One of the nicest things about living in northern climates is the ever changing seasons. For a few weeks, nature puts on one of its most spectacular displays as native trees and shrubs finish out the growing season in a brilliant display of fall colors.
Jack Frost usually gets credit for the beautiful colors, but, in reality, fall color is controlled by both the plant’s genetic factors and the environment. Carotene and xanthophylls are yellow pigments produced in foliage all year; along with chlorophyll, the green pigment. In autumn when short days and cool temperatures slow down the production of chlorophyll, the remaining chlorophyll breaks down and disappears. Then the yellow pigments that have been masked by chlorophyll show up. These pigments give the ginkgo its clear yellow color.
Some plants produce anthocyanins (red and purple pigments) that may mask the yellow pigments. Some maples, dogwood, oaks seem to be on fire with red and purple.
Anthocyanin production increases with increased sugars in the leaves. A fall season with sunny days and cool nights increases sugar content in the leaves and intensify fall reds. This also explains the two-tone effect on green ash which exhibits yellow on leaves inside the tree and purple on the outside leaves where they are exposed to sunlight.
The tans and browns of oaks are caused by tannins which accumulate as the chlorophyll disappears.
Fall color starts in September with poison ivy and sumac and ends in November with the larches and weeping willows. Frost and freezing temperatures will stop the coloration process and blacken the leaves.
With Labor Day come and gone, the river valley is starting to change. A majority of trees are showing some signs of fall with sumac leading the pack displaying its deep, brilliant reds. Don’t forget to go enjoy the fall colors in the weeks to come!