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Why do trees have bark?

The outer layers of trees and woody shrubs are known as bark. Bark has a number of functions in protecting the tree: it gives added rigidity to the structure, insulates the delicate inner layers and helps to shield them from damage by insects and diseases. It also stops water evaporating:  without it the cycle of water rising through the trunk and sugars passing down would not occur.

 Bark needs to be able to allow the tree trunk to expand as it grows year by year and some trees, such as silver birch, as well as some pines and stringy bark eucalyptus shed bits of their bark continually so that this can happen.

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