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The Secrets of Autumn Leaf Colors


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The Secrets of Autumn Leaf Colors

Cheryl J. Shenkle

October 9, 2021

 

In late winters past have you eagerly watched a familiar tree for signs of color in the stem tips while dreaming of soon seeing the first tiny leaves emerging? In the tiniest spring leaves, you will find the same colors, in minute quantities, that you will see during the fall in the mature leaves. The colors of the newly developing leaves may even challenge fall colors for brightness.  They’re just smaller.

What do leaves know about the changing seasons that we don’t?  What directs them in their accuracy?  What can affect the process and change the outcome of what we call the Fall Foliage.

Through millions of years of evolution, leaves have been patterned to develop in the Meristem at the direct center of a branch tip.  In the small bud bundle of the Meristem are all of the cells which will develop into the leaves, flowers and fruits of the upcoming growing season.  In fall, they emerge and harden into tiny buds in the leaf axial of the branch, waiting till the proper time to begin their spring push. Filled with concentrated life, the baby leaves possess the deep rich glow of clean new existence, which although temporary, keeps our earth alive through the chemistry of creating and repairing the healthy air we breathe.

To do so, the tree trunk, which is the porous support structure for the leaves, must remain healthy and unclogged in order to allow the phloem, directly under the bark, to transport fluids from the tiniest root hair to the furthermost cell of every leaf on the tree.  In times of drought, parts of the leaves will not receive enough water and will dry on the edges, wilt or even drop from the tree, the sacrifice needed to allow the remaining leaves to survive. In one season, the average tree will transport thousands of gallons of water, nitrogen and minerals up into the canopy to feed each and every leaf in its network. The water is released back into the atmosphere as oxygen and clean water vapor.  Think of a tree as a bundle of straws transporting food and water up to the leaves, and sugars back to the roots to feed beneficial bacteria which in turn dissolve minerals in the soil for the use of the tree.

Leaves are developed as food factories. Throughout the winter, the tree roots act as food storage to give life back to the leaves in the spring. Just as solar panels collect and change light into electrical energy, leaves capture sunlight and convert it to food for both the tree and the teeming underground bacterial life which breaks down the very rocks in the earth into food for the tree. The bacteria feed minerals to the tree through root hairs, which feeds the leaves, which collect sugars from solar activity and provides it to the bacteria in exchange for minerals.  Simplified, yes, but so complex that we cannot create it for ourselves.  We can simply mimic nature.  Study well and you may be richly rewarded with sweet sap destined for the bacteria!

When you see that one tree with a branch or one section of the trunk sporting bright colors well before the rest of the forest, they’re not over achievers as we think, but they are either suffering from a diseased branch or the tree has a problem in one section of its root zone.  It simply means that the tree was not able to sustain green chlorophyll in that area, so the colors underneath became visible before they should have.

Sometimes trees will turn colors earlier at a higher altitude while others in the valley below are still dapper in their green coats.  Cold air can damage leaves to the point that they can no longer produce chlorophyll.

Wet cycles and drought can also affect the fall colors when they cause damage in the roots of trees during the growing year.  These conditions may cause dull colors, quick or early leaf drop or they may stress a tree to the point that it drops it’s leaves extremely early but did not have enough sugars stored to survive till spring.  This is why some trees must be transplanted early in the summer, and others may do better if planted early in the fall.

At the norm, minus outside triggers, the trees are actually reacting to the shorter days, less sunlight and cooler days.  It’s that simple!

Phenology is the science of the interrelation of how climate, weather and altitude affect seasonal and ecological cycles.  Grandpa knew about this when he planted his corn when the Oak Leaves were the size of a squirrel’s ear.  Grandma knew to prune her roses when the Forsythia bloomed and to plant her potatoes when the Dandelions bloomed.  There is a huge amount of acquired information which is used to get our gardens into the ground as early as possibly while keeping it safe from the elements. Almanacs use this information along with climate records to help gardeners and farmers every year.

One last secret, the leaves don’t fall, they are removed from the tree which uses Abscission cells to cut it off when the tree is done with the leaf.  Now isn’t that a fine Howdy-do!

So the secrets of the leaves are many, and probably we will never discover them all.  Keep a close eye on your trees, they may be trying to tell you more than you realize!

Master Gardeners are available for group presentations.  Contact the office for specifics.

Certified Master Gardeners are local volunteers trained by Penn State to answer Horticulture questions with properly researched information. For a “best practices” answer to your question, call Penn State Jefferson County Extension at 849-7361, Ext 508, e-mail JeffersonMG@psu.edu, or mail your question to 186 Main Street, Suite 3, Brookville, PA 15825. 

Penn State is an equal opportunity, affirmative action employer, and is committed to providing employment opportunities to all qualified applicants without regard to race, color, religion, age, sex, sexual orientation, gender identity, national origin, disability or protected veteran status.

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