As the nights get longer in August and September, trees sense this and begin an orderly process of leaf drop as protection to survive the freezing temperatures and other harsh winter influences.

As the length of the days shortens, the leaves stop their production of chlorophyll, which provides the green color. Other pigments, mostly yellow, that are present in the leaves then show through. The yellow color is the result of carotene and xanthophyll, and is most prevalent in aspen, birch, hickory, beech, tuliptree (yellow poplar) and willow.

Sugars that are trapped in the leaves form red pigments, the anthocyanins. Some trees with red or scarlet leaves in autumn are red and Korean maple, dogwoods, sweetgum, red oak, black oak, scarlet oak, sumac and sassafras. Some trees will produce copious amounts of the red pigments, others produce little or none. Combinations of the red and the yellow pigments create the palette of hues that seem to range across the spectrum.

The variation in color depends on many factors. Weather conditions during the weeks before autumn will have significant impact. Frost is not the key, and in fact can cause the leaves to die and wither before the colors develop. Low levels of sugars in the leaves will result in muted colors in the fall. Temperatures and cloud cover also have an impact: warm nights result in a more rapid break-down of the pigments, and cloudy days can reduce the amount of some pigments that are produced. Drought conditions can actually enhance the development of bright red leaves. Of course, the genetic variation between species and between individuals in a species also has an effect on the colors produced. The best autumn colors are the result of clear, dry, and cool (but not freezing) weather.

	Ginkgo biloba
	Fothergilla
	Korean Mountain Ash (Sorbus alnifolia)
	Blue Beech (Carpinus caroliniana)
	Spiraea fritschiana
	Upright Red Chokeberry (Aronia arbutifolia Erecta)
	Red Oak
	Sugar Maple/ Basswood forest