Why Do Leaves Change Colour in Autumn?

24 Why Do Leaves Change Colour in Autumn? Every year, as the summer days grow shorter, an amazing transformation happens in Canadian forests. As summer changes to autumn, the trees turn colour-changing from summer greens to shades of red, orange, and yellow. It's a truly wonderful sight! From a distance, the forest looks as if it's on fire. When I was a boy, my grandmother used to tell me that a strange little man came in the night with a paint brush to paint the leaves those wonderful colours. And I believed her, for it was a wonderful way of explaining this transformation to a little boy. But as I grew older, my natural curiosity led me to do some research on my own. As always, science had the answer. Trees need food, just like all living organisms. Leaves produce food for the tree. It's just sugar, which is sometimes called glucose. Leaves use sunlight to change water and carbon dioxide into glucose.

The process by which leaves do this is known as photo-synthesis. That's a big word, but it just means “ combining things with light" . A chemical called chlorophyll helps make this happen. Chlorophyll is the reason why leaves are green in the summer. However, Canadian winters are long, cold and dark. There isn't enough sunshine in winter for the leaves to make food. In autumn, as the days shorten, the trees get a signal to slow down. It's time to take a rest. Don't worry, though. They have enough food stored to last all winter. When the leaves stop making food, they no longer need to make chlorophyll. Slowly, the chlorophyll disappears. Remember, this is the chemical that makes leaves green. As the chlorophyll goes away, so does the green colour. We begin to see the other colours that are always there. We could not see them before because green is a strong colour. I still think of my grandmother's explanation some- times. And although I know better now, whenever I look at the gorgeous autumn trees, I can almost see a happy little man with a paint brush.