Back to Nature Questions
To understand the answer to this question, you first need to understand how trees feed themselves. All trees contain chlorophyll, a pigment that gives leaves their green color and masks all other color pigments, such as the yellow, orange, and red of anthocyanins and carotenoids (the same compounds that make carrots orange). The job of chlorophyll in leaf cells is to capture energy from sunlight. Trees use this energy to convert carbon dioxide and water into carbohydrates, like sugar and starch, which nourish them. This is part of the process called photosynthesis. The second part is when a tree draws water up from the ground through its roots, which eventually evaporates from the surface of the leaves. This process of photosynthesis helps trees grow and stay healthy during spring and summer.
During
fall, it’s time for many (but not all) trees to slow down for winter. There
isn’t enough light or water during the winter months for photosynthesis to
take place, so the trees shed their leaves to survive. If the leaves were to
stay on, they would continue to evaporate water and the trees wouldn’t be able
to replenish their supply from frozen ground. During this long rest, trees feed
off the food they stored during the summer.
As the days begin to shorten and get cooler, it signals the trees that it’s time to stop the food-making process. A special layer of cells develops right at the spot where each leaf is attached to the tree. These cells will seal the cut after the leaf finally falls off. But before that happens, they first block the flow of food and water to the leaf. This causes the chlorophyll to break down and fade away, revealing the other bright colors that have been there all along, hidden from our view! The many differences in pigments, chlorophyll levels, and chemical reactions cause a variety of brilliant colors in trees---from the bright reds and oranges of sugar maples and red oaks to the deeper reddish-purples of dogwoods to the vibrant yellows of aspens and birches. Other trees display mostly browns, which often come from wastes remaining in the leaves.
Some years are better than others when it comes to nature’s amazing display of colors. It all depends on temperature, water, and light. Bright days cause more sugar production (which means brighter colors), but rainy days usually increase the intensity. Really dry weather can cause the leaves to drop too quickly. Low temperatures also increase the color brightness, but early frost hurts the show.
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Key Study Words |
| • Chlorophyll • Pigment • Photosynthesis • Evaporate |
There are a number of ways to enjoy autumn leaves with children. Foliage tours with the entire family or class are an ideal informal activity, especially when combined with a picnic, pumpkin shopping, or apple-picking. Fall foliage adds a fascinating element to hiking trips. Older children should be encouraged to bring a camera!
Whether you do decide to go on a foliage trip, or simply to gather leaves in the back yard, another fun activity is pressing leaves. There are a few different methods of doing this, but one of the simplest is to just place favorite leaves between blotter paper (don’t let them overlap), and then stack them between heavy books. Bind each bundle tightly (careful you don’t damage your books), and store them in a warm, dry spot for 1--2 weeks. When they’re dry, you can seal them in wax paper, put them in a photo album to remember the event, or use them for arts & crafts!
Perhaps my favorite activity involving children and autumn leaves involves three easy steps:
Copyright © 2001 by John W. Schlim Jr.
To learn more about fall foliage, check out these cool Web sites:Science
Made Simple
(site for kids includes "I Can Read" section, word scramble, projects,
activities, and more)
St.
Paul Field Office of the USDA Forest Service
(includes information on where to see fall foliage)
New
Hampshire Division of Travel & Tourism Development
(foliage facts with color photos and illustrations, plus a foliage
slideshow)
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