While some consider the 21st of September to be the first official day of fall, the 23rd is the day of the Autumnal Equinox, which either way means Autumn is upon us. Autumn is a time when the sun's angle changes, things become cooler, and all of those beautiful leaves earn a fiery glow before falling. The spectacle is so popular that people plan entire vacations around the possibility of seeing the fall foliage.
Where I live, the leaves are just beginning their change. Here, the most change comes in October, but we've had some early starters. Changing to red, orange, yellow, yellow-green, and even purple is all part of a process that allows the deciduous trees to survive even a harsh winter.
What makes leaves green is chlorophyll. During the growing season (chiefly summer), leaves are so dominated by the green of chlorophyll that all other pigments within the leaf are masked. When the cold sets in, and the sun withdraws, the trees begin a withdrawal process of their own. The sugars that are produced by chlorophyll are drawn back into the tree as this will be its sustenance, and the chlorophyll itself is reduced in number. A layer of cork forms between the branch and the leaf, which eventually will allow the leaf to fall. During the change from chlorophyll-abundance and chlorophyll-absence, colour change will occur.
Chlorophyll is not the only pigment in present in leaves. Carotenoids are neighbours to the green pigment, and visually surface during the withdrawal phase. Carotenoids are what cause yellow, orange, brown, and the colors between, while Anthocyanins bring red and purples. Carotenoids commonly give characteristic colour to many living things like carrots, corn, canaries, and daffodils, as well as egg yolks, rutabagas, buttercups, and bananas. As far as trees go, the radiant yellows and oranges are more specifically seen on hickory, ash, maple, yellow poplar, aspen, birch, black cherry, sycamore, cottonwood, sassafras, and alder trees.
Anthocyanins are not always present in the leaf. They develop in the sap of the leaves in late summer during the breakdown of sugars. The level of light and phosphates in the leaf also hold an influence on the level of Anthocyanins present. Higher phosphate levels are an integral part of the plants sugar breakdown, as in well as the production of Anthocyanins. The brighter the light during this time, the greater the production of anthocyanins and the more brilliant the resulting color display. When the days of autumn are bright and cool, and the nights are chilly but not freezing, the brightest colorations usually develop. They can also be seen in early spring, often coloring the edges of young leaves as they burst from buds. Anthocyanins can be seen in cranberries, red apples, blueberries, cherries, strawberries, and plums. In trees, their fire is most notably found in the maple, oak, sourwood, sweetgum, dogwood, tupelo, black gum and persimmon trees.
Although this process is understood, and has been thoroughly studied, one problem on the way to understanding it entirely is why. Some theories include dropping leaves as a defense from autumnal and wintry pests, some say that leaves simply cannot survive the winter, and another says that it is the only form of a trees excrement.
Whatever the case may be, it's going to be a colorful two months.
Do you like autumn?
Have you ever planned a trip around the changing of the leaves?
What are the colors that most dominantly appear around you?
What colors do you think of when you think of Autumn?
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