Autumn leaves

Published 12:36 pm Wednesday, November 14, 2018

I have had many people this autumn remark on how lovely the colors of the leaves on the broadleaf trees are this year. I can’t say that I have noticed anything particularly more or less beautiful than last year’s colors or the year before. Although some have specifically made note that there seemed to be much more bright red in the mix this year and to a keener eye then I, they may have. Without diving too deep into the science behind the color of leaves I will explain.

Although I know autumn’s spectacular show of color is purely the work of chemical process, I like to think that Mother Nature holds the lock and key to the entire works. A comforting signal from her that the hard work in our gardens and extreme temperatures of summer have past and a time of rest and rejuvenation is soon to arrive. The trees have also been working hard all summer. While we have enjoyed the cooling shade from their canopy of bright green leaves they have been working hard photosynthesizing sunlight which converts water and carbon dioxide into sugar, which in turn feeds them and provides oxygen in the air that we breathe. All of these hardworking trees need a break also.

In spring and summer the leaves of trees are mostly green, this is due to the photosynthetic green pigment Chlorophyll. During photosynthesis chlorophyll is responsible in transforming carbon dioxide and water into carbohydrates and oxygen. The carbohydrates feed the tree and the oxygen is released into the air that we breathe. The entire process is fascinating although very involved, and this is a rudimentary example of it. However, it does explain why most tree leaves are green all summer long.

Autumn’s changes in temperature and amount of daylight trigger the tree’s leaves to stop producing chlorophyll and eventually the food making process, as a result the color of the leaves start changing to yellow, orange and browns. This is due to the decreasing amount of chlorophyll (less green color) and the chemical pigment Carotenoid in the leaf. Carotenoids are responsible for the color of carrots, cantaloupe, sweet potatoes, apricots and plums. Unlike chlorophyll the level of carotenoids in a leaf is not affected by the weather so it remains constant through the year.

In addition to carotenoids some trees will also produce the pigment Anthocyanin which is responsible for the beautiful reds and purple colors. Research has found that anthocyanin is produced in increased amounts when a number of warm sunny days are followed by unusually cold (not freezing) nights one after the other. These cold nights hinder the flow of nutrients through the leaf veins into the branches then into the trunk of the tree. It is believed that anthocyanin helps the tree to recover nutrients from the leaves when this happens.

So natural science and the weather does indeed play a role in the amount of bright red coloration in the tree leaves each autumn.

Some other indicators for a fall bursting with beautiful bright autumn colors are; a temperate summer (not too hot or dry) and plenty of warm sunny days followed by cool evenings at the beginning of fall.

Dawn Conrad can be reached at or