Orange arrows indicate spur wounds. Notice the proximity of the failure point to the uppermost spur wound.
Large big leaf maple tree located very close to a house and spreading over the deck. Three years ago, the tree was aggressively pruned back off the house and deck. Approximately 40% of the canopy was removed and spurs were worn to access the tree.
- Excessive water sprouts are produced at large cuts and overall form has been destroyed.
- The infection of a decay pathogen (that entered through the spur wound) weakened a stem which then failed and damaged the glass railing around the deck.
Damage was caused by the method of pruning. An improper pruning cut can compromise the tree’s ability within the branch socket to stop the spread of decay pathogens.
More than 25% of canopy loss has potential to stress the tree. Excessive removal of one portion of a tree’s canopy can:
- increase the chance of sun scald (especially a south facing portion of the canopy) and leaves the remaining canopy compromised.
- expose large branches and limbs that were once protected to new windthrow causing increased potential of failure.
Notice the concentration of decay at the failure
point which is also the location of a spur wound.
Spurs can significantly damage the tree, opening up the cambium to infection and decay. When climbing on spurs, every step creates a puncture wound that has the potential for fungal or bacterial infection. Fungus and bacteria can penetrate the trees’ natural defences and cause premature failures.
Spurs should only be used on trees slated for removal.
Trees in the urban environment are often found in less than ideal growing conditions which may include:
- compacted, oxygen-poor soils
- soils lacking in organic material
- minimal space or soil (trees surrounded by parking lots/pavement on all sides)
- lack of proper irrigation/change to drainage during nearby construction.
These obstacles and stressors can inhibit growth, leave the tree susceptible to pest and disease, and cause the decline of valuable specimen trees. Continual leaf pickup, lack of soil amendments and heavy rainfall also leave soils lacking the appropriate nutrients required for proper tree growth.
Proper installation of new trees, improving soil by amending, and assuring adequate irrigation can minimize stress to trees.
Another effective and valuable means of improving the health of your trees and shrubs is with a soil injection system. This high-pressure system injects a water soluble or suspended slow release fertilizer six-to-eight inches into the soil surface. The system aerates and waters at the same time and additional products can be added to improve soil conditions.
When To Use Soil Injection
- Trees that are stressed:
- before or after construction
- poor site conditions
- trees showing signs of pests and/or disease.
- Hedging – to encourage dense growth or prior to hard pruning to encourage new growth and minimize stress.
- Trees and shrubs with minimal soil like those in planters found around condos or in formed landscapes.
Soil injection should be used in conjunction with other plant health care practices (like applying mulch or compost) for optimal results.
With the long history of forestry in BC, urban tree work on the West Coast can be confusing. Foresters, utility certified tree workers and ISA arborists carry different certifications and perform different services.
To better understand the difference between these tree workers it helps to look at the objectives of each.
Forestry workers specialize in clearing and maintaining large woodlots in a forest context with the objective of maximizing timber value. Though some skills are transferable to the urban environment (eg. removals), some techniques that are well suited to forestry (like topping and spiral pruning) can pose hazards when applied in an urban setting.
Utility certified arborists understand the dangers of working with electricity and focus on clearing vegetation around electrical wires using specialized equipment. The objective is hazard reduction and public safety.
To understand the expertise of an arborist, it is useful to know the definition of the word arboriculture:
The planting, care, and scientific cultivation of trees and woody vegetation in a non-forest context.
Spurless climber doing residential work.
An ISA certified arborist’s objective is the integration of trees in the urban environment with a focus on tree health and preservation. Asking about the experience and training of anyone working on your trees will tell you if they can achieve your objectives.
Proper pruning is essential in developing a tree with a strong structure and desirable form. Trees that receive the appropriate pruning measures while they are young will require little corrective pruning when they mature.
Here are a few simple principles to know about tree pruning:
Each cut has the potential to change the growth of the tree.
Proper technique is essential. Poor pruning can cause damage that lasts for the life of the tree.
Trees do not heal the way people do.
When a tree is wounded, it must grow over and compartmentalize the wound. As a result, the wound is contained within the tree forever.
Small cuts do less damage to the tree than large cuts.
For that reason, proper pruning (training) of young trees is critical. Waiting to prune a tree until it is mature can create the need for large cuts that the tree cannot easily close.
Making The Cut
The location of the pruning cut is critical to a tree’s response in growth and wound closure.
Pruning cuts should be made just outside the branch collar. Because the branch collar contains trunk or parent branch tissues, the tree will be damaged unnecessarily if it is removed or damaged. In fact, if the cut is large, the tree may suffer permanent internal decay from an improper pruning cut.
Pruning cuts should be made just outside the branch collar.
If a permanent branch is to be shortened, it should be cut back to a lateral branch or bud. Cuts made between buds or branches may lead to stem decay, sprout production, and misdirected growth.
The decision to call in an arborist for tree advice often gets left until faced with a problem of some kind. Perhaps your trees are in decline, have outgrown their location or have a troubling pest or disease. At this point, the only solution is often a costly removal.
Check out these five great reasons to maintain the trees on your property at any stage:
Minimize Building Damage
Pruning trees and shrubs away from existing buildings or structures is called Clearance Pruning. Clearance Pruning improves air circulation reducing decay in wood exteriors and stops rubbing that can cause friction damage.
Clearance pruning around light standards increases visibility and safety at night. Overgrown trees and shrubs interfere with the intended purpose of security lights. Canopy Raising (removing lower branches) of trees, hedges and shrubs that grow close to the ground increases visibility and reduces the likelihood of someone hiding or sleeping behind the foliage.
Clearance pruning around walkways is important to allow adequate clearance for residents and the public to pass by. Removing dead, dying and diseased branches (crown cleaning) will minimize failure that may injure people or damage property. Special attention should be paid to trees near parking lots, patios and playgrounds.
Tree Health & Integrity
Young tree training smaller trees will encourage a strong framework and remove defects early. This keeps trees strong and healthy as they mature and minimizes the need for future pruning.
Containment & Aesthetics
Reducing the perimeter of the canopy by a pre-determined amount (depending on the tree or shrub) will minimize growth while maintaining the form and beauty. Called perimeter reduction, this prolongs the life of plant material to serve its function before outgrowing the location. Trees or shrubs near buildings or other structures should also be clearance pruned during the process.
With all of these pruning objectives, the sooner you begin, the better the outcome.