Some people find the bark of some trees to be very attractive and many species of trees are actually chosen in landscaping projects because of the tree's bark. Other kinds of bark serve a vast variety of roles in medicine, the culinary arts and the creation of many kinds of manufactured products.
Plants have tissue found on the outside of the plant that has random cells that can grow, expanding the size of the plant. Out of these random cells come phloem, which is where the nutrients are carried through the tree, and xylem, which is the wood of the tree. Overlaying this is what is called inner bark and outer bark. The inner bark has some live tissue mixed in it, while the outer bark has no live tissue.
To the plant, the bark provides a great deal of protection. Trees are usually large plants and have to reach a certain size before they are able to reproduce. In order to survive long enough to reach this size, the tree has to be protected from harmful external factors such as strong winds and animals that would like to consume it. The toughness of the bark deters some animals, though some animals can bore within the bark to consume the organic matter within.
Tree bark holds benefits to people. Some tree bark has culinary uses such as in herbs and spices. Some bark such as willow contains medicinal properties. Products like tannin, latex and resin are made out of tree bark. Other tree bark is used to make clothes, canoes and ropes. Some bark has an attractive appearance, causing landscapers to use those tree species for ornamental purposes. Tree bark is also used to make mulch, which helps other species of plant grow.
Trees have a vast array of different kinds of bark. Some bark has thorns that extend outward form the trunk of the tree. Some bark consists of cones that extend outwards. Some bark seems to peel off of the tree, as in some cases of birch. Some bark seems to be made of scaly plates. Bark commonly has grooves running in all directions. Some bark is very smooth with only occasional blotches on it. Some bark is loaded with holes, which are usually the result of animal behavior.
The symptoms of dangerous pests and diseases can be found in the bark of a tree. Some trees experience dieback, where parts of the tree bark seem discolored and parts of the bark even break off. Other bark might have actual pests crawling through holes in it. The outer bark might peel off, exposing the vulnerable inner bark. Bark can also develop cankers, which look like open sores in the tree.