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Temperate Rain Forest by Emma and Gracie

We live in Ketchikan, Alaska, where it rains 25 feet a year! All that water helps trees and other plants grow like crazy. That's why the Tongass National Forest-the largest temperate rain forest in the world-grows so well here. Some days when it's raining, and we can't get out and enjoy nature, we go to the next best thing, the South East Alaska Discovery Center. The United States Forest Service runs this science center, and they have a cool exhibit, which brings the forest inside. The exhibit got us thinking about tree growth. Our DFTV question: How long would it take for a new tree to grow as big as an old growth tree?

What did we do?
You can figure out the growth of a tree by examining its rings. Leslie, a forest ranger, showed us how to estimate a tree's growth without cutting it down. Here's how we set up our investigation. We visited three areas of the forest: thinned, non-thinned, and old growth. In each location, we collected data from 2 small and 2 large trees. Leslie gave us an interesting tape measure, which gives you the diameter of a tree by measuring its circumference. She also gave us an increment borer to take a ring sample from a tree without hurting it. We measured and took ring samples from a total of 12 trees. Then we counted rings and estimated the trees' ages. We figured the growth rate of each tree by dividing diameter by age.

What did we find out?
The non-thinned trees grew twice as fast as the old growth trees, but only half as fast as trees in the thinned area, so we understand why the Forest Service does some thinning. We also noticed that some old growth trees still grow fast, if they have the right environment.

What can you do?
  • You can study the importance of thinning by planting radish seeds. Prepare two small flower boxes with potting soil. In one of them, plant 50 radish seeds. In the other, plant ten seeds. Give them the same access to light and water. Record when the seeds in each box first sprout. As the plants grow, compare the size of the radishes under the soil in each box.
more resources
Go to the DFTV Boards, and tell us about your science investigation.
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