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 This
newsletter is a joint project of SIRS Publishing,
Inc.and the University Corporation for Atmospheric Research |
MAY 1994— VOLUME 1, NO. 4
ARTICLES
What covers about one third of the land surface of the earth, contains about 90 percent of all living matter, and accounts for over half of all solar energy that is converted to chemical energy on our planet? The world's forests.
The word forest may conjure up images of endless stands of pine trees or the majestic redwoods of the west coast, but thousands of different species of trees populate environments as harsh as the subarctic region and as lush as the tropics.
We value the forests for many reasons. They are home to many species of wildlife; humankind relies on them for food, shelter, recreation, and medicine; they serve as inspiration for poet and artist alike. Forests also play a crucial role in the chemistry of our atmosphere and climate. Without forests, our atmosphere and climate would be very different.
The world's forests provide food, shelter, recreation, and
the raw materials for medicines, as well as a home for thousands
of species of animals, insects, and plants. These crucial habitats
are also important contributors to earth's atmospheric chemistry.
(This photo is from the SIRS Photo Essays unit, National Forests.)
Photo by Deborah Lindley
One important role of the forests is their ability to store carbon. Trees remove carbon dioxide (CO2) from the atmosphere in the process known as photosynthesis. Sunlight, CO2, and water are the raw materials of photosynthesis; the ultimate products include oxygen, other gases, and the hundreds of complex chemicals which make up the tissues of leaves, roots, and stems. Much of the carbon which was originally in the atmospheric CO2 molecules is transformed into biomolecules such as carbohydrates, amino acids, cellulose, and enzymes-the "stuff" which makes up the living tree.
Some portion of the carbon turns back into CO2 and is returned to the atmosphere through a process knows as respiration. In this process, the energy stored in some of the complex carbon-containing molecules is released and used by the tree. This flow of carbon between tree and atmosphere is important, because altering it will influence the balance between stored carbon and atmospheric carbon. Much of the carbon remains tied up in the biomolecules. Depending on the part of the tree and the type of the tree, the carbon can remain stored for periods ranging from years to centuries. When the tree dies, decay processes take the carbon on another journey in the forest soils. The ultimate return to atmospheric CO2 can take thousands of years or longer.
Such carbon storage and processing is necessary to maintain our climate. By removing CO2 from the atmosphere, forests affect the concentration of atmospheric CO2, a greenhouse gas. These gases act as a heat blanket that warms the planet, absorbing infrared radiation coming from the surface of the earth that would otherwise escape into space. Although it seems logical that more CO2 will trigger a warmer climate, the earth system is far more complicated. Feedback processes must be considered in computer models of climate change. While scientists at the National Center for Atmospheric Research work to understand these processes and predict how the climate will respond, the importance of the world's forests is certain.
The notion of planting a tree to save the planet is a popular one, and it comes about largely because of the forest's role in storing carbon. While the concept is sound, it is impractical. The r ality is that in the United States alone, we'd each have to plant over 800 trees per year to remove the CO2 we're adding to the atmosphere through the burning of fossil fuels and wood.
Carbon dioxide is only one gas which is exchanged between the atmosphere and forests. The concentrations of many other gases in the lower atmosphere are influenced by vegetation.
Many gases are removed from the atmosphere when they contact the surfaces of plants. This process, known as "dry deposition," reduces the concentration of the gas in the atmosphere. For many pollutants, this removal process is so important that some cities have planted trees and other vegetation to try to improve air quality. Ozone (03) and sulfur dioxide (SO2) are two examples of gases which are taken up readily by trees. The gases can be deposited on the outside of the plant, or, in the daytime, can enter the leaves and affect the internal processes of the plant.
Clearing the land by the slash-and-burn technique, which is
common in the tropics, releases carbon dioxide, methane, and other
gases in amounts sufficient to affect the global atmosphere.
Photo by NCAR
Ozone is perhaps the most-studied pollutant. The gas, which is a component of photochemical smog and a by-product of burning fossil fuels, is suspected of causing billions of dollars of annual crop damage in the United States and to be causing some of the damage to California forests downwind from Los Angeles. Ozone may act visibly, causing yellowing or spotting on leaf surfaces. More often, ozone acts invisibly by reducing photosynthesis or affecting other internal processes. Effects such as these can then influence the abilities of plants to store carbon.
Forests are not only a sink for trace gases; they are also the source of many gases which are important to the chemistry of the troposphere, or lower atmosphere. A very important class of compounds emitted by trees is hydrocarbons. A significant fraction of the carbon absorbed by vegetation as CO2 can end up as a hydrocarbon gas which the plant emits into the atmosphere. Isoprenes and terpenes are two types of hydrocarbons emitted by trees and plants.
Aside from the carbon loss that results when a plant emits hydrocarbons, the process is significant because the gases react with other gases in the atmosphere. With nitrogen oxides (which have natural and manmade sources) and sunlight, the reactive hydrocarbons undergo a series of chemical reactions which can lead to ozone production. Recent research has shown that biogenic hydrocarbons influence ozone concentrations in rural and urban sites of the eastern United States. In the Atmospheric Chemistry Division at NCAR, scientists study the hydrocarbon emissions of several forest species in laboratory and field studies.
Forests and vegetation also play an important role in the water, or hydrologic, cycle. The circulation of water in the lower atmosphere is influenced by transpiration, the process in which plants give off moisture from leaf surfaces. About one-half of the rain which falls on a forest is returned to the atmosphere through transpiration. This has important consequences for the formation of clouds and precipitation. The heat fluxes which accompany water condensation and evaporation also affect atmospheric turbulence, which we notice as storms.
Forests simultaneously influence and are influenced by the chemical and physical climate which surrounds them. The inter-relationships of the vegetation-atmosphere-climate system are a source of both beauty and vulnerability.
Forest decline is a significant worldwide problem. Forests in Germany and eastern Europe have suffered much damage. In the United States, red spruce have declined in the northeast and the ponderosa pine have been damaged in California. Acid rain is declared by some to be the culprit, but the scientific evidence is not conclusive. Other factors relating to atmospheric pollutants or climate may be involved.
Deforestation, especially in the tropics, is also an important concern. The magnitude of the problem is staggering; forested land is being cleared at a rate of about one football field per minute. Subsequently, CO2 is released into the atmosphere by the burning of forest waste, increasing the concentration of the greenhouse gas. Other gases released by the burning further influence atmospheric chemistry. Once the forests are gone, the process of transpiration no longer occurs affecting cloud and precipitation patterns over a region. The change in land use when forests are converted to pastures has other implications for atmospheric chemistry and climate which scientists are studying.
Finally, the forests themselves might be transformed because of climate change. Northern boreal forests may shrink while temperate and tropical forests may expand. Scientists are trying to predict whether such changes will occur and what those changes will do to the feedback processes in the atmosphere. Recognizing the many roles forests play in our climate and atmosphere, there is clearly much more than beauty to ponder when taking a walk in the woods.
Some trees have found, by function and/or tradition, specific and exclusive uses in human activities, such as:
Maple, for bowling lanes
Hickory, for garden and carpentry tool handles
Dogwood, for gear teeth
Pear, for drafting implements
Spruce, for piano sounding boards
Black Walnut, for rifle stocks
Apple, for dulcimers
White Oak (charred), for barrels for aging bourbon whiskey
...Can you think of others? Send them in!
Other tree facts you might not be aware of:
ACTIVITY
In some parts of the world, such as the Denver, Colorado area, forests have been established where there was once a grassy plain. However, on other parts of our planet, forests are being destroyed at an alarming rate, especially in tropical areas. Once gone, these tropical forests may need thousands of years to return to their natural state. Some species of animal life that depend on these forests will be lost forever. If the only seeds of a particular plant go up in flames, then that genetic information is forever gone. It could be a plant very useful to us humans, for a new medicine, perhaps, or simply a plant of unusual beauty.
Here's an exercise to tune your sensibility to that marvel, the tree. Have your students take a trip to the supermarket to use their observational skills. As they travel through the aisles of their supermarket, they should list the items that come from trees. Then have them compare their list with the items listed below. Don't let them look until they have their own list!
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You probably noted all the obvious products from trees, but... did you remember applesauce? How about napkins, greeting cards? Did you count all the paper and cardboard packaging of many products? Cellophane comes from cellulose (from trees). Did you forget cellophane tape? Or products made from latex? In the baking aisle, did you see the shredded coconut, the olive oil, the walnuts?
Did you catch chewing gum (from chicle)? Did you notice that palm oil is used in some baked goods? Did you know that the key ingredient in aspirin (now synthesized) originally came from willow bark?
In the utility section, did you remember brooms and mops (for their handles), matches, some furniture oils, turpentine?
Did you remember sassafras tea and true root beer? How about camphor in liniments, and quinine water? The figs in Fig Newtons?
You remembered nutmeg, of course. And lemon meringue and banana cream pies. You didn't forget almonds in candy bars, or lemonlime soft drinks, did you? Or the gift of gifts: maple syrup!
Was there a single aisle or section that did not contain a product that comes from trees?
Note to Teachers: We'd love to see a compiled list which we could share with other readers. Please send your information to Caroline Hanson, Project LEARN, P.O. Box 3000, Boulder, Colorado, 80307, or to chanson@ncar.ucar.edu
Patrick J. Kennedy, Geoscientist at NCAR
RESOURCES
SIRS Photo Essays, a series of poster collections which "tell a story," offer two units pertaining to forests and the atmosphere"Tropical Rain Forests" and "Old-Growth Forests."
Through visually appealing photos, learn how tropical rain forests play a role in global weather patterns by contributing to total rainfall and by consuming carbon dioxide. Where tropical rain forests are destroyed, soil erosion results, followed by floods and, ultimately, desert. Their disappearance may have dire effects, including a hastening of the global warming trend known as the greenhouse effect, and the extinction of many plant and animal species.
The destruction of old-growth forests represents more than the loss of beautiful scenery. These temperate rain forests help cleanse air and water and provide a habitat for wildlife that can't live anywhere else. The destruction of forests adds carbon dioxide to the atmosphere, contributing to the problem of global warming.
Perfect for libraries and classrooms, SIRS Photo Essays can be arranged on bulletin boards or any wall space, and used in classroom discussions. Along with photographs and brief text, most units include maps, charts and other graphic elements to put the topic in context and promote visual literacy. Posters measure 11 inches by 14 inches and are laminated for long-time use. Each unit includes eight posters and a study guide with references and worksheets to help users analyze the topics . Catalog cards are included. SIRS Photo Essays are $28 per unit.
Another excellent resource for information on this topic, plus many other earth science and social issues topics, is SIRS Researcher CD-ROM. It offers a full-text database of thousands of carefully selected articles from over 800 sources. Since many outstanding articles are irretrievable soon after publication, SIRS research staff selects articles from national and international newspapers, magazines, government publications and journals, and structures them for reference use. Articles are accessed by subject headings index, keyword search or a topic browse mode. SIRS articles are reproduced both in print and CD-ROM formats.
Following is an excerpt from a full-text article from SIRS Researcher:
"Climate Change," by Ronald G. Prim and others. WorldPaper, April 1993. From SIRS Researcher CD-ROM or SIRS Print Science Series.
SIRS Researcher CD-ROM is available for both PC and Macintosh computers. The disc contains the same articles published in the volumes since 1989, which includes articles from SIRS Social/ Critical Issues Series, SIRS Science Series and SIRS Global Perspectives Series. The initial annual subscription for SIRS Researcher CD-ROM is $1,450 (annual updates are $1,250).
For more information on SIRS Photo Essays and SIRS Science Series, please contact SIRS Customer Service at 1-800-232-SIRS or 407-994-0079 (8:30 a.m. to 5:00 p.m. Eastern Time). To request a no obligation, 60-day preview of SIRS Researcher CD-ROM, have your library's media specialist call SIRS Customer Service at the numbers listed above, or via e-mail at custserve@sirs.com
The University Corporation for Atmospheric Research provides information about global climate change through its Information and Outreach Office. If you would like any of the following items, please send your requests to Caroline Hanson, Project LEARN, P.O. Box 3000, Boulder, CO 80307, or send your request via e-mail to chanson@ncar.ucar.edu.
* Learning About Science Easily and Readily: Climate Change and Water Resources
* Learning About Science Easily and Readily: Greenhouse Gases and Their Effects
* The Changing Atmosphere: Challenges and Opportunities
* Weather, Climate, and the Nation's Well-Being
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Now
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Corporation for Atmospheric Research
and SIRS Publishing, Inc.
(Social Issues Resources Series.) Science
Now is published three times during the
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Editor:
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Scientific
Editor:
Pat Kennedy
Contributors:
Bob Henson, NCAR Outreach and Information Staff;
Chris Ennis, Atmospheric Chemistry Division
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