1. Department of Forest Sciences; University of Helsinki; P.O. Box 27 00014 Helsinki Finland
2. Department of Environmental Science; University of Eastern Finland; P.O. Box 1627 70211 Kuopio Finland
3. Faculty of Biological and Environmental Sciences; Ecosystems and Environment Research Programme; University of Helsinki; Niemenkatu 73 15140 Lahti Finland, and
4. Institute for Atmospheric and Earth System Research; Forest Sciences; Helsinki Institute of Sustainability Science; University of Helsinki; Helsinki Finland