Autumn Colors - How Leaves Change Color 

The "Indian summer" days of autumn, when the days are 

clear and sunny and the nights cool and crisp, provide an 

almost irresistible lure to those who enjoy the outdoors. This 

type of weather is also the most favorable for a spectacular 

show of autumn colors, making this season of the year still 

more delightful. 

Scientist don't yet fully understand all of the complicated 

actions-and even more complicated interactions-involving 

pigments, sunlight, moisture, chemicals, hormones, 

temperatures, length of daylight, site, genetic traits, and so on 

that make for a perfect autumn color display. As research 

probes deeper and deeper into the basics of life, and more 

and more answers will be forthcoming. 

But full understanding is not necessary to the enjoyment of 

the lovely days of autumn in forest, city, and countryside. 

Americans are blessed with many opportunities to see this 

yearly splendor. 

The roads, trails, lakes, streams, and recreation areas of the 

National Forests are available for your pleasure. 

The forest roadsides of autumn attract by far the greatest 

number of sightseers. But trails, often winding deep into 

forest solitude, offer special closeness to nature for hikers, 

backpackers, and horseback riders. 

Streams and lakes add special enchantment in the 

fall for fishermen and boaters, and colorful 

backgrounds for photographers. The surfaces of 

quiet forest lakes double the colorful mantle of their 

surrounding hills. 

Hunting in eastern forests often coincides with the 

peak of the color season, and the pleasure of just 

being out-of-doors in the golden days rivals the 

thrill of the hunt. 

And even along city streets the colors blaze forth, 

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Autumn Colors - How Leaves Change Color 

delighting residents of towns fortunate or farsighted 

enough to have retained some trees. 

"Sweet and smiling are thy ways, 

Beauteous, gold Autumn days." 

Will Carleton 

Each acres of 191 million on National Forest 

lands belongs to the people of the United States. 

Together, these acres represent a great treasury 

of natural resources. 

National Forests provide a variety of uses, 

products, and pleasures for people. They were 

originally established to protect watersheds, and 

they still do. But in addition, these forest lands 

are now rich in timber, wildlife, forage, and 

recreation opportunities. 

These and other uses are directed by the Forest 

Service, U.S. Department of Agriculture. 

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Autumn Colors - How Leaves Change Color 

Specialists in many fields coordinate and balance these uses so that one doesn't interfere with another, 

and so that all Americans will receive maximum benefits throughout the years. 

In addition, Forest Service research strives to find new and better ways of managing and using forests and 

their products. Also, through cooperation with State and with private owners of forestland, and Forest 

Service encourages the practice of good forestry throughout the Nation. 

Click on HERE or on image for fuller rendition of illustration below. (It will be worth the wait — 

34 seconds on 28.8 kbs) 

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Autumn Colors - How Leaves Change Color 

A GREEN LEAF IS GREEN because of the presence of a group of pigments known as chlorophylls. 

When they are abundant in the leafs cells, as they are during the growing season, the chlorophylls' green 

color dominates and masks out the colors of any other pigments that may be present in the leaf. Thus the 

leaves of summer are characteristically green. 

The chlorophylls have a vital function: they capture some of the sun's energy and utilize it in the 

manufacture of the plant's food - simple sugars which are produced from water and carbon dioxide. These 

sugars are the basis of the plant's nourishment-the sole source of the carbohydrates needed for growth and 

development. 

In their food-manufacturing process, the chlorophylls themselves break down and thus are being 

continually "used up." During the growing season, however, the plant replenishes the chlorophyll so that 

the supply remain high and the leaves stay green. 

But as autumn approaches, certain influences both inside and outside the plant cause the chlorophylls to 

be replaced at a slower rate than they are being used up. During this period, with the total supply of 

chlorophylls gradually dwindling, the "masking" effect slowly fades away. Then other pigments that have 

been present (along with the chlorophylls) in the cells all during the leaf's life begin to show through. 

These are carotenoids they give us colorations of yellow, brown, orange, and the many hues in between. 

The reds, the purples, and their blended combinations that decorate autumn foliage come from another 

group of pigments in the cells called anthocyanins. These pigments are not present in the leaf throughout 

the growing season as are the carotenoids. They develop in late summer in the sap of the cells of the leaf, 

and this development is the result of complex interactions of many influences - both inside-and outside 

the plant. Their formation depends on the breakdown of sugars in the presence of bright light as the level 

of a certain chemical (phosphate) in the leaf is reduced. 

During the summer growing season, phosphate is at a high level. It has a vital role in the breakdown of 

the sugars manufactured by chlorophyll. 

But in the fall, phosphate, along with the other chemicals and nutrients, moves out of the leaf into the 

stem of the plant. When this happens, the sugar-breakdown process changes, leading to the production of 

anthocyanin pigments. The brighter the light during this period, the greater the production of 

anthocyanins and the more brilliant the resulting color display that we see. When the days of autumn are 

bright and cool, and the nights are chilly but not freezing, the brightest colorations usually develop. 

Anthocyanins temporarily color the edges of some of the very young leaves as they unfold from the buds 

in early spring. They also give the familiar color to such common fruits as cranberries, red apples, 

blueberries, cherries, strawberries, and plums. 

In our autumn forests they show up vividly in the maples, oaks, sourwood, sweetgum, dogwood, tupelo, 

black gum and persimmon. These same pigments often combine with the carotenoids' colors to give us 

the deeper orange, fiery reds, and bronzes typical of many hardwood species. 

The carotenoids occur, along with the chlorophyll pigments, in tiny structures - called plastids - within 

the cells of leaves. Sometimes they are in such abundance in the leaf that they give a plant a yellow-green 

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Autumn Colors - How Leaves Change Color 

color, even during the summer. But usually we become aware of their presence for the first time in 

autumn, when the leaves begin to lose their chlorophyll. 

Carotenoids are common in many living things, giving characteristic color to carrots, corn canaries, and 

daffodils, as well as egg yolks, rutabagas, buttercups, and bananas. 

Their brilliant yellows and oranges tint the leaves of such hardwood species as hickories, ash, maple 

yellow-poplar, aspen, birch, black cherry, sycamore, cottonwood, sassafras, and alder. 

In late summer the veins that carry fluids into and out of the leaf are 

gradually closed off as a layer of special cork cells forms at the base of each 

leaf. As this cork layer develops, water and mineral intake into the leaf is 

reduced, slowly at first, and then more rapidly. It is during this time that the 

chlorophyll begins to decrease. 

Often the veins will still be green after the tissues between them have almost 

completely change color. 

Individual leaves, even of the same species, turn color in many different ways. 

These maple leaves show both a complete change across an entire leaf (top), and 

partial change (bottom), with blocks of tissues turned brilliant red while adjacent 

areas still remain green. 

Or, each leaf may be two or more colors at the same time. The yellow from the 

carotenoid pigments blends with the red from the anthocyanins. 

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Autumn Colors - How Leaves Change Color 

When conditions of temperature, moisture, and the amount and strength 

of sunlight are all in the right combinations, we will be treated to 

spectacular fall colorations. 

The entire trees blaze forth in vivid hues, along city streets as well as 

across the open countryside. 

Occasionally clusters of leaves, or leaves 

of entire branches, will be in full autumn 

dress ahead of others on the same tree. 

Certain species almost always lead off the 

autumn color display. On a yellowpoplar, a single leaf turns to clear yellow 

in late summer, hinting of the color 

season still weeks away. 

USDA Forest Service, Southern Region — Recreation Guide R8-RG-34, 

Slightly Revised: July 1999 

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