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Bark is
sensitive and can be susceptible to both "sunburn" and "frostbite". If a tree that has grown for many years in deep shade is
suddenly exposed to hot sun (when all the trees around it are cut down, for example), the bark may become red and flake off,
injuring the tree. In northern regions, a frost too late in the spring or too early in the fall can kill new bark tissue, as well as leaves and
new branches.
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Why is there such variation in the
color and texture of bark? Certain characteristics have obvious advantages in certain habitats. The thick, rough bark of pine trees
withstands fire far better than the bark of oak trees, and therefore more pines survive the frequent fires in temperate coniferous forests. In
other cases, the advantage of one type of bark over another is less well understood. Smooth bark might take less energy to produce, or
it might help to discourage the growth of moss and lichen. Rough bark might be more effective in keeping wood-boring insects out. No
one knows quite why the types of bark have evolved the way they have. One possibility is that the appearance of bark is not adaptive,
and while all trees must have bark of one form or another, its exact color and texture are not particularly important.
Left: The bark on a Ponderosa pine trunk. Photo by Maya Walters.
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