Montshire Minute: Fall Foliage

Originally aired during the week of September 28, 2002

Monday

Why do leaves turn color in the fall? Believe it or not, the answer has more to do with the disappearance of one color than the sudden appearance of many others. Green is the only leaf color we notice during the summer - that's due to chlorophyll, the chemical that helps the tree manufacture sugar from sunlight. When the weather cools and the chlorophyll disappears, what's left behind? The other colors in the leaf that were there all along, of course! These pigments are hard to see during the summer months but they are not quite invisible. Look closely at a grass stain on a light colored fabric and you'll see what I mean - there may be some yellow smears in there with the green. This is called xanthophyll, the same yellow leaf pigment we see in many autumn leaves.

Tuesday

In yesterday's program, we noted that the green chemical chlorophyll tends to overpower all the other leaf colors that don't come out of hiding until the fall. So what happened to the chlorophyll? This time of year, nutrients move out of the leaves and into the branches, trunk and roots of the tree where they can be stored for the long months of cold that lie ahead. These nutrients will be needed in the spring when its time to develop new leaves. But in the meantime, the lack of nutrition means tree is no longer creating any new chlorophyll - what remains of this chemical in the leaves begins to break down. You'll learn more about the "science behind the scenery" during Montshire Museum's Nature of Fall day on Saturday, October 5. We'll also hosts some trail walks and build some easy to make birdfeeders!

Wednesday

This week we've been exploring the science behind the fall scenery on the program. At a spot where the stem of each leaf joins the twig, a thin ring of cells called the abscission layer begins to form. This layer gradually covers the base of the stem, cutting off nutrients to the leaf. As the leaf stops making food and the chlorophyll fades, sugars trapped inside the leaves react with the sunlight and other leaf chemicals to reveal new colors. Trees with acidic leaf chemicals like the sugar maple tend to show off red colors (these are the same pigments that make radishes, roses, and geraniums red.) In some trees, like the oak, one side of the leaf gets enough sunlight to reveal new pigments but the other side doesn't. This explains why oak leaves are often dark brown on the top and light on the bottom.

Thursday

Why does the fall color seem more brilliant some years than others? Weather seems to play a role. Local foresters say heavy rainfall and high humidity during the summer can lead to early browning of leaves. But cool nights and warm days (good for maple sugaring in the spring) also seems to be a good recipe for leaf peeing - these are conditions that encourage brilliant orange and red colors. Of course, not all trees lose all their leaves every fall - spruces, pines, hemlocks, and firs keep making food all winter. Their needles are really just thin leaves that don't fall away every year. But evergreens aren't really green forever. Their leaves last longer - staying on the tree for two - eight years, depending on the species. Learn more about the "science behind the scenery" during Montshire's Nature of Fall day on Saturday, October 5.

Friday

This week on the program, we've been exploring leaf colors that suddenly come out of hiding in the fall. Here's a simple Montshire experiment you can do to discover some other "hidden" colors. All you need is some absorbent paper (heavy-duty paper towels work great), some water-soluble markers of different colors, and a glass with about one inch of water in the bottom. Cut the paper into long strips about an inch wide. Then, with a marker, draw a thick stripe of color about two inches from the bottom end of one strip. Hold the strip in the glass so that the colored stripe is just above the surface of the water. Now, watch what happens to the color as the paper slowly absorbs the water. Do you see more than one color? Repeat the experiment again with some other markers and watch what happens.