On the Pruning of Trees

by Thomas Wolanski

Thomas Wolanski tells us why it is necessary to prune in order to achieve health.

The process of pruning a tree involves the targeted removal of non-productive and sometimes diseased limbs from the trunk. While it is easier and requires less effort to allow the tree to grow naturally in all directions, the elimination of certain branches is necessary for the long-term health of the tree and allows it to grow unhindered by the detriments associated with diseased or dead branches.

Trees are faced with a wide array of potential issues caused by bacteria, fungi, and viruses. Much like the human skin, tree bark functions as a protective outer layer to fend off the majority of these threats. This will not always be successful, however, and disease can creep into a branch and begin growing unnoticed. Once inside, the disease can spread further and further as time passes and its advance remains unchecked. Thus, what began as a single diseased branch will prove a detriment to the rest of the tree, a weakening factor in the tree’s struggle for life. In the long term, epidemic disease can even kill the tree, a result of its having been left to run rampant for too long. In cases such as these, the healthy parts of the tree (particularly those that contribute to its constitution through nutrient gathering and processing) are progressively overwhelmed by the afflicted portions. The process is gradual, with the sickness sometimes spreading so slowly as to be unnoticeable in its effects in the short term.

When and where to prune is not always a simple decision to make. The tree’s branches contain leaves, which supply the rest of the tree with “food” via their use of sunlight. Each individual branch thus provides benefit for the rest of the tree as a whole through its myriad leaves. In the event of the loss of these leaves or their inability to function (through disease, for example), the branch can no longer produce benefit for the tree and now consumes rather than produces energy. A branch in this state acts against the health and hale of the tree as a whole, leeching life from the tree without offering benefit for its continued existence.

Of further consideration is the need for general pruning in order to stabilize a tree. Certain varieties of tree are prone to growing quite extensive and heavy branches at more or less horizontal angles to the ground. The weight of these branches is obviously being continually added to as it grows, creating a situation in which a very large and unsupported branch might break off from the truck under the strain of its own weight, leaving a wound. External environmental factors, such as wind and snow, can also play a part in raising the likelihood of such an event. Arborists must keep a watchful eye out for branches that appear to be growing this way, and trim them when needed. It is far preferable to intentionally trim a small branch earlier on than it is for the tree to suffer a gaping wound from the loss of a massive branch later on.

After a limb is cut off, the tree immediately sets itself to dealing with the open wound. Callus tissue begins to grow over the damaged area in order to seal it off and heal it. Thus the damaged area is spared further harm. Given enough time and a successful healing process, the tree will completely recover from the short-term injury caused by the loss of the pruned branch and be spared further harm from the once-dangerous infection.

Is humanity very different from a tree?