia, situated at 22.56°S, 17.09°E The aim of the research project was to study the distribution, abundance and reproductive status of the invasive alien D. innoxia in the City of Windhoek. The information gathered will contribute to the knowledge and understanding of weedy invasive aliens in the City Data was collected 121,25 0000 m2 grids that were randomly sampled in the City. The City of Windhoek grided map was used to locate the specific grids. The grids were sub-divided into sixteen 15625 m2 plots to ease observations. In each plot, all D. innoxia were recorded including their height, crown width, number of capsules and number of flowers. Within a radius of one-meter, other organisms and plants associated with D. innoxia were also recorded. The presence and absence of other plant species found in the plots were recorded. ArcView 3.2 was used to develop the distribution map and SPSS 15 was used to analyze the data The study revealed that D. innoxia is widely distributed along riverbanks, disturbed areas and around human settlement. A high infestation of D. innoxia was observed in the drainage lines and within the built-up areas. The occurrence of D. innoxia is influenced by the different types of activities and is associated with disturbances. The study also showed that D. innoxia is a perennial trailing or bushy herb plant with a continuous floral development with no significant difference (?2F (3) = 7, p0.05) in the number of D. innoxia in the different reproductive status within the geo-morphological landforms. However, there was a significant difference (?2F (2) = 5, p0.05) in the number of D. innoxia with the construction and no construction area and within the open spaces and built-up areas. Therefore, D. innoxia is a cosmopolitan opportunistic weed that is abundant in construction areas, drainage lines and around human settlements The Hierarchical Cluster Analysis revealed that Acacia mellifera, Dichrostachys cinerea, Boscia albitrunca and Senecio windhoekensis were the dominant woody and herbaceous vegetation in all the clusters. The Cityof Windhoek is situated in the highland savanna vegetation, all the dominant species characterizing the highland savanna were present. Variation within the vegetation composition was attributed to the different land uses within the City of Windhoek and not to the presence of D. innoxia.

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