Besides being incredibly important to animals and the ecosystem, trees provide a number of services to humans in ways we often take for granted. The joint City of Ottawa / National Capital Commission (2020) climate projections estimate that very hot days in the summer (> 30°C) four times more common by 2050. More extreme heat means more humidity in the air, which leads to more extreme rain events. Preserving and expanding our tree canopy is more important than ever!
Tree canopy, Cathcart Park (Photo: Kate Laing)
In our urban setting, trees provide many important benefits
Air quality and reducing greenhouse gases
Trees remove some air pollutants and sequester carbon dioxide from the air. This contributes to slowing down the effects of climate change.
Stormwater management
Trees reduce stormwater runoff by capturing some water on leaves, and augmenting the net capacity of soils to absorb rainwater by regularly drawing water from these soils and releasing it through its leaves (transpiration). Some trees, like willows, are so good at removing pollutants, that they are used to remediate contaminated soils.
Cooling and temperature regulation
The cooling effect from large trees is significant, both from the shade they provide, but also by reducing the temperature by one to five degrees Celsius through evapo-transpiration (described above). Strategically planted trees reduce cooling demands for buildings and cars by up to 25% by some estimates. People have long planted deciduous trees on the south and west sides of buildings for their shade/cooling effects in the summer, and conifers on the north sides to act as wind breaks in the winter.
Erosion control
Trees have deep and strong root systems that hold soil in place, which is extremely important along our shorelines. Did you know that willow branches that are stuck in soil or water will often root out to make a new tree? Despite not being a native species, willows have proven to bring so many benefits that they are often a species of choice for stream restoration. Willows are planted in our floodplain parks as they can tolerate wet conditions, like our beautiful weeping willows in Bordeleau.
However, our urban trees face so many pressures, on top of natural threats like bacteria, viruses, woodpeckers (who got the better of a 70+ year old maple recently in Cathcart Park) and insect damage. Urban trees face additional pressures such as salt, pollution, urban heat effect, limited root space (especially for sidewalk trees), and mowing or walking over the surface roots. Nature is better at regenerating lost trees in a forest than in mowed, landscaped areas subject to soil compaction. Research shows that the life span of a newly planted urban tree is on average seven years, and it takes decades for a newly planted tree to have an equivalent canopy of a mature tree, so losing mature trees means we will gradually reduce our canopy cover unless we replant at a much higher rate.
What you can do to support our urban tree canopy
Avoid injuring trees
Always be careful near exposed surface roots (when walking/mowing) and bark (when climbing or installing straps, like hammocks). Report any damage to city trees to 3-1-1.
Plant a tree!
If you’d like to plant a tree on your property, but do not have the budget to purchase one at a nursery, you can check out the city’s Trees in Trust program at forestry@ottawa.ca. (Tree planting | City of Ottawa). Ecology Ottawa (ecologyottawa.ca) has occasional giveaway programs. You can also try your luck by asking on Buy Nothing Facebook group, as some folks might have seedlings growing in their yard.
Propose or participate in community tree planting events
Forêt Capitale Forest (forêtcapitaleforest.ca) is a community organization whose mission is to facilitate the planting of trees. They run community planting events in Ottawa and can work with requests if you know if a place that could use some greening.
Keep the trees on your property healthy by
Watering the tree during dry spells, limiting construction near the roots of the tree, and avoiding use of herbicides.
Thinking twice before removing a tree. Some issues can be addressed with proper pruning or other options.
Reaching out to Hidden Harvest (hiddenharvest.ca) if you have a fruit tree that you find difficult to harvest or clean up. Their volunteers pick and share fruit that would otherwise go to waste and help clean up some of the fallen fruit as a side bonus!
Watching for and promptly removing any invasive and noxious species on your property. Invasive species are a serious threat to our ecosystems, because they reproduce so aggressively that they displace native species, often creating monocultures that drastically affect plant biodiversity. Common buckthorn and Japanese knotwood – both of which are common in Lowertown – are two problematic species.
My favourite trees
For small spaces, my favorite trees to plant are the Serviceberry (Amelanchier), an edible native tree that has an elegant foliage, and produces bountiful blueberry-tasting berries in early July. These are mess free, because if humans don’t pick them, the birds will clean them right off the tree. Win-win!
For larger spaces, the majestic Silver Maple (Acer saccharinum), with its beautiful fine leaves, is fast-growing (even in poor soil) and reaches tall heights that cast excellent shade several properties down. If you have one, your neighbours thank you! My backyard would not be the same without the walls of green from two lovely neighboring silver maples, adding privacy, much needed shade, and a lush green view which I much prefer to the back of building facades.
To sum this all up, no one says it better than Dr. Diana Beresford Kroeger:
The forest is far more than a source of timber. It is our collective medicine cabinet. It is our lungs. It is the regulatory system for our climate and our oceans. It is the mantle of our planet. It is the health and well-being of our children and grandchildren. It is our sacred home.
