1. Dept of Geosciences and Geography; Univ. of Helsinki; PO Box 64, FI-00014 Univ. of Helsinki Finland
2. Dept of Plant Science; Univ. of Pretoria; Private Bag X20, Pretoria 0002 South Africa
3. Dept of Ecology and Evolution; Univ. of Lausanne; Biophore CH-1015 Lausanne Switzerland
4. Inst. of Earth Sciences, Univ. of Lausanne; Géopolis CH-1015 Lausanne Switzerland