This lesson is designed to lead students to understand what the forest means to humankind. It is important that they see the forest not only for its products, but also for the environmental benefits and intangible rewards it provides.
The day before beginning this lesson, ask the students to list everything they touch while at home that evening that is in some way derived from trees. Then take their lists and categorize the items as paper products, food products, identifiable wood material (furniture, boards, pencils, bats ,etc.), and wood by-products like medicines, chemicals, and camera film.
In addition to the products we use daily, the forest provides many benefits that most people fail to notice:
Water.Trees take up large quantities of water from the soil. Some is used in the photosynthetic process, some is used as a solvent to transport minerals and nutrients, but most is incorporated in the protoplasm of the tree cells. About 80-90% of a tree's bulk is water, leading some people to view the forest as a massive water storage facility.
About 95% of the water in a tree is recycled into the atmosphere through an evaporative process called transpiration. This occurs mostly from the leaves, and the transpiration rate is highest during hot afternoons in the growing season. The transpired water is constantly being replaced by water brought from the soil. When transpiration occurs more rapidly than water replacement, the tree will wilt.
Tie a plastic bag around the end of a leafy twig and leave it for 24 hours. Collect and measure the amount of water that accumulates. Try it on days when the weather is hot and sunny as well as during cool, cloudy weather. Compare the results.
Forests also affect the quality of water in our streams and lakes. The roots and the organic litter (dead leaves and needles) slow the runoff from rainfall and let the water soak into the soil. Without this buffering effect, soil can be carried by the runoff into streams, adversely affecting streamflow, water quality and aquatic life.
Show the class pictures of eroded, hilly farmland. Discuss the total environmental ramifications, including decreased water quality, fewer fish in the stream, and reduced productivity of the land. How does this affect the people who live in the area? How might it affect people who live miles away, especially downstream? What could the farmer have done to prevent it?
Trees provide a buffer against winter winds, and moisture transpiration in the summer acts as natural air conditioning. Studies of tree-related temperature modification in urban environments have shown that well-placed trees can reduce heating and cooling bills up to 30%. One study by the Federal Energy Administration found that a large, vigorous, well-watered hardwood tree has a cooling capacity of 800,000 BTU's per day. That's the equivalent of 20 window air conditioning units running 20 hours a day!
Place a thermometer in the lower branches of a large, leafy tree and one in an exposed area. Compare the temperatures shown at both sites on a hot afternoon.
A study reported in General Climatology showed 85% less air pollution within a forest than was measured just 300 feet from the forest edge. The basic photosynthetic equation shows how green plants convert water and carbon dioxide into sugars and release oxygen as a by-product:
6 CO2 + 6 H2O > C6H12O6 + 6 O2
From this equation it's fairly obvious that plants take in a pollutant (carbon dioxide) and release pure oxygen into the air. Trees play a significant role in this process: South Carolina's forests, by some estimates, remove 240,000,000 tons of carbon dioxide from the air each year.
Here's a fun exercise to put this in perspective for the students:
An elephant weighs about 5.5 tons. How many elephants are equivalent to the amount of carbon dioxide absorbed by SC forests? If an elephant is 10 feet long, how many miles of elephants would this be?
Answers: 240,000,000 tons is about 4,363,636 elephants; there are 528 elephants per mile, so your parade would be 8,264 miles long. That's enough elephants to reach from Columbia to London and back again. (You can do the same thing with squirrels or rabbits, but the numbers get awfully big and it's a lot harder to get squirrels and rabbits to stay in line.)
Trees also help manage the amount of particulate matter picked up and carried by the wind. Vegetative windbreaks, consisting of several rows of trees, are utilized by farmers on the great plains to slow the force of the wind and prevent topsoil from being blown away. When dust or other particulate matter is picked up by the wind, forested areas buffer the wind speed so the material can settle back to earth.
Aesthetic appeal is very subjective, but it can translate into things more quantitative. Here are some examples:
- Tourism is South Carolina's single biggest money-maker. Parks, camping areas, and tourist towns depend heavily on their appearance to attract tourists, and much of this appeal is based on trees and landscaping. (Trees can help set a mood for tourists. Developers at Myrtle Beach depend heavily on transplanted cabbage palmetto to provide a tropical look, encouraging tourists to stop there rather than go on to Florida.)
- Psychological studies have shown that trees and green space in and around the workplace have a positive impact on worker productivity, job-related stress, and illness-related absenteeism. (The May, 1992 issue of National Geographic Magazine discusses the role of plants in therapy for the mentally ill and rehabilitation of criminals.)
- Noise reduction is a specific area where trees can improve people's attitudes and enjoyment of where they live or work. A strip of trees 100 feet wide can reduce noise from a busy highway by 6-8 decibels, or about 10%. The human ear can detect a volume difference of about one decibel; according to OSHA, hearing can be damaged at volumes of about 85-90 decibels. Sounds in the 120-140 decibel range can actually be painful. The sound volume reduction provided by a buffer of trees can easily make the difference between noise that is tolerable and volumes that are dangerous.
- Visual screening has a great deal to do with our perception of sensory stimulation. A sewage lagoon that is hidden from view may still produce noxious odors, but it is not as annoying as if the lagoon were in full view.
- Property values and marketability of homes are influenced by the trees and landscaping. A study in New England revealed that trees increased residential property values by up to 20%. Urban foresters in South Carolina have reported that planting trees in barren yards can stimulate the sale of residential property; most real estate agents would agree that shaded, landscaped properties sell faster, especially in middle to upper price ranges.