1. Luleå University of Technology, Forskargatan 1, SE-93187 Skellefteå, Sweden, Biosystems Department, Risø National Laboratory for Sustainable Energy, Technical University of Denmark, Frederiksborgvej 399, DK-4000 Roskilde, Denmark, and Forest & Landscape Denmark, Faculty of Life Sciences, University of Copenhagen, Rolighedsvej 23, DK-1985 Frederiksberg C, Denmark