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Universität zu Köln (2002)

Vegetationsökologie und Vegetationsdynamik im Richtersveld (Republik Südafrika)

Gotzmann, Inge Hildegard

Titre : Vegetationsökologie und Vegetationsdynamik im Richtersveld (Republik Südafrika)

Auteur : Gotzmann, Inge Hildegard

Université de soutenance : Universität zu Köln

Grade : Doktorgrade 2002

Résumé
The Richtersveld forms part of the southern Namib desert. Vegetation ecology and dynamics of this region have been analysed on 46 permanent plots. The vegetation has been documented using a very detailed method based on individual plants. The regeneration potential of the vegetation was analysed using grazing exclosure experiments and manipulation experiments. In interviews, herders were asked about their indigenous knowledge concerning grazing value of the plants and about their views concerning grazing impact. The results show a coastal-inland gradient of the vegetation and environmental factors. Four different units were characterised by vegetation, topographic, climatic and edaphic conditions. A total of 227 plant species were found on the plots, most of them chamaephytes and annual plants. About 50 % of the species were succulent, most of them being leaf succulent. Dynamics were remarkably high for desert plant communities. They were explained by the relatively reliable winter-rainfalls. The observed vegetation dynamics were mainly driven by rainfall. Establishment, growth, and reproduction were obviously correlated with rainfall pattern. Apart from annual fluctuations, extreme disturbances such as droughts may have a long-term impact of about two decades on vegetation dynamics. The turnover of the vegetation was very high. Establishment of plants took place approximately yearly. Leaf succulent chamaephytes showed relatively short life spans of less than 20 years. Different strategy types could be detected on the basis of the observed dynamics and can be described by life form and morphological features. Regarding species and individuals, the occupation of niches was understood to be structural and temporal. Competition seems to play a minor role in the observed vegetation types. The grazing factor showed little influence on the vegetation dynamics. This can be interpreted as a result of moderate grazing intensity. Additionally, we assume long-term processes concerning grazing impact. Signs of degradation of soil and vegetation have been detected locally. Regeneration seems to be at least partly possible. The drought years 1998 and 1999 slowed down the regeneration processes.

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