Fall colours come – frost or no frost
For many, fall is the loveliest season of them all. Mother Nature really turns things up with trees that appear to be set on fire against a dense blue sky. It’s still early so we’re just starting to see the first blush of colour on the trees. Yesterday, a woman called wondering if the leaves would turn earlier this year because of the frost we had this week.
Contrary to popular belief, frost does not cause the leaves to change colours. In fact, early frosts can kill leaves, leaving them shriveled and brown.
As the days grow shorter and cooler, broad-leaved trees develop a corky layer of cells across the base of the leaf that cuts off nourishment and makes it easy for the dead leaf to break off
and fall to the ground. As water and minerals are lost, chlorophyll breaks down and with its disappearance, the green colour fades, revealing underlying colours. So, the leaves actually measure the length of day.
However, the range and intensity of autumn colors is greatly influenced by the weather. Low temperatures destroy chlorophyll, but if they stay above freezing, promote the formation of anthocyanins. Bright sunshine also destroys chlorophyll and enhances anthocyanin production. Dry weather, by increasing sugar concentration in sap, also increases the amount of anthocyanin. So the brightest autumn colours are produced when dry, sunny days are followed by cool, dry nights.
The change varies from tree
to tree depending on soil conditions, disease and the weather. Trees on dry hills, especially at the end of a long dry summer, turn early. Early and severe frosts can destroy the multicoloured effect by killing the green tissue in the leaf; the leaves can turn a dull brown or even black. Dark and rainy days can reduce the brilliance of the foliage. As the fall show gets underway, I would love to see and share some photos from every corner of Atlantic Canada. Please send your photos of the fall brilliance or lack thereof to: Weathermail@weatherbyday.ca . Don’t forget to tell me where and when the photo was taken.
Chief Meteorologist Cindy Day