firewood harvest from forests of the murray-darling basin, australia. part 1: long-term, sustainable...
Post on 26-Jun-2016
212 Views
Preview:
TRANSCRIPT
ARTICLE IN PRESS
Available at www.sciencedirect.com
B I O M A S S A N D B I O E N E R G Y 3 2 ( 2 0 0 8 ) 1 2 0 6 – 1 2 1 9
0961-9534/$ - see frodoi:10.1016/j.biomb
�Corresponding autE-mail address: m
http://www.elsevier.com/locate/biombioe
Firewood harvest from forests of the Murray-Darling Basin,Australia. Part 1: Long-term, sustainable supply availablefrom native forests
P.W. Westa,b, E.M. Cawseyc,�, J. Stolc, D. Freudenbergerd
aSchool of Environmental Science and Management, Southern Cross University, Lismore, NSW 2480, AustraliabSciWest Consulting, 16 Windsor Court, Goonellabah, NSW 2480, AustraliacCSIRO Sustainable Ecosystems, GPO Box 284, Canberra, ACT 2601, AustraliadGreening Australia, PO Box 74, Yarralumla, ACT 2600, Australia
a r t i c l e i n f o
Article history:
Received 5 February 2008
Accepted 29 February 2008
Available online 18 April 2008
Keywords:
Firewood
Murray-Darling basin
Eucalypt
Silviculture
Sustained yield
Biodiversity
nt matter & 2008 Publishioe.2008.02.017
hor. Tel.: +61 2 6242 1628;argaret.cawsey@csiro.a
a b s t r a c t
The Murray-Darling Basin is a 1 million km2 agricultural region of south-eastern Australia,
although 29% of it retains native forests. Some are mallee eucalypt types, whilst the
‘principal’ types are dominated mainly by other eucalypt species. One-third of the 6–7
million oven-dry tonne of firewood burnt annually in Australia is obtained from these
forests, principally through collection of coarse woody debris. There are fears that removal
of this debris may prejudice the floral and faunal biodiversity of the Basin. The present
work considers what silvicultural management practices will allow the long-term
maintenance of the native forests of the Basin and their continued contribution to its
biodiversity. It then estimates that the maximum, long-term, annual, sustainable yield of
firewood which could be harvested, by collection of coarse woody debris, from principal
forest types of the Basin would be 10 million oven-dry tonne yr�1. An alternative, harvest of
firewood from live trees by thinning the principal forests and clear-felling mallee forests,
would be able to supply 2.3 million tonne yr�1 sustainably. Whilst coarse woody debris
harvests could supply far more than the present demand for firewood from the Basin, they
would lead to substantial reductions of the debris remaining in the forests; this may be
detrimental to biodiversity maintenance. Live tree harvest does not lead to this problem,
but would barely be able to supply existing firewood demand.
& 2008 Published by Elsevier Ltd.
1. Introduction
The Murray-Darling Basin is the catchment for the largest
river drainage system of Australia. Its total area is 1 M km2,
occupying most of inland, south-eastern, mainland Australia.
Environmental conditions vary widely across the Basin,
particularly as rainfall declines from more than 1000 mm yr�1
in its most easterly and southerly parts to less than 300 mm
yr�1 towards the arid, interior of the continent; about 75% of
ed by Elsevier Ltd.
fax: +61 2 6242 1688.u (E.M. Cawsey).
the Basin has a rainfall of less than 750 mm yr�1. Over the last
200 yr, large areas of the Basin have been cleared for
agriculture; it now produces wheat, rice, cotton, sheep, cattle
and horticultural products. In the wetter regions of the south-
eastern Basin, large areas of exotic softwood (Pinus radiata)
plantation forests have been established. Only small areas
have been established with hardwood plantations.
Native forests remain over at least 29% of the area of the
Basin. These forests have been classified and mapped by the
ARTICLE IN PRESS
B I O M A S S A N D B I O E N E R G Y 3 2 ( 2 0 0 8 ) 1 2 0 6 – 1 2 1 9 1207
National Forest Inventory of Australia [1], based on a
classification system described by Specht and Specht [2] and
Specht et al. [3]. Along the wetter eastern and southern
fringes of the Basin are small areas of ‘tall’ (mature height
430 m), ‘open’ (crowns cover 50–80% of the ground surface)
forest. Moving progressively towards the arid interior of the
continent, the forests grade through ‘medium’ (mature height
11–30 m) and ‘low’ (2–10 m), open forests to medium and low
‘woodlands’ (crowns cover 20–50% of the ground surface).
Both single- and multi-aged forests occur. Some are mono-
specific and others contain a mixture of tree species. The
more complex types, multi-aged and/or mixed-species for-
ests, are most common.
About 9% of the native forest area consists of mallee
eucalypt types (small, multi-stemmed eucalypt species of low
mature height). About 71% is of other eucalypt types, the
dominant species varying with height and openness of the
forest. The remaining 20% of the forests are dominated by one
or other species of the genera Acacia, Callitris, Casuarina or
Melaleuca; often these species occur in mixture with euca-
lypts. The non-mallee eucalypt types, together with the
forests dominated by other genera, will be considered
together here and termed the ‘principal’ forest types of the
Basin. By far, non-mallee eucalypt forests of medium height
are the most common forest type, constituting 66% of the
total area of native forests of the Basin. Fig. 1 shows an
example of this type of forest.
The productivity of the forests of the Basin is much lower
generally than that of the taller, native forests in the higher
rainfall areas of the eastern and southern coastal regions of
Australia. The only native forests of the Basin which have
been used consistently for commercial timber production are
Fig. 1 – An example of a mature stand of non-mallee,
medium height, open eucalypt forest of the Murray-Darling
Basin. Forests with this structure are the most common
native forest type throughout the Basin. This stand
regenerated more than 100 yr ago, after all trees on the site
were killed by ringbarking (girdling). It was used for animal
grazing subsequently. It contains a mixture of Eucalyptus
rossii, Eucalyptus mannifera and Eucalyptus macrorhyncha.
those of White Cypress Pine (Callitris glaucophylla), which are
widespread over the Basin, River Red Gum (Eucalyptus
camaldulensis), which is widespread over the Basin but
confined to riparian areas and some ‘ash’ eucalypt forests
(usually Alpine Ash, Eucalyptus delegatensis), which are located
in higher rainfall and higher altitude areas along the south-
eastern fringe of the Basin. Together, these provide only a very
small proportion of the timber produced commercially from
Australian native forests.
In [4] it was estimated that 6–7 M t of firewood (all firewood
amounts referred to in this paper are oven-dry weights) are
burnt annually in Australia, the bulk for domestic heating.
About 2–2.5 M t of this are obtained from the native forests of
the Basin, mostly from privately owned forests.
Some of the mallee eucalypt woodlands of the Basin
(including species such as Eucalyptus socialis, Eucalyptus
gracilis, Eucalyptus oleosa subsp. oleosa and Eucalyptus dumosa)
have been harvested consistently for firewood (often during
land clearing). Sometimes the large lignotuberous mass at the
base of the stem of these species, from which coppice arises,
is used as firewood and sometimes the stem wood is used.
Large amounts of firewood are obtained also from the
principal native forests of the Basin. Most of this is collected
as fallen, coarse woody debris, although some may be
obtained during land clearing or by felling live trees. Concern
was expressed in [4] that the removal of this debris may have
important consequences for the biodiversity of the Basin. It
was suggested that ‘[o]f particular concern are probable
effects on ecosystem processes such as nutrient cycling and
plant establishment, because of the potential loss of highly
specialised species of invertebrates and fungi.’ As well, it was
believed that loss of coarse woody debris might deprive some
faunal species of their habitat.
The present work establishes a basis for responsible
management of the privately owned, native forests of the
Basin, which are appropriate for firewood harvest. It is
assumed that the objective of management is to ensure
firewood harvesting can continue, whilst conserving the
forests and maintaining, or hopefully increasing, their con-
tribution to the overall biodiversity of the region. The
consequences are examined of both the continuation of
firewood harvesting of coarse woody debris and of an
alternative, where firewood is obtained by felling live trees.
For each alternative, estimates are made of the maximum,
long-term, sustainable yield of firewood which might be
obtained from these forests: in this context, maximum
sustainable yield means removal of firewood at a rate equal
to its rate of replacement by growth of forests. As well,
estimates are made of the amounts of coarse woody debris
which will remain in the forests in the long-term, if firewood
is harvested at the maximum, long-term, sustainable rates.
2. Approach
There are well developed methods available to determine how
a large and complex forest area should be managed to ensure
a long-term, sustainable supply of the ‘products’ which can
be obtained from it (e.g. [5,6]). The approach taken here
ARTICLE IN PRESS
B I O M A S S A N D B I O E N E R G Y 3 2 ( 2 0 0 8 ) 1 2 0 6 – 1 2 1 91208
followed the steps given in [7], which involve:
�
Tpc
Ft
P
P
P
P
M
T
a
Determination of the total area of the forest and stratifica-
tion of that area by those characteristics which are likely to
affect its ability to supply the products (characteristics
such as forest type, age or productive capacity).
�
Choice of a set of possible silvicultural managementregimes which could be applied to produce the products,
in any stand of any particular stratum.
�
Application of a forest growth and yield modelling systemto predict the amounts of the products available from any
stand in the forest, at any time in the future and when any
particular management regime is applied to it.
�
Use of the information from the three preceding steps todetermine what areas of which strata of the entire forest
area should be managed, with which of the possible
silvicultural management regimes, to achieve a long-term,
sustainable supply of the products (usually annually) from
the entire forest area. As well, an estimate of the sustain-
able supply is obtained. This last step often involves
application of a mathematical programming system.
In the present work, only a single forest product, firewood,
will be considered. The next four sections describe how each
of these four steps was implemented here.
3. Forest area and stratification
GIS surfaces of the Murray-Darling Basin were obtained
showing forest cover, forest type and land tenure (National
Forest Inventory, Bureau of Rural Sciences, Australia), digital
elevations, urban areas and water courses (Geosciences
Australia) and land productive capacity (Dr. D. Barrett, CSIRO
Plant Industry, Australia). The measure of productive capacity
was the maximum annual rate of net primary production of
vegetation at a site, referred to here as ‘NPP index’; this is
described in more detail in Appendix A. Over the entire Basin,
the index varied over the range 0.3–14 t ha�1 yr�1.
able 1 – Areas of principal forest types and mallee eucalypt froductive capacity (NPP index) classes, determined as beingollection of coarse woody debris or by thinning live trees
orestype
Site productive capacityclass number
NPP index class(t ha�1 yr�1)
Av
rincipal 1 0.2–3.2
rincipal 2 3.2–4.0
rincipal 3 4.0–6.6
rincipal 4 6.6–14.0
allee – 0.4–11.2
otal
rea
This information was used to compile a map of the Basin
showing the privately owned (or leased) forest areas from
which it might be appropriate to obtain firewood by collection
of coarse woody debris. Public lands were excluded; firewood
supply from these areas is actively regulated by the relevant
state agencies and most firewood comes from privately
managed land [4]. Areas further than 500 km from a capital
city were excluded; the main market for firewood is in the
capital cities and it was considered economically unfeasible
to transport firewood further than this. Mallee forests were
also excluded; they contain negligible amounts of coarse
woody debris. These areas were then stratified into four site
productive capacity classes, defined by NPP index (Table 1)
and by 1-yr age classes (age was defined as the time since the
forest regenerated from bare ground following clearing,
destructive wildfire or other natural calamity). Little informa-
tion was available about forest age to do this reliably.
However, it is believed [8] that a large proportion of the
forests of the Basin regenerated around the turn of the 20th
century, followed by a second period of regeneration in the
1950s. Given this, and from observations by the present
authors of the forests of the Basin, it was assumed that in
2004, 40% of their area would be aged 50–60 yr, 50% would be
100–120 yr and 10% would be 150–178 yr. It was assumed that
forest areas were distributed evenly in each annual age class
across these three periods.
This resulted in a map with an area of 12.3 M ha of principal
forest types, subdivided into 244 site productive capacity� -
age class strata, which could be considered potentially
suitable for firewood harvest by coarse woody debris collec-
tion. Table 1 lists the areas of these forests in each of the four
site productive capacity classes. Fig. 2(a) shows a map of their
distribution across the Basin.
As discussed in more detail later, both principal and mallee
eucalypt forest types can be considered appropriate for
firewood harvests by removing live trees. However, the
logging machinery used to do this would cause much greater
site disturbance than would firewood collection from coarse
woody debris. Accordingly, some additional constraints were
orest types of the Murray-Darling Basin, in various siteappropriate to consider for firewood harvesting, either by
erage NPP index forclass (t ha�1 yr�1)
Area appropriate for firewoodharvesting by different methods
(M ha)
Coarse woodydebris collection
Removal oflive trees
1.9 2.9 2.1
3.4 3.1 2.1
4.9 3.1 2.3
8.3 3.1 2.2
1.2 – 1.1
12.3 9.8
ARTICLE IN PRESS
Fig. 2 – Distribution of forest areas across the Murray-Darling Basin considered appropriate for firewood harvesting.
(a) Principal forest type areas appropriate for harvesting by collection of coarse woody debris only. (b) Principal forest type and
mallee eucalypt areas appropriate for harvesting by removing live trees.
B I O M A S S A N D B I O E N E R G Y 3 2 ( 2 0 0 8 ) 1 2 0 6 – 1 2 1 9 1209
imposed to determine areas of the Basin potentially suitable
to obtain firewood by harvesting live trees. Forest areas with a
slope of 151 or more were excluded, to avoid any possibility of
post-logging soil erosion and the expense and difficulty of
logging steeper slopes. To avoid prejudicing faunal biodiver-
sity through logging, forest areas were excluded where
clearing had reduced forest cover in the landscape generally
to less than 30%, or which were riparian areas within 50 m of
streams or rivers or which were remnant forests with an area
of less than 100 ha.
With these additional exclusions from the previously
determined 12.3 M ha of principle forest types and with the
inclusion of mallee types, a total of 9.8 M ha of forest, 8.7 M ha
of principal forests and 1.1 M ha of mallee forests, then
remained as being potentially suitable for firewood harvesting
by removal of live trees. These were subdivided into 305 site
productive capacity�age class strata. Table 1 lists the areas of
these forests in different site productive capacity classes.
Note that all the mallee forests are located in areas of
relatively low productive capacity in the Basin; 95% of their
total area has an NPP index below 2 t ha�1 yr�1. Accordingly,
all mallee forests were assigned to a single site productive
capacity class stratum. The distribution across the Basin of
these forests is shown in Fig. 2(b).
4. Silvicultural management
The principal consideration in deciding how forests of the
Basin should be managed for firewood production was that
they should continue, and if possible increase, their contribu-
tion to the overall ecological biodiversity of the Basin. With this
in mind, a standard management regime was developed for
harvesting firewood (a) through coarse woody debris collection
from principal forest types, (b) through harvesting live trees by
thinning principal forests or (c) through harvesting live trees
ARTICLE IN PRESS
B I O M A S S A N D B I O E N E R G Y 3 2 ( 2 0 0 8 ) 1 2 0 6 – 1 2 1 91210
from mallee forests. These regimes specify at what stages
during the life of any stand, harvests should occur and what
quantities of firewood should be removed at each harvest.
The overall objective of the present work is to determine
the maximum long-term, steady, sustainable supply of fire-
wood available from the Basin in any calendar year in the
future. Because of variations of site productive capacity and
the uneven distribution of age classes of forests across the
Basin, it will inevitably be impossible to apply the standard
management regime in each and every forest stand across the
Basin to achieve this steady, sustainable yield. In some
calendar years, harvests, which might be due under the
standard regimes, may have to be delayed in some stands, or
brought forward to an earlier year, or even not done at all.
That is, some variations about the standard regimes will have
to be allowed. Determination of how these variations should
be applied is a basic problem faced by any forest manager
responsible for maintaining a long-term, sustainable supply
of forest products from a large, complex forest area.
Sections 4.1–4.3 describe the standard management re-
gimes developed here and the variations from them which
were considered appropriate.
4.1. Coarse woody debris collection in principal foresttypes
Collection of coarse woody debris for firewood is a relatively
benign harvest practice. It causes only minor site disturbance,
principally from vehicle access. It has no effect on the
subsequent growth behaviour of the live trees in the forest.
However, it does affect the amount of woody debris remain-
ing in the forest for maintenance of biodiversity, an issue
discussed in more detail later.
For the ‘standard’ management regime for coarse woody
debris harvest in principal forest types, it was first assumed
that the forest would grow to 178 yr of age on average, the age
which was determined as the average lifespan of forests of
the Basin [9]. After that, it was assumed the forest would be
destroyed by fire, or other natural calamity, and would
regenerate anew. The standard regime then allows collection,
at any stage of development of the stand, of as much as
possible of the firewood available from its coarse woody
debris, with the following constraints:
�
No harvest would be done unless it yielded at least1.5 t ha�1 of firewood; this was considered the minimum
amount that would be worthwhile collecting commer-
cially.
�
The first harvest in any stand would take place around20–25 yr of age, by which time the stand should be well
developed.
�
To avoid too frequent intervention in a stand, subsequentharvests should be done at intervals of 5–10 yr, or delayed
further until 1.5 t ha�1 of firewood became available.
�
No harvests would take place after 178 yr of age, if thestand lived beyond that age.
Seven possible variations of this standard regime were
considered appropriate for any particular stand. The first
possibility was that there was no firewood harvest at all from
the stand. The other six possibilities were simply random
variations of the standard regime. The lifetime for the stand
was selected randomly, within the range 161–195 yr of age.
The age at which the first harvest was done was chosen
randomly from within the range 20–25 yr. The number of
harvests to be done in each rotation was chosen randomly
within the range 20–40. The harvests were then assumed to
be spaced at approximately equal time intervals. However,
the exact timing of any harvest was chosen randomly within
71 yr of the time of exactly equal spacing of harvests, subject
only to delaying any harvest until at least 1.5 t ha�1 of
firewood was available from it.
4.2. Removal of live trees by thinning principal foresttypes
Based on the work of Florence [10], it appeared that the most
appropriate ‘standard’ management regime for thinning
these forests should involve ‘flexible selection practice’ [10,
p. 229]. In Florence’s words this is a ‘regime which aims to
meet a number of objectives, and can result in, or maintain a
highly variable structure. It may take account of both short-
and long-term supplies of wood and, at the same time,
maintain, on environmental grounds, a good level of ecolo-
gical, structural and aesthetic diversity throughout the forest.’
Such a regime is consistent with the present objectives of
producing firewood yields and ensuring maintenance of the
biodiversity of the forest ecosystems of the Basin.
Our experience of the principal forest types of the Basin
suggested that flexible selection practice would involve
selection of trees for harvest at thinning with diameters at
breast height over bark in the range 15–60 cm. The trees
retained would be of good bole form and have canopies in a
suitable condition to allow them to respond to thinning by
accelerating their stem diameter growth rates; although it
was not the aim of the present work to consider the use of
forests of the Basin for wood products other than firewood, it
was assumed that silvicultural practices which might lead
eventually to production of higher value timber products
from trees of larger diameter might have long-term economic
advantage.
Trees with stems in excess of 60 cm diameter would be
retained at thinning, since it is these which provide hollows
important as faunal habitat (e.g. [11–14]), or may, in the
medium term, grow to a size such that they would do so.
Some regeneration would be expected to occur in these
forests after thinning, either as coppice or as seedlings from
natural seed shed; this will ensure maintenance of a high
level of structural diversity.
Insufficient is known presently of the growth dynamics of
the principal forest types of the Basin to prescribe with any
certainty what ages, intensities and frequencies of flexible
selection thinning would be most appropriate in them.
Experience of one forester familiar with them (A. Deane,
State Forests NSW, pers. comm.) suggested that up to three
thinnings might be appropriate in stands of 30–120 yr of age
growing on sites of higher productive capacity. Stands of
lower productive capacity might be thinned twice at most,
when aged 50–150 yr. Various studies of some of the less
ARTICLE IN PRESS
Table 2 – Standard thinning regimes, involving ‘flexibleselection’ practice, for principal forest types of variousproductive capacities (Table 1) in the Murray-DarlingBasin
Siteproductivecapacityclassnumber
Numberof
thinnings
Age rangewithin whichfirst thinningis done (yr)
Delay toeach
subsequentthinning
(yr)
1 2 50–60 30–60
2 2 50–60 30–60
3 3 30–40 40–45
4 3 30–40 40–45
All thinnings would involve removal of 50% of the basal area over
bark of the stand at the time of thinning.
B I O M A S S A N D B I O E N E R G Y 3 2 ( 2 0 0 8 ) 1 2 0 6 – 1 2 1 9 1211
productive forest types of Australia suggests that thinnings
which involve removal of up to 50% of the basal area over bark
of a stand should result in worthwhile acceleration of the
stem diameter growth rates of the retained trees. At the same
time, this intensity of thinning would not be so great that full
occupancy of the site is lost, with a consequent loss of overall
production by the stand [10, pp. 210–213; 15–17].
Given these various considerations, Table 2 shows the
standard thinning regime chosen here for stands of different
productive capacities of the principal forest types of the
Basin. When prescribing a standard regime for any particular
stand in later computations to determine sustainable fire-
wood yields, the age at which the first thinning was done and
the delay to each subsequent thinning were chosen at
random from within the ranges specified in Table 2. As in
Section 4.1, it was assumed that the lifetime of a stand would
be 178 yr of age, after which it would be destroyed by fire or
other natural calamity and would regenerate anew.
When determining long-term, sustainable firewood sup-
plies, the variations about the standard regime prescribed for
any stand were as follows. In each variation, the lifetime of
the stand was chosen randomly within the range 165–191 yr.
The first variation was simply that the stand should remain
unthinned throughout its life. Other variations used ran-
domly selected ages of first thinning and delays to subse-
quent thinnings, from the ranges specified in Table 2. Nine
such other variations were used for stands in site productive
capacity classes 1 and 2, whilst 14 were used for stands in site
productive capacity classes 3 and 4.
4.3. Removal of live trees from mallee forests
Very limited information is available about appropriate
silvicultural management practices for mallee forests of the
Basin. In [18], it was concluded that long-term maintenance
of the mallee ecosystem was best served by a clear-felling
harvest of live trees at 50 yr intervals. This would be followed
by coppice regeneration, which occurs reliably and leads
generally to development of even-aged regrowth stands.
A clear-felling harvest of any particular mallee forest stand,
at an age chosen randomly within the range 40–60 yr of age,
was considered here as its ‘standard’ management regime.
The variations considered about this regime were either that
it was not harvested or nine other variations, where it was
harvested at a different age, also chosen randomly within the
range 40–60 yr.
5. Growth and yield modelling
For the present work, a growth and yield model was
developed for the principal forest types of the Murray-Darling
Basin. This is described in Appendix A. The input required by
the model is the productive capacity of the site (as measured
by NPP index) on which a stand is growing and choices of
when harvests of firewood are to be done by coarse woody
debris and/or by removal of live trees at thinning. The
proportions of the available wood biomass (all plant biomass
amounts referred to in this paper are oven-dry weights) to be
removed at each harvest must be specified also. The model
then predicts, annually for stand ages up to 200 yr, the
amounts of firewood harvested and the amounts of coarse
woody debris and live tree biomass which remain in the
stand.
Using data collated in [18] for clear-felling mallee forests, a
model to predict firewood yields [B0MFðTÞ; t ha�1] at any age T
(yr) was determined as
B0MFðTÞ ¼ 8:91þ 0:274T; if To59, (1a)
and
B0MFðTÞ ¼ 25:1; if TX59. (1b)
6. Determining sustainable firewood yield
Central to the present work is the assumption that respon-
sible management will maintain the existing native forests of
the Basin and their contribution to its biodiversity. The
standard silvicultural regimes for firewood harvest and their
alternatives, as developed in Section 4, were designed to
ensure that these contributions could continue. Of course,
from time to time any particular forest area will reach the end
of its lifespan. To ensure its continued contribution to the
biodiversity of the Basin, it must be assumed that it will then
regenerate and replace itself.
The constraints imposed, both by the management regimes
and the growth rates of the forests, will limit the amount of
firewood which can be harvested. Given these constraints, it
is necessary to determine what combinations of the standard
and alternative silvicultural management regimes must
applied to what areas of the Basin to obtain a steady, annual,
sustainable supply of firewood from the Basin.
As mentioned in Section 2, mathematical programming
systems are used generally by forest managers to determine
both the level of the maximum, long-term, sustainable wood
supply and how the forest area should be managed to achieve
that supply. For the present work, a linear mathematical
programming system was devised to do this, as described in
Sections 6.1 and 6.2.
ARTICLE IN PRESS
B I O M A S S A N D B I O E N E R G Y 3 2 ( 2 0 0 8 ) 1 2 0 6 – 1 2 1 91212
6.1. Mathematical programming system
The ultimate objective of applying the mathematical pro-
gramming system is to estimate the maximum, long-term,
steady, sustainable annual supply of firewood (S, t yr�1), which
can be obtained from the privately owned native forests of the
Basin.
To determine S, a choice must first be made of the specific
period into the future over which the mathematical program-
ming system is to be applied, termed the ‘planning horizon’ of
the system. Suppose this is of length h yr. Suppose the total
area of forest to be harvested for firewood was subdivided
into s strata and the area (ha) of the ith stratum (i ¼ 1ys) was
Ai (ha). Suppose that ri alternative silvicultural management
regimes were considered as possibilities to apply to all or part
of the ith stratum. Suppose also that an area Aik (ha) of that
stratum was then actually managed with the kth (k ¼ 1yri) of
those options. Further, suppose that a weight Fijk (t ha�1) of
firewood was harvested from a stand in the ith stratum
(i ¼ 1ys), during the jth year of the planning horizon
(j ¼ 1yh), when treated with the kth possible management
regime (k ¼ 1yri).
The objective of the linear programming system was then
to determine what area of each stratum should be treated
with which of the silvicultural regime alternatives for that
stratum, to achieve the maximum possible supply of firewood
from the Basin, summed over the entire planning horizon.
That is, the objective function of the system was
MaximiseX
i
Xk
Aik
Xj
Fijk
0@
1A
24
35, (2)
where the Aik are the unknowns to be determined by the
system. Note that the summations in expression (2), and in
the equations below, are for i ¼ 1ys, j ¼ 1yh and k ¼ 1yri.
However, this maximum firewood supply was limited by
two constraints:
�
The sum of the areas treated with the various silviculturalregime alternatives in any stratum must equal the total
area of that stratum. That is, there are s constraints in the
system of the form
Xk
Aik ¼ Ai ði ¼ 1 . . . sÞ. (3)
�
It is desired that the annual supply of firewood from theentire Basin is to be constant at a steady annual amount of
S (t yr�1). However, it is unlikely that a solution will be
obtained to the system if the annual supply is constrained
to be exactly S. Rather, it was assumed that the supply in
any year should be within some (relatively small) propor-
tion (p) of S. This led to h constraints of the form
ð1þ pÞSXX
i
Xk
ðAikFijkÞXð1� pÞS ðj ¼ 1 . . .hÞ. (4)
In using this system, a value was guessed for both S and p. If
no solution for values of the Aik could then be found, a
smaller value of S or larger value of p was chosen and a
solution sought with those new values. Through a trial and
error process, the largest value of S and smallest value of p
were determined for which a solution to the system could be
obtained. Solutions to the system were determined using the
simplex method, as implemented in the MINOS suite of
computer programs, for solving large, complex, mathematical
programming problems [19,20].
6.2. Applying the mathematical programming system
For the present case, a planning horizon of 100 yr was used
(that is h ¼ 100), extending from the 1st of January 2004 until
the 31st December 2103. This was considered to be a length of
time reasonably foreseeable in human terms, both with
respect to the conservation of the forests of the Basin and
development of the firewood industry. The start of the
horizon, 2004, was determined by time at which the present
work was commissioned.
The system was applied twice, once to determine the
maximum, long-term, sustainable, annual supply of firewood
if harvesting involved only collection of coarse woody debris
from the principal forest types and a second time when
firewood was obtained only by felling live trees in both mallee
types and the principal forest types. In each case, the area of
forest to be harvested and its stratification, by site productive
capacity and age class, was as determined in Section 3 and
summarised in Table 1. The silvicultural management regime
options considered as possibilities in each stratum were the
standard regime and each of its alternatives, as discussed in
Section 4. The growth and yield modelling systems (Section 5)
were used to predict firewood harvest yields at any age during
the life of the stands in any one stratum. In applying the
growth and yield model for the principal forest types, it was
assumed that the productive capacity of the forest in any
particular stratum was the average NPP index for that class of
site productive capacity, as specified in Table 1; these class
averages were determined as weighted averages from the NPP
index GIS surface (Section 3), with weighting by the area
distribution of NPP index values across any NPP index class.
The age (Section 3) in 2004 of the forest of any stratum
determined its age at the start of the planning horizon. This
allows firewood harvest yields (the Fijk of the mathematical
programming system) from any stratum to be assigned to the
particular calendar year, during the planning horizon, in
which they are obtained. If the forest of a stratum reached the
end of its lifespan before the end of the planning horizon, it
was assumed to regenerate immediately and start a new
‘rotation’. The management regime option being considered
for the first rotation of that stratum was assumed to apply
also in subsequent rotations. Where firewood was being
harvested by thinning live trees from principal forest types,
any thinning which would have been due to be undertaken
before 2004 was assumed not to have been done.
7. Results
If firewood was harvested from coarse woody debris only
from the eligible principal forest types (Fig. 2a), its maximum,
long-term, sustainable supply was estimated as an average of
10.0 M t yr�1, which the supply constraints (4) ensured did not
vary annually outside the range 8.9–10.9 M t yr�1. This is far in
ARTICLE IN PRESS
B I O M A S S A N D B I O E N E R G Y 3 2 ( 2 0 0 8 ) 1 2 0 6 – 1 2 1 9 1213
excess of the 2–2.5 M t yr�1 of firewood it is believed is
harvested presently from the Basin [4].
When harvesting involved thinning live trees from princi-
pal forest types and clear-felling live trees from mallee
forests, over the areas shown in Fig. 2(b), the maximum,
long-term, sustainable supply was estimated as an average
of 2.3 M t yr�1, which did not vary annually outside the
range 2.1–2.5 M t yr�1. This is about equal to the present
harvest from the Basin. About 78% of this yield would
come from the principal forest types and the rest from mallee
types.
Fig. 3 shows estimates of the biomass of coarse woody
debris that would remain, on average over the entire
harvested areas, year by year over the planning horizon
when firewood was harvested at the maximum, long-term,
sustainable rates; the residual coarse woody debris quantities
were obtained as outputs from the model system at the same
time as firewood yields were determined. As might be
expected, when firewood is harvested by removing live trees
only, far greater amounts of coarse woody debris will remain
than when coarse woody debris is harvested.
With harvests from coarse woody debris only, the results in
Fig. 3 show that the average biomass of coarse woody debris
remaining over the 100 year planning horizon would be
3.0 t ha�1, varying from year to year in the range 2.5–3.7 t ha�1.
These results were averaged over all site productive capacities
across the Basin. In stands of particular productive capacities,
the amounts remaining would increase as productive capa-
city increased, typically from about 1.9 t ha�1 in stands of
productivity class 1 (Table 1) to about 3.3 t ha�1 in stands of
productivity class 4.
Fig. 3 – Average stand biomasses of residual coarse woody
debris, year by year over 2004–2103, after harvesting
firewood at the maximum, long-term, sustainable annual
rate from coarse woody debris of principal forest types only
(- - -), or by thinning live trees from principal forest types
and clear-felling mallee types (—), or if no firewood
harvesting was done at all (— - —). The results for each year
are averaged over the entire areas harvested by each of
these two methods (Fig. 2).
With harvests from live trees only, the average amount of
coarse woody debris remaining would average 17.6 t ha�1 over
the 100 yr, varying from year to year in the range 13.4–21.1 t
ha�1. Again, the residual amount would be higher in stands of
higher productive capacity, typically increasing from about
10.6 t ha�1 in stands of productivity class 1 to about 18.2 t ha�1
in stands of productivity class 4. The substantial decline in
the average amount of coarse woody debris remaining after
about 2050 is a consequence of the age distribution assumed
for the forests of the Basin (Section 3). Younger forests
contain smaller quantities of coarse woody debris; after
2050 the average age of the forests would decline as older
forests are lost through natural calamities and are replaced by
younger, regenerated forests.
Also shown in Fig. 3 is an estimate of how the average
amount of coarse woody debris across the Basin would vary
year by year if there was no harvesting of firewood at all. The
average over the 100 yr is 20.4 t ha�1, varying from year to year
in the range 16.2–23.4 t ha�1. These amounts are greater than
when firewood harvesting was done by live tree removal, even
though this involves no removal of coarse woody debris.
However, live tree removal by thinning reduces the stand
biomass of the live trees remaining in the forests. As evident
in model (11), the amount of coarse woody debris in a stand
increases with the biomass of the live trees in the stands;
hence removal of live trees from a stand leads to a decline in
quantities of coarse woody debris.
8. Discussion
It was estimated that a maximum annual supply of 10 M t yr�1
of firewood could be sustained over the next 100 yr by
harvesting coarse woody debris from the principal forest
types of the Murray-Darling Basin. This is far in excess of the
2–2.5 M t yr�1 believed to be harvested annually at present.
Harvesting this maximum amount would deplete substan-
tially the reserves of coarse woody debris in these forests
(Fig. 3). It remains to be established for forests of the Basin, or
indeed for forests of Australia generally, what quantities of
coarse woody debris need to be retained to ensure the
maintenance of the biodiversity of the flora and fauna of
these ecosystems. However, we believe that biodiversity
would certainly suffer if there was a decline in average coarse
woody debris across the forests of the Basin from the
20 t ha�1, which appears normal if there was no firewood
harvesting (Fig. 3), to as little as 3 t ha�1 if firewood was
harvested from coarse woody debris at the maximum
possible sustainable rate.
However, since the maximum sustainable yield of firewood
harvest from coarse woody debris far exceeds the present
demand, there would be no need to harvest coarse woody
debris from all the 12.3 M ha of forest which were considered
suitable for this (Fig. 2a, Table 1). Harvests could involve
removal of rather less than all the firewood available, perhaps
with advantage to biodiversity maintenance. In any case,
much of the forest of the Basin would be unavailable for
firewood harvest, simply because the owner wished to use it
for some other purpose. Nor is it likely that the maximum
sustainable yield could ever be achieved. It would be
ARTICLE IN PRESS
B I O M A S S A N D B I O E N E R G Y 3 2 ( 2 0 0 8 ) 1 2 0 6 – 1 2 1 91214
impossible to insist that each and every forest property be
managed with the particular harvest management regime
that is necessary to achieve the maximum yield. As well,
wood of some tree species is much preferred for firewood over
others [4], which would exclude some from consideration for
harvesting.
It was estimated that a maximum annual supply of
2.3 M t yr�1 of firewood could be sustained by harvesting live
trees by thinning principal forest types and clear-felling
mallee forests. This is about equal to the present annual
demand for firewood from the Basin. For the same reasons as
those for coarse woody debris collection, it is unlikely that all
of the 9.8 M ha of forests considered suitable for live tree
harvests (Fig. 2b, Table 1) would be available and neither
would the maximum supply ever be achieved. That is to say,
live tree harvests would not be able to replace entirely coarse
woody debris collection to supply existing firewood demand.
An important advantage of live tree harvesting is that coarse
woody debris is retained in the forests (Fig. 3), with possible
advantage to biodiversity maintenance.
Acknowledgements
This work was commissioned by the Australian Common-
wealth Department of Environment and Heritage. It was
financed both by them and CSIRO Sustainable Ecosystems.
For assistance with GIS information and advice in this project
we thank D. Barrett, S. Briggs, S. Doyle, M. Howden,
D. Kennedy, A. Langston, P. Nanninga, D. O’Connell, K. Ord,
D. Osborn, J. Seddon and A. Zerger. A. Deane assisted greatly
with discussion of silvicultural management regimes for
forests of the Basin. A large number of individuals assisted
us in identifying suitable field locations from which data were
collected and we thank, particularly, the land owners who
permitted access to their properties. Particular assistance
with equipment and advice for the model development
aspects of this project was given by J. Banks, N. Coops, J.
Fields, N. Huth, I. Mcleod and D. Spencer.
Appendix A
This appendix describes the growth and yield model devel-
oped in the present work for the principal native forests of the
Murray-Darling Basin. The model concentrates on the pre-
diction of firewood yields, either through collection of coarse
woody debris or by thinning live trees from stands. Model
development was based both on data collected from the
forests during this project and on application of some
relevant, pre-existing work.
A.1. Data
Data were collected from a range of the principal forest types,
scattered across the Murray-Darling Basin. These were found
on 23 different properties and a total of 79 stands were
located on those properties. Five stands were dominated by
non-eucalypt species, whilst the remainder were eucalypt
forest types.
In each stand, the species, diameter at breast height (1.3 m)
over bark and total height of each live tree included in a ‘point
sample’ of the stand [21] were measured. In most stands, the
stem wood volume under bark from ground to tip was
measured, using the ‘centroid method’ [21], for each of two
or three of the trees. In total, stem wood volume was
measured for 252 trees.
The stem wood volume data were used to derive an
individual tree volume function, to estimate tree stem wood
volume (V, m3) from diameter at breast height over bark
(D, cm) and tree total height (H, m) as
V ¼ 0:246� 10�4D1:996H0:947. (5)
This model was used to estimate the stem wood volumes of
live trees measured in the point samples, but for which the
stem wood volume had not been measured directly. Stem
wood volumes were converted to stem wood biomasses,
assuming wood basic densities for each species as given in
[22]. These tree stem biomass results were then used to
estimate the stand stem wood biomass from the point sample
for the live trees for each of the 79 stands.
A similar point sampling method was used to determine
the stem wood biomass of standing dead trees in each stand.
Wood density of those trees was assumed to be that of the live
tree species occurring most commonly in the stand.
In 45 of the stands, a 25�50 m2 rectangular plot was
established about the point at which the point sample was
made. Measurements were made of the length and diameter
at mid-length of any piece of fallen woody debris on the
ground, which had a mid-diameter of 10 cm or more and
length of at least 0.5 m [23]. As it was measured, each piece of
woody debris was assigned to one of three classes (1) wood
was solid when kicked and lacked cavities, cracks or a hollow
pipe, (2) mostly solid when kicked but contained cavities,
cracks or a hollow pipe or (3) gave or crushed when kicked.
The volume of each piece of fallen woody debris was
determined using Huber’s formula [21]. Its biomass was then
determined assuming its density was that of the stem wood of
the live tree species occurring most commonly in the stand.
Debris of class 1 was assumed to have suffered negligible
decay and to be of that density. Debris of classes 2 and 3 were
assumed to have suffered some decay and to have densities of
75% and 30%, respectively, of undecayed wood.
In subsequent model development, data for standing dead
trees and fallen woody debris were combined to determine a
total of woody debris for each stand.
Various stand characteristics were measured also. Since the
principal forests of the Basin include both even- and uneven-
aged forest, it is not practical to determine stand age simply
as the age of the trees. Rather, stand age was defined as the
time since a stand regenerated from bare ground following
clearing, destructive wildfire or other natural calamity. Ages
of the 79 stands were determined from records kept by the
property owners.
The productive capacity of a site, that is the rate of growth
of plants on it, depends on the fertility of its soil and its
weather conditions, particularly temperature and rainfall.
Two attempts have been made to map site productive
capacity right across Australia [9,24]. Both used a combination
of satellite imagery of existing vegetation and growth model
ARTICLE IN PRESS
Table 3 – Minimum-mean-maximum values of standcharacteristics determined for principal forest typestands measured in the Murray-Darling Basin
Stand characteristic Minimum–mean–maximum
Age (yr) 10–82–200
NPP index (t ha�1 yr�1) 2–7–13
Live tree stem wood biomass
(t ha�1)
3–54–190
Live tree stocking density
(stems ha�1)
20–2207–39,773
Coarse woody debris (t ha�1) 0–14–82
B I O M A S S A N D B I O E N E R G Y 3 2 ( 2 0 0 8 ) 1 2 0 6 – 1 2 1 9 1215
systems to estimate the maximum annual rate of net primary
production (above- plus below-ground biomass) of plants
anywhere across the continent. This measure of site produc-
tive capacity will be referred to here as ‘NPP index’.
Arbitrarily, it was decided to use the index developed by
Barrett [9]. Dr. Barrett (CSIRO Plant Industry, Australia) made
available to us a GIS surface with the values of his index for all
of Australia, determined with an accuracy to the nearest
5.2�5.2 km2. From this surface, the NPP index for each of the
79 measured stands was determined.
Table 3 lists the minimum–mean–maximum values of the
characteristics determined from these measurements in the
79 stands (or 45 stands in the case of coarse woody debris
measurements).
A.2. Predicting biomass
These data were used to develop a model to predict stand
stem wood biomass of live trees in the stand at any age, to
about 200 yr of age, [BS(T), t ha�1] as
BSðTÞ ¼ 0:852 expf4:854� 0:231Sþ 0:0177S2
� 0:239½lnðrÞ� � 0:0346½lnðrÞ�2
þ 0:949ðS=TÞ þ 10:815½lnðrÞ=T�
þ 12:485½lnðrÞ=T�2g, (6)
where T (yr) is stand age, S (t ha�1 yr�1) is NPP index, ln( � )
denotes natural logarithms and
r ¼ 0:000181S2:71. (7)
Firewood may be obtained from branch wood of live trees as
well as their stem wood. A model to predict branch wood
biomass was devised as follows. The generalised model for
Australian native forests of Snowdon et al. [25] predicts total
above-ground stand biomass of a stand [BT(T), t ha�1] at any
age T (yr) from its stand stem wood biomass (see Fig. 2.3b of
[25], with rearrangement of the function quoted there) as
BTðTÞ ¼ 1:720BSðTÞ0:962. (8)
Unpublished data from Australian forests (J. Knott, pers.
comm.) suggested that stand branch biomass including bark
[BK(T), t ha�1] at any age T is directly proportional to the
difference between total above-ground and stem wood
biomasses and may be predicted as
BKðTÞ ¼ 0:324½BTðTÞ � BSðTÞ�. (9)
Averaging the results of [26] for several eucalypt species of
the Murray-Darling Basin suggested branch wood stand
biomass [BB(T), t ha�1] at any age T could be estimated from
total branch stand biomass as
BBðTÞ ¼ 0:88BKðTÞ. (10)
Using the coarse woody debris data measured here, a model
was developed to predict the stand biomass of coarse woody
debris [BC(T), t ha�1] in an undisturbed stand (that is where
coarse woody debris had not been lost by removal or fire) at
any age T (yr) as
BCðTÞ ¼ 0:437BSðTÞ. (11)
A.3. Predicting dynamics of coarse woody debris biomass
A model was now developed to predict how coarse woody
debris amounts change from year to year in a stand. From this
point on, it was assumed that the model system would be
used at annual time-step intervals.
Suppose the change in the amount of coarse woody debris
in a stand between ages T and T+1 is denoted as DBC(T)
(t ha�1 yr�1). This can be represented easily as
DBCðTÞ ¼ BCðTþ 1Þ � BCðTÞ (12)
However, over any year from T to T+1, it can be recognised
also that the net change in coarse woody debris is made up of
additions (DBC+(T), t yr�1), as live trees shed limbs or die, and
reductions (DBC�(T), t yr�1), as existing coarse woody debris
rots away. Expressions for these changes were assumed to be
DBCþðTÞ ¼ ½BSðTÞ þ BBðTÞ�tWðTÞ, (13a)
and
DBC�ðTÞ ¼ BCðTÞtC, (13b)
where tW(T) (yr�1) is the proportion of stand branch and stem
wood biomass of live trees converted to coarse woody debris
between T and T+1 and tC (yr�1) is the proportion of existing
coarse woody debris lost through decay. Recognising that
DBCðTÞ ¼ DBCþðTÞ � DBC�ðTÞ, (14)
substituting the right-hand sides of Eqs. (12) and (13) into
Eq. (14) and rearranging, leads to
tWðTÞ ¼ fBCðTþ 1Þ � BCðTÞ½1� tC�g=fBSðTÞ þ BBðTÞg. (15)
Thus tW(T) can be determined at any age T, as long as a
value is available for tC.
A review [27] of Australian and world literature on the rate
of decay of coarse woody debris in forest shows it varies
enormously in different types of forest, from as short as 1 yr
to as long as several hundred years. It varies with the size of
the material, with the quality of the wood and its natural
resistance to decay and with the environmental character-
istics of the site, particularly the moisture and temperature
regimes which affect the activity of decay micro-organisms.
However, Barrett [9] determined that it generally takes an
average of about 23 yr for coarse woody debris to decay
completely in tall forests of Australia; the value of tC is the
reciprocal of this, that is, 0.0435 yr�1. This was assumed to be
an appropriate value of tC for the present model.
ARTICLE IN PRESS
B I O M A S S A N D B I O E N E R G Y 3 2 ( 2 0 0 8 ) 1 2 0 6 – 1 2 1 91216
A.4. Predicting harvest yields
The models developed above were now used as part of a
complete model system to predict amounts of firewood which
can be harvested by collecting coarse woody debris and/or by
removing live trees by thinning, from stands of the principal
forest types of the Murray-Darling Basin. The complete
system was built and is used in two parts.
Consider a stand growing on a site of a particular
productive capacity (NPP index) in the Basin. The first part
of the model system involves prediction of the stand biomass
of the stem and branch wood of living trees and coarse woody
debris annually for each year of the life of the stand, from 1 to
200 yr (or such shorter time as is desired), assuming there is
no loss of wood from a stand during its life (through firewood
harvest by thinning or coarse woody debris removal, fire
passing through it or any other wood removal), other than by
normal decay of coarse woody debris. This is done using
models (6)–(11). As well, values for the rate of conversion of
live tree stem and branch wood to coarse woody debris [tW(T)]
are determined, for all but the last year, using model (15).
The second part of the model system uses these results and
certain other assumptions, which are described below, to
predict the amounts of firewood which can be harvested from
this stand from time to time during its life. At the same time,
an account is kept of the stand branch and stem wood of live
trees and of the coarse woody debris which remain in the
stand year by year as harvesting continues. The user will need
to specify when harvests are to be done, what types of
harvests are to be done (thinning and/or coarse woody debris
removal) and what proportion of the available biomass is to
be removed at each harvest.
In the second part of the model system, a new set of
symbols will be used to represent the stand biomasses of the
live trees and coarse woody debris which remain in the stand
at any age. These will be the same symbols as used above,
except that a prime (0) will be appended to the symbol.
Suppose the model user specifies that, at some age T (yr), a
firewood harvest is done by considering for harvest some
proportion, C(T), of the coarse woody debris biomass then
present in the stand. Not all that coarse woody debris
biomass will be of a size large enough to be used for firewood.
In a study of the firewood industry on part of the eastern
boundary of the Murray-Darling Basin, [26] found that 82% of
biomass harvested for firewood was large enough to be sold
as firewood. Thus, a harvest of coarse woody debris for
firewood will involve removal of an amount B0CFðTÞ (t ha�1) of
the coarse woody debris of the stand, where,
B0CFðTÞ ¼ 0:82CðTÞB0CðTÞ, (16)
where B0CðTÞ (t ha�1) is the biomass of coarse woody debris in
the stand at age T immediately before the harvest. Immedi-
ately this harvest is done, that amount of coarse woody debris
is deducted from B0CðTÞ to give the new amount then
remaining in the stand. Until a firewood harvest is done,
either by thinning live trees or by collecting coarse woody
debris, the values of B0CðTÞ will be the same as the values of
BC(T) from an undisturbed stand.
The amount of coarse woody debris remaining in the stand
in successive years after the harvest is then determined, year
by year, using
B0CðTþ 1Þ ¼ ½B0SðTÞ þ B0BðTÞ�tWðTÞ � B0CðTÞ½1� tC�, (17)
where B0SðTÞ and B0BðTÞ (t ha�1) are the stem and branch wood
stand biomasses of live trees present in the stand at age T and
tW(T) was determined using model (15). Between ages T and
T+1, this model makes additions to the coarse woody debris
from deaths of, or branch shedding by, live trees and
subtractions by decay of existing debris, consistent with
model (13). If the value determined by model (17) is less than
zero, then B0CðTþ 1Þ is set to zero before calculating coarse
woody debris amounts for a subsequent year.
Firewood may be obtained also by harvesting live trees from
a stand, that is by thinning the stand. Suppose the model user
specifies that, at some age (T, yr) a thinning is to be done
which involves removal of some proportion, L(T), of the live
tree wood biomass of the stand; the number of trees actually
removed in such a harvest will depend on the relative sizes of
the trees chosen to be thinned. Thus, an amount B0LFðTÞ
(t ha�1) of firewood would be obtained at the thinning, where,
B0LFðTÞ ¼ 0:82LðTÞ½B0SðTÞ þ B0BðTÞ�, (18)
where B0SðTÞ and B0BðTÞ are the stand wood biomasses of stems
and branches, respectively, of live trees present in the stand
at the time of thinning and it is assumed that 82% of the
harvested biomass will be saleable as firewood, as assumed
for model (16). Immediately the thinning is done, biomass
amounts LðTÞB0SðTÞ and LðTÞB0BðTÞ will be deducted from B0SðTÞ
and B0BðTÞ, respectively, to give their new amounts then
remaining in the stand. Until the first thinning is done,
B0SðTÞ and B0BðTÞ will have the same values as BS(T) and BB(T),
respectively, as determined for the undisturbed stand in the
first part of the model.
To determine subsequent growth of the live trees in a
thinned stand, it was assumed that the total above-ground
biomass production to any age of a thinned stand (that is the
above-ground biomass of the live trees in the stand at that
age, plus the total amount of coarse woody debris that had
been produced up to that age, plus the total amount of live
tree biomass which had been removed from the stand by
thinning up to that age) was the same as the total above-
ground biomass production of the corresponding unthinned
stand to the same age. This assumes that, despite the
immediate loss of foliage biomass from a stand due to
thinning, the photosynthetic capacity of the remaining trees
will increase to just balance the loss. Eventually the trees
remaining after thinning will expand their canopies so that
production by the thinned stand continues to be the same as
if it was unthinned. The validity of this assumption can
judged from various works. This concept, that total produc-
tion by thinned and unthinned stands is the same, has
developed from research undertaken in plantation and highly
productive native forests in various parts of the world [28], but
remains untested for the rather slow growing forests of the
Murray-Darling Basin. However, in the absence of any other
information for the Basin, it seemed a reasonable assumption
to make here.
To apply this assumption, the total above-ground stand
biomass which has been removed from a stand by thinning,
at any age up to and including age T, B0(T) (t ha�1) is
ARTICLE IN PRESS
B I O M A S S A N D B I O E N E R G Y 3 2 ( 2 0 0 8 ) 1 2 0 6 – 1 2 1 9 1217
determined as
B0ðTÞ ¼X
I¼1...TB0LFðIÞ
h i=0:82. (19)
As well, model (13a) is used to determine the cumulative
amount of stand biomass of coarse woody debris that has
been produced up to age T+1 both by the thinned stand
[B0CTðTÞ, t ha�1] and by the corresponding unthinned stand
[BCT(T), t ha�1] as
B0CTðTÞ ¼X
I¼1...T½B0SðIÞ þ B0BðIÞ�tWðIÞ� �
, (20a)
and
BCTðTÞ ¼X
I¼1...T½BSðIÞ þ BBðIÞ�tWðIÞ� �
. (20b)
Assuming then that total production by thinned and
unthinned stands is the same, it follows that, before any
thinning is done at age T+1,
B0TðTþ 1Þ þ B0ðTÞ þ B0CTðTÞ ¼ BTðTþ 1Þ þ BCTðTÞ. (21)
This model can be rearranged to determine the above-
ground stand biomass of the live trees in a thinned stand at
age T+1 as
B0TðTþ 1Þ ¼ BTðTþ 1Þ þ BCTðTÞ � B0ðTÞ � B0CTðTÞ. (22)
Rearrangements of models (8) and (9) can then be used to
convert this total above-ground biomass to stand stem and
Fig. 4 – Scatter plot of the observed stand stem wood
biomasses of live trees (t ha�1), in the 79 stands measured in
the Murray-Darling Basin, against their values predicted by
the model system developed here, assuming each stand
had been undisturbed by thinning during its lifetime. The
solid line shows where the plotted points would lie if there
was exact agreement between the observed and predicted
values.
branch wood biomasses [B0SðTþ 1Þ and B0BðTþ 1Þ, respectively].
To apply this system successfully, it must be assumed that
the first thinning is done at some age after 1 yr of age.
If models (17) and (22) are used in concert year by year, the
model system will keep track of the stand biomasses of live
trees and of coarse woody debris remaining in a stand at any
year, when firewood is being harvested by removing coarse
woody debris and/or by thinning live trees. The amounts of
stand wood biomass harvested for firewood at any of these
harvests will be given by models (16) and (18).
A.5. Testing and applying the model
Formal testing of this model system would require informa-
tion on firewood harvest yields obtained from a large number
of stands in the Murray-Darling Basin which had varying
histories of disturbance over their lifetimes. No such com-
prehensive data set was available here. However, Fig. 4 shows
a scatter plot of the observed stand stem wood biomasses
against values predicted by the model for the 79 stands
measured here, assuming each stand had been undisturbed
by thinning, up to the age at which it was measured. There is
Fig. 5 – Predictions from the model system of the change
with age in the amounts of stand stem plus bark wood
biomass in live trees (—), stand coarse woody debris (- - -)
and the cumulative stand biomass of firewood harvested
(— - —) in a stand where firewood was harvested both by
collecting coarse woody debris and by felling live trees. The
simulated stand was assumed to be growing on a site with
an NPP index of 12 t ha�1 yr�1, which is quite a high
productive capacity for the Murray-Darling Basin. Thinnings
were done at 55 and 105 yr of age, at each of which 50% of
the biomass of the live trees was removed. Coarse woody
debris was collected for firewood every 10 yr, between 20
and 150 yr of age, with all the coarse woody debris of a size
suitable for firewood being collected at each harvest.
ARTICLE IN PRESS
B I O M A S S A N D B I O E N E R G Y 3 2 ( 2 0 0 8 ) 1 2 0 6 – 1 2 1 91218
little indication in the results of Fig. 4 of any marked bias in
stand stem wood live tree biomass prediction, except perhaps
a tendency to underestimate biomasses at higher levels of
biomass; however, the data are insufficient to judge this
adequately.
Using methods of [29], the information in Fig. 4 shows that
the 95% confidence limit about predictions made with the
model of live tree stand stem wood biomass of a single
stand in the Basin is 7153% of the predicted value. This is a
very low precision of estimate, probably too low to be
useful practically. However, if the model is used to predict
the average stand stem wood biomass of stands of a
particular site productive capacity across a wide area of the
Basin, the 95% confidence limit about the predicted average
would be 717% of the predicted value, a far more acceptable
precision of estimate. In the present work, the model was
used only to make predictions of average yields across large
areas.
Unfortunately, insufficient data were available here from
undisturbed stands to undertake a test similar to that of Fig. 4
for coarse woody debris in the measured stands.
As an example of the model in use, Fig. 5 illustrates results
when predicting growth and firewood yields for a stand from
which firewood was harvested both by thinning live trees and
by collecting coarse woody debris. The loss of biomass of live
trees and of coarse woody debris as each harvest was done is
obvious.
The model system developed here should be considered
only as a first approximation to a growth and yield model for
the principal forest types of the Murray-Darling Basin. It was
based on a limited collection of data from only 79 forest
stands, insufficient to sample adequately the complete range
of forest types which occur across the Basin. It then used a
number of other assumptions derived from reports in the
literature, often based on forest types other than those of the
Basin. These limitations reflect the lack of research interest in
the past for forests of the Basin, in turn reflecting the little
commercial use that has been made of them. It will require a
very substantial research effort either to validate fully and/or
develop further this model system.
R E F E R E N C E S
[1] National Forest Inventory. Australia’s state of the forestsreport. Canberra: Bureau of Rural Sciences; 1998.
[2] Specht RL, Specht A. Australian plant communities: dy-namics of structure, growth and biodiversity. Melbourne:Oxford University Press; 1999.
[3] Specht RL, Specht A, Whelan MB, Hegarty EE. Conservationatlas of plant communities in Australia. Lismore, Australia:Southern Cross University Press; 1995.
[4] Driscoll DA, Milkovits G, Freudenberger D. Impact and use offirewood in Australia. Unpublished report, commissioned byenvironment Australia. Canberra: CSIRO Sustainable Eco-systems; 2000.
[5] Davis LS, Johnson KN, Bettinger PS, Howard TE. Forestmanagement. 4th ed. Boston: McGraw Hill; 2001.
[6] Kangas J, Kangas A. Multiple criteria decision support inforest management-the approach, methods applied andexperiences gained. Forest Ecology and Management2005;207:133–43.
[7] Turner BJ, Chikumbo O, Davey SM. Optimisation modellingof sustainable forest management at the regional level: anAustralian example. Ecological Modelling 2002;153:157–79.
[8] Turland JH. Tree level modelling in western New SouthWales’ uneven-aged mixed species forests. In: Mason EG,Perley CJ, editors. Proceedings of the Australian and NewZealand institutes of forestry conference, Wellington, NewZealand, 2003. p. 131–43.
[9] Barrett DJ. Steady state turnover time of carbon in theAustralian terrestrial biosphere. Global BiogeochemicalCycles 2002;16:1108–29.
[10] Florence RG. Ecology and silviculture of eucalypt forests.Melbourne: CSIRO; 1996.
[11] Lindenmayer DB, Cunningham RB, Tanton MT, Smith AP.Characteristics of hollow-bearing trees occupied by arborealmarsupials in the montane ash forests of the centralhighlands of Victoria, south-east Australia. Forest Ecologyand Management 1991;40:289–308.
[12] Gibbons P, Lindenmayer DB, Barry SC, Tanton MT. Hollowformation in eucalypts from temperate forests in south-eastern Australia. Pacific Conservation Biology 2000;6:218–28.
[13] Gibbons P, Lindenmayer DB, Barry SC, Tanton MT. Hollowselection by vertebrate fauna in forests of southeasternAustralia and implications for forest management. BiologicalConservation 2002;103:1–12.
[14] Gibbons P, Lindenmayer DB. Tree hollows and wildlifeconservation in Australia. Melbourne: CSIRO; 2002.
[15] Abbott I, Loneragan O. Response of Jarrah (Eucalyptus margin-ata) regrowth to thinning. Australian Forest Research1983;13:217–29.
[16] Ellis RC, Ratkowsky DA, Mattay JP, Rout AF. Growth ofEucalyptus delegatensis following partial harvesting of multi-aged stands. Australian Forestry 1987;50:95–105.
[17] Horne R. Early espacement of wheatfield white cypress pineregeneration: the effect on secondary regeneration, limb sizeand stand merchantability. Australian Forestry 1990;53:160–7.
[18] Neagle N. The environmental impact and ecological sustain-ability of woodcutting in South Australia. Unpublishedreport, native vegetation conservation Section. Adelaide,South Australia: Department of Environment and NaturalResources; 1994.
[19] Murtagh BA, Saunders MA. Large-scale linearly constrainedoptimization. Mathematical Programming 1978;14:41–72.
[20] Murtagh BA, Saunders MA. MINOS 5.0 users guide. Technicalreport SOL 83-20, systems optimization laboratory, Depart-ment of operations research. Stanford: Stanford University;1983.
[21] West PW. Tree and forest measurement. Berlin: Springer;2004.
[22] Ilic J, Boland D, McDonald M, Downes G, Blakemore P. Woodydensity phase 1-state of knowledge. National carbon ac-counting system, Technical report No. 18. Canberra: Austra-lian Greenhouse Office; 2000.
[23] McKenzie N, Ryan P, Fogarty P, Wood J. Sampling, measure-ment and analytical protocols for carbon estimation in soil,litter and coarse woody debris. National carbon accountingsystem, Technical report No. 14. Canberra: AustralianGreenhouse Office; 2000.
[24] Landsberg JJ, Kesteven J. Spatial estimation of plant produc-tivity. In: Richards GP, editor. Biomass estimation:approaches for assessment of stocks and stock change.National carbon accounting system, Technical report no. 27.Canberra: Australian Greenhouse Office; 2002. p. 33–50.
[25] Snowdon P, Eamus D, Gibbons P, Khanna PK, Keith H, RaisonRJ, et al. Synthesis of allometrics, review of root biomass anddesign of future woody sampling strategies. National carbon
ARTICLE IN PRESS
B I O M A S S A N D B I O E N E R G Y 3 2 ( 2 0 0 8 ) 1 2 0 6 – 1 2 1 9 1219
accounting system, Technical report no. 17. Canberra:Australian Greenhouse Office; 2000.
[26] Wall J. Sustainability of the Armidale fuelwood industry onthe Northern Tablelands of New South Wales: resource yield,supply, demand and management options. Ph.D. thesis.University of New England, Armidale, Australia, 1997.
[27] Mackensen J, Bauhus J. The Decay of coarse woody debris.National carbon accounting system, Technical report no. 6.Canberra: Australian Greenhouse Office; 1999.
[28] West PW. Growing plantation forests. Berlin: Springer; 2006.[29] Reynolds MR. Estimating the error in model predictions.
Forest Science 1984;30:454–69.
top related