1. School of GeoSciences University of Edinburgh Edinburgh EH9 3FF UK
2. ICREA at CREAF Cerdanyola del Vallès Barcelona 08193 Spain
3. Department of Forest Science University of Helsinki PO Box 27 Helsinki FI‐00014 Finland
4. CREAF Cerdanyola del Vallès Barcelona 08193 Spain
5. University of Autònoma Barcelona Cerdanyola del Vallès Barcelona 08193 Spain