Why Leaves Change Colour
It is commonly asked “why do leaves change colour?” Every fall trees reveal beautiful fall colours such as red, yellow, and orange which is the result of a chemical process taking place within the tree.
The Use of A Tree’s Leaves During Summer
During the spring and summer leaves act as food factories where most foods needed for the trees growth are manufactured. An extraordinary and abundant chemical called chlorophyll is used within tree cells to absorb energy from the sun which in turn is used in transforming carbon dioxide and water to carbohydrates, such as sugars and starch. Chlorophyll is the chemical that gives leaves the green color. Along with the green pigment are other colored pigments which are masked most of the year by the great amounts of green coloring.
The Biology of Trees and why Leaves Change Colour
In the fall, because of changes in length of daylight and temperature, leaves stop their food making process. Chlorophyll breaks down, the green color disappears, and other colors such as red, yellow, and orange are unmasked.
As fall colours appear, other changes take place. The point where the stem of the leaf is attached to the tree, a layer of cells develops that severs the tissues that support the leaf. The tree seals the cut which leaves behind a leaf scar.
Most broad-leaved trees in and around Nova Scotia lose their leaves in the fall. However the leaves of some species such as oak and beech may stay on until growth begins in the spring. Also you may wonder why leaves stay on a broken branch sometimes. This is because the process needed for leaf drop can no longer occur, thus leaves hang on. Evergreens such as white pine also have needles that are two years old that turn yellow and fall.
The Effects of Weather on A Tree’s Leaves
Weather can affect color intensity. Temperature, light, and water supply have an influence on the degree and duration of fall color. Low temperatures above freezing will enhance bright reds in maples. Rainy and/or overcast days tend to increase the intensity of fall colors.
Fall Leaf Drop and Tree Health
How and when the leaves change colour can often tell us things about a trees health. Early fall color and leaf drop may be a sign that a tree is under stress and not as healthy as it could be. Also a tree such as a crabapple may drop leaves early which could be a sign of apple scab.
What ever the situation, fall foliage is brilliant and exciting. Enjoy it while it lasts!
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Authored by: Arbor Plant Health Care