Environmental Engineering Reference
In-Depth Information
aD
b
”, where M
frequently in the form of “M
¼
¼
dry weight of the biomass
component, D
diameter at breast height (dbh) (see
Diameter at Breast Height
below), and “a” and “b” are parameters whose specific values are presented in a
number of publications. So the practitioner needs to determine dbh and plug its
value into the equation with the appropriate parameter values obtained from
the literature. Two of the more extensive sources for allometric equations and the
parameters are Ter-Mikaelian and Korzukhin (
1997
), and Jenkins et al. (
2003
).
Ter-Mikaelian and Korzukhin (
1997
) presented biomass equations for 65 North
American tree species based on a literature review. Furthermore, they present
equations that address the following biomass components: foliage, branches,
stem wood, stem bark, total stem (wood + bark), and total aboveground biomass.
The geographic region that generated the data from which the parameter values
were derived is presented. Therefore, the practitioner has several equations avail-
able for each tree species and should select the equation most closely associated
with the site of interest. These equations were developed primarily for timber
species, and as such, some wetland tree species may not be represented. It is also
likely that the relation between dbh and biomass will be different between an
upland situation and a wetland situation. So it should be understood that these
indirect methods will give approximate values. However, they are useful for
comparing sites.
Biomass can be converted to C either by determining C content on specific
samples or by using published values of C content. Carbon analysis should be
conducted on tree cores taken at breast height. If bark represents a significant
proportion of aboveground biomass, bark should be partitioned from bole wood
both in the C analysis and in allometric equations.
¼
7.4.2.3 Diameter at Breast Height
Diameter at breast height is a standard method of expressing the diameter of the
trunk or bole of a standing tree. Tree trunks are measured at the height of an adult's
breast, which is defined differently in different countries. In the U.S., breast height
diameter is measured at a height of 1.4 m. On slopes or in wetlands with pit and
mound topography, the soil surface reference point to determine the 1.4 m above
ground sampling height may not be obvious. In those situations, the reference point
can be set as the highest point on the ground touching the trunk, or set as the average
between the highest and lowest points of ground. A consistent approach to setting
the reference point is critical.
Diameter at breast height is measured with a diameter (or girthing) tape or
calipers. A diameter tape measures the circumference (girth) of the tree; it is
calibrated in divisions of
centimeters (3.14 cm) and gives a directly converted
reading of the diameter. To determine tree diameter, the tape is wrapped (diameter
side facing user) around the tree. Tree diameter is indicated by the alignment of the
number “0” aligns with the rest of the tape. Calipers consist of two parallel arms;
one is fixed, the other slides along a scale. Calipers are held at right-angles to the
trunk with the arms on either side of the trunk. Diameter is directly calculated as the
π
