Why do trees need pruning?
Most pruning is carried out to meet human needs, rather than to help the tree. Trees in an urban environment have to co-exist with people and buildings. Much pruning is carried out in order to allow this co-existance. Reasons for pruning can include:
Although most trees are very strong, well designed structures, sometimes they develop defects that can cause parts of them to fail. In the middle of a forest with no one around this isn't a problem, but by the side of a busy road it is obviously important to remove branches with problems in a controlled way. Pruning is often carried out to minimise the risk of parts of a tree falling and causing injury or damage.
One of the most common form of safety pruning is the removal of dead branches. Another important type of safety pruning is removing low branches over highways, which might otherwise hit high sided vehicles.
Trees cast shade. Sometimes this is valued, and in hotter climates trees are often planted specifically for this reason. But sometimes people feel that trees are casting too much shade and trees are pruned to allow more light to reach a window or garden.
Sometimes a tree grows to be bigger than the space which it occupies, or to be an overbearing presence. One solution might be to remove the tree and plant another of a smaller species, but this can be seen as a drastic solution. Often regular pruning to contain the size of the tree is carried out.
Pruning may be carried out on purely aesthetic grounds, to make a tree more pleasing to the owners eye.
Occassionally pruning is carried out to benefit the health of the tree. This usually involves the removal of diseased branches to prevent the spread of the disease.