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Measurement of the girth of a tree is one of the standard forestry measurements. This measurement is taken at 1.35 meters (4.5 feet) from the ground and known as the Diameter Breast Height (or DBH for short).

This measurement of a tree's diameter can be measured either using calipers, or by using a tool called DBH tape. What is special about DBH tape is it measures the circumference of the tree, and converts this measure to the diameter by dividing by Pi (i.e. the long number 3.14159....). This division is done on the tape, so that every 3.14 cm along the tape, is labeled as one cm. This makes it easy because no calculations are required when using the DBH tape to measure tree diameter.

For this instructable I wanted to show how to make this specialized DBH tape so you could make your own!

You'll need:

  • a permanent marker
  • a long piece of wood, or similar
  • a square tool, or a ruler
  • 5 pieces of specialized lumber strapping (flexible plastic that will wrap around trees for making your DBH)
  • 2-4 clamps
  • a paint pen
  • Tuck tape
  • String

Step 1: Set Up

Lay out a reference board with measurements in pi centimeters (i.e. make a mark every 3.14 cm). Use your square or ruler to mark each interval across the board with your marker.

Then, clamp five lengths of plastic lumber strapping along the reference board.

Step 2: Marking Your DBH Tape

  • Using the reference board as a guide, mark across the strapping at each interval using the paint pen.
    • Make sure you leave about 5 cm at each of the ends of the DBH tape.
  • Next, divide the first unit (from one mark to the other) into 10 equal parts and make those lines. This will allow you to measure to 1/10 of a Pi cm.
  • Number each interval on the DBH tape in order, starting at 1.
  • Choose which end will be the starting end. Then, wrap the starting end with TuckTape to secure a string to hold the DBH tape in place when you are making your measurements.

There you have it - a DBH tape of your very own. Now you can go out and wrap them around trees and know exactly what their diameter is! Then you can return in a year and measure the same trees and see if they've grown! Enjoy.

<p>Very cool! Like this idea quite a bit. thanks!</p>

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