1. Department of Animal and Plant Sciences, The University of Sheffield, Sheffield S10 2TN, UK,
2. Abisko Scientific Research Station, Royal Swedish Academy of Sciences, S‐98107, Abisko, Sweden,
3. Sheffield Centre for Arctic Ecology, The University of Sheffield, Sheffield S10 2TN, UK,
4. Institute of Terrestrial Ecology, Merlewood Research Station, Grange‐over‐Sands, Cumbria LA11 6JU, UK, and
5. Department of Plant Ecology, University of Copenhagen, Øster Farimagsgade 2 D, DK‐1353 Copenhagen K, Denmark