I’ve had several questions lately about the dry summer’s effect on fall leaf color. Certainly soil moisture has some effect on leaf color and extreme dry soil conditions have caused some early leaf drop this fall. However, there are other factors which determine a tree's display of fall colors.
First, a severe summer drought will usually delay the onset of fall colors by several weeks, and we certainly have seen that this year. Additionally, if the fall is warmer than normal, you can expect a less intense show of colors. Although conditions are pointing towards a less than spectacular fall show of color, the recent rains may help improve those possibilities.
For example, the brilliant reds we see in species such as red or sugar maple and white oak are caused by the production of pigments known as anthocyanins. These pigments develop in response to bright light and excess plant sugars in the leaves. That is why bright sunny days and cool nights bring out the best red colors in certain types of trees. You may have noticed some maples responding to those weather conditions last week.
Tree species are also different in their ability to produce a variety of colors. Yellow leaf color is typical in tree species such as birch, elm, hackberry, hickory, sycamore and willow. Carotenoid pigments, present in the leaves throughout the year, are responsible for the yellow color in leaves. As chlorophyll production decreases in the fall, the leaves change from green to yellow. Chlorophyll production decreases primarily because of shorter days and longer nights in the fall.
While day length, soil moisture and air temperature do affect a tree’s fall colors, genetics also affect the timing, types of colors and the intensity. If you are considering the addition of a tree in your landscape you may want to consider its fall color as well as other attributes when shopping at your local tree nursery.
Unfortunately, the display of fall color doesn’t last forever, and this year it may be a short display. As the light intensity decreases in the fall, a layer of cells at the base of the leaf’s stem or petiole becomes enlarged and thickened. When this process is complete the leaf falls to the ground.
As we rapidly approach the average first frost date in central Illinois, October 14, a heavy frost is an increasing possibility and can speed up leaf drop. Heavy rains and windy days can also speed the process of leaf drop.
Whenever those leaves drop in your yard this fall, you may want to take advantage of the leaves’ nutrient content. For example, in a natural forest the stored energy in the leaf decomposes and provides nutrients for future growing seasons. In your yard, a mulching mower can be used to speed up the process of decomposition, allowing the leaf’s stored energy to be used by your lawn and trees.
No matter how spectacular, enjoy nature’s display of colors this fall by taking a walk in your woods or at your local park. If you have questions about trees or forest management call the University of Illinois Coles County Extension Unit office at 217-345-7034.
For more information on University of Illinois Extension programming in Coles, Cumberland, Douglas, Moultrie and Shelby counties, visit our website at http://web.extension.illinois.edu/ccdms/index.html or call us at 217-345-7034.