It's already 'early season viewing' for fall colours. Here's why the leaves change

It's almost the time of year when Canada's forests become a colourful spectacle.

Leaves on deciduous trees — maple, birch, oak and more — are starting their gradual shift toward reds, oranges and yellows as the fall equinox approaches.

Some key temperatures and weather need to be in place for trees to start changing colour, however.

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Imagine each green leaf as a "tiny solar-powered factory," the Nature Conservancy Canada website reads. Each cell converts light into energy for the tree through photosynthesis.

Chlorophyll is responsible for the green colour but as temperatures cool and the sun sets earlier, the tree no longer produces energy for the long winter ahead.

Molecules in the trees will "break down" NCC says, triggering other compounds to appear.

"The same compounds that are responsible for the orange colour of carrots are the triggers for yellow, gold and orange leaf colours — carotenoids and xanthophylls," the NCC website reads.

Trees like poplar and birch have carotenoid-rich leaves, which result in a golden-yellow colour.

According to NCC, yellow leaves are more common in western and northern Canada.

In Ontario and Quebec, red maple trees "dominate."

"The leaves with the highest sugar content contain anthocyanins, which are byproducts of extra sugar formed late in the summer," NCC says.

Some provincial, territorial and national parks in Canada have a fall foliage report that tracks when the leaves are changing colour.

Ontario's Algonquin Park showcases vibrant fall colours that people flock to from all over Canada and the world.

As of Sept. 21, maple trees are just starting to turn colours, but most other trees haven't started yet.

"Good early season viewing of Sugar Maple and Red Maple at the landscape level is beginning," an update on Sept. 18 from Algonquin Park reads. "Sugar Maples that dominate the Algonquin Park landscape are showing an increasing yellow-orange colour hinting at the colour change that will come in the days ahead."