Fall Foliage: Why Do Autumn Leaves Change Color

Taken while on a walk at Kilarney Lake, Fredericton.

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Why do autumn leaves change color? What type of trees—and weather—produce the most vivid fall foliage? Read on . . .

Not all leaves turn vivid colors in the fall. Only a few of our many species of deciduous trees—notably maple, aspen, oak, and gum—produce stellar performances for our annual autumn spectacular in North America.

Several factors contribute to fall color (temperature, precipitation, soil moisture), but the main agent is light, or actually the lack of it. The amount of daylight relates to the timing of the autumnal equinox. See when fall begins.

As the autumn days grow shorter, the reduced light triggers chemical changes in deciduous plants causing a corky wall to form between the twig and the leaf stalk. See how day length is changing in your area!

This "abscission layer" eventually causes the leaf to drop off in the breeze. As the corky cells multiply, they seal off the vessels that supply the leaf with nutrients and water and also block the exit vessels, trapping simple sugars in the leaves. The combination of reduced light, lack of nutrients, and no water add up to the death of the pigment chlorophyll, the "green" in leaves.

Once the green is gone, two other pigments show their bright faces. These pigments, carotene (yellow) and anthocyanin (red), exist in the leaf all summer but are masked by the chlorophyll. (The browns in autumn leaves are the result of tannin, a chemical that exists in many leaves, especially oaks.)

Sugar trapped in autumn leaves by the abscission layer is largely responsible for the vivid color. Some additional anthocyanins are also manufactured by sunlight acting on the trapped sugar. This is why the foliage is so sparkling after several bright fall days and more pastel during rainy spells. In general, a set growing season followed by a dry autumn filled with sunny days and cool, frostless nights produces the most vibrant palette of fall colors.

Of course, if freezing temperatures and a hard frost hits, it can kill the process within the leaf an dlead to poor fall color. Also, drought conditions during late summer and early fall can trigger an early “shutdown” of trees as they prepare for winter, causing leaves to fall early from trees without reaching their full color potential.

Does your area experience fall foliage? Some level of autumn foliage changes in many regions on North America. However, it is the northern tier of states, especially New England, that hold the jackpot for leaf peepers. A combination of the right climate and light conditions and an abundance of the tree varieties that hoard colorful pigments come together there.

While tradition has it that Columbus Day weekend is when the color peaks in New England, the mythical maximum occurs in northern Maine in mid- to late September and "travels" south, reaching the Connecticut shore by late October.

How do you determine the best location in your area for vibrant fall foliage?  Check out this Foliage Leaf Peepr app which reports on the best and brightest colors in the United States.

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Comments

The leaves here in Western,NY

By Kay Newman

The leaves here in Western,NY are beatiful this year.The best I have ever seen in 30+ years I have lived here.

The true fall will not come

By Jim Kirock

The true fall will not come until after the election, and that will be whoever lost it--has "fallen".

Our foliage typically doesent

By Denise Ginther

Our foliage typically doesent peak until October. Im getting very impatient for the arrival of autumn. September is still summer and you wont have that true fall feel until October, when the days grow very short, gets chilly at night, colorful light shows, my yard is covered in white by the first frost and that cool crisp air in the daytime. Ahhh it makes one dream! but its only 22 more days, I think i can make it. Will Virginia see a good light show too? its been too hot this past summer! im looking foward into seeing leaves fall through the chilly breezes

Will our dry summer effect

By Chwayn

Will our dry summer effect the colors of the autumn leaves?

In general, dry weather

By Almanac Staff

In general, dry weather produces the most-vibrant color. So, that's one positive effect of no rain!

Plus it makes the leaves

By Mary beth

Plus it makes the leaves crunch!!

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