I have been driving through Southwestern Ontario and Michigan the past few weeks and once again, I marvel at the beauty of our changing landscape. Cold temperatures and snow will soon be here. For now, we are eyewitnesses to an amazing work of God, where we experience the transformation of the green leaves of summer to the brilliant colours of autumn.
Did you ever wonder how and why a leaf changes colour in the fall? Why a maple leaf turns bright red? Where do the yellows and oranges come from? To answer those questions, we need to understand the purpose and functions of leaves.
Leaves are nature’s food factories. Plants take water from the ground through their roots. They take a gas called carbon dioxide from the air. Plants use sunlight to turn water and carbon dioxide into glucose, which is a type of sugar. Plants use glucose as food for energy and as a building block for growing. The way plants turn water and carbon dioxide into sugar is called photosynthesis, which means ‘putting together with light’. A chemical called chlorophyll helps make photosynthesis happen. Chlorophyll is what gives plants their green colour.
As summer ends and autumn comes, the days get shorter and shorter. This is how trees “know” to begin getting ready for winter.
Weather plays a big role in the onset and length of the fall colour show. Drought can cause leaves to turn brown and drop off early. Cloudy days can slow the creation of the red pigment. Researchers believe shorter days, cooler nights, and lots of sun are the factors needed to begin the annual colour change.
With the cooler conditions, there is not enough light or water for photosynthesis. The trees will rest, and live off the food they stored during the summer. They begin to shut down their food-making factories. The green chlorophyll disappears from the leaves. As the bright green fades away, we begin to see yellow and orange colours.
The yellow colour is right under the green leaves and as chlorophyll breaks down in the aging leaves, the yellow colour appears. Small amounts of these colours have been in the leaves all along. We just can’t see them in the summer, because they are covered up by the green chlorophyll