The change starts when daylight is reduced and the weather gets colder. From the Algonquin Provincial Park website on fall colours; "As the daylight length shortens, and temperatures grow cooler in autumn, trees slow and eventually halt their sugar making process of photosynthesis and begin to prepare for the dormant winter period. During this preparation for winter, trees extract the valued chemical components within their leaves, including the green chlorophyll, for re-use again next growing season (the following spring/summer). As these valued chemical components break down and get extracted from the leaf, underlying pigments get revealed. These now visible pigments (that were in the leaves all along, but hidden by the green chlorophyll) include the orange and yellow colours of pigments such as carotenes and xanthophylls. Red pigments, or anthocyanins, are believed to be specially formed late in the summer and protect sensitive leaves from bright sunlight during the chemical extraction process." We go from a peak of 15 hours, 27 minutes of summer sunlight to 12 hours, 11 minutes at the Autumn Equinox.
On August 18, 2023 the night time temperatures started to hit 14 degrees Celsius and below in Toronto. It seems to rain every second day in the Toronto area this year and while a large part of the world is suffering drought conditions we seem to be producing a record amount of rainfall in 2023. Normal peak fall colours in Ontario stretch from mid-September into October, moving from the north into southern Ontario as autumn progresses.
Big Bend lookout in Arrowhead Provincial Park
Algonquin Park in Central Ontario is in peak fall colour at the end of September, early October.
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