Deciduous trees are trees which shed their leaves annually. In North America, especially in the east, this annual leaf drop is first signaled by a color change in the leaves. The color changes in the leaves create a spectacular mosaic of color in the forested regions.
Leaf drop in deciduous trees is a process botanists call abscission. This comes from a Latin term meaning “to cut off”. This process is controlled in trees by two substances, a gas called ethylene and abscisic acid, both released by the tree. The release of these substances is controlled by changes in the length of the day and temperature. As the day length shortens in the autumn and the temperature cools these substances become more active.
Acting in concert with this, another substance called auxin becomes less active. During the spring and summer months the leaf produces auxin, which has the effect of keeping the leaf attached to the trees. The lower temperatures of autumn and shorter days cause the leaf to produce less auxin, loosening the grip the leaf has on the tree. This is accompanied by chlorophyll breaking down. Chlorophyll is the green pigment in the tree leaf which is responsible for a process called photosynthesis, which is responsible for the conversion of sunlight into food for the tree. Other pigments present in the leaf now become visible, giving the leaf its spectacular fall color. In a fairly short period of time, the leaf falls from the tree and the tree goes to sleep for the winter.
Each fall deciduous trees of North American create a spectacular show as the leaves change color in anticipation of winter. The cooler temperatures and shorter days which trigger this change are harbingers of the coming cold of winter. The delicious weather of autumn is an encouragement to go out into the country to drive, picnic, hike, or any other outdoor activity. The good weather isn’t going to last, so get out and enjoy it now!
© 2006 Paul Wonning is the owner of Gardens and Nature.com a web site about gardening, hiking and other nature related topics. Our blog about gardening is located here =>Hoosier Hurricane - Blog about Gardening
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