Ontario’s fall foliage season has begun, but experts warn that this year’s display may be less vibrant and arrive earlier than usual due to summer drought conditions.
Ian Laidlaw, an ISA-certified arborist and district manager with Davey Tree Expert Company, said trees across the province are showing signs of stress after months of heat and limited rainfall. “The trees have already started changing,” Laidlaw said, noting he observed early leaf colour near his property outside Ottawa in mid-August.
When stressed, trees slow their production of chlorophyll — the compound that gives leaves their green colour — resulting in muted shades of yellow and duller greens before the typical brilliant reds and oranges. “The greens, they’re just not as vibrant,” Laidlaw explained.
Agriculture Canada reported that northern and eastern Ontario experienced unusually dry conditions this summer, with agricultural regions north of Toronto particularly affected. Urban trees may also be more vulnerable than forest trees, which benefit from stronger natural ecosystems.
Beyond this summer’s drought, Laidlaw said repeated climate stressors, such as warmer winter spells causing trees to leave dormancy too early, are compounding long-term challenges. “The trees are stressed out because of the climate. It builds up over time,” he warned.
While localized conditions will determine which areas are most affected, experts say regions hardest hit by drought are likely to see less intense fall colours this year.
Fall foliage typically results when shorter days and cooler temperatures slow photosynthesis, reducing chlorophyll and revealing underlying pigments: carotenes and xanthophylls (orange and yellow) and anthocyanins (red and purple). This year, that process may be more subdued in parts of Ontario.