Bark consumption by small rodents in the northern and southern hemispheres

The distribution and environmental conditions of bark consumption by small rodents were compiled for the northern and southern hemispheres. Main bark consumption occurred under snow at peak cyclic density and in the dry season of annually fluctuating rodent populations, respectively. The species responsible appeared more folivorous in the north. Among woody species that are damaged, a large number were in both cases exotics. Various defences against bark consumption have evolved. including secondary compounds. However, this defence appears inadequate when indigenous trees are grown under new environmental conditions. It is pointed out that the stem and bark are very sensitive components of perennial trees and bushes and that this potential but usually well protected resource will only be used in crucial situations by various mammals. In view of the many unsuccessful attempts to prevent small rodent damage by bark consumption, costs for rodent damage should be included in any cost-benefit analyses for plantations of exotic species or indigenous species under new conditions. Screening and even selection for resistant varieties may be needed at large scale plantations.