SEE THE LIGHT
Article #49, July 2001
By Bill Cook
Working with fourth and fifth graders can cause one to probe the deepest meanings of life. Sometimes these kids ask profound questions, although it’s not profound answers they are looking for.
One such question is; “How much oxygen does a tree produce?” From an ecological standpoint, there are many dimensions to a response. However, the answer the student is looking for is “about 20 pounds per year”. I also mention that trees consume oxygen, too, just like people and animals.
The question leads naturally to a discussion of photosynthesis, an essential life process. Photosynthesis captures light energy and converts it to chemical energy stored in simple sugars. Oxygen is a waste product of the process.
Nearly all the energy for life on Earth comes from the sun via photosynthesis. Ponder that for a minute.
Without photosynthesis our planet would be a barren place. It’s also the reason behind much of our forest management.
It surprises many people that the importance of green plants and photosynthesis has little to do with oxygen. It’s the sugars! The amount of oxygen produced by a tree varies widely, but in any case the contribution by vegetation to Earth’s oxygen supply is rather insignificant.
Photosynthesis begins with the chlorophyll molecule selectively collecting various wavelengths of light. Oddly enough, green light is a useless wavelength for most plants.
Throw in six water molecules and six carbon dioxide molecules, a really hairy set of chemical reactions, and the tree produces a simple sugar, along with six waste oxygen molecules. Within the bonds of the sugar molecule, you will find stored energy from the sun. Remember that it’s these sugars that are critical, not the oxygen.
With these sugars, which I like to call solar batteries, a tree will build all of its tissues and grow. Of course, the tree needs other raw materials, too. That’s what gets pulled up from the soil through the roots. That’s how wood is made.
Photosynthesis is not a very efficient process. Only about ten percent of the incoming solar energy can be converted by green plants. But it’s enough to power our Earthly ecosystems.
What’s all this have to do with forest management?
Well, not all tree species have the same light requirements. Different species have different life strategies. Some require lots of light and put their energy into rapid growth. They grow fast, live recklessly, and die early.
Other species require less light and put more energy into maintenance and defense. These trees tend to grow slower and live longer.
Our forest management systems are designed around the characteristics of various forest types. The idea is to manipulate photosynthesis to improve tree growth and health. There are, of course, more considerations than just photosynthesis and light. However, all successful systems must take photosynthetic ability into account as a major factor.
How about that? There actually is some science involved with forestry! And, how “sweet” it is!
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Bill Cook is an MSU Extension forester providing educational programming for the entire Upper Peninsula. His office is located at the MSU Upper Peninsula Tree Improvement Center near Escanaba. The Center is the headquarters for three MSU Forestry properties in the U.P., with a combined area of about 8,000 acres. He can be reached at firstname.lastname@example.org or 906-786-1575.
by Bill Cook, Forester/Biologist, Michigan State University Extension, 6005
J Road, Escanaba, MI 49829
906-786-1575 (voice), 906-786-9370 (fax), e-mail: email@example.com
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