Scientists Are Trying to Find Out Why Tree Leaves Change Their Color


The Science Behind the Autumn Tree Palette

Have you ever wondered why the leaves of the trees change their color in autumn? Well, we have. As well as a group of scientists from Chicago area, USA. They are trying to find out what is the actual cause for all those vibrant yellow-orange-red-purplish colors that will warm up our eyes and our hearts in the following weeks. A team from Morton Arboretum, Lisle, IL, wants to know what stays behind this amazing natural phenomenon.

It Is Much More than Simple Beauty

Christy Rollison is a forest ecologist at the Center for Tree Science at the Arboretum. She explains, in front of WTTW, that it is actually really hard to tell when and why a tree will change its green color for another one. Rollison says that what we know so far is that trees change their color as a response to the stress coming from their surroundings. 

When the winter approaches, the trees stop producing chlorophyll that is responsible for the green color of their leaves. Chlorophyll itself requites nitrogen. What trees actually do when their leaves change in color is getting back the nitrogen – vital nutrition for their survival and development.  The yellow and orange colors (carotenoids) we later see are pigments that have always been there. The green has been just "covering" them. As for the red shades (anthocyanins), they serve as a sunscreen that doesn't let the compounds in the leaves to break apart by the sunlight, so that the tree could absorb them.

Questions Unanswered 

What is still unclear is how the trees know when to start this process and why the colors vary - from tree to tree and even from branch to branch. The researchers are still trying to figure it out. It is for sure that the temperature and the sunlight are factors but how exactly they influence the process is still unknown.

A worrisome trend is the earlier falling of the leaves. When the temperatures get colder before its usual time in mid a/late autumn (as it is happening more and more often), the trees start losing their leaves before they have changed in color. That means that the trees have not managed to absorb the so needed nutrition for the production of the next leaves. If it happens once, the tree can deal with it, Rollison says. But if it becomes a regular thing, it would be a problem.

In other words, what Rollison and her team are trying to find out is how the trees will behave when and if the environment around them becomes more stressful. An important question and an even more important answer, having in mind the climate changes we see, and the significance the trees have for our life on Earth…



Ask questions, find answers, and share your thoughts and work on science and nature by taking part in the one of a kind international conference on social sciences "When Science Meets Art" in Vienna, Austria, from 9th to 12th of December 2020. Special attention will be paid to the topic "The Beauty Behind Natural Scenes". For more information:

A few days earlier, from 8th to 11th of December, again in Vienna, another scientific conference will take place - "Green Sciences for Green Life". The event will be focused on the connection between humans and nature. For nature is not something  "around" us - it is something that is part of us. And vice versa. For more information on how to take part in this unique event, as a speaker or a delegate, visit:

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Wednesday, 28 July 2021

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