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.
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. Trees provide a buffer against winter winds, and moisture transpiration in the summer acts as natural air conditioning. 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.