Why do leaves change color in the fall?

The information on this page is based on a radio feature about the autumn colors on the Markagunt plateau in the Cedar City Ranger district.

If you'd like to hear the original broadcast visit the KNPR web site and go to the local features section. There you'll be able to listen to the story with RealAudio.

On these pages we'll try to expand on the original feature with information that wasn't presented in the broadcast. In addition to the transcript text you'll find thumbnails of images that correspond to the information being given. If you click on the thumbnail a separate page will open with images that correspond to the text. You'll also find the information that didn't make it into the original broadcast. Teachers and parents will find useful information and activities for elementary school children by going to the Teachers page.

Fall colors on the Markagunt Plateau

green frosts into gold
then burns red and drops away
leaving a bone sky

This haiku by Will Batts inspired by the beauty of the Fall colors captures both the magic of the transformation as well as its most common misconception. Since we were children we’ve believed that it was Jack Frost that caused the trees to change colors. But Phil Eisenhauer with the US Forest Service knows that the process is initiated by a completely different source.

Phil Eisenhauer, Forester, US Forest Service… "Well that can cause the aspens to change color but most of the time the colors begin to change due to the decrease in the photoperiod of the day. As fall approaches the day lengths shorten and all the deciduous trees and conifers too know that as the day lengths shorten fall and winter is approaching so they begin to go into dormancy. So the colors are changing due more to the photo periods. Although, frost can accelerate that, but even here in late September we're over 10,000 ft., and we still have not had a frost here. And as you can see the Aspen are well on their way to turning orange and eventually dropping off."
Link to when leaves changeClick thumbnail for images and additional text

For most of us that’s the real mystery. Not when the leaves change colors, but why the leaves change colors?

Phil Eisenhauer, Forester, US Forest Service… "Well the Aspen leaves in the summer are green. That's because there dominated by chlorophyll until the fall. As the dormancy approaches the chlorophyll leaves the leaf and it leaves the carotenoids, which causes the orange or yellow color. So in the fall the Aspens change color by the chlorophyll leaving the leaf and the carotenoids dominating the leaf color until they eventually fall off to frost or high wind."
Link to why leaves changeClick thumbnail for images and additional text

On the surface that seems like a foreign process to most of us, but in reality we see this take place on a regular basis.

The chemicals that are responsible for the colors in the forest can be found right in your local grocery store. In the herbs and leafy vegetables you find green chlorophyll. The carotenoids are what makes the carrots orange and bananas yellow and anthocyanin is what produces the red in cranberries and apples. And although you don’t normally think about it you see the actual process take place all the time. Green bananas don’t turn yellow. Once the banana is picked it stops producing chlorophyll, and the chlorophyll that is already in the banana starts to break down. As it does the yellow carotenoids that have been there all along eventually show through. The reds are a different story. As the leaf ceases the production of chlorophyll sugar is trapped in the leaf. With the right combination of bright sunlight during the days and cool, but not freezing nights, the glucose is turned into anthocyanin, which turns the leaves varying shades of red. As a result over the course of the fall season the leaves will change from green to different shades of yellow and orange, finally ending up with a wide spectrum of red highlights.

Link to how leaves changeClick thumbnail for images and additional text

So now that you know when and why the leaves change colors the next obvious question is where? Well, I’m glad you asked.

My best recommendation is for you to take a drive up into the Dixie National Forest in southwest Utah. Particularly the area above Cedar City known as the Markagunt Plateau. And if you’ll stop in the US Forest Service office in Cedar City you’ll be able to get maps of the area and some suggested trails to hike.

Once you’re in the forest you’ll find plenty of opportunities to see the fall colors in all their majesty. Because this area is a series of dense forests interspersed with long rolling meadows here you actually can see the forest for the trees. But I’d like to send you to one place in particular.

Phil Eisenhauer, Forester, US Forest Service… Yeah this is a great spot to come to the district to see an excellent overview of the Aspen turning colors here in late September. And the way it contrasts with the conifer forest and the limestone cliffs in the background is really one of the best views here on the Cedar City Ranger District

The Sidney Overlook is several hundred feet above the forest below. And everywhere you look there’s color. Even the anthracite rock outcropping that you’re standing on has every conceivable color of lichen on it. And although it’s not necessary for you to come here to experience the fall colors this place is so inspiring that it may move you to write a haiku of your own.

Link to where leaves changeClick thumbnail for images and additional text

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