A REVIEW OF DAMAGE BY MAMMALS IN NORTH TEMPERATE FORESTS .3. IMPACT ON TREES AND FORESTS

The impact of mammals on trees and forest crops is examined by reviewing the scientific literature. The degree of growth loss, stem deformation and the likelihood of death from browsing all increase with the severity of damage. The effect of the damage depends very much on the tree species, age and season. Many studies reveal that some compensatory growth occurs after browsing, but there is a serious lack of long-term data and more work that links the incidence of damage to ultimate yield loss is required. Browsing can also make trees more or less palatable and this could have a marked effect on the likelihood of recovery, but this subject requires further research for trees growing in British conditions. Bark stripping results in timber staining and decay but does not appear to cause serious growth loss. The amount of stem decay usually increases with wound size and tree vigour but a considerable amount of residual variation remains to be explained. The success of natural regeneration depends on both herbivore and seedling density. Changes in tree species composition reflect the palatability of seedlings as well as their ability to recover. Browsing by deer usually causes a decrease in shrub and herbaceous plant biomass in the ground vegetation and an increase in grasses, ferns and mosses,