Why Do Leaves Change Color?


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.

Up close and personal

The sequence of color

Fall leaf color changes begin at the higher altitudes and progress to lower altitudes. This is due to the cooler temperatures of higher latitudes and elevations. Trees begin to change along the Canadian border (above this boundary is conifer or evergreen forests) and progress downward. Leaves change color first in the mountains and move down the mountains into the valleys and coastal areas.
The color changes in predictable order. It begins with the red maples and progresses to aspens to sugar maples to oaks.

The Best Fall Color Conditions

Leaf color varies depending on temperature and other factors. Lack of enough water from droughts and insect-eating can case poor foliage display. Warmer than normal October nights are also bad for fall color display. During the warm nights, the trees use the sugar produced in their leaves, so not enough sugar is left for a color to develop.

Early Cool Weather Brings Early Fall Colors

The best color displays are developed during sunny fall days and cold, frost-free nights.
If you would like to know when fall foliage colors are at their peak, most Northern and Mid-Atlantic states have hotlines and tourism websites for information.
Eye-popping color of autumn leaves
The eye-popping color of autumn leaves

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.

fallen leaves
fallen leaves

Falling Leaves

After it dies the tiny pipelines that carried water and food between the leaf and the rest of the tree become plugged. The cells which held it to the stem dissolve and separate. The dying leaf hangs by a few strands. These strands dry and twist in the wind. When the strands finally break, it falls to the ground.
Once on the ground, then it is broken down by tiny organisms in the soil. These tiny organisms (bacteria and fungi) convert the leaf into simple substances used for food. These substances are also absorbed by plant roots and provide food for new growth.
The endless circle of life continues.

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.


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