Only occasional patches of color, not fully developed. The predominant color is still green
Some clearly defined color changes can be seen, but they are not yet at their brightest. About three fourths of the foliage is still in green
As much as half the vegetation has changed color. In the earlier changing trees, the colors are bright. Late-changing trees remain primarily green
Most trees are in full color. Deep reds and bright yellows prevail. Very little green vegetation remains. A few trees have yet to reach peak, but are showing very bright, well developed colors. These trees will peak very quickly
Brightness and depth of color have begun to fade. Leaf drop has begun and will accelerate from this point
Midwestern states and those in southerly climes have Sassafras, Sumac, Virginia Creeper, Dogwood, Blackgum and a few others. While these will generally make the change earlier than hardwoods, they may not turn as early as in northern states because of the latitude.
The mountain states of Colorado, Utah, Wyoming, Idaho, Montana, California, and to an extent Arizona and New Mexico, have Aspen and Birch, which produce bright yellows, particularly at higher elevations. In these states there can often be simultaneous areas from low to peak, depending on elevation.
Throughout September and October, one strong rain or snowstorm in any of the northern tier or mountain states can bring a sudden end to the foliage season.
Color change occurs when a tree enters dormancy, which is caused by photosynthesis as days shorten. Food in the upper portion of the tree travels to the roots, leaving visible pigment, which was present during the summer but covered by chlorophyll.
Drought tolerance plays a role. Hardwoods such as maples (red and orange), hickory (golden yellow) and Oak (bronze and rust) have greater tolerance and turn later. Birch, Dogwood, Poplar and other softer woods are fewer droughts tolerant and turn earlier
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