forest

Keeping the urban forest green

Trees need TLC to survive, thrive
Wednesday, August 2, 2017
By Robert Lis

Trees are an underrated natural wonder. Besides providing shelter and shade, they offer environmental, economic and social benefits so it’s important to take care of them.

Maintaining trees as part of any landscape adds value to a property and its community throughout the life of the woody plants. Properly scheduled maintenance helps to ensure trees mature gracefully, retaining both their beauty and functionality from year to year. Maintenance performed by qualified and experienced professionals can help to extend the life of trees in the harsh urban environment.

Trees in cities and suburbs are subject to challenges that rural trees do not experience, including improper planting, soil compaction, exposure to high levels of pollutants and mechanical injury. Having a certified arborist regularly assess and care for a property’s trees can assist with early identification and mitigation of these common stress factors for urban trees. In fact, most modern city bylaws require a report by a certified arborist for any site proposal involving tree removal or potential injury to nearby trees.

A Cut Above

Pruning is the most common tree maintenance procedure. It involves a strategic approach to improving the health, structural integrity and overall appearance of a tree. There are a variety of pruning techniques that can be performed, based on tree species, location and limb health.

The most common reason for pruning is to address practical issues, such as allowing for structural clearance, reducing shade case on lawns and gardens, and improving flower and fruit production. Pruning can also be used as an early intervention to prevent future tree failures and improve landscape sightlines (known as vista pruning, whereby the crown is reduced or tree thinned).

A certified arborist can identify the tolerance level of individual tree species for utility pruning. As a general rule, pruning should not exceed more than a 15 to 25 per cent reduction of the overall canopy of any tree. More aggressive pruning may be required when factors such as sightlines or shade levels are a consideration. In these cases, gradual pruning can help to limit the overall stress experienced by the tree and reduce the risk of tree failure. Not only is aggressive pruning stressful for a tree but it can actually result in an increase in the occurrence of unwanted growth, rather than limiting it.

Over pruning, including practices such as tree topping (where whole tops of trees or large upper main branches are removed, leaving stubs), can create hazardous trees and increase the likelihood of future failures. In the rare instances where heavy reductions or topping is required, there needs to be a commitment to increased maintenance in the future.

Pruning for the improved health and structure of a tree can be best achieved through regular scheduled maintenance. Frequent, gradual pruning is easier on the tree than pruning a large volume at sporadic intervals. A certified arborist can determine the best time of year to perform pruning, based on the tree species and extent of crown cleaning required. Healthy branch structures have optimal spacing to allow for the most advantageous future growth and strong resilience to wind and snow loads.

Removing dead wood is an essential part of pruning and may be required annually, depending on the species and condition of the tree. Removing dead wood improves airflow and light penetration, as well as reduces the risk of pest and fungal infections. Once the dead wood has been expunged, additional branches are then removed in order to optimize the future structure of the tree. This selective pruning takes the most experience since it is based on growth rates and patterns of individual species, as well as the unique site conditions affecting tree growth.

For juvenile trees, pruning is focused on improving health and removing growth that will eventually become undesirable in the given landscape. Mature trees are pruned to remove structural elements, such as diseased branches, rubbing branches and non-advantageous new growth

A certified arborist can also use pruning techniques to train trees to grow away from surrounding structures, as well as lift the tree canopy to allow for the use of riding lawn mowers. While the greatest benefit is seen with regularly scheduled maintenance, even a small amount of pruning, especially in young trees, will promote healthy branch structure. Structural deficiencies such as co-dominant growth (when two or more branches emerge from the same junction or tree fork) can be avoided by pruning a juvenile tree before the problem becomes defining for it.

From the Roots Up

If a tree has a good structure and has been pruned regularly but still has an ill appearance, it could indicate there is a problem below the surface. Improper planting practices can lead to girdled roots or ineffective buttress (structural) roots. It is important for the long-term health and stability of any new tree to involve a qualified professional in the tree planting process.

For new plantings and established trees alike, soil compaction (hardening) can be overlooked or an unavoidable challenge. Soil compaction occurs when soil is continually traversed by pedestrians, bicycles or mechanical traffic, such as lawn mowers or other landscaping vehicles. It’s problematic because water is unable to easily penetrate the soil surface, it limits oxygen supply and hampers the ability of tree roots to grow into surrounding areas. Soil compaction is one of the main reasons modern city bylaws require ‘tree protection zones’ or ‘tree buffer areas’ on construction sites. In more extreme cases, an arborist can use methods to aerate the soil and bring some growth potential back to an area of high traffic.

It is beneficial to apply a five to 10-centimetre area of mulch to the critical root zone of a tree; however, mulch or soil should never be piled up around a tree’s trunk. Doing so can lead to decay around the base of a tree, which can make it susceptible to pests and diseases, and increase the overall stress a tree endures in an urban environment. Mulch is not used to introduce nutrients into the soil; instead, it’s applied to enhance the aesthetics of a landscape, moderate soil temperatures and maintain soil moisture.

If necessary, a controlled-release fertilizer can be applied to improve the mineral or nutrient content of the soil. However, it is always preferable to identify and address issues in the landscape that limit the growth potential of a tree, rather than using fertilizers as an artificial prop.

Having a certified arborist regularly assess trees and landscape conditions can help to promote the health of the roots as well as the trees. An arborist can identify factors that have the potential to cause significant root damage, such as proposed construction or landscaping projects, or even continued root injury from flower planting or lawn cutting.

Robert Lis is an ISA certified arborist that co-owns and operates The Urban Arborist Inc. with Jason Chhangur. Together, they have more than 20 years’ experience. Established in 2014, the company provides arborist services in the Greater Toronto Area, ranging from planning and development, tree removal, pruning, planting and a variety of plant health care treatments and plans.

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