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Red in the Fall
November 06, 2019 by Haya Aldoori

It’s hard to talk about the season Fall without talking about the changing of the leaves. When things start to cool down, deciduous trees start to break down the green chlorophyll in their leaves and redistribute the nutrients contained there to their trunk and roots. This will keep them going throughout the winter, where so many of their necessary resources are limited. Once the chlorophyll breaks down, the yellow (xanthophyll) and orange (carotene) pigments, which were there all along, are revealed.

Now with the colour red, things are a bit different. Rather than being revealed when the chlorophyll breaks down, like the other colours, the red (anthocyanin) pigment is actively produced from built up sugars. We can see that this is the case from the reds of trees like sugar maples, and sumac, which generally produce more sugars than other trees!

Photo by Andrew Yee

This leads us to wonder: why would a tree that is working on storing energy for the winter use its precious energy to turn the leaves red before dropping them? There are many different widely debated theories. One of the two most popular theories is that the red leaves are a form of “sunscreen” for the tree. The red helps absorb the sunlight that would otherwise damage the leaves during that time of year. The second popular theory is that the red leaves work like the wings of the monarch butterfly, warning unwanted/harmful insects about bad-tasting defensive poisons or chemicals.

So it turns out that the answer to this question is that there is no clear-cut answer. That doesn’t mean that we can’t enjoy the beautiful red, orange, and yellow, colour display during the season of change!

Keep an eye out for red leaves on the High Park trees during your next Fall visit!

FUN FACT: The red (anthocyanin) pigment is also what gives apples their red colour and grapes their purple-red colour.

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