1. European Commission, Research Directorate General, B-1049 Brussels, Belgium,
2. ALTERRA, Wageningen University and Research Center, NL-6700 AA Wageningen, The Netherlands,
3. Unit of Physics, Faculté Universitaire des Sciences Agronomiques, B-5030 Gembloux, Belgium,
4. European Forest Institute, Joensuu, Finland,
5. Energy Analysis Department, Environmental Energy Technologies Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720,