Bark consumption by voles in relation to geographical origin of tree species

Abstract

Voles have caused more damage by bark consumption to Picea abies and Pinus contorta seedlings from southern than those from northern origins when planted in northern Scandinavia. In field and laboratory experiments, indigenous Scandinavian tree species from different origins and of various phenological stages were tested for susceptability to vole attacks. Seedlings from northern sites and late phenological stages were most severely attacked by both bank voles Clethrionomys glareolus and field voles Microtus agrestis, while a few aspen clones differed independently of origin. Bark consumption by the two vole species was strongly and negatively related to the concentration of crude fibre in the examined twigs. Bank voles also reacted positively to the content of nitrogen‐free extracts. Differences in preferences for seedlings from different geographical regions appear to result from differences in the bark at the end of growth and in the frost‐hardening process in autumn. Plants transferred northwards probably will not harden in a climatically appropriate way, will contain low concentration of fibre in winter, and will be a preferred food for voles.