The most common thing people associate with falls in temperate parts of the world is the leaves on trees changing color. People travel all over the country to go see the beautiful transition to the winter months. But have you ever wondered why the trees are doing this or what is causing such a change?
Trees go through this process to shield themselves from the cold months to come. Trunks, Stems, and buds have evolved to naturally withstand the extreme cold but soft tissue-like leaves would freeze off anyways so plants naturally evolved to dispose of them. Even evergreen trees go through a process to enter dormancy but it is less obvious to the naked eye. There are many factors that signal trees to begin to prepare themselves for the winter to come. The biggest factor is the day lengths and light intensity dropping off significantly as we enter October. This happens very regularly and doesn’t vary much from year to year. Other variables such as temperatures, rain, and nutrients also can play a role in how bright or colorful the displays look visually to us but the tree is still entering dormancy regardless of how pretty its colors look.
During the year huge amounts of chlorophyll is being produced by the trees and they appear green. There are also two other major pigments within the leaf: Carotenoids, which are yellows/oranges, and Anthocyanin which produce reds/purples. As the days shorten the leaf veins slowly close and stop the flow of fluids up into the leaves. Once the leaves are completely sealed off the chlorophyll production stops leaving only the carotenoids and anthocyanins in the leaf. Factors such as rain and temperatures play a role in how fast/slow the leaf veins are closing. Warm sunny days and cool nights without frost or rain produce the most spectacular colors as these conditions allow the most anthocyanins and carotenoids to build up in the leaf.