It’s the second week of October and many of the trees in the southern third of Wisconsin are just starting to change their colors.
The weather that we’ve been having is more like a spring rainy period, but that is not the case. Until this week, most of the trees in the southern third of the state were just starting to turn into the magnificent fall hues of yellow, red, purple, orange, brown and may colors in between.
I’ve been under the impression that the fall color change was totally dependent on a fall frost and a frost was needed to set this process in motion. But I’ve been mistaken.
The leaf color change is the result of chemical processes that take place in the trees as the seasons change from summer to winter. Most of the trees' growth is manufactured by the leaves which serve as food factories during the spring and summer. The food-making process takes place in the leaf in numerous cells containing chlorophyll, which makes leaves their green color. This “special” chemical absorbs from sunlight the energy needed to transform carbon dioxide into carbohydrates such as sugar and starch.
Along with the green pigment are yellow to orange pigments, carotenes, and xanthophylls’ pigments. These pigments give the orange color to as an example, a carrot. Most of the year, these colors are hidden by great amounts of the green coloring.
In the fall, because of the change in daylight and temperature, leaves stop their food-making process. The chlorophyll breaks down, the green color vanishes, and the yellow to orange colors give visible and gives some of their fall color.
At the same time, other chemical changes may occur which form, additional colors through the development of red anthocyanin pigments. Some of these mixtures give rise to the reddish and purplish fall colors of dogwoods and sumacs while some give the brilliant orange to sugar maples. The fall foliage of some trees is only yellow. Others, such as oaks, show mostly brown. All of these colors are due to the various mixing of amounts of chlorophyll residue and mixing other pigments in the leaf during the fall season.
As the fall colors appear, there are other changes taking place. At the point where the stem is attached tree, a layer of cells develop and cuts the tissues the support the leaf. At the same time, the leaf seals the cut, so whenever the leaf falls, it leaves a tree scar. Most of the leaves in the North and Wisconsin drop their leaves in the fall. But some trees like oak with its dead brown leaves and a few others, keep their leaves until the spring when new growth starts growing.
Some of the conifers, pins, spruce, firs, hemlocks, hemlocks and cedars are evergreen in all parts of the country. The needle like leaves remain green year round and some leaves may stay the tree from two to four years.
Weather affects the color intensity. Water supply, temperature, and light have an influence on the duration and intensity of the falls color. Above freezing temperatures will affect the anthocyanin formation producing bright red in maples. But, an early frost will weaken the magnificent red color. Rainy or overcast days tend to increase the intensity of fall colors. The best time to take a ride and take in the colors of fall would be on a clear, dry, and cool but not a freezing day.