Assessment of vegetation diversity, structure, cover and the influence of fire along the rainfall gradient in the Kalahari, east of Namibia using long-term data.
Shidolo, Emma Laili Kaunapawa
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Change in climatic condition has a considerable potential to cause change in vegetation structure and functioning of ecosystems. Savanna ecosystems in southern Africa are threatened by reduced rainfalls and wet seasons, coupled with frequent and extended periods of drought. The Kalahari landscape has been described as vulnerable to global climate change. Widespread remobilisation of dune fields are predicted over the next 50 to 80 years. However, there is a lack of long-term research done using empirical data to understand the dynamics of vegetation under this circumstances over a longer period of time. Therefore, the objective of this study is to assess if there was change in species diversity, richness, cover and structure of vegetation over the years within four selected permanent observatory sites located along the Kalahari basin. This is as well to determine the influence of fire and rainfall regime on vegetation. Vegetation patterns of woody plant and grasses was assessed on four permanently established observatory site along the north south rainfall gradient, east of Namibia. A total of 368 plots found in typical Kalahari sandy soil were sampled using a Braun blanquet method between 2001 and 2016, each plot was 1000 m2. The changes in woody and grass cover was assessed using 95th percentile trend-lines and driving factors were determined by ordinations using the Non-metric multidimensional Scaling. The one-way ANOVA revealed a significant changes in the decreasing Shannon-Wiener diversity index and species richness along the study area and within specific sample sites over the years. These changes were corresponding to the decreasing rainfall patterns recorded. Furthermore, there was a strong shifting movement observed in the arid vegetation distribution which was advancing further up the north-eastern region, despite it being recognised as an open woodland savanna area due to high rainfall. The shrub vegetation for both broad-leafed and fine-leafed was increasing over the years through the study area, which caused a decrease in grass cover due to high shrub-grass competition for resources. Reduced cover could make the unconsolidated Kalahari top soil highly vulnerable to soil erosion by either wind or water. Consequently, this could trigger remobilization of dune and altering of the landscape. Even though long-term monitoring of vegetation in Namibia is a fairly recent concept, the results of this research advocates the importance of such studies as ways of providing us with information for conservation and planning purposes in response to threats caused by climate change.
- Masters Theses