Green leaves are made mostly of chlorophyll. Chlorophyll gives trees the ability to use sunlight, water, and air to make glucose. Glucose is what gives plants the energy they need to live. During the growing season, trees have enough sunlight and water to continue making chlorophyll, so their leaves stay green.
Chlorophyll absorbs light in the red and blue end of the spectrum, and reflects light in the green part of the spectrum. That is why we see green leaves. Most trees make enough chlorophyll during the summer to cover the red and blue pigments that absorb those wavelengths. When chlorophyll production slows down during the fall, the hidden pigments that absorbed red and blue light become visible again. Those pigments reflect the light in different ways, creating the Colors we see in fall.
Why do leaves turn red and yellow?
Carotenoids create the yellow and orange Colors. These were always present in the leaves under the green. Carotenoids allow some plants to capture light when there is little chlorophyll. This creates the yellow Colors of daffodils and corn. In fall, when chlorophyll decreases, the Carotenoids take over and cause the yellow and orange Colors we see in maple trees, birch, aspen, etc.
Anthocyanins create reds and purples
Anthocyanins create the reds and purples. These are created when the tree makes them after chlorophyll has broken down. Anthocyanins may be protecting the leaves from burning when exposed to too much light. We see this especially in oak, maple, sumac and dogwood.
What makes fall foliage brilliant?
Weather makes a difference in how well we see fall Colors. A wet spring followed by a hot summer means that leaves are likely to develop well and provide good color. A string of Sunny Days and cool nights around the first week of october usually provides great color. On the other hand:
- A frost kills leaves prematurely.
- Drought stresses trees, killing their leaves early.
- Too much rain close to halloween may dilute the color.
When do leaves drop from trees?
As the tree stops using chlorophyll, it closes off circulation to the leaves by forming an abscission layer. This causes the leaves to dry out slowly and eventually fall off. This way, the tree can save energy by no longer circulating water through dead leaves. The dried-out leaves then fall away, ending their year-long cycle.
Why does nature make such beautiful color displays?
Fall color displays are a natural result of deciduous trees trying to survive each year. By stopping growth and recycling plant material every year, deciduous trees are able to store more energy reserves to carry them through colder periods. While beautiful to us, fall color is simply a sign that deciduous trees are preparing for their own version of hibernation.
Q & a
How long does fall color last?
Peak fall color usually lasts about 1–2 weeks although it can vary. If leaves start falling soon after they reach peak color, it shortens the viewing window.
Do all trees go through color changes like deciduous trees?
Only deciduous trees go through changes of color. Conifers and evergreen trees retain their leaves year round and do not go through similar color changes. Many deciduous trees do not go through vibrant red or yellow displays either and often turn brown before they fall off.
Will i be able to predict when my leaves will change color?
It is difficult to predict exactly when your leaves will change color since it depends on various factors such as day length, temperature and precipitation levels. General rule-of-thumb is that areas further north or at higher elevations will start displaying Colors sooner.
Are there any climate effects on fall color?
Research suggests that global warming patterns are changing where and when fall Colors occur. Longer springs combined with longer summers mean that trees may stop producing chlorophyll later than usual. Also, warmer autumns combined with increased instances of early frosts will limit the types of trees that can produce vibrant Colors. Droughts and early frosts will also affect color displays by stressing trees and causing them to drop their leaves before they can Display all possible Colors.
What are abscission layers?
An abscission layer is a specialized area of tissue that separates an old leaf from a young leaf or twig on a deciduous tree. After an abscission layer has developed, it slowly cuts off flow of water through the petiole until the leaf falls off the tree. This process allows the tree to cut itself loose from dying leaves, saving water and reducing transpiration losses. It is very similar to how animals heal wounds. An animal will form a scab to seal off the damaged area. Similarly, a tree forms an abscission layer to seal off the damaged area (the petiole). Abscission layers are very important to allow deciduous trees to survive each year. Without them, trees would lose enormous amounts of water through transpiration alone. Trees would have difficulty storing energy reserves for cold periods if they did not recycle plant materials every year. Abscission layers play a crucial role in helping deciduous trees grow successfully each year.
I hope you learned a lot about why leaves change color! Now you know that it’s not magic—just science! Next time you look at a tree with brightly colored leaves, think about how hard that tree worked all year just for us to enjoy this beautiful sight. Enjoy your walks through nature this fall season!
References:
Https://www.youtube.com/watch?v=hx8ljyp6cgu
www.nature.org/en/get-involved/how-to-help/plant/species/why-do-leaves-change-color-fall/
www.purdue.edu/newsroom/releases/2017/q3/facts-about-autumn-foliage.html
Sources
- The Science of Fall Colors — U.S. Forest Service
- What Causes Leaves to Change Color in the Fall? — Scientific American
- The science of fall colour depends on good weather, and there’s never enough of it — Nature
- Why is autumn foliage so vibrant? The answer lies in chemistry — Phys.org
- Explaining the Science Behind Autumn’s Colors — University of Wyoming
- Autumn leaf color — Wikipedia
