1. School of Forestry and Environmental Studies, Yale University, 360 Prospect Street, New Haven, CT 06511-2104, USA.
2. Department of Forest Resource Management and Geomatics, Swedish University of Agricultural Sciences, 90183 Umeå, Sweden.
3. Department of Ecology and Natural Resource Management, Norwegian University of Life Sciences, P.O. Box 5003, NO-1432, Ås, Norway.
4. 614.4/Biosperic Science Branch, NASA-Goddard Space Flight Center, Greenbelt, MD 20771, USA.