It's that time of the year again.  The air is crisp and clear, corn stalks rustle in the wind and bright orange pumpkins grace the fields.  White-tailed bucks are sporting newly polished antlers and the first fallen leaves are crackling underfoot.  It's hard to miss the wondrous display of golds and reds, yellows and oranges splashed across the Pennsylvania countryside.

Over the centuries, many explanations have been offered as to why leaves change color each fall.  According to a native American Indian legend, celestial hunters slew the Great Bear in the autumn, and his blood dripping on the forests, changed many leaves to red.  Other trees were turned yellow by the fat that splattered out of the kettle as the hunters cooked the meat.

You may have heard as a child that Jack Frost creates the colors of fall by painting the forests with his brush, but in actuality the change in coloring is the result of chemical processes which take place in the tree as the season changes from summer to winter.

All during the spring and summer, the leaves have served as factories manufacturing most of the foods necessary for the tree's growth.  This food-making process takes place in the leaf in cells containing the pigment chlorophyll, which gives the leaf its green color.  Chlorophyll absorbs energy from sunlight, transforming carbon dioxide and water to carbohydrates, such as sugars and starch.  Along with the green pigment, leaves also contain yellow or orange carotenoids, the same substance which gives the carrot its familiar orange color.

As the days grow shorter and the nights longer, a chemical clock inside the trees turns on, releasing a hormone that stops the food-making process.   As autumn progresses, chlorophyll breaks down, revealing the color of the leaves beneath their mask of green.  The process is somewhat like a child scratching away the black crayon covering of a brightly colored drawing to expose the underlying colors.

The leaf's chemical makeup has a lot to do with what color is revealed.  Some experts believe that the amount of iron, magnesium, phosphorous, or sodium in a tree, and the acidity of the chemicals in the leaves, determines whether the leaves turn red or purplish, like dogwood and sumac, or fiery orange, like the sugar maple, or yellow, like aspen, birch, and hickory.  Warm sunny days followed by nights below 45 degrees Fahrenheit may intensify the brilliant reds of autumn.

Sugar is made in the leaves during the daytime as usual, but cool nights prevent it from moving from the leaves.  Trapped, the sugars form the red pigment anthocyanin, which in fall, is present in the scarlet leaves of such trees as red oak, red maple, sweetgum, and sassafras.

The degree of color may also vary from tree to tree.  Some trees directly exposed to the sun turn red, while those on the shady side of the same tree may turn yellow.  Still others may just fade from green to brown before they fall.

Autumn is as much a time of reflection as it is a time of change- a stop on the continuous cycle of life.  After the leaves turn color and die, they fall to the ground and create a carpet of mulch.   Animals, insects, and fungi help decompose the leaves, releasing their nutrients to growing plants and trees and adding organic material to the soil.  The minerals once taken up by the tree return to the soil, completing a cycle that begins each spring.

Discover Autumn Home | How Do Leaves Change Color? | Take a Fall Hike
 Autumn Driving Tours