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TECHNICAL REPORT
GREENHOUSE ALLIES PROJECT
Measurement of carbon sequestration
in small non-industrial forest plantations.
(continued)
Appendix B
Greenhouse Allies Carbon Sampling Methodology
B.1 Introduction
Accurately assessing the carbon stored in your plantation requires strict adherence to
measurement procedures. The broad steps involved are:
1. plantation assessment and stratification;
2. plantation mapping;
3. establishment of permanent measurement plots;
4. plot measurement and data capture; and
5. data analysis.
Each of these steps will be described in turn and standard (or suggested) procedures
given where they have been determined.
B.2 Plantation Assessment and Stratification
In order to reduce variability between sample unitsand therefore the precision of
the final results and ultimately the amount of carbon able to be claimedplantations
should be stratified (divided) into areas where tree growth is relatively homogenous
(Figure B.1).
Figure B.1: A depiction of various types of plantings on a property that can be described as strata
because of their different nature, here according to age, species or site differences. Within each of
these the variation may be expected to be minimal, whereas between these there may be significant
variation. Calculating the carbon within a stratum and then adding the estimates up to form a
property figure minimises the error of the overall estimate of the carbon held on a property.
Stratification may be based on year of planting, species or species mix, soil type,
slope, aspect, management regime, or any other factor that, in the opinion of the
measurer, will have a significant affect on tree growth compared to other strata. In
conjunction with plantation mapping (described below), notes must be made about
the characteristics of each stratum. A form is being developed to assist you with this.
B.3 Plantation Mapping
Your plantation should be accurately mapped. This may be done using various
methods including aerial photos or ground surveys, with a compass and tape
measure or global positioning system (GPS), using Geographic Information Systems
(GISs) or other survey tools. The map is required to determine stratum and
plantation location, stratum and plantation area, location of permanent plots, and to
act as a permanent record of plantation establishment (useful, for example, for
complying with section 11(2)(c) of the NSW Plantations and Reafforestation Act
1999).
Information to be included on maps should include:
- title;
- property location;
- North point;
- scale;
- author;
- date of mapping;
- plantation boundaries;
- clearly demarcated strata;
- area of each stratum;
- landmarks (public roads, farm buildings, farm roads, power lines, watercourses,
drains, etc.); and
- location of permanent plots in relation to permanent landmarks (see below).
B.4 Establishing Permanent Measurement Plots
B.4.1 Purpose of permanent measurement plots
Permanent measurement plots provide a way of monitoring the growth of your
plantation without having to measure all of the trees in it. They should be
representative of each stratum in which they are located and should be managed no
differently to other areas of the stratum they represent. The data obtained for the
trees in each plot s ? `d6 E (p@
Jy JdueTP"8! y identify
the individuals for remeasuring. Remeasuring the same trees provides a sensitive
correction for initial size of the trees rather than choosing separate areas each time.
B.4.2 Positioning permanent plots
Plots should be located randomly within each stratum using objective methods. Two
possible methods are given below:
1. One method (suitable for large plantings) is to locate permanent plots on the map
prior to positioning them in the field using a grid and random number generator
such as found on many hand-held calculators. Plots are then located in the field
using a compass and tape measure.
2. Another method (suitable for small plantings) involves the use of a tape measure
and random number generator. This method is adopted to avoid bias in selection
of sites for plots to be located. A tape measure is laid along one edge of the
planting, a point along the tape is selected by random number (tables of random
numbers can be found in many statistical texts, but opening a page in a phone
book and selecting a string of numbers of the right length can also be used).
From this point a new random number is selected to determine the distance to
the centre of the plot in a direction perpendicular to the tape. Exact locations of
the plots should then be noted on the map.
The resulting plots need to be located clearly so they can be found again (Figure B.2).
Figure B.2: A stylised property showing three different strata with plots randomly located
within each. The total area of the planting estimated in the first carbon measure should exclude the
area of dead trees. Each stratum will have an error based on the variation both within and between
the plots and the effectiveness of the plots (plot size and number).
Other methods may also be used, however it is vital that plots are located randomly
within strata. Biasing plot locations to the best areas of a stratum will artificially
inflate final figures, leading to scepticism among both the public and purchasers of
carbon rights, and a loss of validity of the whole process.
B.4.3 Marking permanent plots
The location of permanent plots should be accurately mapped, with their location
described in terms of bearing and location from an obvious and (preferably) close
landmark. If using marker pegs, ensure they are not in a position vulnerable to
disturbance by activities such as slashing.
Taking bearings to unmarked permanent plots from landmarks will get the field
worker to the general vicinity of the plot centre, however to find the exact location
of the plot it will generally be necessary to mark the location of the centre of
permanent plots in the field. Obviously marking the location of permanent plots has
the potential where, subconsciously or otherwise, the plots may be managed
differently to other areas of the stratum. This will lead to the permanent plot being
unrepresentative of the stratum as a whole and give inaccuracies in carbon and tree
volume estimates. In order to avoid this, methods for marking permanent plot
locations in the field should be used that allow the observant carbon monitor to
locate the exact centre of the plot, yet are unremarkable enough to not affect
management practices. Two methods of marking permanent plots in the field in this
way include:
1. the use of unobtrusive items as markers, such as a painted rock or star picket; or
2. burial of a star picket or other metal object at the plot centre, for location by
metal-detector.
Using these methods, there is still the potential that the plot will be identifiable
during management operations and management practices altered, or alternatively
that the marker will be moved or destroyed during routine operations such as
slashing. To avoid disturbance, plot centres may be located in the row space rather
than the interrow space. Avoiding management biases is ultimately up to the forest
manager.
B.4.4 Number and size of permanent plots
Overview
In field work to date the number of plots per stratum and the size of permanent
plots in each stratum have been prescriptive (although at times prescriptions were
not strictly adhered to): a minimum of three circular plots per strata, and large
enough to contain 10-15 trees per plot. Plot size is generally (but not necessarily)
consistent between strata, but for purposes of analysis did not vary within a stratum.
In all cases to date plot size has been between 5 and 8 metres radius.
Results to date indicate that the prescriptions described above are adequate for
measurement of simple plantings such as monocultures or plantings involving few
species. When applied to multi-species plantations, however, the results are less
consistent, often generating imprecise estimates of carbon and tree biomass.
Establishing appropriate measurement regimes including appropriate plot size/plot
number prescriptions for multi-species plantations, and further improving sampling
procedures for simple plantations, will be addressed in the next project about to
commence. The estimates for very young plantings (those less than 2.5 years) were
all unreliable.
With the previous points in mind, the following sampling prescriptions may be
applied to monocultures or plantings with low variability in species.
Number of permanent plots
A minimum of three permanent plots are required per stratum. More plots per
stratum make final stratum estimates more accurate, however greater labour costs
associated with increased sampling effort may prove to negate the economic gains
from any improvements in precision, especially in small plantations. With this in
mind we recommend three or four permanent plots per stratum.
Plot shape
Plots should be circular radiating around the central marker. Where the planting is
very narrow (as may be the case for shelterbelts), and parts of a circular plot would
lie outside the planted area, rectangular plots may be used, their area should be at
least 100m2.
Plot size
Plot size depends on tree spacing, the plot must be big enough to encompass at least
10 trees per plot. Plot size may vary between strata, but must be the same for each
plot with in a stratum. Plots of radius 7 m appear adequate in most cases.
B.5 Plot Measurement and Data Capture
Plots should be measured as follows:
1. position (and permanently mark) or locate the central point of the plot using the
methods described above;
2. using a tape measure, identify all trees within 7 m (or other radius as appropriate)
of the centre of the plot;
3. using a standard plot measurement form (to be provided at a later date), note the
stratum and plot number, the species of each tree encountered and its diameter at
breast height over bark (at 1.3 m); and
4. continue to the next plot until all plots measured using this format.
The diameter of a tree at breast height is a universal measure of the size of the tree
(Figure B.3). This common and easily-measured datum can allow many other
predictions to be made. During the active growth period, the height of the tree is
closely related to the diameter at breast height, as is the weight of leaves, branches
and roots.
Figure B.3: Key items for measurement of a tree, in particular the position of Diameter at Breast
Height (D.B.H.) which is measured at 1.3 m above the ground. A second diameter measurement is
often taken in order to calculate the degree of taper in the tree (Dx). In very small trees this may be
at 10 cm, but in older trees this is often taken at 30 cm above the ground.
B.6 Data analysis
Once the diameters are estimated for the trees within each plot, data will generally
be given to a specialist for statistical interpretation and conversion to biomass and
carbon. At present there are several methods suggested for this estimation. The
primary one used in this project to date has been the protocol proposed in the
Vegetation Sinks Workbook (VSW) (Forestry Technical Services, AACM
International & Clean Commodities Inc. for the Australian Greenhouse Office 1998).
The steps to get from measures of diameter at breast height to carbon content for a
property are outlined as follows.
Firstly, the height of the individual is estimated from the diameter at breast height
over bark (dbhob) using species-specific equations, and then the volume of the stem
is calculated using a standard (or, if available, a specific) volume equation. The stem
biomass is calculated by multiplying the estimated volume by the oven dry density
of the wood using samples of wood obtained from your plantations. The total above
ground biomass is estimated from the stem biomass using the harvest index (the
ratio of stem biomass to total above-ground biomass) which is 0.68 for Pinus radiata
and 0.70 for eucalypts, and to total tree biomass using the root:shoot ratio
(determined from whole tree destructive sampling or a default ratio of 0.2). Carbon
is then calculated by multiplying whole tree biomass by 0.5 (the VSW standard for
the proportion of carbon in tree biomass). These figures are then be used to calculate
plot and stratum figureswith confidence intervalsof dbh, height, stem biomass,
total biomass and total carbon for each property. This is the procedure used for the
results attached.
This method can be improved by developing more specific techniques, and these
include using equations that can convert diameter at breast height over bark directly
to standing biomass and thence to carbon. Very few such equations are available and
are generally understood to vary according to species and location. The six suites of
harvests done during this project provided very good predictions of biomass from
basic in-field measurements (see the Overview of the Technical Report enclosed).
From these few species the estimates using the VSW can be seen to be very
conservative, and therefore, as our knowledge increases the amount of standing
carbon believed to be held in plantings such as those we have measured may be
expected to increase.
B.7 References
Forestry Technical Services, AACM International & Clean Commodities Inc. for the Australian
Greenhouse Office (1998) Greenhouse Challenge Vegetation Sinks Workbook. Version 1.0.
Commonwealth of Australia.
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