Winter Threats to Canadian Trees: Keeping Our Urban and Rural Forests Healthy

Canada’s winter, with its snowy landscapes and crisp air, is breathtaking—but it’s a challenging season for our trees. Both urban and rural trees face unique threats during the colder months that can impact their health and survival. Let’s dive into these challenges, why they matter, and what we can do to help.

The Freeze and Thaw Cycle

Winter in Canada isn’t just cold—it’s unpredictable. Freeze-thaw cycles are one of the biggest threats to trees in urban and rural settings. During the day, warmer temperatures thaw water inside trees, and at night, the drop in temperature refreezes it. This expansion and contraction can lead to frost cracks—vertical splits in the bark that make trees more vulnerable to disease, pests, and further damage.

This phenomenon is sometimes called “Southwest disease” because branches or trees exposed to the sun in the Southwest often experience the greatest temperature swings. These cracks typically run parallel to the branch and are usually cosmetic unless they remain open for years and develop rot behind them. However, horizontal cracks are much more serious and should be inspected by a professional.

Thin-barked trees like maples, cherries, and young oaks are especially prone to this issue. In urban areas, ornamental and young trees are most at risk because they often lack the protective canopy of a forest.

What You Can Do

One simple way to help is to wrap the trunks of vulnerable trees with tree guards or burlap before winter hits. This acts like a protective layer, moderating temperature swings and reducing the chance of frost cracks.

Canadian suburban street in winter after heavy snowfall. Photo by Andrew, Adobe Stock.

De-icing Chemicals

De-icing chemicals help keep our roads and walkways safe but can pose a significant threat to trees, particularly in urban environments. Road salt—typically sodium chloride, magnesium chloride, or potassium chloride—lowers the freezing point of water, making it effective at melting ice. However, it can also leach into soil, where tree roots absorb it, drawing water away from the roots and causing dehydration.

Salt splashes on tree bark and buds can also cause “salt burn,” which appears as browning or dying branches. In some cases, salt spray creates “witches’ brooms”—clusters of abnormal, twiggy growth resembling a broom. This is especially common near high-speed roads and highways.
Urban street trees, particularly those planted near sidewalks, parking lots, and roads, are at the highest risk. Common species like lindens, pines, cedars, and spruces often show the greatest salt stress.

What You Can Do

To reduce harm to your trees, consider using eco-friendly de-icers, like calcium magnesium acetate (CMA), which are less harmful to trees. If you notice salt damage, rinse the affected area with water in early spring to flush salts from the soil. Be mindful of where snow is piled after clearing driveways or roads—avoid piling it near trees whenever possible.

Heavy snowfall on the thin branches of a tree. Photo by labalajadia, Adobe Stock.

Heavy Snow and Ice

Heavy snowfalls and ice storms are a staple of Canadian winters, but for trees, the weight of snow and ice can be a major burden. Snow can accumulate on branches, and if it’s wet and heavy, it may cause them to bend or break. Ice storms can coat branches with a layer of ice, adding weight and snapping limbs. When branches break, they create open wounds that make trees susceptible to pests and diseases.

Trees with dense canopies, like evergreens (cedars, pines, and spruces), are particularly vulnerable to heavy snow building up on their wide branches. Also at risk are fruit-bearing trees which tend to grow wider than taller, and trees with large horizontal branches. In urban areas, young trees with smaller branches and some tight branch unions are particularly vulnerable, as it’s easier to break the main branch.

What You Can Do

A good preventative measure is pruning. Remove weak or overhanging branches in late fall to reduce the likelihood of breakage. For young or vulnerable trees, gently shake off excess snow after a storm, but avoid trying to knock off ice, as you risk breaking the branches in the attempt.

Eastern cottontail (Sylvilagus floridanus) nibbling a tree in winter. Photo by Mircea Costina, Adobe Stock.

Hungry Winter Guests

Winter is a tough time for wildlife, and some critters turn to trees for food and shelter. Small animals like mice, voles, and rabbits often eat the bark of young trees when food is scarce. Girdling —when the bark around the tree is completely eaten— can be deadly. It disrupts the tree’s ability to transport nutrients. In rural areas, deer can cause damage by snacking on buds and lower branches.

Young, thin-barked trees are the most vulnerable. Newly planted trees in parks and gardens are often targets. Fruit and nut trees are also at risk, especially if they are not fenced.

What You Can Do

Use tree guards or fencing around the base of the tree to prevent animals from chewing on the bark. In rural areas, applying a non-toxic repellent can discourage deer from feeding on young trees.

Winter burn on the tips of a tree. Photo by Amelia, Adobe Stock.

Winter’s Hidden Threat

It may seem counterintuitive, but winter drought can be a real problem for trees, especially evergreens. When the ground freezes, trees can no longer access water in the soil, even though they continue to lose moisture through transpiration. This can lead to winter burn, a condition where needles brown and die, particularly in areas exposed to strong, dry winds.

Evergreens, such as pines, spruces, and firs, are the most affected, particularly those exposed to harsh winter winds. Rural trees in open areas and urban trees along windy streets are at the highest risk.

What You Can Do

Watering trees thoroughly in late fall before the ground freezes can help mitigate the risk. Mulching around the base of trees also helps by retaining soil moisture and moderating soil temperature. For evergreens, setting up a windbreak, like burlap screens, can reduce wind exposure.

Giving Our Trees a Helping Hand

Canadian trees face a variety of threats in winter, from the harsh freeze-thaw cycle to hungry wildlife. Whether in an urban park or a rural landscape, trees are essential to our environment, and they need our care to thrive through winter’s challenges.

By understanding these threats and taking a few simple actions—like mulching, using eco-friendly de-icers, wrapping young trees, and pruning strategically—we can help our trees make it through the toughest months of the year. In doing so, we not only protect the health of our forests but also ensure that our urban and rural landscapes continue to provide the benefits we rely on, from clean air to vibrant ecosystems.

A little preparation goes a long way, and our trees will thank us come spring!