Why Do Leaves Change Color? with a VideoDonna L. Long

Post revised 20 September 2019

The leaves are really beginning to change here in Philadelphia.

The leaves of most trees are green during the growing seasons of spring and summer. During this season, they change from light to dark green. The green color comes from a substance called chlorophyll. Chlorophyll absorbs light energy for use in photosynthesis, a food-making process that occurs in green plants.

The shorter days and cooler nights of fall signal the end of the growing season. Shorter days mean less sunlight is available and trees shut down their food-making processes. The chlorophyll breaks down and the green pigment is no longer seen. But before they die, the pigments that were hidden by the abundance of green, show themselves.

The sequence of color

Fall leaf color changes begin at the higher altitudes and progress to lower altitudes. This is due to the cooler temperatures of higher latitudes and elevations. Trees begin to change along the Canadian border (above this boundary is conifer or evergreen forests) and progress downward. Leaves change color first in the mountains and move down the mountains into the valleys and coastal areas.

The color changes in a predictable order. It begins with the red maples and progresses to aspens to sugar maples to oaks.

The Best Fall Color Conditions

Leaf color varies depending on temperature and other factors. Lack of enough water from droughts and insect-eating can case poor foliage display. Warmer than normal October nights are also bad for fall color display. During the warm nights, the trees use the sugar produced in their leaves, so not enough sugar is left for a color to develop.

Early Cool Weather Brings Early Fall Colors

The best color displays are developed during sunny fall days and cold, frost-free nights.

If you would like to know when fall foliage colors are at their peak, most Northern and Mid-Atlantic states have hotlines and tourism websites for information.

Brilliant Eye-Popping Colors

The uniform greens give way to the golds, oranges, reds, purples, and bronzes. These pigments are caused by the following substances.

yellow color by the pigment xanthophyll
orange-red tones by the carotene pigments.
red and purple by pigments called anthocyanins

The autumn color depends on which of the pigments is most plentiful. As the chlorophyll and other colorful pigments break down, all leaves become brownish.

Fire against the sky. Photo by Donna L. Long.

Each Species of a Plant has its Characteristic Fall Colors

Red and yellow are the main colors of autumn foliage in the east, and yellow and dark green are the main colors of autumn in the mountains and hills of the West. The dark green colors are from the numerous evergreen (conifer) trees.

In the north, there are more deciduous trees and therefore more trees which change color. In the south are more evergreen species.

In the west, on mountains and hillsides, the bright yellow quaking aspens are vivid against a forest of dark green evergreens, such as spruce and fir trees.

In the east, the predominant colors are the browns of oaks, golds, and yellows of the hickories, sycamores and other species. The reds of red maples and sumacs typify the October displays and draw many foliage watching visitors each year.

Falling Leaves

After it dies the tiny pipelines that carried water and food between the leaf and the rest of the tree become plugged. The cells which held it to the stem dissolve and separate. The dying leaf hangs by a few strands. These strands dry and twist in the wind. When the strands finally break, it falls to the ground.

Once on the ground, then it is broken down by tiny organisms in the soil. These tiny organisms (bacteria and fungi) convert the leaf into simple substances used for food. These substances are also absorbed by plant roots and provide food for new growth.

The endless circle of life continues.

Glowing gold leaves in the Wissahickon Valley Park. Photo by Donna L. Long.

Regions of the World with Colorful Fall Foliage

Only three regions of the world have the deciduous tree cover that supports the spectacular fall foliage color:

Eastern North America
The British Isles and parts of northwestern Europe
Northeastern China and northern Japan

Specific Regions with Fall Foliage

1. most of southern mainland Canada

2. most of eastern part of United States (New England and small areas of the forest further west)

3. Adirondack, Appalachian, Smoky, and the Rocky Mountains

4. Scandinavian, Northern, and Western Europe north of the Alps

5. the Caucasus region near the Black Sea and Eastern Asia, including much of northern and eastern China, as well as Korea and Japan

Specific Places in the World with Autumn Foliage

North America

New England, USA
Maine, USA
Green Mountains, Vermont, USA
Nova Scotia and Quebec, Canada
Cascade Mountains, Pacific Northwest, USA
Catskills, Adirondacks, New York State, USA
Pennsylvania Poconos
Ohio
Great Smoky Mountains, USA
New Mexico (cottonwood, poplar, aspen trees)
Rocky Mountains, Colorado, USA
Lost Maples State Park, Texas, USA

Europe

Bavaria, Germany
Burgundy, Provence, France
Slovenia, Julian Alps, Eurasia
The Dolomites, Italy

This Video Explains How Leaves Change Colors in the Fall

Fall Foliage Reports

“Pennsylvania has a longer and more varied fall foliage season than any other state in the nation — or anywhere in the world.” (dncr.pa.gov)

Other regions of the world have more conifer or evergreens trees that don’t have the leaf color changing of deciduous trees.

These websites have foliage changing information.

The U.S. Nationwide Foliage Forecast – Old Farmer’s Almanac

Canadian Fall Foliage Report

Fall in PA (Pennsylvania Foliage Watch) gives information about each region and provides a weekly foliage report.

PA Department of Natural Resources – DCNR Foliage Reports

Pocono Mountains in PA Fall Foliage Report

New England Foliage Reports

Maine Foliage Report

New York Fall Foliage Report

Virginia Fall Foliage Report

Minnesota Fall Drives

Autumn in the Natural World

Autumn in the Natural World makes complex processes easy to understand, to the wonders of the autumn season. In easy to understand language the essential natural processes of the changing colors of leaves, why trees shed leaves, and how a pond can still freeze and still support life are explained. Learn the key star constellation which signals the end of summer and the growing season. Learn why the moon’s of autumn loom so large in the night sky.

Available in pdf and paperback starting at $5.99

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One comment

Nature in Autumn: An Overview - Donna L. Long says:

December 16 at 7:44 pm

[…] the Northern Hemisphere, tree leaves change color beginning at the Canadian border and moving down the mountains and into valleys and coastal areas. […]