Ducks sun themselves in Halifax's Frog Pond. (Brian DuBreuil/CBC)
Forces of nature
Why leaves go red
Autumn leaves drift by our windows and here's why
Last Updated October 16, 2007
Fall is my favourite season in Los Angeles, watching the little birds turn colour and fall from the trees. — David Letterman
Seems to be a vintage year for fall colours this autumn, certainly in Jim McCready's neck of the woods, which is a large sweep of Canada from southern Quebec across southern Ontario and west across the Great Lakes.
McCready is a professional forester and arborist with Tree Canada, based in Ottawa. His region is known as the Great Lakes-St. Lawrence forest (GLSL) and he has been in the business of understanding, overseeing and nurturing trees for more than 30 years.
How many tree species in the world?
"I wouldn't hazard a guess," McCready told CBCNews.ca. "I wouldn't even guess how many there are in Canada, not even in my region."
Which is understandable, as an alphabetical list of trees species in Canada starts with the Alaska paper birch and runs all the way to the yellow-twig dogwood, with stops at the Japanese walnut, shagbark hickory, western hemlock, Ponderosa pine and feltleaf willow. Thousands, tens of thousands - more!
Take the oak, one of the strongest, hardest trees in the world. It is the national tree of England, Estonia, France, Germany, Lithuania, Poland, the United States and Wales. In classical mythology, it is the symbol of Zeus. There are hundreds of species of oak trees alone.
It doesn't take McCready long to get warmed up to the topic of trees and leaves. If he was starting afresh and had to find the perfect tree for his home, in Carlton Place outside of Ottawa, he'd choose the sugar maple, which produces the leaf depicted on the Canadian flag.
"You need to plant it on the southwest side of the lot, to get shade and an air-conditioned, cooling effect in summer," he explained. "When the leaves fall, you get the warming effect of the sun all winter."
And don't confuse a sugar maple with a Norway maple, he warns. The Norway maple is a European tree and tends to be aggressive in its growth and root structure. Going one on one against a Canadian sugar maple, the Norway maple would win.
The slowest-growing, longest-living shade tree?
The red oak, McCready says.
The fastest-growing, if you want quick shade?
Any of the poplars, he said, warning that though they do grow quickly, they tend to be fragile and subject to stress, especially in urban environments.
McCready grew up in Toronto, where he studied forestry at the University of Toronto, and he remembers making "doneywhackers" out of horse chestnut seeds. You drilled into the bulbous horse chestnut seed and drew a thread into it and — voila! — a "doneywhacker."
How do you spell "doneywhacker," we asked.
"Any way you want," McCready said.
On the prairies, kids liked to make acorn pipes by hollowing out the pulp of the acorn and inserting a straw into the base.
McCready says 2007 is a vintage year for fall colours in his region because of a nearly perfect mix of a dry, sunny summer, with cool, wet September nights.
Much of the rest of Canada also has experienced superb conditions for trees. The sugar maple in particular is turning brilliant hues of bright red and yellow this year and will reach a crescendo of colours in a week or two.
"Everything starts in summer," McCready said. "This year was brighter and drier than most."
Why change colour?
So, how, and why, do leaves change colour? The "why" is because the leaves need a break, a winter of rest, after a summer of busily photosynthesizing, using sunlight to convert water and carbon dioxide into sugar. McCready can recognize a sick tree by the way it turns colour and sheds leaves too early, which means it doesn't have long to live.
Pigments are responsible for the colours of the leaves in the fall: chlorophyll for green; carotenoid for yellow, orange and brown; anthocyanins for red. As sunlight decreases, the tree stops producing chlorophyll and the carotenoid in the leaves shows through with yellows, oranges and soft browns.
In a year such as this, the reds in the leaves are sensational — the best in years — because warm, sunny autumn days are giving way to cool, but not freezing, nights. The warm, sunny days allow the leaves to produce sugar, and the cool nights keep the sugar sap from flowing from the leaf veins to the branches and trunk.
Get out there and see for yourself.
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