1. School of Geography, Archaeology and Environmental Studies, University of the Witwatersrand, Johannesburg, South Africa
2. Department of Geography, University of the Free State, South Africa, South Africa
3. School of Animal, Plant and Environmental Sciences, University of the Witwatersrand, Johannesburg, South Africa
4. Centre for Invasion Biology, School of Animal, Plant and Environmental Sciences, University of Witwatersrand, Johannesburg, South Africa
5. Agricultural Research Council-Institute for Soil, Climate and Water (ARC-ISCW), Geo-Information Science Division, Pretoria, South Africa