Lab 1: Forest Mensuration
Foresters have to be able to measure the height of trees quickly for a variety of reasons. In this lab, you will practice measuring the same tree three times with three different methods:
1. 2. 3.
Kuhns' Method Hypsometer Method Bellnet's Method or Repeating Pencil Method
Find a tree and measure it using 3 of these 4 methods on the same tree. Enter your answers in Lab 1 under Tests & Quizzes. You will leave answers blank for 1 of the 4 methods. This lab will be hand graded.
1. Kuhns' Method (Required)
Figure 1: step 3
Method
The total height of the tree is considered to be the distance between the base of the tree trunk and the topmost twig. One can measure the tree's height with a straight stick. Find a stick and measure it to be sure it is long enough. a. Grasp the stick so that one end is resting on your cheekbone (See photo 1)
b. Flip the stick straight up and down at arm's length in front of you and make sure the portion above your hand is the same as what you measured from your eye to your hand (see photo 2).
c. Step backwards until the tree's base appears to rest on the top of your fist, while the top of the stick appears to touch the top of the tree (see image 3).
d. At this exact point, the height of the tree is equal to the distance from the base of the tree to you. Place a stake in the ground and measure (in feet) from the trunk of the tree to the stake to find the height!
problems
1. What was the length of the stick you used to help measure the tree? 2. What was the distance from you to the base of the tree? 3. How did you measure the distance from you to the base of the tree (e.g. paces, yardstick, tape measure,
etc.)? 4. How tall did you find out the tree to be? 5. What are potential sources of error with this technique?
2. Hypsometer Method (Required)
Method
A hypsometer is basically a long stick divided into even units that are correlated to units on the ground. a. With a yardstick in hand, stand exactly 25 feet from the tree being measured. b. Hold the yardstick, with the zero end downward, 25 inches from your eye. c. Line up the bottom of the yardstick with the base of the tree.
d. Without moving your head, look to the top of the tree. e. Where it crosses the yardstick, read off the measurement in inches. f. Each inch will equal one foot in the tree's height. g. If the tree is taller than your hypsometer will measure, stand 50 feet away. Again hold it 25 inches from
your eye, as before, only this time multiply your result by 2 to get the correct height. If it is taller still, then step back to 75 feet, multiplying your result by 3, or 100 feet, multiplying the result by 4, etc. If you are using a meter stick, the procedure is basically the same. Stand 5 meters from the tree. Hold the meter stick 50cm from your eye. Each 10 centimeters will equal one meter of the tree's height. If standing at 10 meters, double the result; at 15m, triple it, etc. Granted, a five-meter tree isn't very tall, but it is a convenient scale to start with for the sake of mathematical progression.
problems
6. How did you measure the distance from the tree to you? 7. Where did the tree top cross the hypsometer? 8. How tall did you find out the tree to be? 9. What are the potential sources for error with this method? 10. How far back did you stand to measure the height of the tree?
3. Bellnet's Method (Use only if sun is shining.)
Method
You need a Sunny Day
a. b. c.
Measure Yardstick Shadow Measure Tree Shadow find out Tree Height using the ratio:
Yardstick Shadow/Yardstick Height = Tree Shadow/Tree Height
problems
11. What was the length of the yardstick shadow? 12. What was the length of the shadow of the tree? 13. What is the height of the tree? 14. What are two potential sources of errors associated with this method?
Or 3. Repeating Pencil Method (Use if sun is not shining)
Method
a. Let your partner stand the base of the tree. Move a distance away from the tree then, holding your pencil at arms length, between your thumb and forefinger so that it brackets the height of your partner (the top and bottom of the pencil coincide with the top of the head and the bottom of the feet of your partner).
b. Now, use this length to step out the height of the tree in "pencil lengths". You can now measure the height of your partner and multiply this by the number of pencils high the tree is.
c. Repeat three times from different distances and find out an average to improve the accuracy. Report the average of your three trials below in # 2.
problems (7.5 points each)
11. What was your partner's height? 12. How many pencil heights did the tree appear to be? 13. How high is your tree using this method? 14. What are two potential sources of errors associated with this technique?
Final Thoughts