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Pre-logging carbon accounts in old-growth forests, viaallometry: An example of mixed-forest in Tasmania,AustraliaC. Dean a b , N. B. Fitzgerald c & G. W. Wardell-Johnson ba School of Biological, Earth and Environmental Sciences, University of NSW, Sydney, NSW,2052, Australiab Curtin Institute for Biodiversity and Climate, School of Science, Curtin University, GPO BoxU1987, Perth, WA, 6845, Australiac The Wilderness Society, GPO Box 716, Hobart, TAS, 7001, Australia
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OLD GROWTH FORESTS
Pre-logging carbon accounts in old-growth forests, via allometry:An example of mixed-forest in Tasmania, Australia
C. DEAN1,2, N. B. FITZGERALD3, & G. W. WARDELL-JOHNSON2
1School of Biological, Earth and Environmental Sciences, University of NSW, Sydney, NSW 2052, Australia; 2Curtin
Institute for Biodiversity and Climate, School of Science, Curtin University, GPO Box U1987, Perth, WA 6845, Australia;3The Wilderness Society, GPO Box 716, Hobart, TAS 7001, Australia
AbstractUncertainty in past and future anthropogenic carbon emissions obscures climate change modelling. Available allometrics areinsufficient for regional-level accounting of old-growth, pre-logging carbon stocks. The project goal was to determine theaboveground carbon (biomass and necromass) for a typical old-growth Eucalyptus delegatensis-dominated mixed-forest inTasmania. Allometrics were developed for aboveground biomass of Eucalyptus delegatensis and generic rainforest understoreyspecies. A total of 207 eucalypts with DBH 0.21–4.5 m, and 897 rainforest understorey trees with DBH 0.01–2.52 m weremeasured across 7.7 ha. DBH frequency distribution of E. delegatensis showed at least two age cohorts and distinct positiveskew, whereas its DBH carbon distribution showed distinct negative skew. Half of the eucalypt biomass was from trees withDBH4 2.4(0.1) m, and 16% with DBH� 3.5 m (from *1.1 trees ha71) – indicating the importance of allometrics for highDBH. Aboveground carbon was 622(180) Mg ha71, with *20% from understorey and *25% from necromass. The carbonin aboveground biomass was above the median value for temperate forests. The long-term aboveground-carbon emissionsfrom clearfelling the same forest type from 1999 to 2009 is likely to be 2.9(+1.3) Tg, depending on the growth and seralstages of the forest logged.
Keywords: Allometric, carbon distribution, carbon emissions, logging, mixed-forest, old-growth
Introduction
Accounting of forestry’s industrial carbon emissions
is important not only to determine the carbon fluxes
accompanying present and future industrial activity
but also in climate change modelling. Uncertainty in
anthropogenic emissions contributes to *28C un-
certainty in the temperature effect of climate change
(Meir et al. 2006). Also, positive feedback from
climate change will increasingly detract from the
carbon stores of forests in some localities (Houghton
1997; Kashian et al. 2006) but the magnitude of
positive feedback is obscured by high uncertainty in
past and future emissions from land-use, which
includes forestry (Gloor et al. 2010).
Australian old-growth forests have amongst the
highest carbon stocks globally, particularly the tall
(434 m) wet-eucalypt forests of the temperate and
maritime-temperate south-east (e.g. Dean & Rox-
burgh 2006; Keith et al. 2009; Wood et al. 2010).
The wet-eucalypt forests are comprised of wet-
sclerophyll and mixed-forests (Hickey 1994).
Mixed-forests, in south-east Australia, are a compo-
site of an upper canopy of tall-eucalypt with a
[closed] cool-temperate rainforest understorey below
(Gilbert 1959). In the absence of stand-replacing
fire, wet-sclerophyll can lead to mixed-forests and
subsequently to rainforest (Gilbert 1959; Ashton &
Attiwill 1994). Mixed-forests represent the spatial
and/or temporal overlap, between two forest types
with different regeneration patterns. The interacting
effects of fire and logging influence the landscape
mosaic of these forests (Lindenmayer et al. 2009),
with spatio-temporal implications for determining
carbon dynamics. Determining stand-level carbon
stocks in forests of varying seral stages is a crucial
first step to investigating landscape-level, long-term
carbon dynamics.
Modelling of clearfell logging in old-growth, wet-
eucalypt forests of Tasmanian (Australia), has shown
Correspondence: C. Dean, PO Box 3520, Rundle Mall, Adelaide, SA 5000, Australia. Tel: þ61 8 8268 8230. Fax: þ61 2 9385 1558.
Email: [email protected], [email protected], [email protected]
Plant Biosystems, 2011; 1–14, iFirst article
ISSN 1126-3504 print/ISSN 1724-5575 online ª 2011 Societa Botanica Italiana
http://dx.doi.org/10.1080/11263504.2011.638332
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a long-term efflux of approximately half the original
carbon stock (Dean & Wardell-Johnson 2010). This
occurred when old-growth logging was followed by
an intense, eucalypt-regeneration burn and conver-
sion was to either plantation or to native eucalypt
forest by aerial sowing with eucalypt seed (i.e.
clearfell, burn and sow – CBS silviculture; Ellis
et al. 1982). The old-growth, wet-eucalypt forests,
have long-been a prime source of pulpwood and high
quality sawlogs (Felmingham et al. 2004; Elliot et al.
2008). Conversion of these old-growth forests
proceeded from the c. 1940s (Helms 1945), although
logging in the remaining old-growth is to be phased
out in State forests, by 2030 (Forestry Tasmania
2009). From the 1960s, production increased and
pulpwood export dominated (Florence 1993), multi-
plying at least fourfold from 1970–1980 to *2.2 Tg
year71 (dry weight) and remaining near that level to
2000 (Tasmanian Government 2006).
The magnitude of the long-term emissions (i.e.
2000 years, for stabilisation of wood-product carbon
and soil carbon levels) is logically dependent on the
original long-term mean of the pre-logged forest (and
the logging-cycle forest carbon plus wood-products).
Short-term emissions (i.e. over the first harvest
rotation) are more dependent on stocks immediately
prior to logging. In both cases carbon accounting of
commercial forestry activities relies on knowledge of
the pre-logging carbon stock. Developments in forest
inventory to-date in Australia have concentrated
mostly on post-harvest stands up to merchantable
age. Consequently, allometrics for advanced-mature
and old-growth trees are rare. Allometrics suitable
for carbon accounting were developed for all growth
stages of wet-Eucalyptus regnans F. Muell. (swamp
gum or mountain ash) forests with eucalypt DBH up
to 6.44 m. (Dean et al. 2003; Dean & Roxburgh
2006) (thus enabling both long-term and short-term
emission forecasts). This old-growth forest type was
a primary target in the Florentine and Styx valleys
(Tasmania), although the closely related wet E.
delegatensis R. Baker (white-top/gum-top stringy
bark, alpine ash)- and E. obliqua L’Herit. (brown-
top stringy bark, messmate) mixed-forests were also
logged (Australian Newsprint Mills 1960s coupe
inventories, unpublished, Forestry Tasmania; Walk-
er & Felton 2007). Logging of old-growth wet-
eucalypt forest for pulpwood and sawlogs is ongoing
on State and private land across Tasmania.
Here we aim to provide the first account of
aboveground (biomass and necromass) carbon for a
typical old-growth E. delegatensis mixed-forest stand,
prior to logging, based on field inventory. This
entails construction of applicable allometrics, devel-
oped from state-of-the-art allometrics and the
currently, publically available literature and software.
As error margins are important in interpreting
carbon accounts, we also estimate the errors in
aboveground carbon. Representativeness of likely
emissions is also presented, from a review of logging
records. Although soil carbon can notably decrease
after several logging cycles (e.g. Ferre et al. 2005;
Johnson et al. 2010) it was not examined as part of
this study due to resource constraints.
Materials and methods
Study site
The study site was located in the Florentine valley of
southern Tasmania. The geology, climate and forest
ecology of the Florentine valley are described in
Gilbert (1959). The valley is in the southern-central
distribution of wet-E. delegatensis forests in Tasma-
nia, with a high-rainfall region of rainforests to the
west, and agricultural areas and dryer forests to the
east (Figure 1). Although the wet-eucalypt forests in
the mid-elevation Florentine valley are dominated by
E. regnans (Gilbert 1959) the upper Florentine wet-
eucalypt forests are dominated by E. delegatensis, E.
obliqua and E. regnans (approximately 1500, 800 and
350 ha respectively). The study site was centred in
the upper Florentine Valley at 42 440 36.1000 S, 146
240 41.0600 E, within the planned logging area
(coupe) FO044A, of *60 ha. Mean annual pre-
cipitation at the study site was 1600 mm year71, and
elevation across the site was 448 m in the north to
505 m in the south. Ground slope within data
collection plots, averaged 5(2)8. The study site was
on Ordovician limestone, overlain in parts with
Holocene sediments.
The density of eucalypt trees in the old-growth E.
delegatensis mixed-forest at the study site varied from
under 5% to over 40% crown cover (Figure 2). At
the landscape-scale the mixed-forest was inter-
spersed with rainforest and the more-frequently
burnt, wet-sclerophyll forest (Figure 3). The rain-
forest understorey was dominated by Nothofagus
cunninghamii f. Hook. (myrtle beech, or myrtle),
Atherosperma moschatum Labill. (sassafras) and in
some locations Phyllocladus aspleniifolius Labill.
(celery-top pine) (Figure 4) – typical of mixed-forests
in Tasmania. There was a low abundance and cover
of other typical understorey species: [Acacia dealbata
Link. (silver wattle), Nematoleposis squamea Labill.
ssp. squamea (lancewood or satinwood) and Acacia
melanoxylon R. Br. (blackwood)]. Mean dominant
height of the mature eucalypts ranged from approxi-
mately 41–76 m (from Forestry Tasmania’s photo
interpretation), and myrtles reached up to *40 m.
The northern part of the coupe (wet-sclerophyll) had
been subject to moderate or low-intensity wildfire
in the past 100 years. The forest in the remainder
of the coupe (with myrtles present) appeared to be
2 C. Dean et al.
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post-wildfire regeneration following a fire several 100
years ago and had not since been subject to fire. The
site had not been logged prior to 2009. Data were
collected from mid-2009 to 2010 and recent logging
had terminated when fieldwork began.
Field data collection and processing
The centres of 10 circular plots for data collection
were positioned randomly within the unlogged
portion of the operational boundary of the coupe.
Each plot comprised three nested sub-plots of 7, 30
and 60 m radius. The diameter at breast height
(1.3 m) (DBH) was the primary data type recorded.
Other data recorded were species, growth stage
(regrowth, mature or senescent), trunk hollow size,
burl size, evidence of fire or other feature likely to
impact on carbon accounting. DBH was corrected
for burls and adventitious roots. Trees with DBH
ranges from 0.01 to 50.2 m, 0.2 to 51.0 m and
41.0 m were recorded in the 7, 30 and 60 m sub-
plots respectively. Dimensions of necromass (snags,
and fallen logs and branches (coarse woody debris,
Figure 1. Distribution of E. delegatensis- wet-sclerophyll and mixed-forest from TASVEG, overlaid on mean annual precipitation. The colour
scheme for E. delegatensis was from the FullCAM layer of aboveground, potential biomass (Richards & Brack 2004).
Figure 2. Aerial photograph looking approximately north and
showing the upper Florentine Valley in the foreground; showing
both senescent and intact E. delegatensis over rainforest under-
storey in old-growth forest. Pale-green, conical-shaped trees are
sassafras. Photo corrected for perspective distortion. Original
photo: R. Blakers, 2010.
Old-growth pre-logging C, via allometry 3
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CWD) with at least one diameter40.2 m were
recorded in the 30 m plots. Seven DBH-tree-height
pairs were measured using a clinometer and laser
rangefinder, for comparison with reported sizes
elsewhere.
Due to resource constraints four of the plots could
only be measured out to 30 m, and in one plot the
60 m circle partially overlaid a clearfelled area.
Spatial density data were corrected for these detrac-
tions during processing. Plot area was also corrected
for the average ground slope across each plot. The
total area sampled (after corrections) was 7.656 ha.
We used allometric equations to estimate the
biomass for each tree based on the measured DBH.
This value was then discounted to account for decay
in mature and senescent trees. Biomass of dead
wood was estimated by calculating the volume of the
log and discounting for decay.
For necromass, heights, lengths and diameters
were recorded. The size of hollows were also
measured, or estimated where out of reach. A decay
class was recorded, being one of H, M and S (hard,
medium and soft) corresponding to 100%, 66.66%
and 33.33% undecayed mass present for the
corresponding volume. That decay class was also
used in the field to represent voids, that were either
too numerous or irregular to be measured as hollows.
Allometrics
The two main approaches for deriving tree biomass
(or carbon) allometrics are destructive sampling
(including weighing and carbon assay) and taper
formulas. Our approach was to combine information
from published reports that had used both of these
methods. A commonly used approximation where
carbon assay is not performed (e.g. as part of
destructive sampling) is to assume that C is 50
wt% of dry vegetative matter (biomass or necro-
mass). For wet-sclerophyll E. obliqua in Tasmania,
Ximenes et al. (2008) found the fraction in stem
cross sections to be 0.497(0.004), being close to
0.5 – which was used throughout in the present work.
Allometrics for mainland populations of E. delega-
tensis ssp. delegatensis are not differentiated here from
those for the Tasmanian endemic subspecies
E. delegatensis ssp. tasmaniensis Boland, due to
similarity in growth habit. Previously (e.g. in the
1960s logging records) the Tasmanian variety was
known as E. gigantea f. Hook.
Figure 3. Landscape-level mosaic in the upper Florentine Valley:
cool temperate rainforest in riparian zones, juxtaposed with mixed-
forest – where the rainforest persists beneath emergent E.
delegatensis. Photo: N. Fitzgerald, 2010.
Figure 4. Mixed-forest in the southern part of the study area,
viewed from within recent clearing at the edge of the aggregate
retention operation; showing spatially dispersed, old-growth E.
delegatensis (both senescent and intact) over a dense rainforest
understorey of varied-sized myrtle (darker, mid-height trees) and
sassafras (lighter, shorter trees). Photo: N. Fitzgerald, 2010.
4 C. Dean et al.
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The available biomass allometric for the dominant
canopy species (E. delegatensis) covered the DBH
range 0.119–0.832 m (Raison et al. unpublished, in
Keith et al. 2000), which was too limited, as the
mature trees in the Florentine reached over 4.5 m.
Merchantable volume allometrics covered the DBH
range 0.616–1.656 m (Wang & Hamilton 2003).
However, biomass allometrics for the related ash
species, E. obliqua and E. regnans, covered the DBH
ranges 0.262–2.84 m (Keith et al. 2000) and 0.01–
10.0 m (Dean et al. 2003; Dean & Roxburgh 2006)
respectively.
The relationships between biomass and between
stem volumes, for these three eucalypts, are known
within limited ranges of DBH. Their stem volumes
can be calculated using the Farm Forestry Toolbox
(FFT, Warner 2007). Within the FFT the majority
of stem taper formulas and their accommodated
range of DBH, for species encountered in this study,
were commercial-in-confidence and consequently
they could not be deployed in this project. Only
one of the formulas was publically available – for E.
obliqua (Goodwin 1992), which accommodated
DBH 0.1–2.8 m. However, from the FFT, it was
noted that for a given DBH and height, stem volume
was in the order wet E. obliqua4E. delegatensis4E.
regnans. Biomass allometrics based on DBH alone
for the three species are compared in Keith et al.
(2000) over the DBH range 0.1–1.0 m: the same
sequence applies to biomass as for volume (from the
FFT). Thus the sequence represents common trends
in both taper and basic density. Thus combining E.
obliqua and E. regnans would have provided a reliable
approximation for E. delegatensis.
The allometric for merchantable volume could not
be directly converted to one for biomass owing to the
location-specific criteria for merchantability and the
absence of an accompanying allometric for entire
stem volume. However in the same report there was a
merchantable volume allometric for E. regnans over a
comparable DBH range (Wang & Hamilton 2003).
We derived one new allometric using the approxima-
tion that merchantable volume was an equal fraction
of the whole stem volume for both species. When
combined with the allometric for E. regnans stem
volume from Dean and Roxburgh (2006) the ratio of
merchantable volumes for the two species yielded the
stem volume of E. delegatensis, for a given DBH. The
stem volume was converted to dry biomass using the
basic density of 524 kg m73 for E. delegatensis (Ilic
1997) and combined with other aboveground com-
ponents (e.g. branches and leaves) as for E. regnans
from Dean et al. (2003), to provide an allometric for
aboveground biomass for E. delegatensis. The corre-
sponding allometric was called Edel_by_ratio.
Thus, there were three possible biomass allo-
metrics: for E. delegatensis: E. obliqua, E. regnans and
Edel_by_ratio. As none of the three was over-
whelmingly more suited to E. delegatensis over the
sampled range of DBH, the average of the three
was used. That average was fitted by [non-linear]
regression to a logistic form. A range of equation
types was examined using [automated] symbolic
regression (‘‘Eureqa’’ software, Schmidt & Lipson,
2009), but the fit was only improved on the logistic
form when using an order five polynomial (i.e. six
parameters instead of the three for the logistic
function). The logistic function was therefore
retained, and it had the additional benefits of
being better-defined than the polynomial for high
DBH (similarly when compared with log/log
allometrics, which can increase exponentially) and
providing reasonable biomass for DBH below
0.1 m. Adoption of the logistic form was also
found suitable for juvenile to advanced-mature E.
regnans allometry (e.g. Dean et al. 2003, Dean &
Roxburgh 2006).
For the rainforest species, no species-specific
biomass allometrics were available. For some of the
observed species, stem volume could be calculated
using the FFT, however the formulas were not
available, their DBH range was unknown, and we
had not measured tree heights. Two generic biomass
allometrics for rainforest species were: (1) for
temperate rainforest species (Keith et al. 2000) and
(2) wet-sclerophyll and mixed-forest species (Dean
et al. 2003). The Keith et al. (2000) allometric was
comprised of two parts: generic rainforest and a
correction for temperate rainforest (in the form of
data points), both covering the DBH range 0.1–
1.0 m. We derived a single allometric for temperate
rainforest from those two components. The allo-
metric given in Dean et al. (2003) was intended for
use within the spatio-temporal carbon modelling
software, CAR4D. In applications of CAR4D how-
ever the formula was rarely used in its raw form, but
adjusted to suit environmental conditions through
scaling magnitude and growth rate. The most
common adjustment for mixed-forest was to scale
the magnitude by 0.5 (e.g. Dean et al. 2004; Dean &
Roxburgh 2006). That adjustment was applied here.
Thus there were two allometrics available for the
rainforest species: (1) temperate rainforest and (2)
Dean et al. 2003/2004. As neither of these two
allometrics was overwhelmingly more suited to the
understorey in E. delegatensis mixed-forest over
the sampled range of DBH, we used the average of
the two (which additionally provided a gauge of
uncertainty effects in understorey biomass). That
average was formulated as a logistic function, fitted by
[non-linear] regression. As for E. delegatensis, sym-
bolic regression revealed that the fit could only be
improved using a polynomial of order 5, and there-
fore the logistic function was retained.
Old-growth pre-logging C, via allometry 5
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DBH size distributions of species (per hectare)
for the plots were tallied across the study area,
corrected for plot size (in projection), allocated to
DBH classes and graphed as histograms. DBH
class width was varied between species to provide
maximum clarity in the histograms, (e.g. class
width for E. delegatensis was 0.2 m). The above-
ground biomass allometrics were applied to the
categories, rather than to the trees separately prior
to tallying. The C in aboveground biomass per unit
area for E. delegatensis, in the sample plots, was
calculated using the three allometrics, and aver-
aged; the average was equivalent to using the
derived logistic function. The C in biomass for E.
delegatensis was multiplied by 0.7, 0.75, 0.8 and 1
to test the effect of accommodating senescence on
stand-level carbon stocks (i.e. the sensitivity of the
allometrics to senescence). Similarly to E. delega-
tensis, the C in aboveground understorey biomass
was calculated from both contributing allometrics,
and that average was equivalent to using the
derived logistic function.
The allometric used for determining the carbon in
snags was the average of the three eucalypt allo-
metrics described above for aboveground biomass.
Apart from height loss, to accommodate general loss
of branches, bark, and unrecorded internal voids, the
calculated aboveground mass was multiplied by
0.6666, in addition to the recorded decay class
factor. For example, a snag of decay class S (i.e.
0.33333) had the necromass of an equivalent-sized
living tree, multiplied by 0.2222. Loss of height was
interpreted by multiplying the necromass from the
allometric by the proportion of the original height
remaining. That, in effect, assumed a cylindrical
stem and was therefore more conservative than
volume based on stem taper, when more of the
upper stem had decomposed. The original height
was estimated from the height-DBH relationship for
E. regnans (Dean et al. 2003) but with an adjustment
to accommodate E. delegatensis possibly being of
shorter stature, and to blend with the measured
DBH-height pairs; i.e. a new allometric was derived.
Parameters in that height allometric were varied to
gauge its impact on calculated necromass. The
volume of hollows, fallen logs and branches was
calculated as a frustum of a cone. For snags and
stumps the volume was converted to mass using the
basic density of 524 kg m73 for E. delegatensis (Ilic
1997) and applying the same decay factors as for
the solid section (i.e. all necromass was calculated
as if it were E. delegatensis). For fallen logs and
branches the volume was converted to mass using a
conservative basic density of 400 kg m73, and the
recorded decay class. Necromass was pooled and
calculated on a per plot basis, then averaged over
the study area.
State-wide, wet-eucalypt data
Spatio-temporal, electronic records of forestry opera-
tions in wet-sclerophyll and mixed- E. delegatensis
forests from 1999 to 2009 were obtained from the
Forest Practices Authority (FPA) (the limit of electro-
nic records to-date). The data were examined for
trends in areas logged, and silvicultural prescriptions
over that period, for the forest type in our study area.
Potential biomasses for wet- E. delegatensis, E.
obliqua and E. regnans forests, can be calculated from
the continental potential biomass layers from Berry
and Roderick (2006) (termed B&R here onwards)
and FullCAM (Richards & Brack 2004), by over-
laying them (using GIS) on the vegetation commu-
nity layer (TASVEG, DPIW 2010). The FullCAM
and B&R potential biomass layers were derived by
remote sensing and ground-truthing but with mini-
mal calibration for mature wet-eucalypt (i.e. higher
biomass) forests, resulting in the biomass being
underestimated for that forest type (Richards &
Brack 2004; Berry & Roderick 2006; Berry personal
communication 2010; Keith et al. 2010). Thus those
layers are unsuitable for calculation of absolute
values, for mature wet-eucalypts in Tasmania but
nevertheless, they are satisfactory for ranking relative
potential biomass of similar wet-eucalypt forest types
within a region. We used them to compare relative
biomass for the three, major, ash wet-eucalypt forests
in Tasmania, and to compare the potential biomass
at the study site against that for the average wet-
eucalypt E. delegatensis forest in Tasmania.
The B&R layer quantified C in biomass (including
roots), whereas the FullCAM layer included only C
in aboveground biomass. To average the two layers,
15% (representing root biomass) was subtracted
from the B&R layer before averaging with that from
FullCAM (the figure of 15% was an average of
10.5% for ash eucalypts (Feller 1980) and 20% for
temperate, high-biomass eucalypt forests (Mokany
et al. 2006)). The B&R and FullCAM layers did not
have common medians across the range of vegetation
communities in Tasmania. Therefore, to compare
the relative potential biomass for forests dominated
by the three eucalypts used in allometrics here, the
potential biomasses for each vegetation community
in Tasmania were scaled from 0 to 1 (normalised),
separately for the two layers. Once normalised, the
average between the two layers for each forest-type
was calculated to yield a single ranking scheme.
Results
Allometrics
Comparison of existing stem volume allometrics for
E. obliqua, E. delegatensis and E. regnans (Figure 5)
6 C. Dean et al.
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showed that extrapolation of the allometric for E.
delegatensis beyond its range to accommodate mature
trees would have produced unreasonably high
volumes (Figure 5). The stem volume of E.
delegatensis, from the ratio of merchantable volumes
of E. delegatensis and E. regnans derived from the
allometrics reported in Wang and Hamilton (2003)
was:
Edel by ratio ¼ Ereg vol
� ð0:62400 þ ð3:6428exp
� ð�0:3337DBH0:57072ÞÞÞð1Þ
where Edel_by_ratio is the stem volume of E.
delegatensis in m3, Ereg_vol is the stem volume of E.
regnans in m3 from Dean and Roxburgh (2006), and
DBH is in metres. The stem volumes from Equation
1 (‘‘Edel_by_ratio’’) were higher than for E. regnans
at small DBH (e.g. E. delegatensis volume was twice
that of E. regnans when DBH 0.08 m), but the ratio
decreased to 1 when DBH 0.285 m, after which it
yielded E delegatensis volumes less than those of E.
regnans (Figure 5).
The averaging of the allometrics for E. obliqua, E.
regnans and Edel_by_ratio produced volumes that
were below that for E. regnans for DBH from 0.15–
3.3 m but above, thereafter (Figure 5). It also
generally fitted the sequence of stem volumes
calculated for the species from the FFT but indicated
lower biomass for higher DBH (i.e. it was more
conservative). The logistic function for E. delegatensis
aboveground biomass, corresponding to the average
of the three contributing allometrics (E. obliqua, E.
regnans and Edel_by_ratio) was:
Edel AGB¼1612:4
� 1� 1
1þ DBHþ0:01ð Þ=12:714ð Þ2:2283
! !
ð2Þ
where Edel_AGB is in Mg of dry matter, and DBH is
in metres (R2¼ 1.00, N¼ 800, DBH¼ 0.01–8.0 m).
The forecast biomasses from Equation 2 (i.e. the
average of the three allometrics) were generally
between those of E. obliqua and Edel_by_ratio and
close to those for E. regnans, for most values of DBH
(similar to the corresponding relationships for stem
volumes, Figure 5).
Combining the biomass allometric for generic
rainforest species with the correction points for
temperate rainforest species from Keith et al.
(2000) gave the following biomass allometric for
temperate rainforest species:
Temp rain AGB ¼ 0:001exp
� ð2:5667 lnðDBHÞ þ 8:9133ÞÞðð3Þ
where Temp_rain_AGB is aboveground dry biomass
in Mg and DBH is in metres. The average of the two
allometrics for understorey biomass could be repre-
sented by the following logistic function:
und ave ¼ 209:72
� 1� 1
1þ DBHþ 0:01ð Þ=4:0551ð Þ2:5063
! !
ð4Þ
Figure 5. Stem volume versus DBH for different allometrics tested for E. delegatensis. Covering DBH range encountered on the study site
(left), and close-up at small DBH (right). Dotted lines are where an allometric from the literature was extrapolated beyond its originally
intended DBH range (and may therefore yield unrealistic volumes). The crosses show volumes calculated using the FFT, for individual trees
which had their DBH and height measured (DBH range accommodated in FFT is unknown).
Old-growth pre-logging C, via allometry 7
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where und_ave is aboveground dry biomass in Mg,
and DBH is in metres (R2¼ 1.00, N¼ 300,
DBH¼ 0.01–3.0 m). Equation 4 (i.e. the average of
the two allometrics) produced biomasses in between
the two averaged allometrics (as expected) but did
not increase exponentially for high DBH, e.g. when
DBH was41 m (Figure 6).
Stand-level distributions
The stand density of rainforest understorey out-
numbered that of the eucalypt canopy by around
fourfold (Table I). Conversely, average DBH of the
eucalypts was fivefold that of the understorey.
Apart from annual growth increments and long-
evity, that difference is related to the continual
regeneration of the myrtles and sassafras without
fire (Read & Hill 1988, Ashton 2000), which was
indicated in the stand-density-DBH histograms,
showing marked positive skew (Figure 7). Celery-
top pine is more likely to require fire for
regeneration than do myrtle or sassafras – accord-
ingly the smallest specimens were noted in the
same plot where a eucalypts had notable fire scars.
A single age-cohort of ash eucalypts usually has a
DBH frequency distribution in the shape of a log-
normal distribution, i.e. showing a positive skew
(e.g. Ashton 2000). From Figure 7 this implies
Figure 6. Allometrics for carbon in biomass, for rainforest
understorey species. Dotted line indicates extrapolation. ‘‘Aver-
age’’ corresponds to Equation 4 (multiplied by 0.5 to convert from
biomass to carbon).
Table I. Numbers of species present and primary DBH statistics
(standard deviation in brackets).
Species N
DBH (m)
Minimum Maximum Average
E. delegatensis 207 0.21 4.50 1.63 (0.81)
Understorey total 897 0.01 2.52 0.31 (0.29)
Myrtle 353 0.01 2.52 0.41 (0.37)
Sassafras 332 0.01 2.05 0.30 (0.20)
Celery-top pine 83 0.01 0.51 0.17 (0.13)
Figure 7. DBH frequency histograms. Those for understorey
species were converted to natural logarithms (on the ordinate) for
clarity. Where the number of stems per hectare in any DBH class
was51 then the ordinate was shifted upwards for clarity (factor
noted on axis label). Error bars (positive) are the standard errors
corresponding to variability between the 10 sample plots.
8 C. Dean et al.
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that there were at least two age cohorts of E.
delegatensis present, which was corroborated by the
presence of frequency peak where the youngest
cohort overlapped the next-oldest cohort (near
DBH¼ 1 m).
The E. delegatensis DBH frequency distribution
(which was a compound of separate cohorts) showed
a positive skew (sample skewness 1.6) (Figure 7) but
E. delegatensis DBH carbon distributions (Figure 8)
showed a negative skew (for the allometric average,
sample skewness was -0.41). That negative skew was
more pronounced using the extrapolated allometric
for E. obliqua (sample skewness 71.3) – correspond-
ing to its much higher biomass for high DBH when
compared to the other allometrics (Figure 5). With
the derived biomass allometric (Equation 2, i.e. the
average of the three contributing allometrics) being
conservative, it is noteworthy that the relatively small
percentage of high DBH trees (*1.1 tree per
hectare) from DBH 3.5–4.5 m contributed *16%
to the stand-level, E. delegatensis biomass. The
contribution of high DBH trees is also reflected in
the DBH cut-off that represents 50% of the carbon
distribution, being at 2.4(0.1) m (Table I). That
DBH value did not significantly alter with varying the
senescence.
The effect of eucalypt senescence on the DBH
carbon distribution was only marginally noticeable
in the histograms and was probably more related to
the difference between plots. For example the
maximum difference (between with- and without
senescence) for any DBH class was *13%,
(between DBH classes 2.1 and 2.9 m), but it was
only 3% for the DBH class of 2.7 m. Overall, the
effect of attributing 30% missing biomass to
senescent trees only altered the stand-level
E. delegatensis biomass by *8% (e.g. from the
average of the three allometrics, Table II).
The DBH carbon distributions for understorey
species, when pooled together, showed a marked
positively-skewed distribution (Figure 9). However,
for celery-top pine and sassafras, the higher
DBH classes (0.525 m and 2.05 m respectively)
contributed more to the stand-level carbon
stocks than did their minimum DBH classes, even
though those upper DBH classes were not near
the upper limit of the Dean et al. 2003/2004
allometric.
The understorey contributed 129(28) Mg ha71
(27%) to the stand-level carbon in biomass, with the
majority of that (66%), coming from myrtle (Table
III). The contribution of only 2% from celery-top
pine was due to its limited occurrence and smaller
average size.
For E. delegatensis the 25%-senescence scenario
was considered most likely and sufficiently conser-
vative for this site. Using the carbon in biomass for
that scenario from the E. delegatensis allometric-
average [466(132) Mg ha71] (Table II), and the
understorey carbon from the understorey allometric-
average [129(28) Mg ha71] (Table III), gave the
stand-level carbon in biomass of 469(132) Mg ha71.
Variation of parameters, within realistic ranges, for
the height allometric for snags only contributed to
*5% variation in the total necromass of 153(51) Mg
ha71, due to the relatively small contribution from
snags (Table IV). Combining the stand-level biomass
carbon with the necromass carbon, gave a stand-level
Figure 8. DBH carbon histograms for E. delegatensis using different
allometrics. Error bars (positive) are the [fractional] standard
errors corresponding to variability between the 10 sample plots
[multiplied by the category values].
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Table II. Carbon density for E. delegatensis in the study site using different allometrics and different percentage of missing biomass for trees
recorded as senescent; and DBH category above which lies 50% of the stand-level carbon. The allometrics used for ‘‘Eobl_equiv’’ and for
‘‘Ereg_equiv’’ were from Keith et al. 2000 (extrapolated) and Dean et al. 2003 and Dean & Roxburgh 2006. That for ‘‘Edel_by_ratio’’ was
from Equation 1. (Standard deviations in brackets are from the average of the three allometrics).
Allometric
Eobl_equiv Ereg_equiv Edel_by_ratio
Average
% of total
stand biomass
Stand-level C (Mg ha71)
0% Senescence 459 382 242 361 (110) 78
20% Senescence 438 364 231 344 (105) 74
25% Senescence 432 359 228 340 (104) 73
30% Senescence 427 355 225 336 (103) 72
DBH cut-off for
50% of stand C (m) 2.54 2.39 2.37 2.43 (0.09)
Figure 9. DBH carbon histograms for rainforest understorey using different allometrics (all-understorey and dominant species separately).
‘‘ctp’’ is celery-top pine. Error bars (positive) are the [fractional] standard errors corresponding to variability between the 10 sample plots
[multiplied by the category values].
10 C. Dean et al.
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aboveground carbon of 619(180) Mg ha71. Thus the
understorey contributed *20% to the total, and
necromass contributed *25%, of which 83(13)%
was from fallen logs, i.e. fallen logs contributed
*21% to aboveground carbon, which was roughly
equivalent to the *20% contribution from the
understorey species in total.
State-wide data and logging emissions
The average carbon in biomass for the 10 plots, as
derived by GIS analysis from the FullCAM & B&R
layers, was 69.5(0.4) and 115.5 Mg ha71 respec-
tively, which was within one standard deviation of
the State-wide averages of 66(37) and 101(15) Mg
ha71 (Table V). Thus the site was reasonably
representative for potential carbon density in that
forest type, State-wide. Using the 50% long-term
decline in carbon stocks noted for conversion of
old-growth forests to a harvesting cycle (Dean &
Wardell-Johnson 2010), if the forest in the study
was clearfelled and converted to CBS logging
cycles then the forecasted, long-term above-
ground-carbon emission is 311(90) Mg ha71.
The logging records from the FPA revealed that
conversion of wet E. delegatensis forest to plantation
had declined overall from 1999 to 2009 at a rate of
*89 ha year71 (R2¼ 0.42), however CBS-type
logging showed a slight increase (*28 ha year71,
R2¼ 0.36, p¼ 0.053). The total area of wet E.
delegatensis forest logged in that period was 38225
ha (Table V), of which 7920 ha was converted to
plantation and 5523 ha was converted through
CBS. The long-term aboveground-carbon emission
from that clearfelling (using the 50% figure), using
the unit-area, long-term emission of 311(90) Mg
ha71, is likely to be as high as 4.2(1.2) Tg,
depending on the growth and seral stage at the
time of logging the primary forest. Additionally,
from State-wide inventory, Moroni et al. (2010)
found 232 Mg ha71 for mature (i.e.� 110 years)
wet-eucalypt forests (averaged over all eucalypt
types, mixed-forest and wet-sclerophyll forest).
However their carbon density for mature forest
was not significantly different to their value for
average-aged forest, and there was no differentia-
tion of carbon densities between old-growth and
early mature forest even though the former can be
50% higher (Dean 2011). Nevertheless, assuming
their value was applicable to mature, primary, wet
E. delegatensis forest then the long-term carbon
emission (50% of stock) would be 1.6 Tg. An
average of our carbon density (which appears
representative of potential biomass in E. delegatensis
State-wide) with that from Moronoi et al. (2010),
may well be representative of the growth and seral
stages of the forests logged from 1999 to 2009:
giving a long-term aboveground-carbon emission of
1.6-to-4.2 Tg, i.e. 2.9(+1.3) Tg.
Table III. Carbon in aboveground biomass for understorey species, from allometrics; and DBH category above- which is 50% of stand-level
carbon. The allometric ‘‘Keith et al. (2000) extrapolated’’ is Equation 3 (standard deviations in brackets are from the average of the two
allometrics).
Allometric
From Keith et al. 2000.
extrapolated Dean et al. 2003/2004
Average
% understorey % of total stand biomass
Stand-level C (Mg ha71)
All understorey 149 109 129(28) 100 27
Myrtle 95 69 82(18) 66 17
Sassafras 44 32 38(8) 29 8.1
Celery-top pine 4.2 3.4 3.8(0.5) 1.9 0.81
DBH cut-off for 50% of stand C (m)
All understorey 0.70 0.62 0.60(0.06)
Myrtle 0.82 0.77 0.81(0.04)
Sassafras 0.50 0.45 0.50(0.04)
Celery-top pine 0.22 0.23 0.23(0.01)
Table IV. Carbon in necromass (within the 30 m radius circle)
summed per plot, separated into snags and fallen logs (standard
deviation in brackets).
Plot
Snags
(Mg ha71)
Fallen logs
(Mg ha71)
Necromass
(Mg ha71)
Fallen logs
% of total
1 26.8 141.5 168.3 84.1
2 2.5 196.0 198.5 98.7
3 10.4 124.0 134.4 92.3
4 83.9 142.0 225.9 62.9
5 13.8 91.4 105.2 86.9
6 43.7 83.8 127.4 65.7
7 9.2 75.5 84.7 89.1
8 7.3 215.0 222.3 96.7
9 32.2 65.8 98.0 67.2
10 16.1 149.9 166.1 90.3
Average 25(24) 128(51) 153(51) 83(13)
Old-growth pre-logging C, via allometry 11
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Discussion
Allometric derivation
The allometrics derived were stable over all of the
DBH values measured in the field, i.e. they did not
increase exponentially at high DBH and did not
produce negative values for DBH50.1 m. The
Edel_by_ratio may have produced E. delegatensis
values of biomass too high when DBH was below
0.29 m, but that effect would have been cancelled to
some degree by averaging with the other two
allometrics. Additionally, when the E. delegatensis
biomass for the study site was tallied then high
biomass at low DBH values was not observed
(Figure 8). For DBH4 0.53 m, stem volume from
Edel_by_ratio was the smallest of all allometrics,
which concords with the more-pronounced buttres-
sing of E. regnans (which produces faster tapering up
the length of the stem and hence lower volumes for
the same DBH). For the same reason, the similarity
of biomass calculated for E. delegatensis (from the
average allometric, Equation 2), and for E. regnans,
indicates that Equation 2 (i.e. the average of the three
allometrics) was conservative. That was confirmed
by comparison with the relative volumes and
biomasses for the three eucalypt species described
above, and by the volumes from the FFT being
higher (for high DBH) than the average allometric.
Thus it is unlikely that E. delegatensis biomass was
overestimated in this study.
The allometric derived for the understorey in the
mixed-forest, being of logistic form, was similarly
stable at high values of DBH. Until destructive
sampling is undertaken (such as during logging
operations, e.g. Ximenes et al. 2008), or accurate
taper formulas for the rainforest species become
publically available, the accuracy of their carbon
stocks cannot be increased. Although an average of
the allometrics for mixed-forest (Dean et al. 2003,
2004) and temperate rainforest (Equation 3) was
derived (Equation 4) and applied here, there was no
compelling reason to assume its effect was more
accurate than that from the original mixed-forest
allometric alone. In fact, as the temperate rainforest
allometric had to be extrapolated far beyond its DBH
range used in its construction, the original mixed-
forest allometric may be a more reliable representa-
tion. That would decrease the carbon contribution
from understorey species by 15%, and reduce
the total aboveground carbon by 3% to 602 (174)
Mg ha71.
Carbon distribution and significance
Three factors indicating the importance of reliable
allometrics for high DBH eucalypts, from the present
study are: (1) the negative skew on the DBH carbon
distribution, (2) the 50% DBH cut-off of 2.4(0.1) m
for E. delegatensis and (3) the 16% contribution to
eucalypt carbon stocks from the *1.1 trees ha71
with DBH� 3.5 m. If the study site had comprised
only a single age cohort then the high DBH trees
would have contributed a marginally higher percen-
tage. The E. obliqua biomass allometrics can accom-
modate up to DBH 2.8 m, but that is the highest in
the review of allometrics in Keith et al. (2000). The
E. regnans allometrics (Dean et al. 2003; Dean &
Roxburgh 2006) were calibrated with trees up to
*6.44 m DBH and corrected for cross-sectional
area deficit. Thus, in general, more work is required
on carbon accounting of old-growth wet-eucalypt
forests. The higher standard error on the highest
DBH category in the carbon DBH histograms of
some of the understorey trees indicates the more-
sporadic location of such large trees.
The necromass contribution of 25% to above-
ground carbon is above the mean value for the wider
category of Australian tall-open forests (Woldendorp
& Keenan 2005). The absolute value of the stock
however, agrees with other values for Tasmania,
which increase with more southern latitudes (i.e.
cooler temperatures), and the proportion of necro-
mass in fallen logs agrees with higher values noted
in old-growth forests (Woldendorp & Keenan
2005).
The high, measured biomass compared with the
potential value in the FullCAM and B&R layers
concurs with that found previously for wet-eucalypt
forest (e.g. Dean & Wardell-Johnson 2010). The
current, wide use of the FullCAM layer suggests that
Table V. Hectarages of main wet-eucalypt types logged from 1999 to 2009; and average potential carbon in biomass derived by overlaying
the FullCAM and B&R layers on vegetation mapping (TASVEG). Values were normalised (state-wide, 0 to 1 for the two layers) then
averaged, to allow comparison between forest types.
Wet eucalypt
Area
logged (ha)
Area
remaining (ha)
Number of TASVEG
polygons (thousands)
C in biomass (Mg ha71)
FullCAM B&R Normalised & Average
E. delegatensis 38,224 276,378 4135 66(37) 101(15) 0.59
E. obliqua 60,384 464,082 7425 84(53) 106(24) 0.73
E. regnans 20,485 76,891 1230 82(53) 117(20) 0.76
12 C. Dean et al.
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analysis of old-growth carbon stocks can provide
useful calibration points for its adjustment.
The 466(132) Mg ha71 of aboveground biomass
carbon found here, is in between that for old-growth
forests measured elsewhere, and just above the
median value for temperate forests in the review of
Keith et al. 2009. For example, it is above that found
in the Carpathian mountains (Szwagrzyk & Gazda
2007 – 268 Mg ha71, Keeton et al. 2010 – 160 Mg
ha71) but lower than other sites in Tasmania (Dean
& Roxburgh 2006 – 723 and 642 Mg ha71, for E.
regnans and E. obliqua respectively), in Victoria
(Australia) (Van Pelt et al. 2004 – *843 Mg ha71;
Keith et al. 2009 – 1819 Mg ha71 for E. regnans) and
in the USA [e.g. Van Pelt et al. 2004 – *647 Mg
ha71 for Pseudotsuga menziesii Mirb. (Franco)]. A
value of 723 rather than 850 Mg ha71 of Wood et al.
(2010) is used here for the Tasmanian E. regnans, as
the latter included root carbon. Nevertheless, the
aboveground biomass carbon measured in this work,
when compared with two other old-growth Tasmania
examples (Dean & Roxburgh 2006), aligns well
with the sequence of normalised Tasmanian state-
wide potential biomass layers (Table V): i.e.
4665 6425 723 Mg ha71 corresponding to
0.595 0.735 0.76 for E. delegatensis, E. obliqua
and E. regnans respectively.
Aboveground carbon, one of the major carbon
pools, is the easiest pool to measure in native forests.
These carbon stocks in old-growth wet-eucalypt
forests, under certain combinations of age classes,
can be much higher than those used in routine
accounting (e.g. Keith et al. 2009). With the land-
scape-level, age-averaged stock of carbon being the
pre-logging benchmark, it is necessary to account for
such potentials. Upper stock limits are likely when
the forest has significant old-growth characteristics,
with other components that may be either younger
age classes of the canopy species (recruits resulting
from non-stand-replacing fires or non-fire-induced
recruits) or rainforest understorey species capable of
continuous regeneration in the absence of fire. The
data collection and processing presented here pro-
vide a clear example of how the pre-logging stocks
can be tallied for use in regional comparisons.
Acknowledgements
The authors are indebted to numerous volunteers
who performed fieldwork and support. The authors
also thank, for helpful comments and/or data:
Stephen Roxburgh (CSIRO), Sandy Berry (ANU);
Bureau of Meteorology, Adrian Goodwin (Bushlo-
gic), Department of Climate Change and Energy
Efficiency, Forestry Tasmania, Daniel Livingston
(FPA), Private Forests Tasmania, and two anon-
ymous reviewers.
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