1. Organismal and Evolutionary Biology (OEB), Viikki Plant Science Centre (ViPS), Faculty of Biological and Environmental Sciences University of Helsinki 00014 Helsinki Finland
2. Department of Forest Ecology and Management Swedish University of Agricultural Sciences 901 83 Umeå Sweden
3. Faculty of Science, Institute for Atmospheric and Earth System Research/Physics University of Helsinki PO Box 68, Gustaf Hällströminkatu 2b Helsinki 00014 Finland
4. Faculty of Agriculture and Forestry, Institute for Atmospheric and Earth System Research/Forest Sciences University of Helsinki PO Box 27 Helsinki 00014 Finland
5. School of Biosciences University of Nottingham Sutton Bonington Campus Sutton Bonington LE12 5RD UK