Fall is here! That means sweaters, pumpkin spice lattes, crisp mornings, spooky decorations, and, inevitably, some kid asking you why the leaves change colours. So, let’s get you prepared!
Why are most leaves green in the first place?
The mitochondria may be the powerhouse of most cells, but the chloroplast is the energy factory of the plant cell. Inside the chloroplast is a green pigment called chlorophyll. During the summer, when there’s lots of light, chlorophyll is abundant, and trees use it to get energy from the sun. Lots of other pigments are present in the leaves, but there’s just so much chlorophyll that those other pigments are masked. Once fall comes along and it’s about to get cold and dark, trees stop producing so much chlorophyll, and all the other pigments in the leaves become visible.
Why do some trees turn yellow and others red?
Different species of trees usually turn different colours. Aspens and birches are known for their beautiful golden yellows. This yellow comes from carotenoids, a pigment also found in egg yolks, corn and bananas. Carotenoids are special because they don’t need sunlight to keep being produced, so they can help trees get that last little bit of fall light. Maples, on the other hand, are renowned for their striking reds. Reds are rarer and come from a pigment called anthocyanin, which only develops once summer comes to a close, replacing the disappearing chlorophyll.
Why are some falls more vibrant than others?
Droughts can stress trees out, leading to prematurely browning leaves. Leaves are full of pores and lose a lot of water. This is partly why trees drop their leaves over the winter, so they don’t lose water when the ground is frozen and they are unable to replace what is lost. This also means dry conditions sometimes trigger the same instinct, with trees pulling everything important out of their leaves and allowing them to fall, preserving all that sugar, water, and other good stuff for the next summer. Droughts, forest fires, and hectic weather conditions, such as those seen this year, are becoming more common due to climate change, and can all lead to less vibrant autumns.
Did you know?
Fallen leaves are used by lots of little critters to insulate themselves to survive the winter! If you want to help your local pollinators, consider leaving the leaves on the ground over the winter in at least a part of your yard.
Learn more about fall colours at https://thecanadianencyclopedia.ca/en/article/autumn-colours
Lia Robles Gil is a science communicator who has lived all over Canada, but currently resides in Lunenburg. You can find them on Instagram and Bluesky @liaroblesgil
