1. Terrestrial Ecology Section, Department of Biology, University of Copenhagen, DK-2100 Copenhagen Ø, Denmark
2. Center for Permafrost (CENPERM), University of Copenhagen, DK-1350 Copenhagen K, Denmark
3. Institute of Environmental Assessment and Water Research (IDAEA), CSIC, ES-08034 Barcelona, Catalonia, Spain
4. Department of Physical Geography and Ecosystem Science, Lund University, SE-22362 Lund, Sweden
5. Department of Earth System Science, University of California, Irvine, CA 92697
6. Department of Geosciences, University of Oslo, 0316 Oslo, Norway