The Critical Role of Trees in Combatting Climate Change

Julia Thomson

From the west coast rainforests to the urban concrete jungles to a few steps outside our front doors, trees are everywhere in the Canadian landscape. Their prevalence means they are often taken for granted, but trees are critical to life on this planet—and their importance is increasing.

Vegetation in all forms provides the oxygen that people and animals need to live. Plants take in the carbon dioxide we produce through respiration and burning fossil fuels, and they release oxygen. Whether it’s phytoplankton in the ocean or the maple tree in our backyard, plants are at the root of the life cycle. They create the basic living conditions for all other species.

Trees’ ability to absorb carbon dioxide has become even more important as the climate changes and atmospheric carbon levels increase. Nothing that humans do to capture carbon is as efficient as the natural environment.

“Trees are very important because they’re actually the cheapest solution to our climate change problems,” says Nicholas Schwetz, an ISA-certifi

A forest in its natural state.

ed arborist and terrestrial ecologist in Victoria. “They’re readily available, very, very adaptable, and they will continue to produce oxygen and feed wildlife and cycle nutrients. They just do their thing automatically.”

 

When trees are allowed to do their thing, the environment thrives.

In the forest, roots grow through rich, fertile, undisturbed soil. From their roots, trees absorb nutrients, which become the building blocks of bark, branches and leaves. Those leaves capture rainfall. Slowing the water’s descent makes it more easily absorbed into the ground, as opposed to running off in a torrent causing erosion and flooding. Trees provide shade, sheltering other plants on the forest floor. As leaves, branches and eventually trees themselves fall to the ground and decompose, nutrients return to the soil to be used again and again.

However, forests cover just 35 per cent of Canada. To combat climate change, improve air quality and enhance our environment, we must increase the number of trees in our urban and suburban environments. There are several things that we can do to help them thrive.

Tree Care 101

When planting a new tree, the first step is to look at your site. Evaluate the sun patterns, soil type, moisture content and the amount of space you have. Select a species suited to those conditions.

Many people believe a tree can be as big underground as it is above. In fact, the roots of a tree can extend three times the diameter of the crown, but only one to two meters below the soil surface. Wide and shallow is the true form of tree roots, but the root zone may be constricted. In an urban landscape where trees are crammed into small cutouts in the sidewalk at the edge of the road, the root network will not grow very large. Likewise, roots have difficulty growing under a road or driveway.

“If your front yard is maybe six metres by eight metres then that’s going to be the root zone,” explains Schwetz. He advises people to choose smaller species that don’t grow as tall or have more upright crowns, rather than a variety that is going to overtake the whole yard.

Once you have selected the type of tree, choose the right size. Schwetz recommends planting calipers, as opposed to saplings. Caliper trees are classified by the diameter of their trunks, measured with calipers, and are older and stronger than saplings. A caliper that is 5 to 8 centimetres in diameter is usually young enough to adjust to transplanting and strong enough to establish itself in its new site.

Newly planted trees will require some maintenance and attention over their first few years.

Most essential is adequate water. A good rule of thumb for watering is every day for a week, every week for a month, every month for a year. By the second growing season, the tree should be adapted and able to uptake enough water from the ground. However, Schwetz cautions, “Given climate change, if you haven’t had a normal rain cycle in a month it’s definitely a good idea to water young trees.”

Some common practices, such as stakes, rodent guards, mulch volcanoes or pruning, may not be necessary. Most caliper trees can stand on their own and do not need to be staked, unless it’s in a windy area and in danger of blowing down. Stakes should be used carefully and only until roots are established— usually a year after planting. After that, they can be removed. Take care not to damage the thin bark of a young tree, which can constrict the flow of water and nutrients, and harm the tree’s overall health and future.

Trauma Care

Trees adapt to many different growing conditions, can tolerate a certain amount of stress and at least partially recover from serious injuries.

Trees are known to grow around stakes, fences, nails hammered into the wood, or even bicycles chained to the trunk. If the tree is small, it may be able to heal over the foreign item and seal it off, but some objects can cut off the circulatory system of the trunk and cause problems later on. If you encounter something deeply embedded in a tree, Schwetz advises leaving it in place rather than digging it out, as you might cause more damage.

Breakage can be another point of stress for trees, opening them up to disease, pests and decay. Repair the damage by pruning the broken limb down to a crotch where the branch would reach the trunk. That site is home to cells which will naturally close the wound.

Tree damaged by neglected stake and collar in fall 2012.

Sometimes a tree may sprout suckers at the site of a break. Schwetz explains, “The tree is trying to compensate by growing extra branches to cover what was lost, but those are weaker attachments because it’s not coming out from the ends of the twigs and growing in a normal fashion.” Remove the suckers and the tree will start to seal.

Beyond accidental breaks, humans also frequently remove parts of trees. Roots are cut as driveways or roads are installed. Branches are pruned as they grow too close to houses or hydro wires.

The same tree in summer 2019. (Photos: Julia Thomson)

 

A general guideline is that no more than 20 per cent of the root or crown should be removed within a year. This limit ensures that you are not taking away the energy production of that tree. Removing more than 20 per cent causes the tree to put all of its energy into the healing process as opposed to the sugar production that it needs to grow.

Lawn trimmers are another common source of injury, nicking the bark at the base of the tree. The cuts may happen repeatedly, more quickly than the tree can heal. These gashes open a vector for pests and disease and can cut off water and nutrient transport.

Tree damaged by neglected stake and collar in fall 2012.

When it comes to pest management, consulting a certified arborist is usually helpful. Schwetz says, “There’s a lot of native insects that go through cycles and they don’t actually harm the tree usually to the point that it dies. They utilize it for maybe one part of their life cycle but they’re not having a major impact. However if you have something like emerald ash borer, that goes through and kills every ash tree.”

A professional can identify the pest, its impact on the tree, and appropriate treatment.

The same tree in summer 2019. (Photos: Julia Thomson)

While trees are one of our best defences against climate change, they are also threatened by shifting weather patterns. “We’re seeing in BC when you have the days where it’s 30 plus degrees constantly that’s a lot of evaporation happening,” says Schwetz. “Without the rain cycle, trees are getting stressed and drying out. Watering is something that landowners should be watching closely. Give it the water, and it will start to maintain itself. It’s an easy management tool to use.”

Some trauma is obvious—broken branches, insects, eaten leaves, split bark. More subtle things to watch out for include an over-abundance of blossoms (a sign the tree may be trying desperately to reproduce), leaves curling or dying back, a sparse crown and epicormic shoots (suckers growing from a bud on the trunk).

It can be very difficult to identify one thing that causes a tree to decline. Because they’re long-lived species, it might take years or even decades before you really see the full effect of a stressor. However, even under stress, trees provide an important function of animal habitats, nutrient cycling, oxygen production and carbon storage.

Maintaining tree health ensures they have the natural defences to combat pests, disease, climate change and other challenges. It also ensures that trees are able to fulfill their critical role in the earth’s life cycle.