If you’ve been walking through Toronto’s parks or tree-lined streets lately, you may have noticed something surprising: flashes of red, yellow and orange already on display, peaking through the canopies of the city’s trees. According to experts, this shift is arriving ahead of schedule.
Dr. Laura M. Bolt, an assistant professor of forest conservation biology at the University of Toronto, explains that leaves turn when days shorten and nights cool, which signals trees to stop producing chlorophyll — the green pigment that masks other colours. When chlorophyll fades, yellows, reds and oranges are revealed. She says the change is “a few weeks on the early side this year.”
WHY THIS YEAR LOOKS DIFFERENT
Normally, this process begins around mid-September. But this summer’s dry conditions have stressed trees, accelerating leaf loss and showing more of the fall colours ahead of schedule.
“Drought stress is a major factor this year in many areas of Ontario,” Bolt told Now Toronto on Friday, adding that trees under stress often display duller foliage.
Marcus Maddalena, nature reserves manager at Ontario Nature, says he has seen the same trend unfold across southern Ontario after an unusually hot and dry summer.
Maddalena explains that when trees are stressed and can’t photosynthesize properly, they drop their leaves early to conserve energy.
“There are a few different ways that trees will respond to heat stress and drought conditions, but mid-summer, when drought is bad, you might see leaves looking like they’re wilted. You might see curls or brown tips from that heat stress and that drought. And if that’s prolonged through the season and they aren’t able to recover, you will see them start to drop their leaves a little bit earlier as a response to those drought conditions,” Maddalena said.
Toronto and Region Conservation Authority (TRCA) Senior Manager of Terrestrial Inventories and Monitoring, Sue Hayes, says her field teams have observed a similar shift.
Based on biologists’ observations, colour changes appear to be happening about a week earlier than usual. She attributes this largely to drought, noting that some trees are shedding leaves outright rather than turning bright colours before falling.
BIGGER IMPLICATIONS FOR FORESTS AND WILDLIFE
Early colour change might seem like a small adjustment, but experts caution that years with repeated stress can add up and have major consequences.
Bolt warns that shifts in vegetation cycles can affect wildlife, since animals may lose access to preferred food sources at key times. This can force them to rely on less nutritious alternatives, ultimately impacting their health.
“If typical food sources are not available for animals at specific times of year, this means that they would be forced to eat less desirable and nutritious fallback foods,” she said. “That could have negative effects on their health and long-term viability at the population level.”
Hayes points out that stress isn’t just about drought — it’s compounded by pests and diseases that thrive under warmer winters and longer hot days, such as emerald ash borer and spongy moth outbreaks.
“All of those things can compound the stress on the trees,” she said.
Maddalena adds that climate change is amplifying these pressures by making extreme weather more frequent.
“It is, in part, because climate change is worsening some of these extreme weather patterns. It’s making extreme weather more common, and as a result, the natural world has a hard time figuring out what to do with those weather patterns,” he said.
Urban areas face even greater challenges, since concrete and asphalt trap heat, leaving street trees more vulnerable.
WHAT CAN BE DONE
Experts agree that individuals and communities can help combat the issue. Planting native, drought-tolerant species and expanding naturalized spaces can create healthier canopies and protect against climate stressors.
“If you do have an outdoor space where you can plant trees, plant native species, and plant trees… The more natural space and the more sort of canopy there is, the more resilient individual [trees] within that system will be,” Maddalena said.
He also recommends resources like the Grow Me Instead guide, which offers alternatives to common garden plants that are better suited to Ontario’s changing conditions.
For all three experts, the early splash of fall colour isn’t just a seasonal curiosity; it’s a reminder of how Ontario’s forests and the wildlife that depend on them are adapting under mounting environmental stress.
