A few branches stripped of bark do not usually harm a tree. Bark on the tree's trunk is much more important to the tree's survival than the bark on the branches, though an affected branch may die and drop. When large numbers of branches are stripped and die, however, it thins and alters the tree canopy; too thin a canopy sometimes hinders the tree's ability to make enough food to support itself.
The Purpose of Bark
Bark is sometimes referred to as the tree's "armor," protecting the living inner wood from the elements of weather and disease. The outermost layer of bark is dead, and as the tree grows outward, this outer layer cracks and sheds and makes way for the bark underneath. The inner living layers of bark are the highway through which nutrients are carried, and are called the phloem. It is when the phloem is damaged, or the highway is cut off, that the tree suffers. Such damage is called “girdling.” A girdled tree has lost a continuous ring of bark around its entire circumference and everything above the girdle dies.
Tree squirrels like the gray squirrel and fox squirrel strip the bark from the trunk and branches of trees. The greatest damage typically occurs in the spring and fall. The theories behind the squirrel's behavior range from squirrels being driven by hunger or thirst to pregnant females using gnawing as a method of pain management, according to the Internet Center for Wildlife Damage Management -- a project of the University of Nebraska, and Clemson, Cornell and Utah State universities. Whatever the reason, squirrels cause a great deal of tree damage through bark stripping.
Bears cause extensive damage to trees through stripping the trunks and girdling trees. When they come out of hibernation in the spring in search of food, the sapwood of trees is often the most ready source. Bears strip the bark and eat the sapwood, often killing the tree, and are so ravenous that they can easily damage up to 70 trees per day, according to the U.S. Forest Service.
Other animals that strip bark from trunks and branches and damage trees are deer, porcupines, rabbits, mice and beavers. Deer and porcupines focus on the branches, and if enough bark is stripped from enough branches, the tree's growth is significantly slowed. Tree growth is also thwarted when these animal consume new twigs. Rabbits, mice and beavers are only able to strip a tree as far as they can reach from the ground, and do the most damage by girdling trees.
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