Passing trees planted along roads and walkways helps us feel more connected to nature each day. Cities across Canada – and the entire world – have implemented programs to plant new trees to liven up the city streets, shade sidewalks, provide homes to animals and clean the neighborhood air.

However, these street trees are subjected to damage and contaminates that are causing them to wither and die prematurely. The same cities implementing tree planting initiatives are seeing increasing mortality rates for urban trees just a few years after planting.

The cost of removing and replanting these trees also climbs as the number of dying street trees increases, so proper planning for street tree planting and maintenance, and maintaining already-planted trees is extremely important.

Potential causes of premature street tree death

Street trees sit close to urban life, meaning they are subjected to potential harm on top of being placed in somewhat-restricted locations. The cause of street tree death may be multi-faceted as populations climb and city maintenance budgets tighten.

One recent article from a winter city suggests that road salt is to blame for the premature death of street trees. De-icing salt used in winter may be a contributing factor. Some tree species are more resistant than others, but many buds and needles are harmed, regardless of the tree type. The tree’s soil can also be damaged, causing less nutrient and water uptake by the trees.

Soil materials may also be at fault. The composition of the soil may not be appropriate for the types of trees planted. Soil compaction may also be an issue. If people or small mammals walk around the base of the tree near the street, they can compact the soil near the roots and cut off underground pockets useful for holding and transporting air and water.

Street trees often don’t have space beneath the ground to extend their root systems, either. Pipes, asphalt and concrete stand in the way of the already-limited space trees have to put down roots. Poor planting designs for trees with large root systems may restrict the growth of said trees and cause premature withering or death.

Street lights might also affect these trees. Trees “sleep” at night like humans do, and a constant source of light above their canopies may affect the way they photosynthesize. Light may also deter animals and other organisms from living in or growing on the tree, disrupting its ecosystem.

Finally, a lack of appropriate maintenance may be at fault. Trees near the street need to be pruned so residents don’t encounter structural problems and the tree maintains healthy branches.  All trees must be watered adequately, as well, even during droughts.

One challenge cities need to solve is how to improve the flow of rainwater toward street trees so they are irrigated naturally and the water doesn’t merely runoff into the sewer systems.

Ways to improve street tree planning and maturity

Appropriate tree selection and planning is necessary to ensure the longevity of these street trees and prevent the high costs of removal and replanting. City planners must ensure they consider soil, tree type, irrigation methods, space limitations and urban hazards before planting trees.

The idea isn’t to plant a large number of trees along streets, but to carefully select the right type of trees, soil conditions and maintenance plans to help these street trees mature and grow to live long lifespans. City planners must also consider climate change and what the future of soil and precipitation will look like in 10 or 20 years.

To learn more about soil and tree growth in urban environments, reach out to us at admin@soiladvocates.ca

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