1. Department of Zoology; Stockholm University; SE-10691; Stockholm; Sweden
2. Norwegian Institute for Nature Research; N-7845; Trondheim; Norway
3. Department of Arctic and Marine Biology; University of Tromsø; N-9037; Tromsø; Norway
4. Metsähallitus-Finnish Park and Forest Service; FI-99801; Ivalo; Finland
5. Vantaa Research Centre; Finnish Forest Research Institute; Vantaa; Finland