BMP - Tree Inventories - 20

Diameter

Tree trunk diameter should be recorded. It provides an estimate of tree age
from which the forest's overall age structure can be derived to aid long-range
management decisions, and to enable value to be estimated. Diameter can
also be used for estimating maintenance time and costs.
* Diameter is measured at
a standard height. In the
United States, the standard
height is 4.5 ft (1.4 m)
above grade (referred to as
diameter at breast height,
dbh). Most other countries
use 1.3 m as their standard
measurement height.
* It is sufficient for many
purposes to use size-class
[e.g., 1 to 6 in (2 to 16 cm),
7 to 12 in (17 to 31cm), etc.]
because exact diameters
quickly lose their accuracy,
and are time-consuming to
collect.
9. A data collector measuring diameter
* Standard criteria should Figure
at breast height (dbh).
be adopted for measuring
the diameter of common exceptions, such as trees on slopes and
multi-stemmed trees. Trees on slopes are typically measured at 4.5
ft (1.4 m) above grade on the uphill side of the trunk, although for
some purposes it may be preferable to use the downhill side. Multistemmed trees can be defined by the location of the pith union (e.g.,
below ground) or the bottom of the stem union [e.g., below 1 ft (0.3
m)]. The stems' diameters can be listed individually, averaged, or
summed (the least preferred method). The method of determining
multi-stemmed trees must be clearly stated and consistently applied.

* Diameter tapes with 0.1-in (3 mm) increments can be specified for
the highest level of precision, although a Biltmore stick is faster
and provides a useful measurement. Rounding to the nearest inch or
centimeter is standard practice.
20

BMP - Tree Inventories

Table of Contents for the Digital Edition of BMP - Tree Inventories