Questions and Answers
What does dbh stand for?
Where do we measure dbh?
At 4.5 feet above the ground.
A forester measures a tree dbh as 12 inches. Can you guess whether he was using 1-inch or 2-inch dbh classes?
No, because it can be either.
What does D-tape really measure?
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Is a 1-inch interval between 7 and 8 inches the same distance as another 1-inch interval between 12 and 13 inches?
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I measured the diameter of a tree using two different instruments and obtained readings of 12.3" and 12.5". Which reading belonged to the D-tape and which to the calipers?
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Compute the dib of a tree, given that its dob is 17.5" and single bark thickness is 0.4".
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What do you call instruments that measure tree diameters?
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What do you call instruments that measure tree heights?
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What is the total height if you used a Suunto clinometer with a percent scale to measure total height from a 60-foot distance, and the readings were +5 and +92?
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What is the total height if you used a Haga altimeter with a topographic scale to measure from a 90-foot distance, and the readings were -4 and +89?
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How far should you be from a tree in order to measure its height?
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What are convenient distances for hypsometers with percent scales?
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What are convenient distances for hypsometers with topographic scales?
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Define Girard form class.
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If a tree measured 14.2" in dbh, 12.5" at 17.3', and 0.3" in single bark thickness, compute the Girard form class for that tree.
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Assuming that the average Girard form class for a particular stand is 80, what is the approximate scaling diameter of the butt log of a tree measuring 13.2" in dbh?
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A ring count at breast height reveals 15 rings. How old is the tree?
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Study Notes
Measuring Standing Trees
- Diameter at Breast Height (dbh): Measured at 4.5 feet above ground to standardize tree measurements and avoid breast height interference.
- Measurement Classes: A dbh of 12 inches could belong to either 1-inch or 2-inch classes, making it ambiguous without additional context.
- D-tape Function: Primarily measures the circumference of a tree rather than the diameter directly.
D-tape Calibration
- Measurement Consistency: 1-inch intervals measured using D-tape maintain the same distance regardless of the diameter range owing to the use of π intervals.
- Instrumentation Readings: D-tape tends to overestimate tree diameter, leading to a reading of 12.5 inches for D-tape when compared to 12.3 inches from calipers.
Calculating Diameter Inside Bark (dib)
- Dib Computation: To calculate dib, subtract double the bark thickness from the dbh; for a tree with a 17.5" dbh and 0.4" bark, dib is 16.7".
Instruments for Measurement
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Diameter Measuring Instruments:
- Calipers
- Biltmore Stick
- D-tape (collectively called dendrometers)
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Height Measuring Instruments:
- Abney Hand Level
- Suunto Clinometer
- Haga Altimeter
- Merritt Hyposometer (collectively referred to as hypsometers)
Height Measurement Techniques
- Distance for Height Measurement: Ideal distance for measuring a tree's height is greater than its height.
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Convenient Measurement Distances:
- Hypsometers with percent scales: 100 feet
- Hypsometers with topographic scales: Typically measured in chains.
Calculating Tree Height Examples
- Using Suunto Clinometer: For a reading of +5 and +92 at a 60-foot distance, the total height calculated is 52.2 feet.
- Using Haga Altimeter: With readings of -4 and +89 at a 90-foot distance, the total height determined is 127 feet.
Girard Form Class
- Definition: The Girard form class is calculated as dib at 17.3 feet divided by dbh, multiplied by 100. A value closer to 100 indicates a more cylindrical log.
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Example Calculation:
- For a tree with a dbh of 14.2", and a diameter of 12.5" at 17.3 feet, with bark thickness of 0.3", the Girard form class is 84.
Scaling Diameter
- Scaling Diameter Approximation: With an average Girard form class of 80, the scaling diameter for a tree with a 13.2" dbh is estimated at 10.86".
Tree Aging through Ring Count
-
Age Determination: A ring count reveals a tree age of 15 years, with variations:
- Hardwood: 5 years per ring
- Pine: 3 years per ring
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Description
Test your knowledge on measuring standing trees with a focus on diameter at breast height (dbh) and related concepts. This quiz includes essential definitions and practical application scenarios relevant to forestry. Perfect for students preparing for RNR 2102.
