1. Department
of Ecology and Environmental Science, Umeå University, 901 87 Umeå, Sweden
2. Department
of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences,
Box 7050, 750 07 Uppsala, Sweden
3. Department
of Geological Sciences, Stockholm University, 106 91 Stockholm, Sweden
4. Department
of Forest Ecology and Management, Swedish University of Agricultural Sciences, 901 83 Umeå, Sweden