Street Trees

The Western Hemlock Looper Moth outbreak and last year’s extreme heat have caused significant damage to a number of trees in the City. In September 2022, we’ll be removing dead conifer trees located in Mosquito Creek Park. Learn more in the news article.

Urban forestry is the care and management of our tree population in urban settings, including Street Trees, which adds to and improves our urban environment. The City enjoys a diversity of urban forest with a mosaic of unique settings, including trees in private yards, lining our streets, shading streams and creeks, and beautifying our parks and natural areas.

Why Street Trees?

The City's tree population is a critical part of the urban infrastructure. Each tree is part of an urban canopy that helps absorb carbon dioxide, pulls particulate matter from the air, prevents floods by filtering rain water, and reduces the urban heat island effect by shading to keep temperatures at liveable levels. They also attract wildlife, and provide other aesthetic, social, and economic benefits.

Hemlock Looper Moths

The Western Hemlock Looper is a native species which is part of the natural coastal forest ecosystem that feeds on trees, including Western Hemlock (preferred), Douglas Fir, and Western Red Cedar trees. The species can also feed on other hosts such as Subalpine Fir, Amabilis Fir, Grand Fir and Spruce trees when populations are high. Learn more on the Province of BC website.

The adults (moths) fly in September to October, lay eggs (on branches, tree trunks or on forest floor), the eggs overwinter. and in the spring the caterpillars emerge and begin feeding. The loopers are considered wasteful feeders as they consume only parts of needles and feed throughout a tree crown.

An outbreak of Western Hemlock Looper moths can result in damage to trees and forested areas. The most recent outbreak, which started in 2019, appears to be quite significant, but it is not abnormal.  Susceptible forests (i.e. those hit the hardest) will have mature and over-mature Western Hemlock trees (or stressed trees).  The killing or removal of these over-mature or susceptible trees is an important component of ecosystem dynamics, and is essential in recharging ecosystems by allowing younger/suppressed trees to emerge and also support the recycling of nutrients. This is a natural and important process.

Hemlock Looper Moth Frequently Asked Questions (FAQs)

How long will the outbreak last?

Outbreaks can last three to four years. The most recent outbreak started in 2019. Outbreaks are not uncommon and populations build every 11 – 15 years in our region. The length and intensity of the outbreak depends on weather and other environmental factors.

Can we control the outbreak?

There are no practical measures we can take. This is particularly true on the North Shore, as the Looper moth outbreak has primarily taken place on our water supply lands, and it's not our practice to spray pesticides or herbicides in these areas in order to maintain the high quality of our water supply. This event is part of a natural ecosystem cycle, and the best approach is to let nature run its course.

Which trees are being damaged?

The moths primarily feed on Western Hemlock trees, but also feed on other hosts including Douglas Fir, Western Red Cedar, Subalpine Fir, Amabilis Fir, Grand Fir and Spruce trees when populations are high. Deciduous trees such as native maples and forest understory vegetation may also be hosts.

Will the trees die?

Some trees that are less tolerant of being defoliated, Western Hemlock in particular, may succumb to the damage.

Are the dead trees a hazard?

Not immediately, as generally the trees were healthy prior to being defoliated and dying. It will require years of decay before trees become structurally weaker.

Trees that have pre-existing major structural defects and decay, on a case-by-case basis, may have to be removed sooner if there is a nearby target at risk. If privately-owned trees are within striking distances of homes or yards it is recommended that homeowners have a trained arborist inspect the site. For any tree concerns on the public property please contact the City of North Vancouver.

Will dead trees lead to an increase in wildfire risk?

While the presence of recently dead or dying trees is commonly associated with increased fire risk, Looper moth outbreaks reduce long-term fire risk by reducing ladder and forest canopy fuels and contributing to forest stand diversity - particularly in even-aged second-growth forests such as those affected in the Capilano Watershed.

Will dead trees on a steep slope hazard area result in instability issues?

This will depend on many geotechnical factors and the severity of tree mortality. As the trees were generally heathy prior to dying, the roots systems and especially the main structural roots will take a long-time to decay, therefore providing stability for many years while new native vegetation and trees establish.

A geotechnical engineer will make recommendations to determine the risk associated with significant tree loss on slopes with known stability and erosion issues.

What can we do to help?

Unfortunately, there's not a lot we can do to control an outbreak. We do ask that you have patience during an outbreak as it completes its natural cycle, and see whether defoliated trees recover their health.

Hemlock Looper Moth
Image source: D. Gordon E. Robertson, CC BY-SA 3.0 via Wikimedia Commons

Aphid Infestation and Control

Aphids are small soft-bodied insects that feed on plants. They secrete a sugary substance called honeydew. This drips from leaves and ‘black sooty mold’ can form. This can be washed away and doesn’t harm plants or trees.

Aphids are affected by weather. Rain prevents winged aphids from dispersing, and knocks aphids off plants. Hot, dry weather increases the ability for aphids to reproduce and make new colonies.

Aphid Management

The City of North Vancouver has a targeted maintenance practice to control aphid infestations through the release of beneficial predatory insects.

The Integrated Pest Management (IPM) approach has been very effective in controlling out breaks of aphids and complies with the City’s Cosmetic Pesticide Control Bylaw, 2009, No. 8041.

Early in the summer, vials containing aphid predatory midge (Aa) pupae in a vermiculite medium are installed on targeted trees. There is usually a time lag between one and three weeks before predator populations catch up with the aphid populations.

What You Can Do to Reduce Aphid Populations

Use a hard jet of water to dislodge aphids, ensuring to spray under the leaves and into the middle of the canopy. This should be done either in the morning or late evening, so leaves remain dry during the day.

Apply a sticky band (such as Tanglefoot or Stik-Em) around tree trunks to restrict ant movement (i.e. ants protect aphids, and aphids provide ants with food). Place a protective band underneath the barrier first. Prune any branches touching the ground, buildings, or other plants.

High nitrogen levels favour aphid reproduction. Too much fertilizer promotes succulent new growth that attracts aphids. Avoid over-fertilization and use slow-release rather than highly soluble fertilizers.

Finally, preserve and encourage the presence of natural aphid predators such as birds, spiders, ladybugs, lacewing, hover fly larvae and parasitic wasps.

>> Download Aphid Control and Infestation PDF

Tree Topping

Tree topping, also known as pollarding, stubbing, dehorning, rounding over, or heading; is the cutting and removal of healthy tree branches to reduce height.

It’s not a viable method of height reduction, does not reduce the ‘risk’ associated with tree size, and may actually increase risk due to decay and rapid regrowth.

When pruned properly, trees have the ability to heal. When topped, trees suffer from multiple large wounds and are often unable to prevent fungi from entering them. This can severely weaken or kill the tree.

Rapid Regrowth & Hazards
Topping is thought to reduce height. However, to survive, trees produce numerous shoots below each topping cut. These shoots grow rapidly and can grow up to 20 feet in one year. Topped trees will grow back rapidly until they reach their original size, usually within two years. Although the regrowth is quick, the new shoots are weaker and do not have the structural integrity of the original branches. This means they are prone to break and are particularly vulnerable during wind storms.

The ‘Ugly Factor’
Trees grow into beautiful, natural shapes, providing habitats for animals and birds. When topped, trees look like ugly stubs. New shoots grow straight up giving the tree an unnatural form. Topped trees never regain their natural grace and beauty.

Topping results in high-maintenance pruning in subsequent years to deal with the rapid regrowth and storm damage. If topping is truly successful, the tree will die and this will require additional funds to remove the tree. There’s another hidden cost associated with topping: curb appeal. Healthy, well-maintained trees can add 10 to 20 percent to the value of your property. Disfigured, topped trees are considered an impending expense.

Best Alternative
Consult and hire a professional arborist. They can determine the type of pruning necessary to maintain or improve the health, appearance and safety of your trees.

>> Download Tree Topping PDF

Frequently Asked Questions About Trees

Who owns the trees?

  • Trees on City property: Street trees are City owned trees planted between the curb and your property line.
  • Trees on private property: The City does not regulate trees on private property unless they are in a riparian zone.

What if there's a problem with a tree?

  • Vandalism and car accidents involving trees: We repair or replace City trees that have been vandalized, cut down or damaged due to car accidents. We recover damages to pay for repairs or replacements. Replacement costs for mature trees can be up to $20,000.
  • Request for City tree maintenance: If a City tree needs attention please contact the Engineering, Parks and Environment at 604-983-7333 or complete the online service request form.

Tree Watering

Many street trees have a green watering bag at their base. The bags slowly release water to help the tree get established.

Although the City fills the bags using our watering trucks, if you see a bag looking empty, please top it up with water! The warm summer months can leave young trees in distress, usually indicated by brown or falling leaves.

If there's no watering bag, you can help the street trees near your home to establish their root systems by watering the trees with a slow running hose for 10 minutes twice a week (note: during the summer months, regional water restrictions don't apply to trees and shrubs, but always remember to be water-wise, and aim to water in the evenings and early mornings).


Contact Info

Engineering, Parks & Environment Department
Tel: 604-983-7333

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