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See "Four Seasons of A Tree"
A Featured Event: Fall Foliage
A fall hike through a local park breathing in the cool, crisp air, listening to geese fly overhead and admiring the changing deciduous trees is one of the best Canadian outdoor experiences. In many northern and central areas of Canada the leaves are now nearing their peak colours whereas further south this seasonal transition is just beginning.
The colour shift is keyed by day length, rather than temperature or frost -- as the days grow shorter, the trees begin to pull nutrients back into the tree for storage over the winter, and the production of chlorophyll (the green pigment that captures the sun’s energy) shuts down. As the greens fade, reds, yellows and oranges that had been hiding there begin to show. Carotenes give us the yellows and oranges, while anthocyanins provide the reds. Try this activity to witness the invisible colours right in the classroom.
The intensity of the colour has more to do with sunlight than with temperature. Colours will be more intense if there’s been a good growing season – plenty of water and sunlight. Also, reds are more intense when fall sunshine allows the production of additional sugars and cool, but not freezing nights slow the enzyme activity that destroys the anthocyanin pigments. Near to above normal temperatures forecast in many parts of Canada should lead to a reasonable fall colour season, except where mid-summer droughts were severe. A milder than normal late fall may extend colours in Ontario and Quebec.
Colour can be quite variable, both within and among different species. White Ash can vary from yellow to purple. Male Red Maples tend to be red and females yellow. For oranges, look to Sugar Maples and Staghorn Sumac; for yellows, Silver Maple, Trembling Aspen and White Birch; for reds, Red Maple , Pin Cherry and oaks . There is some evidence that individual trees turn a similar colour each fall. Try your own observational experiment by noting the colours of trees nearby your home or school in a journal or painting and compare the colours in subsequent years.
Finally, a corky layer, which formed between the leaf and the tree prior to fall colour production, eventually weakens and detaches as the leaves fall and drift on the autumn winds. The leaves find their way to forest floor, where although dead, they become part of an important cycle -- providing life for decomposers, providing food for numerous soil organisms, and putting nutrients back in the soil. Some trees, however – oaks and beeches in particular – don’t form this corky layer and remain on the tree long into the winter and at times even the next spring. These trees are termed marcescent.
So with all this in mind, why not head outside, do some "leaf peeping" and discover the remarkable variety of trees and colours in your area. Eastern Canada is especially well known for its fall foliage. Leaf forecasts are provided by most provinces and/or regions. Canada's Parks also offer fall colours and a variety of activities and events that provide great outdoor experiences.