Trees, it’s all about leaves and degrees 

By: Kristina Swerhun

Whistler Naturalists

Evergreen conifer trees are abundant in Whistler. They give colour to the landscape year round and, covered with snow, they typify a classic mountain scene.

Ever wonder why we don’t have more deciduous trees here? Why don’t we have more maples, alders and cottonwoods that lose their leaves every winter?

It all comes down to the leaf. Deciduous trees don’t spend as much energy producing their leaves since they loose them each year, becoming inactive over winter. They tend to grow thin, broad leaves with little structural support. While they are usually able to photosynthesize (the process by which green plants use sunlight to produce sugars — and the byproduct oxygen — from carbon dioxide and water) at a higher rate than evergreens, the disadvantage is that they have to spend energy each year to produce their leaves.

Also, deciduous trees will drop their leaves even if there might be a couple weeks of good growing weather left, since they will only grow when there is a low risk of frost. When you see their leaves changing colour, it’s because the tree has stopped producing green chlorophyll (necessary for photosynthesis) in order to cut its losses before the leaves are lost.

Coniferous evergreen trees spend more energy making their needles and protecting them, and in our typical short growing season, have a definite advantage. They can photosynthesize later in the fall and start earlier in the spring. Only frozen ground limits when conifers can photosynthesize, because the tree must be able to absorb water from the soil.

Besides having a longer growing season, conifers are also more efficient at growing at low temperatures than deciduous trees, and are common worldwide at high elevations.

The needles of evergreens are also naturally suited to help them survive cold, wind and snow. They have a heavy layer of wax on top to reduce the loss of moisture. They have chemicals inside that act like antifreeze to protect against damage from ice formation. They’re also narrow, which means they hold less snow and give the tree less risk of a heavy snow load, which could lead to breaking branches.

You may wonder why then do we find deciduous trees growing on old logging roads? Surrounded by conifers, they are especially noticeable crossing the hillside during spring and fall. A lot of the time the tree that you’re seeing is red alder. Red alder is an aggressive, fast-growing hardwood that thrives on disturbed sites.

Alder also has an advantage since it improves disturbed soils by fixing atmospheric nitrogen into the soil. It can do this because it houses symbiotic bacteria which colonize its roots and provide the tree with nitrogen in exchange for carbohydrates.

Red alder establishes itself and grows faster than conifers. However, it is short lived and is considered old at 50 years. In comparison, conifers are considered old from 500-1,000 years, and will replace red alder over time.


Upcoming events: If you’d like to test your knowledge on identifying Whistler’s trees, stop by the Whistler Naturalists table at Enviro Fest. It’s happening on June 9 from 11 a.m. to 4 p.m. in Mountain Square. If the kids are interested in a Wild Things Scavenger Hunt, accompany them to Rebagliati Park from 10 to 11 a.m. on June 9 with Naturalist Cara Richard.

Breeding Bird Survey. Saturday, June 9, 8 a.m. at One Mile Lake, Pemberton. Join the annual foray with the six birding gurus who conduct the annual Breeding Bird Survey (nearing its 30th year!). We'll meet at 8 a.m. sharp and convoy to different viewing spots in the Pemberton area. Call Bob Brett for more information (604-932-8900).


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