Autumn is a beautiful time of year in Illinois. The red, purple, orange, yellow, brown and bronze shades of the leaves reflect the great diversity of more than 250 tree species in our state. Our fall color season lasts for several weeks, normally starting in northern Illinois counties by the third or fourth week in September. Leaf color begins to change during the second week in October in central Illinois and by the last two weeks of October in the southern part of the state. The peak of fall color in Illinois normally occurs by mid-October in northern and central Illinois and by late October or early November in the southern third of the state.
The changing colors of the leaves on deciduous trees, those that lose their leaves in autumn and grow new ones in spring, make fall a beautiful season in Illinois , bringing new wonders each day. Did you ever think about why leaves change color?
Leaves change color in autumn as the hours of daylight decline and the angle of the sun gets lower in the sky. The pigment chlorophyll is present in huge amounts in leaves during the spring and summer months. Chlorophyll appears to be green because it reflects the green part of sunlight. If you've seen a rainbow, you know that sunlight is actually a combination of colors: red; orange, yellow, green; blue; indigo; violet. Chlorophyll absorbs energy from the other colors in sunlight and uses it to transform carbon dioxide and water into sugars that are used as food by the tree.
As the duration of daylight and the angle of the sun decrease in late summer and fall, chlorophyll production is reduced, and it begins to disappear. Carotenoids , pigments that have been present in the leaves throughout the growing season but were not seen due to the vast amount of chlorophyll, begin to appear as yellow and orange colors in the leaves. The yellow carotenoid is called xanthophyll, and the orange pigment is carotene.
Anthocyanins form in the leaves of some tree species in the fall and produce red and purple shades. These pigments develop from the sugars that are trapped in leaves. On warm, sunny fall days, the leaves produce sugars. At night, as the air cools, plant transport slows, and the sugars are unable to be transported from the leaves. The brighter the fall sunlight, the more sugars are produced, and the more brilliant the colors. Anthocyanins react to soil chemistry, affecting the color displayed in the leaf. In acid soil, the leaf may be red in the fall. If the same type of tree was growing on alkaline soil, though, its leaves might be purple in the fall.
Weather is the most important factor in how colorful leaves will be in the fall. Ample rainfall in the summer leads to healthy trees with many pigments and sugars in the leaves. These leaves will provide beautiful fall colors. Bright, sunny skies in late summer and early fall lead to more red, yellow, bronze and orange shades on leaves. Numerous cloudy days during this time period may cause the production of more gold and yellow tints. In drought conditions, leaves may drop from the trees without much color change at all. If the temperatures turn too cold, leaves can die before they change colors. However, in some years fall color is abundant even though weather conditions are not ideal.
Tree species that produce deep red, bronze and orange shades on autumn leaves include the red oak, sugar maple, flowering dogwood, persimmon, sweet gum, sumac and tupelo gum. Trees with bright orange and yellow tints on leaves in the fall include sugar maple, cottonwood, wild black cherry, ash, birch, hickory, sassafras and tulip tree. Deep purple and red shades are the fall colors of tree-climbing vines including Virginia creeper and poison ivy.