Fall is a wonderful time of the year, especially when the trees have a good display of colors.
There is a reason why our trees turn so pretty in the fall and why they are green the rest of the year. The color in our trees, during any part of the year, is due to four different pigments that are present in the leaves: chlorophyll, carotene, tannin and anthocyanin. During the spring and summer, chlorophyll is the primary pigment in leaves. It is constantly being generated by the trees, as it is easily broken down by bright sunlight. When this compound is being produced in the spring and summer, it is the most prevalent and that is why we see the green in the leaves.
As the nights gets cooler and the days get shorter, the tree produces a membrane between the branches and the leaves, causing them to no longer receive any chlorophyll that the tree might still be producing. This membrane also leads to the eventual shedding of the leaves in the fall. At this time, the other pigments are allowed to show up in the leaves.
Carotene is the pigment that is responsible for yellow and orange colored leaves. Carotene is always in the leaves, as it aids in the capture of sunlight for photosynthesis, but it is at a lower amount than chlorophyll, so the green color shows up as the predominant pigment.
Tannins are our least favorite pigment color--they make the brown-colored leaves. Tannins are always present in leaves but are not shown until the chlorophyll and carotene are gone. These often accumulate in the dead portions of the leaves, which is why dead areas of our leaves turn brown in color.
Anthocyanin is the pigment that is responsible for pink, red, and purple leaves. This pigment is usually not present in the leaves until the fall. Some trees have red or purple colored leaves during the entire growing season because they have higher amounts of anthocyanins than chlorophyll throughout the whole growing season. Other trees don’t produce any anthocyanins and those are the trees that turn yellow, orange or brown during the fall. Those trees and shrubs that turn red in the fall form anthocyanins when the concentration of sugar in the leaf increases. Low temperatures and bright sunshine destroys chlorophyll, and when the temperatures stay above freezing during this time, anthocyanins are produced.
So, what causes our trees to turn bright and colorful in the fall and why are some years better than others? The brightest fall colors are produced when dry, sunny days are followed by cool, dry nights. The dry, sunny days are needed to break-down the chlorophyll in the leaves allowing the other pigments to be dominant in the leaves. The cool, dry nights are also necessary for fall colors because trees need to avoid freezing temperatures which can injure or kill the leaves, causing them to stop producing much sugar at all. The sugar content is what increases the amount of the anthocyanin, or red pigment. The yellow and brown will be present, but the red is necessary as well.
You don’t have to travel far to get amazing fall colors from the trees. There are many places right here in Nebraska to go for a wonderful fall color display in the trees. Indian Cave State Park in the far southeast portion of the state, Ponca State Park in northeast Nebraska, the Nebraska National Forests and even your own backyard are great locations to find fall tree displays. Look around, they are not that hard to find, just as long as we have dry, sunny days followed by cool, dry nights and minimal frost until later in the season, we will have a beautiful display of trees in the fall.