Diameter at breast height

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Measurement of tree circumference, the tape calibrated to show diameter, at breast height, making sure that the tape is perfectly level and that the tape is not kinked, so as not to skew the reading of the diameter. Using a DTApe.JPG
Measurement of tree circumference, the tape calibrated to show diameter, at breast height, making sure that the tape is perfectly level and that the tape is not kinked, so as not to skew the reading of the diameter.

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.

Contents

Electronic calipers can measure diameter at breast height and send measured data via Bluetooth to a field computer. Electronic caliper.jpg
Electronic calipers can measure diameter at breast height and send measured data via Bluetooth to a field computer.

Tree trunks are measured at the height of an adult's breast, which is defined differently in different countries and situations. In many countries, DBH is measured at approximately 1.3 m (4.3 ft) above ground. [1] [2]

Global variation and scientific precision

The height can make a substantial difference to the measured diameter. [3]

In the United States, DBH is typically measured at 4.5 ft (1.37 m) above ground. [4] [5] In some countries, such as Australia, New Zealand, Burma, India, Malaysia, and South Africa, breast height diameter has historically been measured at a height of 1.4 m (4 ft 7 in), but because of much active research into allometrics that are being applied to trees and forests, the convention of 1.3 m (4.3 ft) is more appropriate.[ citation needed ] Ornamental trees are usually measured at 1.5 metres above ground.[ citation needed ]

Some authors [6] have argued that the term DBH should be abolished because the heights at which the diameter is measured are excessively variable and imprecise, and imprecise measurements could strongly influence forestry calculations such as biomass. Alternatives proposed [ by whom? ] have included Dx whereby the x denotes the exact height above the floor (and along the stem) at which the diameter is measured.[ citation needed ] For instance D130 denotes a diameter measured at 130 cm above the floor and along the stem.

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. Other ambiguous settings for determining the exact place where to measure the diameter is given in Dahdouh-Guebas & Koedam (2006). [7]

Methodology

A tree caliper Kluppeneinsatz.jpg
A tree caliper

The two most common instruments used to measure DBH are a girthing (or diameter) tape and calipers.

A girthing tape actually measures the girth (circumference) of the tree; the girthing tape is calibrated in divisions of π centimetres (3.14159 cm). The measure assumes the trunk has a circular cross-section and gives a directly converted reading of the diameter.[ citation needed ] It is accurate for most plantation trees.[ according to whom? ]

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.[ citation needed ]

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. [8] 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". [9]

See also

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The following outline is provided as an overview of and guide to forestry:

Basal area is the cross-sectional area of trees at breast height. It is a common way to describe stand density. In forest management, basal area usually refers to merchantable timber and is given on a per hectare or per acre basis. If you cut down all the merchantable trees on an acre at 4 ½ feet off the ground and measured the square inches on the top of each stump (πr*r), added them all together and divided by square feet, that would be the basal area on that acre. In forest ecology, basal area is used as a relatively easily-measured surrogate of total forest biomass and structural complexity, and change in basal area over time is an important indicator of forest recovery during succession .

<span class="mw-page-title-main">Diameter tape</span> Measurement tool

A diameter tape (D-tape) is a measuring tape used to estimate the diameter of a cylinder object, typically the stem of a tree or pipe. A diameter tape has either metric or imperial measurements reduced by the value of π. This means the tape measures the diameter of the object. It is assumed that the cylinder object is a perfect circle. The diameter tape provides an approximation of diameter; most commonly used in dendrometry.

<span class="mw-page-title-main">Tree allometry</span> Quantitative relations between some key characteristic dimensions of trees

Tree allometry establishes quantitative relations between some key characteristic dimensions of trees and other properties. To the extent these statistical relations, established on the basis of detailed measurements on a small sample of typical trees, hold for other individuals, they permit extrapolations and estimations of a host of dendrometric quantities on the basis of a single measurements.

Forest inventory is the systematic collection of data and forest information for assessment or analysis. An estimate of the value and possible uses of timber is an important part of the broader information required to sustain ecosystems. When taking forest inventory the following are important things to measure and note: species, diameter at breast height (DBH), height, site quality, age, and defects. From the data collected one can calculate the number of trees per acre, the basal area, the volume of trees in an area, and the value of the timber. Inventories can be done for other reasons than just calculating the value. A forest can be cruised to visually assess timber and determine potential fire hazards and the risk of fire. The results of this type of inventory can be used in preventive actions and also awareness. Wildlife surveys can be undertaken in conjunction with timber inventory to determine the number and type of wildlife within a forest. The aim of the statistical forest inventory is to provide comprehensive information about the state and dynamics of forests for strategic and management planning. Merely looking at the forest for assessment is called taxation.

The Biltmore stick is a tool used by foresters to estimate tree trunk diameter at breast height. The tool very often includes a hypsometer scale to estimate height as well. It looks much like an everyday yardstick. With practice a Biltmore stick is considered to be exceptionally accurate, more often within 13 millimetres on diameters. Some foresters use the tool regularly, however, many prefer to use more accurate tools such as a diameter tape to measure diameter at breast height (DBH) and a clinometer to measure height. On the other end of the spectrum, some foresters consider the use of a Biltmore stick to be no more accurate than their own visual estimates, and make it practice for their surveys to be largely completed in this manner.

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<span class="mw-page-title-main">Dendrometry</span>

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Tree height is the vertical distance between the base of the tree and the tip of the highest branch on the tree, and is difficult to measure accurately. It is not the same as the length of the trunk. If a tree is leaning, the trunk length may be greater than the height of the tree. The base of the tree is where the projection of the pith (center) of the tree intersects the existing supporting surface upon which the tree is growing or where the seed sprouted. If the tree is growing on the side of a cliff, the base of the tree is at the point where the pith would intersect the cliff side. Roots extending down from that point would not add to the height of the tree. On a slope this base point is considered as halfway between the ground level at the upper and lower sides of the tree. Tree height can be measured in a number of ways with varying degrees of accuracy.

<span class="mw-page-title-main">Tree girth measurement</span>

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In forestry, a tree crown measurement is one of the tree measurements taken at the crown of a tree, which consists of the mass of foliage and branches growing outward from the trunk of the tree. The average crown spread is the average horizontal width of the crown, taken from dripline to dripline as one moves around the crown. The dripline is the outer boundary to the area located directly under the outer circumference of the tree branches. When the tree canopy gets wet, any excess water is shed to the ground along this dripline. Some listings will also list the maximum crown spread which represents the greatest width from dripline to dripline across the crown. Other crown measurements that are commonly taken include limb length, crown volume, and foliage density. Canopy mapping surveys the position and size of all of the limbs down to a certain size in the crown of the tree and is commonly used when measuring the overall wood volume of a tree.

Tree volume is one of many parameters that are measured to document the size of individual trees. Tree volume measurements serve a variety of purposes, some economic, some scientific, and some for sporting competitions. Measurements may include just the volume of the trunk, or the volume of the trunk and the branches depending on the detail needed and the sophistication of the measurement methodology.

Trees have a wide variety of sizes and shapes and growth habits. Specimens may grow as individual trunks, multitrunk masses, coppices, clonal colonies, or even more exotic tree complexes. Most champion tree programs focus finding and measuring the largest single-trunk example of each species. There are three basic parameters commonly measured to characterize the size of a single trunk tree: tree height measurement, tree girth measurement, and tree crown measurement. Foresters also perform tree volume measurements. A detailed guideline to these basic measurements is provided in The Tree Measuring Guidelines of the Eastern Native Tree Society by Will Blozan.

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<span class="mw-page-title-main">Tree caliper</span> Tool for measuring the diameter of the cross-section of trunks

A tree caliper is a special caliper to measure the diameter at breast height of a tree. When used in forestry, the term "caliper" can refer to the diameter of a tree's trunk at breast height itself. The measurement is generally made at 4.5 feet (1.4 m) to 5 feet (1.5 m) above the soil.

References

  1. Cris Brack, PhD (UBC) Standard point on tree bole for measurement Archived 2010-05-12 at the Wayback Machine . Forest Measurement and Modelling. Retrieved 2009-04-18.
  2. Feldpausch et al 2011, Height-diameter allometry of tropical forest trees. Biogeosciences 8, 1081-1106.
  3. Paul, K.I. et al. 2017. Measurements of stem diameter: implications for individual- and stand-level errors. Environmental Monitoring and Assessment 189, 416.
  4. United States Department of Agriculture - U.S. Forest Service. October 2019. Forest Inventory and Analysis: National Core Field Guide. Volume I: Field Data Collection Procedures for Phase 2 Plots. Version 9.0.
  5. Burns, Russell M. (1990). Silvics of North America: Hardwoods. Vol. 2. United States Forest Service. ISBN   9780160292606..
  6. Brokaw, N. & J. Thompson, 2000. The H for DBH. Forest Ecology and Management 129: 89-91.
  7. Dahdouh-Guebas, Farid; Koedam, Nico (15 June 2006). "Empirical estimate of the reliability of the use of the Point-Centred Quarter Method (PCQM): Solutions to ambiguous field situations and description of the PCQM+ protocol" (PDF). Forest Ecology and Management. 228 (1): 1–18. doi:10.1016/j.foreco.2005.10.076.
  8. Mackie, E. D. and Matthews, R. W. (2006). Forest Mensuration, a handbook for practitioners. HMSO, Edinburgh. ISBN   0-85538-621-5
  9. White, J. (1998). Estimating the Age of Large and Veteran Trees in Britain. Forestry Commission Information Note 12. Surrey.