1. Institute of Meteorology and Climate Research - Atmospheric Environmental Research (IMK-IFU), Karlsruhe Institute of Technology (KIT); Garmisch-Partenkirchen 82467 Germany
2. College of Natural Resources, University of Idaho; Moscow ID 83844-1133 USA
3. Natural Resources Canada, Canadian Forest Service, Northern Forestry Centre; Edmonton AB T6H 3S5 Canada