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Why Prune a Tree?

Why Prune a Tree?

A question I have been asked is “If trees don’t get pruned in the forest, then why do we do it in the city?”.  So why prune a tree?

That is a great question but it starts with an inaccurate premise. Trees in the forest do get pruned yet instead of a person doing the work, nature takes care of it.

In a forest, trees tend to grow more upwards than outwards. They pursue the direction in which they can receive the most light. If they grew outwards that would infringe upon the tree next to it but since trees generally maintain healthy social lives they prefer not to infringe on the adjacent tree. In addition, branches near the bottom will naturally shed themselves early because their light is minimal and they want to make space for new trees to grow underneath them. For more on how trees communicate see this Ted video http://www.openculture.com/2017/10/the-social-lives-of-trees.html

Tree Pruning

City trees

Trees in the city on the other hand have a far less interactive life. They grow and grow on all sides with few other trees telling them to slow down. The result of rapid growth are a number of issues that hinder the health of a tree; codominant stems, ingrown branches, crossing/rubbing branches, tight scaffold branch spacing, and poor air circulation that increases risk of diseases. Simply put, nature isn’t shedding branches the way they should and the tree needs to be thinned out.

Factors in Uncontrolled Growth

There are two other factors unique to the city that results in uncontrolled growth. One relates to the urban heat island effect. The warmer the area due to the presence of asphalt, concrete, lack of shade/greenery, and assuming there is an adequate source of water, the more it encourages growth. The other factor for accelerated growth is the additional presence of CO2. CO2 is the basic building block for photosynthesis to occur. The more CO2 the more photosynthesis can occur. The more photosynthesis that occurs, the more the tree grows. For more on the effects of tree growth in a city, check out the following article https://earther.com/urban-trees-grow-differently-than-rural-trees-1820421054

All that to say, city trees grow bigger and faster than their forested counterparts. This is not natural to a tree as trees historically are raised in a forested environment where their growth is better regulated. It is the job of the arborist to best simulate the pruning practices that naturally exist in a forest. Every cut is precise and no cut is without its purpose. The first and foremost purpose is the safety of persons and property. As much as we arborists love trees, we would never want to place persons and property at an imminent risk.  Safety is priority as to why prune a tree.  You may also be interested in why due diligence is key to insurance claims.  Secondly, we prune to extend the life of a tree for as long as possible. Thirdly, we greatly value the aesthetics of a tree and want to offer a service that pleases the eye.