Optional Laboratory: Measuring Tree Heights
- How is the Pythagorean theorem used to determine tree heights?
- Draw a large tree on your paper. Draw a person to the same relative scale as the tree. Superimpose a right triangle on the tree and person. Relate the equation A
^{2}+ B^{2}= C^{2}to your drawing. A clinometer is based upon this equation. - One student should stand with the end of a 100 foot tape at the midsection of a tree to be measured. The other student should walk away from the tree on level ground, extending the tape. Mark the point 100 feet away.
- Taking turns, students should look through the clinometer eyepiece towards the tree top and read the tree height on the right hand side of the clinometer. Record the measurement in the data table.
- Practice on other trees.
- Use a clinometer correctly.
- Locate the tree apex.
- Develop a pacing stride for 50 or 100 feet.
- Measure the tree height.
Crown Classes in Even-Aged StandsIn even-aged forests a simple classification has long been standard in this country. It involves the recognition of five crown classes based on their position in the canopy. __Dominant trees.__The crowns of dominant trees rise somewhat above the general level of the canopy so that they enjoy full light from above and also laterally.__Codominant trees.__These are not quite as tall as dominants. Their crowns receive overhead light but they may be hemmed to a certain degree laterally by dominants. They comprise the main canopy of the forest.__Intermediate trees.__These crowns occupy a definitely subordinate position, but may receive some direct overhead light through holes in the canopy.__Suppressed trees (or overtopped).__These are definitely submerged members of the forest community having little free overhead light. They exist by virtue of the sunlight that filters through the canopy or the direct light that may be received through some chance break.__Dead trees.__
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- Have students pace along a 100 foot section of trail or pavement. Students should count either every other pace, or every pace; whatever they choose, they should be consistent. Have students continue pacing until they become comfortable with a fairly consistent count. This technique of having a 'built-in' pace will permit the student to measure tree heights without having to use a tape measure and still be fairly accurate. This technique also allows a student to measure the tree height alone without the aid of another student.
- Choose a tree on a slope. Have the student pace out 100 feet across the slope to measure the tree height. Now have the student pace out 100 feet from the same tree either up or down the slope. Have the student read the tree height and compare it to the height when read across the slope. If the student paced out down the slope the reading will be higher and lower if paced up the slope. Reinforce the idea of trying to choose an 'across slope' direction when pacing out from the tree. There are conversion tables available to correct for slope when it is impossible to pace across the slope.
- Choose a tree on a flat terrain to pace out 100 feet to measure the height. Now have the student go out 50 feet from the tree (use a tape since the student has not developed a 'built-in' 100 foot pace yet) and measure the tree height. Ask the student to compare the two measurements. The 50 foot reading should be approximately twice the 100 foot reading.
*Manual Of Forest Mensuration.*Beers, T. and Miller, C., T & C Enterprises, West Lafayette, Indiana. 1973.*Earths Trees: Environmental Learning Series.*Earthwise. WP Press, Tucson, AZ. 1992.
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