Description

DBH is an initialism that curtails 'Diameter at Breast Height', which is a standard 4.5 feet above the ground-line in English units, or a standard 1.3 meters in metric units. In this Conclave event, competitors must stand at least 10 feet away from each specimen and estimate its DBH to the nearest 0.1 inches. They may not place a thumb or other scaling object between their eye and the tree. The competition consists of 10 trees, 5 conifers and 5 hardwoods. The absolute value of the deviations between estimated and measured DBH are summed across the 10 trees, and the competitor with the lowest total deviation wins. The absolute value is used so that over-estimating the diameter of one tree is not canceled out by under-estimating the diameter of the next. DBH estimation has been a Conclave event every year since at least 1960.

DBH Estimation Example Photos

Photo Credit: Students estimating the diameter of the marked pine at the 59^th Southern Forestry Conclave hosted by Clemson University. Photo by Jeremy Stovall.

Photo Credit: Often forked trees or other trees with unusual features are given as specimens to make DBH estimation more challenging. Photo by Jeremy Stovall.

Academic Background

DBH estimation is an important skill for foresters to learn if they are to become efficient timber cruisers. More information on timber cruising is available on the timber estimation event page.

Resources

For Conclave, it is important to spend extra time practicing DBH estimation of large trees. While you are unlikely to miss a 6.0 inch DBH tree by very much, you could easily miss a 50.0 inch dbh tree by many inches. These trees tend to make or break the winners of this event each year. While a straight, single-trunked tree growing on flat ground is fairly easy to estimate, there are many different specialized situations that occur commonly in the woods which make DBH estimation more challenging.

Specialized situations you may encounter at Conclave include:

A tree on a hill: estimate from 4.5 feet above the ground on the uphill side of the tree.
A tree forked above 4.5 feet: if you can't see daylight in a fork at 4.5 feet, simply estimate DBH as usual.
A tree forked below 4.5 feet: if you can see daylight in the fork at 4.5 feet, treat each portion of the fork as a separate tree. You must only estimate DBH of the stem indicated by the judge.
A tree that is elliptical, or off-round: walk around the tree, estimate the largest and smallest DBH, and average them.