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.
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