The leaves are really beginning to change here in Philadelphia.
The leaves of most trees are green during the growing seasons of spring and summer. During this season, they change from light to dark green. The green color comes from a substance called chlorophyll.Chlorophyll absorbs light energy for use in photosynthesis, a food-making process that occurs in green plants.
The shorter days and cooler nights of fall signal the end of the growing season. Shorter days mean less sunlight is available and trees shut down their food-making processes. The chlorophyll breaks down and the green pigment is no longer seen. But before they die, the pigments that were hidden by the abundance of green, show themselves.
The sequence of color
The Best Fall Color Conditions
Early Cool Weather Brings Early Fall Colors
Brilliant Eye-Popping Colors
The uniform greens give way to the golds, oranges, reds, purples, and bronzes. These pigments are caused by the following substances.
- yellow color by the pigment xanthophyll
- orange-red tones by the carotene pigments.
- red and purple by pigments called anthocyanins
The autumn color depends on which of the pigments is most plentiful. As the chlorophyll and other colorful pigments break down, all leaves become brownish.
Each Species of a Plant has their Characteristic Fall Colors
Red and yellow are the main colors of autumn foliage in the east, and yellow and dark green are the main colors of autumn in the mountains and hills of the West. The dark green colors are from the numerous evergreen (conifer) trees.
In the north, there are more deciduous trees and therefore more trees which change color. In the south are more evergreen species.
In the west, on mountains and hillsides, the bright yellow quaking aspens are vivid against a forest of dark green evergreens, such as spruce and fir trees.
In the east, the predominant colors are the browns of oaks, golds, and yellows of the hickories, sycamores and other species. The reds of red maples and sumacs typify the October displays and draw many foliage watching visitors each year.
This year (2011) peak foliage is estimated period of full color between October 22 thru 31.
Fall in PA (Pennsylvania Foliage Watch) gives information about each region and provides a weekly foliage report.