1. Bjerknes Centre for Climate Research, Allégaten 55, N-5007 Bergen, Norway;
2. Bjerknes Centre for Climate Research, Allégaten 55, N-5007 Bergen, Norway; Botanical Institute, University of Bergen, Allégaten 41, N-5007 Bergen, Norway
3. Bjerknes Centre for Climate Research, Allégaten 55, N-5007 Bergen, Norway; Botanical Institute, University of Bergen, Allégaten 41, N-5007 Bergen, Norway; Environmental Change Research Centre, University College London, 26 Bedford Way, London WC1H 0AP, UK