Topographic controls on the invasion of Pteronia incana (Blue bush) onto hillslopes in Ngqushwa (formerly Peddie) district,Eastern Cape,South Africa |
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| Authors: | V Kakembo K Rowntree AR Palmer |
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| Institution: | 1. Department of Geosciences, Nelson Mandela Metropolitan University, Port Elizabeth, South Africa;2. Catchment Research Group, Rhodes University, Grahamstown, South Africa;3. ARC-Range and Forage Institute, PO Box 101 Grahamstown, South Africa |
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| Abstract: | The role of topographic factors in the invasion of hillslopes by Pteronia incana, an unpalatable shrub, was investigated. The study combined field observations with image analysis based on high-resolution infrared imagery. A Digital Elevation Model (DEM) of 20 m spatial resolution was used to derive terrain parameters. The Topographic Wetness Index (WI), a component of the TOPMODEL, was derived from the DEM and its relationship with the spatial distribution of P. incana was explored. The absence/presence of P. incana was noted to be strongly influenced by slope angle and aspect. The probability for P. incana occurrence increased with slope steepness and southerly slope orientation. Abandoned and grazing lands were identified as the main invasion hotspots on hillslopes. The combined influence of slope gradient and aspect, and land use was noted to have promoted the invasion. This is borne out by the concentration of the invasion on abandoned steep slopes with a southerly orientation. |
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| Keywords: | Vegetation invasion Land abandonment Slope Aspect Wetness index |
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