Proceedings World Bioenergy 2010

(Gagnet and Unbyn) [4]. The second samples were taken
in May and the first days of June 2003, before the trees
started to grow, and the end of August and September
after the growing season had finished. In 2003, birches
were only sampled in August and September when the
leaves were developed but had not started to fall. In 2004,
biomass sampling from the thinned plots was done in
April.
2.3 Operations in the field
The sample tree was cut down at a stump height of
about 2 cm. DBH was marked and measured by cross
callipering, starting towards the north side of the tree. All
trees were measured in the same direction. The north side
of the tree was also marked to aid selection of sample
branches after felling. The thickness of the bark on Pinus
sylvestris and Picea abies was measured using a bark
gauge at the height of 1.35 m. The total length of the tree
and the length of living crown were measured with a
tape-measure. The living crown was defined as the first
living branch, if no more than two whorls of dead
branches separated the first living branch and the next
living branches.
The living crown was divided into four sections or strata
(25% of the crown each) (Figure 1). One branch was
chosen from each stratum for dry weight determination.
The sampled branch was subjectively selected to
represent all the branches from that section of the crown.
The first branch, from the first section of the crown, was
chosen from the first quarter (0 - 90 o ) of the stem circle
starting at north. The second branch was sampled from
the second quarter (90 – 180 o ) in the second section of
the crown, the third from the third quarter in the third
section and the fourth branch was from the fourth section
of the crown and the fourth quarter of the stem. All
branches from each section of the living crown were
weighed, and a sample of dead branches was also
collected from below the living crown for determination
of the DW of dead branches.
Figure 1. Sample tree for biomass studies
44 world bioenergy 2010
All branches were cut using pruning shears, and live and
dead branches were weighed separately. Six stem discs
were taken, the first from the butt end of the stem, from
the height of 130 cm (= DBH) and four further discs were
taken from 30%, 55%, 70% and 85% of the stem height
(Figure 1). The diameter of the disc was cross-callipered
over bark and all discs were cut to a 50 mm thickness.
The discs and the single sample branch were weighed in
the field on a laboratory balance (6 kg maximum ±
0.0005 kg). The log sections and all other branches were
weighed on a scale (30 kg maximum ± 0.002 kg).
2.3 In the laboratory
The four branches, a sample of dead branches from
below the living crown, and the 6 discs were put in
separate airtight bags and stored in a freezer (-20°C)
within 8 hours of sampling, until the dry weight was to be
determined. The bark was separated from the disc before
drying and all samples were dried in a ventilated oven
(85°C for 48 hours). The discs were dried to constant
weight, that is to say to the point where further drying
resulted in a decrease in weight of < 1%.
2.4 Statistics
Anderson-Darling´s test for normality was performed
on the data using MINITAB 13 [5]. A logarithmic
transformation was applied to the data to obtain a
constant variance [6. ]The regressions in this paper are
based on the following model:
Yi = β 0 + β 1x i + ε I (I = 1,2,…..n)
[7]. In this simple linear form, Y i is referred to as log DW
(kg), β 0 the intercept and x i to ln DBH * ln H.
The models were fitted using MINITAB 13 [5] software.
Statistical analysis of mean residuals for the sites showed
no significant difference between sites (results not
presented) [5]. Biomass for all treatments, each species
and component, was related to the natural logarithm of
DBH (cm) multiplied by the natural logarithm of height
(H) (dm). Biomass functions were created for all species
(i.e. Pinus sylvestris, Picea abies and Betula spp.), and
for all tree fractions (whole tree, stem, branches and
foliage).
For each biomass function, the correction for logarithmic
error was calculated as
[6].
3 RESULTS
3.1 Pinus sylvestris
The regression explained 77% - 97% of the biomass
variation (table 2 – 4). In the case of the PCT stand,
biomass functions were only established for Pinus
sylvestris (tables 2 – 4). For the whole tree and stem
fractions, no significant differences between trees
originating from the dense stand or the PCT stand could
be detected. Therefore, only one biomass function was
constructed for Pinus sylvestris for these fractions (table