Environmental Engineering Reference
In-Depth Information
biomass using published allometric equations that depend on dbh. Sources of these
equations include Whittaker et al. (
1974
) and Vadeboncoeur et al. (
2007
). Carbon
content can be determined from coarse roots excavated on site or from core samples
taken with increment corers from roots leaving the tree base.
7.4.2.6 Fine Root Biomass
Fine roots (
<
2 mm diameter) typically contribute
<
5 % of the total tree biomass
(DeAngelis et al.
1981
; Vogt et al.
1996
). However, it has been estimated that fine
root production constitutes about 30-50 % of the C being cycled annually through
forest ecosystems (Grier et al.
1981
; Vogt et al.
1996
). Therefore, fine roots
constitute a small but functionally critical fraction of ecosystem biomass. Hertel
and Leuschner (
2002
) consider fine root production and root exudation as the least
known processes of the C cycle of forests. However, both processes supply organic
C to microbes critical to biogeochemical cycling. In addition, fine root production
and turnover may be a sensitive indicator of changing soil environments, and
therefore, ecosystem health (Bloomfield et al.
1996
).
The sequential root coring method is commonly used to collect fine root biomass
data. In this approach, roots are collected from soil cores taken sequentially
throughout the year, typically at 1-2 month intervals. It employs a metal tube
sharpened on one end which is manually driven into the ground to collect the soil
cores. There is no set size for the corer. It should be at least as long as the depth of
the soil to be sampled. The wider the corer, the easier it is to extract the soil from
the corer while maintaining the integrity of the soil core. This is critical if the soil
core is to be divided into sub-samples based on depth. Vogt and Persson (
1991
)
used corers with a diameter of 33 mm and a length of 150 mm. Persson (
1978
) used
a corer with an internal diameter at the hardened steel cutting edge of 6.7 cm while
the upper part of the tube had an internal diameter 2 mm larger which facilitates
removal of the soil cores by inverting the corer. Typically, the soil core is divided
into sub-samples based on horizon. Horizon thickness should be noted prior to
sampling so that a sampling volume can be determined. Horizon thickness is
determined from an adjacent spade slice as core insertion can compact the soil.
This is especially a problem with organic horizons. Thickness of the sub-samples is
also determined to allow for the correction of volume lost due to compression when
calculating root density. Soil sub-samples are transferred to plastic bags, sealed, and
transported to the laboratory for processing. Prior to processing, samples are stored
at 4
C. Live roots can be distinguished from dead roots (necromass) under a
dissecting microscope after staining. The necessary techniques are presented by
Hertel and Leuschner (
2002
) and Knievel (
1973
).
Combining the sequential root coring method with the 'minimum-maximum
method' (SC - MM) allows for an estimate of biomass production without
distinguishing between biomass and necromass (Edwards and Harris
1977
). With
the minimum-maximum method, biomass production is calculated as the differ-
ence between the minimum value and maximum value of fine root biomass and
