Why We Prune Trees
Trees are living organisms that require proper care in order to grow and thrive, especially in a city environment. Improper care can shorten trees' lives, and can even eventually pose hazards to the community. Proper pruning helps contribute to the ongoing good health of Claremont's community forest.
The International Society of Arboriculture (ISA) is a highly respected organization of professionals dedicated to, and trained in, quality tree care. The City of Claremont follows ISA guidelines in all avenues of tree planting and care, especially pruning. The City's Community Services Department maintains a highly trained Forestry Maintenance Crew. Claremont uses an ISA Certified Arborist, and contracted crews are required to have at least one certified supervisor overseeing all tree work.
To keep mature trees safe and healthy, the City may sometimes remove:
- dead, dying, broken and/or diseased limbs
- "sucker" growth sprouting from the base of the tree
- crossing or weakly attached limbs to maintain a strong branch structure
- foliage to lighten the ends of branches and let light into the dense canopies
Taking into consideration a tree's growth rate, ISA guidelines state that no more than 25% of a tree's living branches and foliage should ever be eliminated. Slow-growing species should be pruned no more than 10%, while fast-growing varieties can handle up to 25%. Young urban trees have unique pruning needs, and our City staff keeps careful track of each new tree to ensure it receives proper care and maintains a natural shape.
Frequency of pruning is also important to a tree's health. Based on their growth patterns, City street trees are generally placed in one of three cycles for pruning:
- Low (every nine years),
- Medium (every six years), or
- High (every three years).
Citizen requests for tree pruning can be made to the Community Services Department at 909-399-5431. City staff will inspect each tree and grant or deny a request based on the needs of the tree (as detailed in the criteria listed above) and public safety concerns. If you wish to do additional work beyond what the City provides, you may obtain a permit to have your tree pruned to City standards by a private arborist.
Natural Target Pruning
When urban trees enjoy good health, their natural systems control decay from pests and disease. Proper pruning goes a long way towards promoting this process. Claremont uses Natural Target Pruning to care for its trees, and you can also use this process for pruning your own trees:
- First, find the branch collar (the bulge or wrinkle where the branch meets the trunk).
- Next, cut the limb just outside the collar. If the branch is large or heavy it's best to remove it in smaller sections. Make an undercut (see diagram) before making the final cut to prevent bark from tearing. Eliminating the excess weight will make the final cut much easier and reduce the risk of damaging the tree.
- Make the final cut, being certain to keep it smooth. Cutting this way allows the wound to heal properly and for the tree to begin its natural line of defense against pests and disease. Leaving stubs or cutting inside the collar compromises the tree's natural ability to control decay, which can structurally weaken the tree and make it unsafe.
Despite what any other sources say, the tops of trees should never be cut off! Commonly referred to as "topping," this drastic procedure can be deadly for trees. Sometimes trees can recover from this process but, along with the regrowth, topped trees must also battle severe health and structural problems.
When a tree is "topped," it loses massive amounts of live growth. Since the process is not as precise or delicate or pruning, cuts are often quickly and carelessly made, leaving stubs behind. A tree's foliage provides nourishment through photosynthesis—if this energy source has been radically diminished, the tree must call on its reserves of stored energy to put out new growth. This dense output of greenery is, therefore, weakly attached and may make the tree unstable in windy or stormy weather.
Persistent topping forces a tree to constantly deplete its stored energy and shortens its lifespan. It might eventually become so weak that any adverse condition, such as drought or pest infection, will kill it. For all these reasons, topping street trees is forbidden in the City of Claremont.
Options to topping do exist, depending on the situation and your particular needs:
- Crown Reduction: this allows you to decrease the tree's height while retaining its natural shape. Useful if your tree is growing into an overhead obstacle such as a more dominant tree. For overhead power line clearance, please contact your local utility company.
- Thinning: this is the reduction in a crown's density by removing some limbs in the top and around the periphery of the canopy, as well as branches along the trunk, to create more space and newer growth. This process is especially helpful in reducing the hazards of wind damage.
- Windowing: this less-intensive form of thinning involves the removal of branches only in specific parts of the tree. It can help you maintain a beautiful view of the surrounding area without sacrificing the health of the tree.
Call the Community Services Department at 909-399-5431 if you:
- Witness a City tree being improperly pruned
- Have any questions about the pruning of City trees
- Want to request that a City tree be pruned
- Know of a tree that has suffered storm damage
- Have an interest in learning how to prune and maintain a City tree yourself
- Want more information about caring for your privately-owned trees