Diameter at breast height, or DBH, is a standard measure when talking about trees. The DBH refers to the tree diameter measured at 4.5 feet or 1.3 meters above the ground. DBH is one of the most commonly used dendrometric measurement terms, to estimate the amount of timber volume in a single tree or stand of trees by using the allometric correlation between stem diameter, tree height and timber volume.
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The measure for DBH can also be used to estimate tree age in very old tree individuals, since the increment of the diameter is constant and non-reversible feature in the growth.
Bark thickness and texture vary greatly between tree species and can have effects on the diameter measure. The bark can be several centimeters thick, and a measurement of stem diameter over bark can be much greater than of the wood below bark. If you are working with a computer caliper to measure tree diameters, a bark deduction can be set in the software. To check the thickness of bark, a simple bark gauge is recommended. The bark gauge consists of a shaft with a sharp point which is pushed through the bark until the underlying wood is felt. The sleeve around the shaft is then shifted to the surface of the bark and the bark thickness read from the calibrated shaft.
The height for DBH should be equal to the height of an adult&#;s breast. This measure can differ depending on situation and country. In many cases, the exact height makes little difference to the measured diameter, although it may influence your calculations of the forestry biomass. If the ground is sloping, the reference point may be taken as the highest point on the ground touching the trunk, or as an average between the highest and lowest points of ground. In other cases, the DBH will be at an anomalous place of the trunk, such as a swelling. The girth should then be measured below the swelling, where the diameter is smallest.
There are two dominant methods and tools to measure tree diameters: diameter tapes and diameter calipers. Which method and what instruments you select can depend on different things, such as common standards in your company, area or country, the accuracy demands and what type of vegetation you are working in. For any type of diameter measurement method that you choose to work with, it is important to not squeeze too firmly when getting the measure. For example, no pressure should be used when applying the caliper jaws around the stem.
The diameter tape will be small and easy to carry around with you in the forest. A diameter caliper will be more bulky and heavier to carry. On the other hand, the diameter caliper offers quicker results. As caliper manufacturers, we have put great efforts in lowering the weight and slimming all parts for our calipers, without compromising the product quality. Several Haglöf Sweden caliper models offer for example patented foldable jaws, that make transporting and storing of the caliper easier.
Diameter tapes will measure the average diameter corresponding to the girth of the tree, wheras calipers measure stems across one diameter of their cross-section. When using a caliper to measure the stem diameter, it is common to take two diameter measurements at right angles to each other. The square root of the product of the two diameters is then used as the measure of stem diameter.
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With a diameter tape, you will measure the circumference of the trunk and divide this measure by 3 to get the diameter, since the tape is calibrated in divisions of π (Pi) centimeters (3. cm). There are diameter tapes that offer a scale for the conversion from circumference to diameter. The measurement with a diameter tape will presuppose that the tree trunk has a circular cross-section, which is also typically accurate for many plantation trees. Our studies show that diameter tapes generally will over-estimate the diameter, if the tree diameter is irregular. The error when using a diameter caliper will, most often, be smaller compared to a tape and when performing 2x measuring.
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For example, producing any medical tubing product with an &#;out-of-tolerance&#; diameter or roundness, often down to ten-thousandths of an inch, affects the performance of life-critical devices such as catheters, drug delivery and surgical tubing, and other medical devices.
With communication cables, such as Coaxial and twisted-pair LAN products, any error in the diameter or roundness of the conductor or insulation directly impacts the cable&#;s performance characteristics -- rendering the product useless for the designed application.
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