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Why do leaves change colour in the fall?

Monday, September 16th 2019, 4:08 pm - Autumn is often referred to as the "picture perfect" season as splashes of colour fill trees across the country.

Pockets of vibrant reds and yellow are slowly beginning to show, but green currently remains dominant.

But get ready: Peak viewing season is about to begin, with colours typically at their most vibrant near the end of September and into October.

Leslie Karniszewski, Elliot Lake, ON

"Temperature plays a factor in the coloration of trees, but the most important factor is called the photoperiod or the length of daylight," Bob Osbourne of Cornhill, NB told The Weather Network.

"The shortening of the number of hours of daylight is the trigger for trees to start shutting down. A cork-like layer forms between the leaf stem and the branch, which will eventually fall off and it also protects the tree from any kind of fungal or bacterial infection. As it shuts down, it begins to stop water and nutrients from coming into the leaf and the chlorophyll dies."

Stephen Hove, Okotoks, AB

"Something that you probably didn't know about trees is that their natural colour isn't green," says Weather Network meteorologist Erin Wenckstern.

"It's actually yellow and orange but during the spring and summer months trees are full of chlorophyll, which is a molecule that plays an important role in photosynthesis, which is how trees get their energy."

Nicolette Wain-Lowe, ON, Canada

Stress is a big factor in coloration. It may be a matter of too much or too little water, or other nutritional factors. You can spot a stressed tree by its leaves, which change colour before the others.

Visit our Complete Guide to Fall 2019 for an in depth look at the Fall Forecast, tips to plan for it and a sneak peek at the winter ahead

Tree stress can affect whether the fall show will be sensational or not. Things like drought, extreme temperatures and air pollution can make the leaves dull.

Natascha Robertson,Bridgetown, NS

"The most famous of all the trees is the Sugar Maple," adds Osbourne, "with its combination of orange, yellow, and sometimes red. One of the most spectacular of the trees is the native Red Maple with its vivid red color. These are the trees we most associate with fall."

Kishore YG, Ontario

THE SCIENCE BEHIND THE 'SMELL' OF FALL

If you associate certain earthy scents with the fall season, you aren't alone.

Neuroscientist Rachel Herz told the CBC people associate certain smells with fall due to chemistry, biology, and psychology that can trigger certain memories and emotions -- and no two people experience this 'scent' the same way.

Don Hunt, Kaslo, BC

Neuroscientist Rachel Herz told the CBC people associate certain smells with fall due to chemistry, biology, and psychology that can trigger certain memories and emotions -- and no two people experience this 'scent' the same way.

"In summer, we have just more of a mixture of scent and sort of a wide blend of scent ... we smell a lot more of everything around us," she told the publication.

Cheryl, Rice Lake Conservation Area, ON

Earthy smells can often be traced back to decomposing plants and tree leaves.

Do you have a photo or video you'd like to share? Upload them to The Weather Network.

VIDEO: BEST FALL FOLIAGE, FALL 2018

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