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Questions and Answers
What does dbh stand for?
What does dbh stand for?
- Depth at Breast Height
- Diameter at Breast Height (correct)
- Diameter at Height
- Diameter at Base Height
Where do we measure dbh?
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?
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?
What does D-tape really measure?
Is a 1-inch interval between 7 and 8 inches the same distance as another 1-inch interval between 12 and 13 inches?
Is a 1-inch interval between 7 and 8 inches the same distance as another 1-inch interval between 12 and 13 inches?
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?
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?
Compute the dib of a tree, given that its dob is 17.5" and single bark thickness is 0.4".
Compute the dib of a tree, given that its dob is 17.5" and single bark thickness is 0.4".
What do you call instruments that measure tree diameters?
What do you call instruments that measure tree diameters?
What do you call instruments that measure tree heights?
What do you call instruments that measure tree heights?
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?
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?
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?
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?
How far should you be from a tree in order to measure its height?
How far should you be from a tree in order to measure its height?
What are convenient distances for hypsometers with percent scales?
What are convenient distances for hypsometers with percent scales?
What are convenient distances for hypsometers with topographic scales?
What are convenient distances for hypsometers with topographic scales?
Define Girard form class.
Define Girard form class.
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.
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.
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?
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?
A ring count at breast height reveals 15 rings. How old is the tree?
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
-
Diameter Measuring Instruments:
- Calipers
- Biltmore Stick
- D-tape (collectively called dendrometers)
-
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.
- 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.
- 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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