What could drought-stricken forests mean for Canada’s fall foliage?

An Ontario biologist says drought-stricken parts of Canada could be in for some underwhelming fall foliage if stressed trees lose out on the energy needed to generate some of the season’s most brilliant colours.

Biology professor Susan Dudley at McMaster University says trees in dried out parts of the country could see their leaves die off rather than turn red.

As the days shorten, green chlorophyll in tree leaves starts to break down and reveals the yellow and orange pigments underneath.

Yet Dudley says some trees, such as maple, oak and sumac, synthesize a pigment in the autumn responsible for turning their leaves into the reds and purples associated with the most brilliant foliage.

If a tree is too stressed, such as from intense drought, Dudley says the leaves may die off before that new pigment can fully develop and give off its most vibrant colour.

In southern Ontario, Dudley says what she’s seeing so far is brown leaves associated with rapid stress-induced death, not an early start to the fall colours.

READ MORE: Another beluga and a seal die at Niagara Falls’ Marineland

While it may be too early to know how the fall spectacle will play out, Dudley said it’s not looking good but favourable weather could alter the gloomy outlook.

“I can’t look at it and make a prediction for a good fall foliage season at all,” she said.

Leaves get their red or purple colour from anthocyanins, a pigment scientists believe may act as “sunscreen,” shielding cells from excess sunlight so they can continue to absorb good nutrients from the leaves even while the photosynthetic machinery is breaking down, Dudley said.

“These stressed trees are not going to have the energy to do as much protection as they would have,” she said.

Around 70 per cent of Canada was experiencing abnormally dry or drought conditions as of the end of July, according to the national drought monitor.

This report by The Canadian Press was first published Sept. 4, 2025.

Jordan Omstead, The Canadian Press