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TECHNICAL REPORT
GREENHOUSE ALLIES PROJECT
Measurement of carbon sequestration
in small non-industrial forest plantations.
(continued)
3 Wood density
The wood density of the species is critical to the conversion of volume of the main
biomass component of the tree, the stem, to dry matter. Samples were taken at 1.3
m height (breast height) for many species and the resultant figures show
surprisingly little variability within the species, despite site and some size variation.
The wood density of the species follows the ecological classes that might be expected
(Specht and Specht 1999 p. 226), with slow-growing hardwoods such as ironbark (E.
sideroxylon) and mature-phase rainforest species such as white booyong (Heritiera
trifoliolatum) having the densest timber, with fast-growing species such as blue
fig/silver quandong (Elaeocarpus grandis) and radiata pine (Pinus radiata) having the
least dense wood. The wood density of the young individuals being considered here
is often much less than that in the published literature for mature individuals,
emphasising the necessity of taking appropriate measurements (Figure 6).
Figure 6: Wood density taken at breast height (1.3 m) for species occurring in the plantations being
measured for the Greenhouse Allies project. These are given as basic densities (oven dry) and are
compared with figures from Bootle (1983) for mature trees where available. The species are ranked
from most to least dense and species codes are for the first three letters of the genus and first four of
the species epithets (e.g. ELAGRAN = Elaeocarpus grandis; EUCSIDE = Eucalyptus sideroxylon).
The wood density within the tree was expected to vary with position in the tree, and
measurements were made of harvested trees to ascertain whether measurements at
a height of 1.3 m were truly representative. The figures for E. grandis show there is
some variation around the wood density at 1.3 m and this is greatest the larger the
tree (Figure 7). There is a general decline in wood density with height up the tree for
both E. grandis and Pinus radiata (Figure 8) but this is less marked in the pine than in
the eucalypt. The situation is similar for the other species, E. saligna (Figure 9), E.
nitens and Grevillea robusta (Figure 10). Variation in wood density with height
appears greater the smaller the tree. The small number of samples per tree (3) for
Grevillea robusta may contribute to the variability of measurements observed with
that species (Figure 10), although the greater number of samples per tree for E.
saligna does not appear to have improved a high degree of variability there. From
general observations taking wood density at a height of 1.3 m as an estimate of the
overall wood density of the tree is not as accurate as taking a series of samples at
different heights, but without further statistical analyses of more samples, it appears
to be a median value.
The wood density values obtained from measurements at 1.3 m for each species
were applied in the modified Vegetation Sinks Workbook methodology for
conversion of stem volume to stem biomass.
Figure 7: Variation in wood density (undried: green, and oven dried) with height in five
individuals of Eucalyptus grandis harvested at Rawdon Island. Note that the average density for
the trees was as follows: dbhob 14.7 cm: 1035 (av. green density), 421 (av. oven dry density); 11.2 cm:
11065, 453.3; 9.0 cm: 10835, 423.5; 8.5 cm: 10988, 378.1; 5.7cm: 10749, 469.3.
Figure 8: Variation in wood density (undried: green, and oven dried) with height in five
individuals of Pinus radiata. harvested at Taylor’s property on the New England Tableland.
Figure 9: Variation in wood density (undried: green, and oven dried) with height in three
individuals of Eucalyptus saligna. harvested at Robinson’s property on the Mid-north Coast.
Figure 10: Variation in wood density (undried: green, and oven dried) with height in two
individuals of Eucalyptus nitens and six individuals of Grevillea robusta harvested respectively a t
Ebor (Coward’s) on the New England Tableland and Rocky Creek Dam in the Northern Rivers
region.
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