Topographic controls on the invasion of Pteronia incana (Blue bush) onto hillslopes in Ngqushwa (formerly Peddie) district, Eastern Cape, South Africa

Kakembo, V; Rowntree, K; Palmer, A

Topographic controls on the invasion of Pteronia incana (Blue bush) onto hillslopes in Ngqushwa (formerly Peddie) district, Eastern Cape, South Africa

Kakembo, V Rowntree, K Palmer, A

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Publisher:: Elsevier
Publication Type:: Journal Article
Citation:: Catena, 2007, 70 (2), pp. 185 - 199
Issue Date:: 2007-01

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Field	Value	Language
dc.contributor.author	Kakembo, V	en_US
dc.contributor.author	Rowntree, K	en_US
dc.contributor.author	Palmer, A	en_US
dc.date.issued	2007-01	en_US
dc.identifier.citation	Catena, 2007, 70 (2), pp. 185 - 199	en_US
dc.identifier.issn	0341-8162	en_US
dc.identifier.uri	http://hdl.handle.net/10453/657
dc.description.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. The WI confirmed the bearing local topographic variations have on P. incana spatial distribution such that, P. incana was associated with the low WI values of convexities. The coupling between local topography and soil surface crusting underpins soil moisture variability. This in turn determines the competition between the patchy P. incana and grass species and the eventual replacement of the latter by the former. Restoration efforts of the invaded lands should focus on trapping of sediment and litter, and moisture retention on the inter-patch bare areas.	en_US
dc.publisher	Elsevier	en_US
dc.relation.ispartof	Catena	en_US
dc.relation.isbasedon	10.1016/j.catena.2006.08.005	en_US
dc.subject.classification	Geochemistry & Geophysics	en_US
dc.title	Topographic controls on the invasion of Pteronia incana (Blue bush) onto hillslopes in Ngqushwa (formerly Peddie) district, Eastern Cape, South Africa	en_US
dc.type	Journal Article
utslib.citation.volume	2	en_US
utslib.citation.volume	70	en_US
utslib.for	0406 Physical Geography and Environmental Geoscience	en_US
utslib.for	0403 Geology	en_US
utslib.for	0503 Soil Sciences	en_US
pubs.embargo.period	Not known	en_US
pubs.organisational-group	/University of Technology Sydney
pubs.organisational-group	/University of Technology Sydney/Faculty of Science
utslib.copyright.status	closed_access
pubs.consider-herdc	true	en_US
pubs.issue	2	en_US
pubs.volume	70	en_US

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. The WI confirmed the bearing local topographic variations have on P. incana spatial distribution such that, P. incana was associated with the low WI values of convexities. The coupling between local topography and soil surface crusting underpins soil moisture variability. This in turn determines the competition between the patchy P. incana and grass species and the eventual replacement of the latter by the former. Restoration efforts of the invaded lands should focus on trapping of sediment and litter, and moisture retention on the inter-patch bare areas.

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http://hdl.handle.net/10453/657