2.2 CALCULATION OF BASIC DENSITY WATER-IMMERSION In the procedure outlined, basic density is calculated
by the formula:
Basic Density = m
=oven dry weight; V=volume of fully
Basic Density = 1/((m-m
) (maximum moisture approach)
where m=weight of a completely saturated sample;
=Density of the cell wall which is 1530 (units
2.2.1 Equipment and Procedure The equipment required is simple, but must be
maintained in good working order if accurate
results are to be obtained.
An electronic balance (accurate to at least
0.1g) is preferable for weighing the sections.
A container holding enough water to fully
submerge the sample.
A fine needle point to hold the submerged
wood samples at a minimal fixed depth.
A well-ventilated oven with automatic
temperature control is needed for drying
the sections. The oven requires shelves of
wire mesh or other open material to allow
free internal circulation of air. Otherwise,
the sections may not dry thoroughly. The
temperature at any point inside the oven
should neither exceed 105°C nor fall below
101°C; this degree of uniformity is generally
achieved by using a double-shell
construction or by the use of a circulating
fan inside the oven. Below 100°C the
sections may not be dried completely, and
above 105°C they may char.
Figure 1: Example of a temperature controlled oven for drying sections 2.2.2 Procedure for water displacement determinations 1.
Remove wood core from tree.
Scrape away all loose splinters and sawdust
and place in a tight fitting container to
prevent it from drying out.
In the laboratory, place the sample (full
core) into water for at least half an hour to
ensure adequate swelling.
Place the water container on the pan of the
electronic scales and re-zero (stand and
needle not included).
Remove the sample from the water, wipe
with a damp cloth, and then completely
submerge in the container on the electronic
scales, without touching the container, as
shown in the diagram below.
National Carbon Accounting System Technical Report 3 1
The fully swollen sample does not need to be fully saturated
Figure 2: Diagram of water displacement method for measuring volume. 6.
As the density of water under normal
laboratory conditions is equal to 1000
, the measured weight of the
displaced water is equal to the volume of
Note: for scale readings in grams, the
volume can be read directly from the scales
Place the specimen in an oven for drying.
Be sure to maintain the oven temperature
within the limits 101-105°C.
10. Do not overcrowd the oven, but leave
spaces between the sections.
Do not add fresh sections to the oven if it
contains sections almost ready for final
12. After 24 hours, remove the section from the
oven, reweigh it, and record the weight.
13. Sections must be weighed immediately after
removal from the oven, as they reabsorb
moisture from the air very quickly.
14. Replace the section in the oven and reweigh
at intervals of 4 hours, until there is no
further loss in weight. This weight is m
equation 1 and 2.
15. Calculate basic density using equation 1.
2.3 MAXIMUM SATURATION This procedure is simpler to carry out than the
water-displacement method. It requires only two
weight determinations: the weight of the completely
water-saturated wood specimen (m in equation 2)
and its oven dry weight (m
Place samples in water at room temperature
in a vacuum flask and apply vacuum
intermittently until no more water is
absorbed and the specimens have reached
constant weight. In practice this takes
about two to three weeks.
After the specimens are saturated, place
them in damp cloth for 20 minutes to
remove excess surface water without drying
Weigh the samples quickly to prevent errors
from drying out.
Use equation 2 to calculate basic density
is the same as that in equation 1).
2.4 NONDESTRUCTIVE ESTIMATION USING THE PILODYN A typical pilodyn instrument and its use is shown in
Australian Greenhouse Office 4
2.4.1 Calibration and use of the Pilodyn •
Select an aspect (North), make a small
window in the bark with a bark punch to
expose the xylem.
Depress the pildyn head on to the cleared
wood and fire the pin.
Take a reading of the depth of pin
penetration from the side of the instrument.
Repeat penetration reading on opposite side
Determine the mean for each tree and
As an indirect measure of density, the depth of pin
penetration must be calibrated for each species at
every site under investigation.
This can be carried out by taking increment cores
from a number of trees representing the extremes of
the pilodyn readings. Basic density of the cores can
be determined using water immersion or maximum
3. ESTIMATING WOOD DENSITY OF WHOLE TREES (WHOLE TREE CORRELATIONS) 3.1 Background: Most of the research to date has focused on
industrial concerns, and the available data examines
only variation in the merchantable stem (commonly
base to 70% total tree height). The following
sampling protocol has been used extensively for
plantation studies and is intended to provide a basis
for estimating the average density of the
merchantable stem. Some modifications have been
made to accommodate the different nature of this
study. These are noted specifically at the end of the
protocol description. The reader is referred to the
general protocol detailed in Downes et al. (1997) for
The aim of this section is to provide a rationale and
a procedure for obtaining estimates of whole tree
wood density for a given species at a given site.
Wood density varies in trees from pith to bark and
from base to apex within a tree. Similarly wood
density of branches is likely to vary, but little
information is available. In order to determine the
National Carbon Accounting System Technical Report 5 Figure 3. Pilodyn tester used for estimating basic density in a eucalypt log
total amount of carbon locked up in woody tissue,
both the volume and density of that tissue must be
The majority of studies looking at density variation
have been done on commercial timbers,
predominantly plantation species. Little or no data
are available on patterns of variation in non-
commercial species. The studies on plantation
species have indicated several important factors.
Annual ring average density generally
increases from pith to bark in all species
(softwood and hardwood) with the rate and
pattern of increase dependent upon species
and growth pattern. Growth pattern
reflects the proportions of the ring that is
produced at different times of the year
which controls the average density of the
ring. In general increasing growth rate will
result in more wood production in spring.
This wood has a lower density. Therefore
faster growth rate generally results in lower
annual ring density. Rainfall appears to
have a dominant effect here.
Wood density varies from base to apex. The
pattern appears to differ between softwoods
(radiata pine) and hardwoods (eucalypts).
Density has a cylindrical symmetry in
softwoods (see description in Downes et al. 1997) resulting in a reduction in density
with height. In eucalypts the pattern
appears to be more conical with the
interaction between the radial and
longitudinal variation allowing density to
vary from constant to increasing with
height. Based on studies with plantation
species the general pattern appears to be a
gradual increase with height.
3.2 Sampling protocol The method of sampling can have major effects on
the data ultimately produced by a study and its
interpretation (see Chapter 3, Downes et al. 1997).
For sampling to be most effective, there needs to be
a clear understanding of why the samples are being
taken, and how they are going to be analysed. The
choice of methods for sampling and analysis of
wood properties should consider the need to
interpret the resultant data within the context of
existing scientific literature. Therefore, ancillary
information about the site and sample population
should be collected to facilitate this process. This
section endeavours to provide a protocol for
collecting and processing wood samples for analysis
of wood density and subsequent data interpretation.
3.3 Necessary site data Collection of site data should be done as part of
routine practice in sampling studies. These data can
then contribute to a larger database that can be used
to develop a broader understanding of wood
Necessary data should include the following:
Height of sampling point and total tree
Diameter measured over bark at the
Location; latitude and longitude; altitude.
Each of these factors can affect growth rates
and their patterns across the year.
Compass direction of core.
Measure of site quality if available (with
explanations as required). A definition of
the site index should be provided.
Median rainfall and seasonal distribution if
available. Patterns of rainfall can have as
marked an effect on wood properties, as
total amounts. A more consistent growth
pattern resulting from an even spread of
rainfall throughout the year will produce a
more uniform wood than a site where
rainfall is concentrated in particular
Soil type according to Northcote (1987).
Australian Greenhouse Office 6
3.4 Obtaining the sample The proposed protocol consists of two components:
An initial calibration procedure (destructive
The non-destructive sampling program.
Given that there are large variations between sites
and species, the pattern of wood property variation
has to be calibrated for each site/species
combination until sufficient information is available
to understand the effects on tree growth and wood
properties (see explanatory note 1).
3.5 Destructive sampling Objective: To obtain a calibration for relating
density measured from 12 mm increment cores at
1.1m height to whole tree density.
The number of trees required per site depends
statistically on the variability between trees. In
general this will not be known for either a given
species or site selected for measurement. Thus
based on the amount of sampling required in the
overall program and the extensive data base being
generated, we recommend that six trees per species
per site be destructively sampled (see explanatory
All activities should be undertaken in accordance
with the relevant codes of forest practice.
Destructive collection involves the use of a chain
saw, which should only be used by trained
Generalised destructive sampling procedure 1.
Select trees for destructive sampling that
represent the trees to be sampled in the
non-destructive sampling, that is, across the
total size range (for core sampling this will
generally be in excess of 15 cm dbhob).
Mark the north aspect on the bark.
Remove a 12 mm increment core from the
stem at approx. 1.1 m.
Fell the tree and trim branches along the
length of trunk.
Measure total tree height taking into
account the height of the falling cut above
Sample from the top of the tree towards the
base. Calculate and mark on the tree the
percentage height points (2, 10, 40 and 70%
of total height; see explanatory note 3),
taking the lowest disc from as close above
the scarf as possible.
Cut 50 mm discs and label them.
3.6 Sampling using 12 mm increment cores Objective: To increase the accuracy of the whole-
tree density estimate in a given species and site by
taking 12 mm increment cores from 1.1 m above
ground and estimating whole tree density.
The non-destructive sampling procedure provides
an effective means of increasing the estimation
accuracy by allowing more trees to be sampled
quickly. The between tree variability is thus
determined more accurately and provides a basis
for determining confidence in the final result.
3.7 How many to sample The number of trees sampled will depend on the
variability across the site in terms of slope, soil type
and rainfall. Assuming a moderately uniform site
we recommend the non-destructive sampling of an
additional 24 trees, providing a total sample of 30
trees per site. Actual numbers will need to be
determined site by site, in the light of various
constraints including the environmental sensitivity
of the sampling process.
3.8 Where to sample The logistics of core sampling require that a
motorised coring system be used. This is
determined by the need for speed and the difficulty
of hand coring. The coring height is thus
determined by the physical constraints of the coring
National Carbon Accounting System Technical Report 7
process. In general it is most comfortable to core at
approx. 1.1 m above ground. Research studies
indicate that the correlations between samples taken
at this height and those of the whole tree are
3.9 How to take an increment core sample The increment core The most common form of non-destructive sample
used is the increment core which is a sample that
represents a radius or diameter is obtained from the
stem at a given height. For wood quality studies,
12 mm cores are commonly used. The larger the
corer, the greater the difficulty in getting a manual
corer started in the tree, and in turning the corer.
This is a particular difficulty in eucalypts.
Choice of corer Corer type. The cutting edge of the core drill bits should be
clean, sharp and free of defects. Manual corers are
commercially available from most forestry
suppliers. The motor-driven corer recently
developed by CSIRO Forestry and Forest Products is
recommended [Trecor, Cyclone Hardware (Ph: 1800
335 019)]. Increment cores can be taken using the
Trecor corer powered by a petrol motor (currently
the Tanaka TED 262R is the only suitable motor on
the market, but is slightly underpowered). There
have been some problems with the sharpness of
new or resharpened corer bits, so it is important to
ensure that all bits are adequately sharpened before
commencing field work.
Corer length. The Trecor bits come in two lengths (300 and
500 mm). It is not necessary to remove the bark
before using the corer (unlike the pilodyn).
When sampling trees with a diameter larger than
the length of the shorter bit (300 mm) we suggest
starting with the short bit and changing to the
longer (500 mm) bit to finish. This can usually be
done without breaking the wood core. Finishing the
core with the short bit, when the longer one would
be more appropriate, may result in the core
becoming jammed. Jamming can also occur when a
core breaks off within a tree stem and the corer
‘chews’ the broken end of the core while trying to
slide back onto it. This breakage may be due to
poor technique or decay within a tree. An extractor
is available to remove a core from a tree with a
diameter greater than 500 mm. The extractor is
inserted beside the core (after the bit is removed
from the coupling) to cut the attached end of the
core. If an extractor is used, it is not possible to get
a bark-to-bark core.
Recent results indicate that it is best to leave the
hole unplugged rather than to try to seal it.
Attempts to seal it tend to result in a moist warm
environment within the tree favouring the growth of
3.10 Sample coding Accurate sample coding is vital. When samples are
analysed, any uncertainty about their origins will
cause uncertainty in the whole project. Sample
coding needs to meet the following criteria:
be permanently written on, or attached to,
the wood surface;
writing must be legible and resistant to
ethanol and water; and
must contain sufficient information so that
its origin is beyond doubt.
There are several brands of pencils suitable for this
purpose. The Staedler copying pencil is available
from specialist stationery stores and will write on
wet surfaces. The Aquarellable pencil does a similar
task. Lumber crayons are also useful, as are Tag
pens. The use of plastic labels (e.g. ‘Dymo’ labels,
‘Tytags’) stapled onto discs and billets is adequate.
An alternative protocol has been found to be
efficient. Sample codes are written onto ‘Tytags’,
which are stapled to the tree to be sampled, or
Australian Greenhouse Office 8
flagging tape is tied around the tree. The person
taking the core removes the tag and fastens it to the
core by elastic bands (one each end). The core is
then placed in the appropriate storage facility. In
this way, the chance of wrongly labelling the core, or
sampling the wrong tree, is minimised. Some form
of cross checking the sample coding is also needed.
A copy of the master sheet of sample codes should
be kept and sent with the samples for analysis.
Careful attention to the coding of samples is vital.
Mislabelling of samples will result in wasted time,
effort and money.
3.11 Steps in non-destructive sampling using a motorised corer 1.
Select corer and length of bit required and
ensure that bits are sharp.
Place corer in a stationary position against
Drill into the tree, applying enough
pressure to get the tip to bite into the wood.
The corer works best when just enough
pressure is applied. Do not force the corer
as the corer may jam in the tree causing it to
overheat and char the core surface.
Withdraw the corer bit while it is still
spinning at full throttle to allow the
shavings to clear. This requires some
Repeat steps 5 and 6 until the corer drills
through the tree.
Remove the core by releasing the bit from
the coupling. The core should come out
easily from the motor end of the bit. Be
careful not to damage the cutting edges of
the corer while extracting the core.
Code the sample.
3.12 Sample storage Prepare wood samples, discs or cores, for storage
within 24 hours of removal from the tree. On no
account leave wood samples for more than 24 hours
at ambient temperature in the green state.
The major issues in sample storage and preparation
prevention of fungal degradation;
prevention of lumen collapse; and
clear, accurate and logical sample coding.
As soon as a wood sample is removed from a tree,
fungal spores will contaminate the surface. Spores
can germinate, and subsequent growth can damage
the wood considerably in a short time. Fungal
hyphae can spread rapidly through wood, altering
wood chemistry and degrading cell walls. In
softwoods, the growth of wood staining fungi (blue
stain) can happen quickly.
Prevention of fungal degradation Fungal growth in stored samples can be prevented
and/or minimised in several ways:
Placing discs or cores in plastic bags and
storing them in a freezer, until further
preparation is required;
Storing samples in 4% formalin; and
Storing samples in 95–100% ethanol.
The treatment of samples with chemicals needs to
be done with consideration of intended analyses; for
example, the introduction of foreign substances can
affect density. The use of strong solvents can also
extract fibre wall constituents. When the samples
are prepared for analysis care is needed to minimise
dimensional and chemical changes. On no account
should the samples be allowed to air dry prior to
volume determination. Eucalypts are exceptionally
prone to shrinkage and collapse, a phenomenon that
markedly alters wood density.
3.13 Time required for field sampling Travelling time to and from sites will vary.
Assuming that the site is relatively accessible we
National Carbon Accounting System Technical Report 9
estimate that the destructive sampling of 6 trees and
the coring of an additional 24 trees can be
accomplished in one working day by 2 trained
technicians. The time required would be increased
by the nature of the site including accessibility, tree
size, the area of the site and the resultant time
required for tree selection. Other site specific issues
may also need to be considered.