Resource information
Wild herbivorous mammals may damage treeline vegetation an cause soil erosion at a local scale. In many high
mountain areas of Europe and North America, large numbers of red deer have become a threat to the maintenance
of high-elevation forests and attempts to restore the climatic treeline. In northern Fennoscandia, overgrazing by
reindeer in combination with mass outbreaks of the autumnal moth are influencing treeline dynamics. Moose are
also increasingly involved damaging treeline forest. In the Alps, the re-introduction of ibex is causing local damage
to subalpine forests and tree establishment above the forest limit as well as aggravating soil erosion. High-elevation
forests and treeline in Europe are susceptible to the deleterious impact of wild ungulate populations because of
former extensive pastoral use. Rodents may damage tree seedlings and saplings by girdling, root cutting, bark
stripping and burrowing. Hares damage young trees by gnawing. Large numbers of small rodents may occasionally
impede tree regeneration by depleting the seed sources. Rodents do not contribute to forest expansion beyond the
current treeline. Among birds, nutcrackers are highly effective in influencing tree distribution patterns and treeline
dynamics. Without the nutcracker caching of stone pine seeds any upward advance of the trees in response to
climatic warming would be impossible. Some bird species such as black grouse, willow grouse and ptarmigan can
impair tree growth by feeding on buds, catkins and fresh terminal shoots.
