Why do we prune trees?
Trees are pruned in the urban landscape for a number of different reasons. Typically an arborist is called when there is a perceived problem with a tree. It might be a health issue, a pest problem or maybe the tree is starting to out grow its space. A certified arborist can identify the problem and recommend a solution. Basic tree maintenance would include the removal of deadwood, this improves the aesthetic appearance of the tree and reduces a potential for pathogens. Pruning a tree for branch structure is by far the most important part of the pruning process. The tree is pruned to select strong limbs that will make up the framework of the mature tree. Conflicting branches are removed. Co-dominant leaders are subordinated to promote a strong leader. Proactive training to young trees will ensure a strong healthy tree and will save you money in the long run.
These same basic practices apply when pruning mature trees, but the difference is that a mature tree has a set structure. It is very difficult to change the structure of a mature tree. So what this means is the pruning practice would be based on the management of the set structure. In some cases a large limb may need to be removed, but this should be avoided if possible. Removing large limbs on a mature tree can lead to decay problems. During the pruning process a certified arborist can identify structural defects, weak unions, cracks or storm damage. In some cases reducing the width or end weight to reduce risk of failure. The majority of the work should be done in the tips of the crown. A very common pruning practice is over-thinning of the interior of the tree. This will actually weaken the tree and may lead to branch failure. This is called lions tailing.
Restoration to trees that have been heavily damaged by storms or mutilated by poor pruning practices can be cleaned up and retrained to improve their strength, health and appearance. In most cases it will take a number of pruning cycles to restore the tree, but the tree will most likely never return to its original state.
There are other practical reasons for pruning trees such a clearance for a building, roadway or light standard. There are Calgary city bylaws section 68( 6) stating trees can't overhang a laneway or obstruct a public sidewalk.
Now that we have covered the basics when it comes to tree management practices. Lets discuss advanced Arboriculture and how it can be applied to your garden.