Urban Forest

Trees – a collective heritage

Trees are an important part of Westmount’s character and history. From the time of the Iroquois, to the arrival of the French and British, to the present, the local landscape has been defined by its patchwork of charming paths and roads winding through the forested western slope of Mount Royal.

The word forest isn’t reserved only for expanses of trees in remote areas. An urban forest – sometimes called green infrastructure – is defined as all of the trees and other vegetation within a built-up area, both public and private. In a sea of grey infrastructure, trees represent a vital bridge between city dwellers and the natural world.

Originally composed of maples, birches, and elms, the local forest changed with the arrival of European settlers, who gradually introduced orchard trees and ornamentals, and later, some hardy species well suited to the rigours of an increasingly urban environment.

Westmount’s urban forest

Many of the trees in the City have an extensive history. As part of our shared heritage, these trees are treasures to preserve, particularly in today’s urban environment. All measures are taken to protect and care for these historic trees for as long as possible.

In addition to its management of public trees, Westmount encourages the planting of trees on private property. Each spring, it offers a limited number of young ornamental or fruit trees at no charge for residents that wish to plant them on their property.

Westmount’s contemporary urban forest, like many other North American cities, is composed primarily of Norway maple (Acer platanoides) varieties, many of them planted in the mid-20th century as a sturdy, fast-growing replacement for the rapid loss of American elms to Dutch elm disease.


The City is committed to the development of a proactive forest management strategy. Thanks to new technologies, leading-edge arboricultural practices, and science-based decision-making, Westmount’s urban forest is becoming healthier, safer, and more biologically diverse.

By planting ecologically-appropriate tree cultivars – the right tree in the right place – and by using best management practices (BMP), the City will ensure a vibrant urban forest for future generations.

Why tree removal is necessary

Westmount is committed to the ongoing observation, evaluation, and maintenance of its trees, replacing them when necessary to ensure a robust, abundant and biologically-diverse forest throughout its territory.

The typical life expectancy of an urban tree is 60 years. The majority of Westmount’s Norway maples, estimated to be between 60 to 80 years of age, are likely now in decline and many will reach the end of their lifespan within a short period. Pruning, cabling, and other maintenance techniques are used where appropriate to prolong the life of trees and ensure public safety. In many cases, however, felling is a better option to improve the biological and age diversity of the forest.


Urban forests provide crucial ecosystem services such as improved mental and physical health, improved air, water and soil quality, stormwater management, wildlife habitat, shade, and a reduction in the heat-island effect.

An aesthically-pleasing abundance of trees also provides economic value, contributing to higher property values and more successful business districts.


Evaluating the health of a tree is not a simple process; it involves specialized equipment and professional expertise. It may result in the detection of structural problems or a diagnosis of a disease that reduces the tree’s vigour and negatively impacts the growth of other trees around it. In recent years, the Emerald Ash Borer (Agrilus planipennis), an invasive beetle from Asia, has killed Ash trees, causing immense damage to wild and urban forests in the northeast part of the continent.


For permit application and submittal requirements, please click here to apply for a permit from the Urban Planning Department.

For a list of permitted tree species for planting or replacement, please consult the list of suitable trees.

 New by-law concerning tree felling

By-law 1494, which came into effect May 2, 2016, modified the requirement for the felling of trees.

City authorization for tree felling on private property is required in all cases, except if the tree is not more than 10 cm (4 in.) in diameter, when measured at a height of 1.5 m (5 ft.) from the ground.

In order to protect Westmount’s tree canopy, tree cutting is only authorized in the following circumstances, and after the issuance of a certificate of authorization for tree cutting:

  • based on an arboriculturist’s report, the tree is dead or in a state of irreversible blight, with more than 50% of the crown consisting of dead wood;
  • the tree is within the building site of a projected construction (structure or retaining wall) or within   3 meters of the building site of a projected construction (structure or retaining wall) – Please note that a building permit or landscaping certificate is a pre-requisite in this context;
  • the tree is located within the building site of a swimming pool or, in the case of the front yard, within the building site of accessory parking or means of access to a building, but only if no other area is available elsewhere on the parcel of land for such construction – Please note that a building permit or landscaping certificate is a pre-requisite in this context;
  • based on an arboriculturist’s report, the tree is likely to spread a disease or is an exotic invasive species and accordingly, must be replaced;
  • based on an arboriculturalist’s report, if the tree represents a dangerous condition due to an irreversible situation resulting from a disease or structural deficiency affecting its solidity;
  • If the tree causes serious damage to a property – Please note that the City may require a report signed by an engineer.

In all cases, the applicant must justify the request. To apply for a certificate of authorization, please go to the Urban Planning Department with the following documents:

  • A letter from the building owner authorizing the certificate application, if the request is made by a third party;
  • A letter from the association of co-owners authorizing the proposed modification, if applicable;
  • A copy of a certificate of location indicating the location of the tree to be removed;
  • A clear and colour photograph of the tree to be removed;
  • An arboriculturist’s report, written and signed by an arborist (certification or diploma) or a landscape architect (AAPQ), if applicable;
  • A report signed by an engineer, if applicable;
  • A plan indicating the proposed replacement program (by an arborist or landscape architect), if applicable;
  • A tree protection method for the surrounding trees, if applicable;
  • A site plan showing existing and proposed landscaping, if applicable;
  • An official cost estimate, excluding taxes, provided by a professional to intervene on said tree(s).

Certificates of authorization are subject to fees outlined in the Municipal tariffs bylaw.

For further information, please visit: https://westmount.org/en/construction-and-renovation/

In all cases, the applicant must justify the request. Please take note that the request may take up to two (2) weeks to process.

The property owner is responsible for the disposal of the branches and trunk of a felled tree.

Emerald Ash Borer (Agrilus Planipennis)

The Emerald Ash Borer (EAB) is a highly destructive insect pest of ash trees. Native to eastern Asia, this pest was first discovered in Canada and the U.S. in 2002. The EAB has killed millions of ash trees in Southwestern Ontario, Michigan and surrounding states, and poses a major economic and environmental threat to urban and forested areas in both countries. The EAB attacks and kills all species of ash (except Mountain ash which is not a true ash).

How does the EAB spread?

While the EAB can fly up to several kilometres, another significant factor contributing to its spread is the movement of firewood, nursery stock, trees, logs, lumber, wood with bark attached and wood or bark chips.

Signs of infestation

Tree decline, including:

  • thinning crown
  • diminished density of leaves
  • evidence of adult beetle feeding on leaves
  • long shoots growing from the trunk or branches
  • vertical cracks in the trunk
  • small D-shaped emergence holes
  • S-shaped tunnels under the bark filled with fine sawdust

Preventive Measures

Montreal’s major project (french only)

“The project, led by the Service de l’environnement of Montréal,
consists in releasing natural enemies of the emerald ash borer (EAB).
Several thousand parasitoids will be released at different times
during the summer in some natural woodlots, such as Westmount’s
Summit Woods Green Space. This classical biological control project,
through the use of exotic natural enemies of the EAB, is a long-term
strategy for the conservation of natural woodlots in urban areas.”

Westmount statement: Biological control (PDF)

Don’t move firewood

Transporting firewood can destroy millions of trees

Invasive insects and diseases can live in cut wood. Moving untreated firewood, even just a few kilometres to or from a campground or a cottage, is a common way for invasive insects and diseases to spread.

Forest Tent Caterpillar (Malacosoma disstria)


The Forest Tent Caterpillar is an insect native to North America that is widely found throughout the continent. In fact, it is one of the best known defoliating insects.

The Forest Tent Caterpillar breeds only once a year. The first caterpillars appear in early May, when the leaves of the aspen tree, its preferred host, are spread out. From the time they appear until they reach maturity, around mid-June, they greedily devour the tender foliage. During this time, they undergo five larval moults.

Hosts and damage

In Canada, the Forest Tent Caterpillar has been observed on 29 different species, including 27 types of hardwoods. However, its preferred hosts remain, in decreasing order, aspen, white birch, sugar maple, willows and red oak. The red maple does not attract it at all.

Forest Tent Caterpillars can occasionally severely, if not completely, defoliate their hosts over large areas.

Intervention and Control

A variety of treatments can be used to protect ornamental trees, such as spraying with water containing dishwashing detergent (1 tsp. per liter). The biological insecticide, Bacillus thuringiensis (B.t.), sold under various brand names, is also effective against forest tent caterpillar. The insect that ingests it dies a few days later. B.t. must therefore be applied very early in the spring, as soon as the foliage has reached its maximum size, to ensure that the insecticide is deposited on an adequate surface. In high value stands, B.t. can be applied if the egg population survey in the fall indicates that significant damage will occur the following spring.

Comments associated with a public tree

The Public Works Department intervenes only on public trees. If you cannot find the tree on the map, please include your address in the message field. PLEASE NOTE: If you request an evaluation for work on trees near power lines, please contact Hydro Westmount Customer Service at 514 925-1414.

  • The site number can be found on the above map; it is attributed to a given point on the map. Each point represents a tree, stump, or planting space.