1. a Department of Soil Science , Stellenbosch University , Private Bag X1, Matieland , 7602 , South Africa
2. b South African National Biodiversity Institute , Private Bag X7, Claremont , 7735 , South Africa
3. c Centre for African Ecology , School of A.P.E.S., University of the Witwatersrand , Johannesburg, Private Bag X03, PO Wits , 2050 , South Africa
4. d Terrestrial Ecology Research Unit, Departments of Botany & Zoology , University of Port Elizabeth , Port Elizabeth , 6031 , South Africa