1. Department of Forest Sciences, Viikki Tropical Resources Institute, University of Helsinki, Helsinki, Finland
2. Faculty of Forestry, University of Khartoum, Khartoum, Sudan
3. Department of Forest Sciences, University of Helsinki, Helsinki, Finland
4. Department of Environmental Chemistry/Faculty of Sciences, Universidad Católica de la Santísima Concepción, Concepción, Chile
5. Department of Life Sciences, Imperial College London, Ascot, UK
6. Department of Environmental and Biological Sciences, University of Eastern Finland, Kuopio, Finland