"Autumn leaves don't fall, they fly. They take their time and wander on this, their only chance to soar," is a beautiful quote by Delia Owen.
Autumn is a breathtaking and sun-dappled season filled with nostalgia and dewy memories. The trees change their leaves, painting the landscape in vibrant hues of gold, red, and orange.
But do you know why tree leaves change colour in the fall? Being green all year round, why do the tree leaves suddenly start changing colours in October or November, preparing for the long winter ahead by shutting down their food-making factories?
The reason for the colour change is tied directly to the tree's need to conserve energy and nutrients. In this article, we'll understand the science behind the change of leaves' colour in fall.
Why Do Leaves Change Colour in the Fall?
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Ever stopped to think about why trees, which stay green pretty much all summer, suddenly switch gears and show off those fiery reds, oranges, and yellows once autumn rolls around?
It's a pretty neat trick that trees use to prepare for the cold months ahead. Let me break it down for you in a way that's easy to follow:
The Green "Paint"
Throughout summer, the leaves are green because they are full of chlorophyll. Chlorophyll is essential because it allows leaves to convert sunlight into food for the tree, a process known as photosynthesis.
Shorter Days and Cooler Weather
When the fall comes, the days become shorter and the nights get longer and cooler. The tree experiences these changes and knows that winter is coming. It realises that there will not be enough sunlight or water to sustain the food factory.
Shutting Down the Factory
The tree begins to shut down the food factory for the winter. It stops making new chlorophyll, and the old chlorophyll that is already in the leaves begins to break down.
Revealing the Hidden Colours
As the green chlorophyll disappears, other colours in the leaves start to appear:
- Yellows and Oranges: These colours are caused by pigments called carotenoids. They're always in the leaf, but the bright green chlorophyll is so strong that it hides them completely during the summer.
Creating New Colours
Some leaves create brand new colours like:
- Reds and Purples: These are caused by pigments called anthocyanins. As autumn arrives, the tree begins producing these pigments to shield the leaf while it withdraws the last of its essential nutrients—such as sugars—into the branches and trunk for winter storage.
Dropping the Leaves
After the tree has gathered as much as it can from the leaves, it closes off the connection at the stem. This makes the leaf dry up and eventually drop to the ground.
Shedding leaves is essentially the tree's way of preparing for the cold months ahead, helping it conserve water and energy until spring returns.
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