Diameter at breast height
Encyclopedia
Diameter at breast height, or DBH, is a standard method of expressing the diameter
of the trunk
or bole of a standing tree
. DBH is one of the most common dendrometric
measurements.
Tree trunks are measured at the height of an adult's breast, which is defined differently in different countries and situations. In continental Europe, Australia, the UK, and Canada the diameter is measured at 1.3 metres above ground. In The US, New Zealand, Burma, India, Malaysia, and South Africa, breast height diameter is measured at a height of 1.4 metres. Previously 4.5 ft (1.37 m) was used. In many cases the height makes little difference to the measured diameter. Ornamental tree
s are usually measured at 1.5 metres above ground.
On sloping ground, the "above ground" reference point is usually taken as the highest point on the ground touching the trunk, but some use the average between the highest and lowest points of ground. If the DBH point falls on a swelling in the trunk it is customary to measure the girth below the swelling at the point where the diameter is smallest.
The two most common instruments used to measure DBH are a girthing (or diameter) tape and caliper
s.
A girthing tape actually measures the girth (circumference
) of the tree; the girthing tape is calibrated in divisions of π
centimetres (3.14159 cm), thus giving a directly converted reading of the diameter. This assumes the trunk has a circular cross-section, which is typically accurate for most plantation
trees.
Calipers consist of two parallel arms one of which is fixed and the other able to slide along a scale. Calipers are held at right-angles to the trunk with the arms on either side of the trunk. Precision can be improved on non-circular stems by averaging two caliper measurements taken at right-angles. Electronic calipers are also available enabling highly accurate measurements to be taken and stored for further analysis.
DBH is used in estimating the amount of timber
volume in a single tree or stand of trees utilising the allometric
correlation between stem diameter, tree height and timber volume, (Mackie, 2006). It can also be used in the estimation of the age of veteran trees, given that diameter increment is the only, "constant non-reversible feature of tree growth", (White, 1998).
Diameter
In geometry, a diameter of a circle is any straight line segment that passes through the center of the circle and whose endpoints are on the circle. The diameters are the longest chords of the circle...
of the trunk
Trunk (botany)
In botany, trunk refers to the main wooden axis of a tree that supports the branches and is supported by and directly attached to the roots. The trunk is covered by the bark, which is an important diagnostic feature in tree identification, and which often differs markedly from the bottom of the...
or bole of a standing tree
Tree
A tree is a perennial woody plant. It is most often defined as a woody plant that has many secondary branches supported clear of the ground on a single main stem or trunk with clear apical dominance. A minimum height specification at maturity is cited by some authors, varying from 3 m to...
. DBH is one of the most common dendrometric
Dendrometry
Dendrometry is the branch of botany that is concerned with the measurement of the various dimensions of trees, such as their diameter, size, shape, age, overall volume, thickness of the bark, etc., as well as the statistical properties of tree stands, including measures of central tendency and...
measurements.
Tree trunks are measured at the height of an adult's breast, which is defined differently in different countries and situations. In continental Europe, Australia, the UK, and Canada the diameter is measured at 1.3 metres above ground. In The US, New Zealand, Burma, India, Malaysia, and South Africa, breast height diameter is measured at a height of 1.4 metres. Previously 4.5 ft (1.37 m) was used. In many cases the height makes little difference to the measured diameter. Ornamental tree
Ornamental plant
Ornamental plants are plants that are grown for decorative purposes in gardens and landscape design projects, as house plants, for cut flowers and specimen display...
s are usually measured at 1.5 metres above ground.
On sloping ground, the "above ground" reference point is usually taken as the highest point on the ground touching the trunk, but some use the average between the highest and lowest points of ground. If the DBH point falls on a swelling in the trunk it is customary to measure the girth below the swelling at the point where the diameter is smallest.
The two most common instruments used to measure DBH are a girthing (or diameter) tape and caliper
Caliper
A caliper is a device used to measure the distance between two opposing sides of an object. A caliper can be as simple as a compass with inward or outward-facing points...
s.
A girthing tape actually measures the girth (circumference
Circumference
The circumference is the distance around a closed curve. Circumference is a special perimeter.-Circumference of a circle:The circumference of a circle is the length around it....
) of the tree; the girthing tape is calibrated in divisions of π
Pi
' is a mathematical constant that is the ratio of any circle's circumference to its diameter. is approximately equal to 3.14. Many formulae in mathematics, science, and engineering involve , which makes it one of the most important mathematical constants...
centimetres (3.14159 cm), thus giving a directly converted reading of the diameter. This assumes the trunk has a circular cross-section, which is typically accurate for most plantation
Plantation
A plantation is a long artificially established forest, farm or estate, where crops are grown for sale, often in distant markets rather than for local on-site consumption...
trees.
DBH is used in estimating the amount of timber
Lumber
Lumber or timber is wood in any of its stages from felling through readiness for use as structural material for construction, or wood pulp for paper production....
volume in a single tree or stand of trees utilising the allometric
Tree allometry
Tree allometry establishes quantitative relations between some key characteristic dimensions of trees and other properties...
correlation between stem diameter, tree height and timber volume, (Mackie, 2006). It can also be used in the estimation of the age of veteran trees, given that diameter increment is the only, "constant non-reversible feature of tree growth", (White, 1998).