Best fall ever? Maybe! Here's why Quebec's leaves are bursting with colour

Think Quebec's fall foliage is particularly nice this year? You're not alone.

Experts say that conditions aligned this year to create especially dramatic colours across the province — and even those who study trees are impressed.

"Walking through part of the forest, it was like walking through a bowl full of yellow paint," said David Wees, a faculty lecturer in plant sciences at McGill University. 

"Everything was so gold and yellow. It was very, very intense!"

Wees explained that while daylight is what triggers the leaves to change, the actual colour palette and rich tones are heavily influenced by the weather — both leading into, and during the autumn season.

A delicate balance

Wees explained that the yellow and orange pigments — known as carotenoids — are present in the leaves year-round but are only visible as the days get shorter and the green chlorophyll fades. So those soft, golden hues? Practically guaranteed.

Where it gets tricky is with the flaming reds that give the fall season its depth. Wees said the seeds of a nice season are sown back in the late summer.

The ideal? "A lot of sunny weather, not too dry, not too wet," Wees said. 

This past summer fit the bill, compared to say, last year, when it was very hot and very dry, stressing the trees and curbing their colour, he said.

But a nice summer doesn't guarantee a colourful fall. Wees said the autumn conditions also have to align: the red comes from anthocyanin pigments, which are only produced once the cold weather kicks in.

But not too cold. A frost will cause the leaves to "pretty much dry up and drop off the trees," Wees said. 

"So the best weather for really bright colours would be bright sunshine, warm but not excessively hot — and then when we get into early fall, cool nights but not freezing," he said.

"It's sort of a delicate balancing act."

Colour in the city

In the city, though, you're more likely to see yellows and oranges, regardless of the weather. 

"When people think of red leaves, people think maples, but that's mostly sugar maple and red maple, which don't do very well in the city ... [they] don't like road salt, among other things," Wees said.

Urban maples are likely to be the Norway maple variety, he said — a heartier, but less showy tree, more prone to yellow leaves.

Joshua Jarry, a horticultural information specialist at the Montreal Botanical Garden, agreed that it's been an "almost perfect" year for the fall leaves — and said there's plenty of colour popping in their arboretum.

"We enjoy having so many nice colours in the various gardens we have … it really gives a variety that makes [everyone] happy," he said.

Jarry said their trees appear to be keeping their leaves longer, giving themselves time to reabsorb nutrients. Once they're done, they'll let the leaves fall, he said.

"Trees are like humans, or any living thing. We don't want to work when we don't get anything in return," he said, laughing.

A changing climate

While Wees said the leaves are beautiful to look at, it also makes him appreciate how many factors contribute to the display.

"All these things — the weather, climate, soil and choice of plants — all play out to make this mix of colours that vary so much from place to place."

But that climate is changing, and Wees said it's hard to predict what that might mean for the leaves. More sun would lead to brighter colours, but dry weather could stress the trees, which would prove to be a problem, he said.

"What will be the biggest factor? Will it be the drought stress or will it be the increased sunshine?" he asked. "I am not sure we can really say yet."