They Are Really Pretty This Time Of The Year.

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Trees Lining Rest-Haven Memorial Park | Photo by Suzanne Chuey

I don’t know about you but I first heard the explanation of their beauty in an elementary school science class. Unlike snowflakes, where no two are supposed to be exactly alike, these gifts of nature can have many that look exactly like the others. I’m speaking of leaves. The season of Autumn is when they change from a deep green color to vibrant reds, yellows, and orange colors. The questions are which trees have leaves that change colors, and exactly how does it happen?

I’ll start with the trees that do not change colors in Autumn.

Sun Through The Trees South Hills Of Eugene | Photo by Tim Chuey
Sun Through The Trees
South Hills Of Eugene | Photo by Tim Chuey

They are the evergreens including pines, firs, spruces, and cedars which don’t lose their leaves or needles. We have a lot of those in Oregon, but it is within the city and town limits and along the rivers where we find a diversity of tree species and beautiful colors. What makes the deciduous trees different? It is their pigmentation. There are two pigments at work here. The first is carotene which produces the color yellow and the other pigment is anthocyanin which produces the color red. Now these colors are actually in the leaves all year long but the process called photosynthesis produces chlorophyll which courses through the circulatory system of the leaf producing the green color.

What triggers the drop in chlorophyl production? It’s a combination of two elements: the shorter days give the leaves less sunshine and cooler temperatures also contribute to the chemical change. The leaves eventually die and fall off. The same conditions of less sunlight and cooler temperatures cause that. The decreased sunlight makes the veins in the leaf start to close up and when they do a separation layer of cells lines up at the base of the leaf’s stem. The process of closing off the stem allows scar tissue to harden on the branch side and the stem side to prevent loss of fluids from the tree itself. The separation layer does not fully detach the dead leaves on oak trees and that is why they can stay on the tree all winter long.

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Red Maple Trees Lining Rest-Haven Memorial Park | Photo by Tim Chuey

The colors of the leaves also identify the species of tree from which they came. Oaks produce red, brown, or russet colored leaves, Hickories golden bronze leaves, Dogwood purple-red leaves, Birch bright yellow leaves, Poplar golden yellow leaves, and Maple trees produce three different colors: Sugar Maple orange-red, Black Maple glowing yellow, and Red Maple produces  bright scarlet leaves.

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Photosynthesis | Image by sactree.com

Photosynthesis as defined by Wikipedia “is a process used by plants and other organisms to convert light energy, normally from the sun, into chemical energy that can be used to fuel the organisms’ activities. Carbohydrates, such as sugars, are synthesized from carbon dioxide and water, hence the name photosynthesis, from the Greek phos ‘meaning light’ and synthesis, ‘putting together.’ Oxygen is also released, mostly as a waste product.” A waste product for the plant, but vital for animal and human survival.

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transpiration overview | Image by McGraw-Hill Companies, Inc.

A second process called transpiration transports water into the plants from their roots in the ground, their stems, and their leaves with evaporation taking place mainly on the leaves to return the moisture back to the atmosphere.

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Leaves On The Ground | Photo by Suzanne Chuey

After taking into account all of the chemical and biological processes that make trees possible there is no scientific explanation for the enjoyment kids-of-all-ages can have jumping into a pile of dry leaves in the Fall. One of the disadvantages of having the beautiful deciduous trees in Autumn is having to rake up and dispose of the leaves. In the city of Eugene they are collected at the curb twice in the season and in Springfield they are picked up in bags.

Since this is also the rain season it is good to remember to keep the storm drains on your street clear of leaves and other debris to help prevent the flash flooding of the streets due to stopped up drains when we do get a heavy rainfall.

Let me know what you would like me to talk about or explain. You can comment below or email me at: [email protected].

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