Content uploaded by John Bartle
Author content
All content in this area was uploaded by John Bartle on Dec 24, 2015
Content may be subject to copyright.
96 John Bartle
et al
BACKGROUND
During the 1990s the potential scale and impact of dryland
salinity became apparent and emerged as the leading
environmental issue in Australia. Major reviews focused
national attention on the problem (National Land and
Water Resources Audit 2000; Murray Darling Basin
Ministerial Council 2000; State Salinity Council 2000;
National Farm Forestry Roundtable 2000). This work
shows that salinity-related damage has many impacts
beyond the obvious land and water resource losses,
including biodiversity loss (450 potential species
extinctions in W.A. according to State Salinity Council
2000), infrastructure attrition and flood risk (Bowman
and Ruprecht 2000), possible catchment-wide litigation
(Turley 2000) and international sanction (Bartle 1999a).
The consequences and costs of these less tangible impacts
of salinity are still poorly defined.
Dryland salinity is inherently difficult to manage. In
contrast to salinity arising from irrigated agriculture,
dryland salinity involves only diffuse recharge from rainfall
(i.e. no managed irrigated component), large areas, and
Acacia species as large-scale crop plants in the Western
Australian wheatbelt
JOHN BARTLE1, DON COOPER1, GRAEME OLSEN2 AND JEROME CARSLAKE1
1 Department of Conservation and Land Management, Locked Bag 104, Bentley Delivery Centre, Western Australia 6983
2 Olsen & Vickery, PO Box 357 Waroona, Western Australia 6215; email: golsen@iinet.net.au
Corresponding author: John Bartle, Manager, Farm Forestry Unit; phone 08 9334 0321; email: johnb@calm.wa.gov.au
SUMMARY
Revegetation with perennial plants is a well-accepted tool in salinity control across the agricultural regions of southern
Australia but the scale on which revegetation must be undertaken in order to have significant impact on salinity has
become clear only recently. This scale is so large that it must involve extensive change in the commercial plant base of
agriculture. Hence, an array of profitable perennial plants must be developed to complement existing annual crops.
Apart from their role in salinity control, new perennial plant crops can bring a range of other benefits to agricultural
areas, including improved erosion control, protection of biodiversity (and in some cases its enhancement), diversification
of farm incomes, and regional development resulting from local processing of perennial plant products.
This paper discusses some issues relevant to the development of new industries based on woody perennial crops. They
include size of markets, using the whole plant to make multiple products, crop rotation length, temporal and spatial
integration of perennial crops into agriculture, the financial consequences for farmers growing woody crops, and the
desirability of deriving new crops from native species. These issues provide useful guidelines for the objective selection
of potential new commercial crop species. From this foundation, a selection and development project called ‘Search’
has evolved, to systematically assess potential new large-scale tree crops and processing industries based on native
species, select those with high potential for commercial development, and take the first steps towards their development.
The genus Acacia provides considerable potential for the development of new perennial crops. Acacia species appear
to be especially suited for use as phase crops in rotation with conventional annual crops, or as low cost, direct-seeded
coppice crops. A large number of Acacia species occur naturally in the Western Australian wheatbelt and several have
attributes that may make them suitable for commercial development. Potential products include solid wood, panel
board, paper, gum, tannin, fodder, edible seed, and large-scale generic products such as solid fuel for electricity
production, liquid transport fuel and charcoal products.
long distances and time delays between recharge and
discharge. Also, unlike intensive irrigated systems,
broadscale dryland agricultural systems produce low
returns per hectare, from which treatments for dryland
salinity must ultimately be financed.
Two categories of treatment are available. Both are
complex and costly:
• recharge control: a preventative strategy, using water
at or near where it infiltrates the soil and enters
groundwater systems. This can be achieved most
effectively by increasing the proportion of deep-rooted
perennial vegetation (both non-commercial and
commercial) on agricultural land.
• discharge control: ameliorative measures to collect and
safely dispose of groundwater that has accumulated in
low landscape positions and is close enough to the
surface to affect soils. Where this water is not too salty
it can be used by salt-tolerant plants, some with grazing
and timber value. However, groundwater in discharge
areas is often too saline to be used by plants, and its
control requires engineering works such as drains,
pumps and discharge basins.
Conservation
Science W. Aust. 4 (3) : 96–108 (2002)
Acacia
species as large-scale crops in the Western Australian wheatbelt
97
These two types of treatment are complementary because
they apply sequentially along the same hydrologic flow
path, and neither forms a complete, efficient management
system on its own. If the amount of recharge can be
diminished by increased use of perennial plants, then the
amount of discharge will be reduced in the longer term
and become more manageable. Similarly, regardless of the
effectiveness of upslope recharge control, engineering
treatments will be required to cope with highly saline
groundwater emerging in discharge areas.
Recent hydrological research contends that perennial
plants are able to control recharge on agricultural land
only if they cover a substantial proportion of it, i.e. up to
80% (Hatton and Nulsen 1999; George et al. 1999). This
would require a ‘revolution’ in agriculture (Bartle 1999a;
Stirzaker et al. 2000). Not surprisingly, the requirement
for such radical change, and the perceived difficulty of
achieving it, give rise to the pessimistic view that we should
learn to live with the problem rather than solve it! For
example, the Western Australian State Salinity Council
(2002) adopted the proposition that a substantial
proportion of public funds available for salinity be invested
in a few high-value areas to ensure their successful
treatment, implying continued degradation of the balance.
What alternatives are there to this bleak outlook?
Despite significant investments of public money in
promoting it, large-scale revegetation with non-
commercial species is unlikely to occur, because:
• farmers are unlikely to revegetate with non-commercial
plants if their costs exceed the benefits,
• in most cases, the benefits to individual farmers from
non-commercial revegetation are low;
Ethical imperatives, volunteer participation, peer pressure
and integrated catchment management, the laudable
tenets of landcare, will not be sufficient motivation if
revegetation on the necessary scale would bankrupt farm
businesses (Pannell 2000).
The solution is very simple in concept – expand and
diversify the range of profitable perennial crops and
pastures used in agriculture. So the question becomes:
what are the prospects for increasing the extent and
diversity of commercially viable perennial crops and
pastures? There are opportunities in some areas to increase
the use of existing perennial pastures and expand the area
of farm forestry, but this alone will not be sufficient. A
range of new herbaceous and woody perennial plants and
associated industries is required.
A start has been made on woody crop development
with the domestication of mallee eucalypts in Western
Australia. Bartle (2001) reviewed the development of
mallee and its influence on the Search Project (NHT
973849), a project funded by the Natural Heritage Trust,
that aims to generalise the experience gained with mallee
by applying it systematically to screen new woody crop
and product prospects. More recently, this approach has
been incorporated into the new Cooperative Research
Centre for plant-based management of dryland salinity
(www.crcsalinity.com).
This paper presents a conceptual framework for
assessing attributes of tree crops that favour both their
large-scale commercial success and salinity control. It then
assesses the genus Acacia as a source of new woody crop
germplasm for the Western Australian wheatbelt.
DEVELOPMENT OF NEW TREE CROPS
Four aspects to consider and integrate when developing
new tree crops are the type of crop (layout, duration, type
of material produced), type of site (recharge or discharge),
type of product (market size, feedstock requirements) and
species suitability (biological attributes). Each is described
briefly below.
Woody crop types
There is currently no large-scale tree crop in use in the
wheatbelt regions of southern Australia. However, three
conceptual woody perennial crop types have potential for
development:
1. Short-rotation coppice crops: where harvest occurs
every 2 to 5 years from successive crops regenerated
from rootstocks that re-sprout or coppice after each
harvest. Interest in short-rotation coppice crops has
been stimulated by the experience with mallee
development in W.A. (Bartle 2001). Coppice crops
are costly to establish (with seedlings) but are ready
for harvest at an early age and can regrow many times
from the same stump. They are well suited to planting
in permanent belts oriented along the contour, or in
other strategic locations, to intercept downslope water
movement. In this concentrated form they are readily
integrated into large-scale annual cropping systems in
alley farming layouts.
2. Short-rotation phase crops: where the crop occupies a
phase within the annual crop rotation and is harvested
once and removed at age 3 to 6 years. The high cost
of seedling propagation is a significant barrier to
profitable production of large-volume, low-value
products by phase crops (Harper et al. 2000). Hence,
species that can be readily established by direct seeding,
such as those with large seeds, are the most likely
candidates to be developed. Phase cropping can be
used to dewater cropland where soil characteristics limit
the rate of lateral movement of subsurface water and
therefore limit the potential for water consumption
by permanent belts of perennial plants. The woody
plant phase has the potential to improve soil structure
and to utilise leguminous species to enhance
subsequent annual crop production but this is offset
to some extent by clean-up costs after harvest, and an
increased risk that the dewatered soil profile will reduce
yield in the following annual crop. Phase cropping has
yet to attract much investment in research and
development, despite being conceptually attractive.
98 John Bartle
et al
3. Long-rotation crops: where the production cycle is
greater than 10 years and may be as long as 100 years.
Long rotation crops require intensive, long-term
capital investment and very careful site selection. They
are suited to planting in belts or small blocks and, in
addition to timber products, they can provide shelter
and aesthetic benefits. The long rotation period enables
production of large logs that can be sold into existing
timber industries. They have greatest potential in the
wetter wheatbelt regions where growth rates are higher,
rotation length will be shorter and where they will be
comparatively close to current timber industries
(Moore 2001).
Economic analysis of crop types
The relative economics of the three different crop types
described above, and their profitability compared to
current agricultural returns, will determine their
attractiveness to farmers, and hence influence their priority
for development.
To assess the economic performance of each crop type,
discounted cash flows over 25 years were calculated. The
results for each crop type were compared with each other,
and with the discounted value of conventional agriculture
based on annual plants.
Data were generated for four rainfall zones ranging
from 300 to 600 mm mean annual rainfall. Results for
the 400 mm rainfall zone are presented here. Production
cost and yield were estimated for each crop type, and then
used to calculate the ‘stumpage’, or selling price of the
crop standing in the field, that would be necessary for
each crop type to achieve a return equivalent to
conventional agriculture (that is, averaging $65 per hectare
annually over a 25-year period). These calculated ‘break
even’ stumpages were then compared with estimates of
stumpages that are likely to be paid by timber and biomass
industries. Note that no allowance is made in this analysis
for any positive or negative indirect effects of woody
perennial crops such as erosion control, shelter, salinity
control, and interactions with other crops.
Estimated values of production parameters used in the
financial analysis are presented in Table 1, and results are
presented in Table 2.
TABLE 1
Estimated parameters for input to financial analysis of crop types in a 400 mm/yr rainfall area in south-western WA.
COPPICE PHASE LONG ROTATION
Establishment cost $/ha11500 / 380 1350 / 300 1200 / 300
Density (stems/ha) 2667 2000 500 planted100 harvested
Grazing revenue $/ha/yr 0 0 20
Annual costs $/ha 30 30 25
Prune and thin ($/ha)1575 / 675
First harvest age (yrs) 5 4 25
First harvest (t/ha)260 70 90
Coppice interval (yrs) 3
Coppice harvest (t/ha) 2 60
1 First value is for planted seedlings. Second value is for direct seeding.
2 Coppice and phase crops harvest tonnages are for total biomass. Long-rotation harvest tonnage is for sawlogs only.
Notes: Establishment by seedlings varies with planting density.
The cost of direct seeding is based on assumptions of the likely outcome of a modest investment in research.
Coppice crop establishment by direct seeding incurs a higher cost than direct seeding of phase crops or long-rotation crops, as
smaller, more specialised machinery is required to seed narrow belts.
Phase crop costs include $200 per hectare for site clean-up after each harvest, to prepare the land for a resumption of annual
cropping. Coppice and long-rotation crops do not include clean-up costs, as it is assumed that the land will be used for the
same purpose again.
TABLE 2
Impact of establishment technique on the economics of woody crop types in the 400 mm annual rainfall zone.
CROP TYPE SEEDLING ESTABLISHMENT DIRECT SEEDING
Break Average Calculated Break Average Calculated Estimated
even1debt2 stumpage3 even1debt2 stumpage3 stumpage4
Coppice 14 931 14 8 332 8 15
Phase 16 432 32 8 126 14 15
Long rotation 25 1417 130 25 696 87 60
1years to break even.
2average debt ($ per hectare) over period to break-even.
3selling price necessary to make return equivalent to that of conventional agriculture (in $ per tonne of biomass for short
rotation crops, and $ per cubic metre of wood for long rotation crops).
4estimate of stumpage likely to apply for each crop types (same price basis as 3).
Acacia
species as large-scale crops in the Western Australian wheatbelt
99
The sensitivity of cash flow to establishment method
is examined under two scenarios: current technology using
containerised seedlings, and future technology using large-
scale direct seeding. Seedling propagation is expensive, as
indicated in Table 1, and greatly increases costs compared
to direct seeding.
Graphs of discounted cash flows are shown in Fig. 1
(establishment using containerised seedlings) and Fig. 2
(establishment by direct seeding). Note that phase crops
are shown to follow each other without break, to enable
comparison of all three crop types over a 25-year period.
Each successive phase crop is assumed to be located on a
different piece of land.
The results of the financial analysis, shown in Table 2,
indicate that coppice crops established by planting
seedlings can produce biomass for a stumpage of $14 per
tonne. This is slightly less than the $15 per tonne shown
in Enecon’s (2001) feasibility study to be a commercially
viable purchase price for mallee biomass feedstocks. In
contrast, phase crops established by seedlings would
produce biomass at $32 per tonne, over twice the expected
-2000
-1500
-1000
-500
0
500
1000
0 5 10 15 20 25
Year
Long rotati on
Coppice crop
Phase cropping
Opportunity Cost $65/ ha/yr
Figure 1: Discounted cash flow using conventional establishment.
Figure 2: Discounted cash flow using direct seeding
establishment.
price. Phase crops would have to be established by direct
seeding to achieve production at $15 per tonne. If coppice
crops could be established by direct seeding, biomass could
be produced for $8 per tonne, a price likely to stimulate
large-scale demand by wood processing and bioenergy
industries. The economics of long-rotation crops are far
less favourable. Even using direct seeding, the selling price
would have to be above the estimated stumpage of $60
per cubic metre used in this analysis.
For long-rotation crops the average debt load of $1417
per hectare over the 25-year period to harvest indicates a
major financing constraint that is beyond the resources of
most farm businesses. For this reason, long-rotation crops
are unlikely to be planted on a large scale unless long-
term arrangements involving external finance are
developed. The debt level is much lower for coppice and
phase crops and must be carried for a shorter period,
because the time to break even for these crops is much
shorter than for long-rotation crops. Coppice and phase
crops are more likely to be within the financing ability of
farm businesses.
This financial analysis indicates several important
directions for the development of tree crops:
• Direct seeding provides a major economic advantage.
Hence, large-seeded plants like Acacia that are
relatively easy to establish by direct seeding have a
significant advantage over small-seeded ones like
eucalypts for which there is currently no adequate
direct-seeding method.
• Direct-seeded Acacia phase crops could produce
biomass at a cost similar to mallee coppice crops. The
cost of re-establishing phase crops after each harvest is
offset by the benefit of direct seeding.
• Very low cost biomass, produced from coppice crops,
requires the development of direct-seeding techniques
for fine seeded species like mallee eucalypts, or selection
and development of Acacia species that establish easily
by direct seeding and also coppice strongly and reliably
after harvest.
• Long-rotation crops carry the burden of a large, long-
term capital requirement that will limit their use. Their
economics could be improved by developing species
that produce high value ‘appearance grade’ wood
rather than general construction timber.
Site types based on the hydrological
setting
From the hydrological point of view sites fall into two
major categories and several subcategories.
Recharge sites: where the water table is well below the
soil surface and rainfall may infiltrate to some depth in
the soil profile. Subcategories are:
high recharge sites: where light-textured soils permit
rapid, deep infiltration; water use and productivity under
annual plant agriculture are low; potential for lateral
movement of water within the profile is high; and
groundwater salinity is comparatively low. On these sites,
100 John Bartle
et al
woody crops in belt configuration have the potential to
intercept down-slope movement of perched or deep
groundwater, as observed by White et al. (2002).
low recharge sites: where soils are heavier-textured;
leakage past annual plant root systems is less; salt storage
in the profile is greater; groundwater salinity is higher;
and lateral transmission of groundwater is slower. On these
sites phase crops could be used intermittently but
extensively to reduce soil water storage and prevent net
recharge (Harper et al. 2000).
Discharge sites: where infiltration is impeded by a
shallow water table. Groundwater is usually brackish or
saline and may be discharging from the surface. The soil
is poorly drained and only species that can tolerate
waterlogging and salinity are present. Barrett-Lennard
(2001) has proposed three subcategories based on
potential productivity:
high: where groundwater is sufficiently deep that
salt accumulation in the upper soil profile
is not great enough to affect productivity.
medium: where the soil is salt affected but still able
to support saltland pastures.
low: where salt has accumulated to the extent
that only halophytes can survive.
Large-scale woody crop development is likely to focus
on species and crop types suited to recharge sites and high
productivity discharge sites, because plant survival and
growth rates are likely to be highest in these areas.
Product types
The scale of perennial plant cover necessary to arrest
salinity is very large. Therefore it is essential to choose
products and markets that have the capacity to absorb
very large-volume production. This argument was
presented more fully by Bartle (2001). Table 3 lists
products that could be produced from wheatbelt woody
crops. It includes estimates of market size, and the
development period for potential markets. For example,
alcohols made from woody biomass are still undergoing
technological development as transport fuels, but within
a generation they could compete in these very large
markets, at a time when the dominance of petroleum could
be declining (Foran and Mardon 2000).
The priority for selection and development of tree crops
will be dominated by their commercial potential. In the
case of grazing, sawn timber, food and flowers, the nature
of the product will limit the number of suitable species
from which selections can be made. For panel and paper
products, bioenergy and derived chemicals, feedstock
criteria may be less demanding, allowing selection from a
greater diversity of species; they may also allow a range of
species grown in different locations to contribute
feedstocks to a single processing centre. Bioenergy and
derived chemicals are likely to be the least discriminating
uses for biomass, and are most likely to be profitable when
made from low-cost residues, for example, from biomass
remaining after the removal of a select woodchip product
for panel board manufacture.
To be profitable, it is almost certain that new woody
crops will have to provide feedstock to two or more
different products, to fully utilise 100 per cent of the
biomass produced, and to maximise the revenue they earn.
Indeed, this complementarity between products has been
a factor in achieving commercial feasibility in integrated
mallee processing, where activated carbon, eucalyptus oil
and electricity will be produced concurrently from mallee
biomass feedstocks (Enecon 2001).
Local processing of most raw materials from new
woody crops will be essential because of their low value
per tonne and high sensitivity to transport costs. Although
this may be a disadvantage for some product types, it
provides significant regional economic benefits, including
TABLE 3
Potential large scale products from woody plant crops.
PRODUCT CATEGORY PRODUCT TYPE MARKET SIZE1DEVELOPMENT PERIOD2
Grazing Meat Large Current
Wool Large Current
Manufactured feeds Medium Current
Wood Sawn wood (appearance, construction) Large Current
Panels (particle board, medium density fibreboard (MDF), Large 2010-2020
oriented strand board (OSB))
Processed wood (pulp/paper, charcoal) Large 2005-2020
Bioenergy Solid fuel (electricity, heat, desalination) Very large 2002-2025
Liquid fuel (alcohols, biodiesel) Very large 2015-2030
Chemicals Extracts (oils, gums, tannins, resins) Medium 2002-2010
Derived (pyrolytic liquids, commodity chemicals) Large 2020-2040
Food and flowers Staple food (bulk grain) Large 2005-2010
Bush tucker Tiny Current
Ingredients (oils, edible gums etc.) Small 2005-2010
Flowers Tiny Current
1Potential market volume in land area, very large > 5 million ha, large 1 to 5 million ha, medium 100,000 to 1 million ha,
small 10,000 to 100,000 ha, tiny < 10,000 ha.
2Period during which significant industry development is likely to occur.
Acacia
species as large-scale crops in the Western Australian wheatbelt
101
local investment and employment, plus greater stability
to farm budgets and rural economies due to year-round
harvesting and processing (CSIRO Land and Water et al.
2001).
Biological attributes
A large number of biological attributes may be important
in selecting species for development as crop plants. Major
categories are:
• survival, growth rate and yield: any species being
considered for use as a commercial crop must have
good yield potential over the required rotation length.
• morphology: plant morphology determines the range
of products for which any species might be suited. Each
product type in Table 3 could require plants of different
morphology. An overriding requirement is that plants
be of a form amenable to low-cost harvest.
• breeding biology: influences issues such as collection
of propagules, method and ease of genetic
improvement, method of establishment in the field,
and assessment of weed risk.
• conservation biology: including natural distribution,
diversity within species, status and security of native
populations, and relationships with other species.
• adaptability: how easy new crops are to establish and
manage, and how tolerant they are of the farm
environment (climate, soils, pests and diseases, grazing
animals, herbicides).
Native species score highly on many of the biological
attributes listed above and therefore deserve further
investigation of their commercial potential. Native species
are well adapted to their natural environment, are less likely
to become weeds in native vegetation, and may contribute
directly to the maintenance of biodiversity in rural areas.
A key point in their favour is that their genetic resource is
available locally (Bartle 2001).
ATTRIBUTES OF
ACACIA
The preceding sections give a broad perspective on the
role of tree crops in agricultural systems. This section
surveys the potential of Acacia species to be developed as
commercially viable woody crops for salinity control.
Diversity, geographical range and ecology
Acacia is a large genus with a wide diversity of plant form
and function and a large geographical range. Many species
have large variation between provenances. A large part of
the diversity in the genus occurs in Australia, where many
species are endemic. This localisation of Acacia diversity
provides an opportunity for Australian researchers to sift
through the local flora for potentially commercial species,
and then to select or breed productive crop lines from the
full range of genetic diversity within those species.
Acacia species occur in all the dryland farming regions
of southern Australia, on a full suite of habitats and ranging
from small shrubs to trees. There are major centres of
diversity in both the central wheatbelt of W.A. and in the
inland slopes of the south-east of the Murray-Darling
basin. Species that occur naturally in the southern
Australian wheatbelt would be expected to be well adapted
to many of the conditions they would encounter if grown
as commercial crops in that region. For species that occur
naturally in several different environments, it may be
possible to select from different populations to produce
different commercial lines of the same species, to suit
different types of farm environment. Or, closely related
species with different environmental requirements could
be grown in different farm situations as part of the same
industry, as long as their wood (or other saleable plant
parts) had sufficiently similar attributes that could be
processed together.
Many species fill a ‘pioneer’ role (rapid re-colonisers
after disturbance). Such species have attributes that are
potentially valuable in crops (easy establishment, rapid early
growth) but these same attributes may pre-dispose them
to weediness. Weed risk can be offset by developing local
or regional species in preference to introduced species.
Alternatively, weed risk can be controlled by various weed
reduction strategies such as developing sterile hybrids, non-
flowering forms or lines with reduced hard-seeded
dormancy, or by developing management practices that
eliminate flowering.
Many faster-growing Acacia species are also short-
lived. This attribute is unlikely to be a disadvantage for
short-rotation phase crops but may make some species
unsuitable for use as coppice crops.
Commercial potential
In keeping with their diversity of form, function and
distribution, Acacia species have found a wide range of
commercial uses. Some of the larger species are used for
sawn timber, firewood, charcoal, panel board pulp
manufacture, and are grown in large commercial
plantations (El-Lakany 1987; Brown and Ho Chin Ko
1997). Other commercial uses include tannin production
from bark (Barbour 2000), and edible gum exuded from
wounds on the stem, most notably from Acacia senegal,
the source of gum arabic (Anderson and Wang Weiping
1990). Acacia saligna is used as a fodder crop in North
Africa (El-Lakany 1987; Dumancic and Le Houerou
1981), and is being planted in farming areas in southern
Australia as a combined landcare and supplementary
fodder species (Lefroy et al. 1992). Edible seed from over
40 species from the dry zone may have been included in
the diet of Australian aborigines (Devitt 1992). A small
industry now exists to supply niche ‘bush food’ markets
in Australia (Maslin et al. 1998, Simpson and Chudleigh
2001), and some Australian species have been introduced
into famine-prone semi-arid regions in sub-Saharan Africa
(Harwood 1994).
Many Acacia species are likely to provide suitable
feedstocks for large-scale generic products such as solid
fuels for electricity production, liquid transport fuel,
charcoal and other pyrolytic products, and various
102 John Bartle
et al
commodity chemicals, as the feedstock specifications
required for these products are very broad.
Most existing commercial uses of Acacia utilise species
that are not commonly found in the wheatbelt of southern
Australia and, in some cases, are not native to Australia.
However, it is likely that some wheatbelt Acacia species
also possess commercially desirable characteristics that,
once identified, could lead to their development as
commercial crop plants. Screening Western Australian
wheatbelt species for desirable feedstock characteristics,
growth rate and form is being carried out by the ‘Search
Project’.
Water use potential
While virtually any woody perennial species is likely to
consume more water than annual crops, there is likely to
be considerable variability in water use potential between
species, especially within a large and diverse genus such as
Acacia.
High water use is an important selection criterion for
potential Acacia crop plants that are intended to play a
role in salinity management in agricultural areas. Partial
selection for high water use is likely to occur coincidentally
during preliminary selection of Acacia species for
commercial crops, since two key factors for commercial
success, namely high survival rates in medium to low
rainfall areas, and high biomass production rates, are most
likely to coincide in plants that are effective at extracting
water from soil. Although the relationship between water
use and a plant’s root size and distribution is complicated
by many factors, including the availability of water and
nutrients (Brouwer 1963, cited in van Noordwijk et al.
1996), and management of the plant’s above ground parts
(van Noordwijk et al. 1996), a useful first approximation
is that ‘the more extensive the root system is, the higher
nutrient and water uptake efficiency may be’ (van
Noordwijk and de Willigen 1991).
Once several highly productive Acacia species have
been identified for potential crop development, further
testing will be needed to find particular forms with
optimum root architecture and water use characteristics
for the sites on which they are to be grown, and the
functions they are expected to perform. Techniques
suitable for low cost assessment of plant water use are
available and could be used at this stage.
Various aspects of tree root architecture also need
exploring, including the effect of pruning or removing
the tops, as practised in short-rotation coppice crops. Some
studies have found that increased severity of pruning results
in an increased proportion of roots near the soil surface,
due to new roots growing from the stem base (Hairiah
et al. 1992, cited in van Noordwijk et al. 1996). The
relevance of this finding for Acacia coppice crops should
be tested, as it has implications for both water use and
competition between Acacia belts and adjoining crops.
Some species have a propensity to develop deep root
systems, others shallow ones, and the actual root pattern
for a species on a particular site is determined by the
interaction between genotype and environment (Kerfoot
1963, cited in van Noordwijk et al. 1996). It is likely that
at least some Acacia species, especially those adapted to
dry environments, are deep rooted, or would grow deep
roots if grown as an agricultural crop, since deep
rootedness is common in xerophytic species where there
is access to groundwater (van Noordwijk et al. 1996).
Knight et al. (2002) reported finding live tree roots at a
depth of 16 metres under 4-year old belts of Acacia saligna
and Atriplex nummularia (saltbush), while at a similar
depth soils under adjacent annual plants had none,
although it was not specified whether the deep roots were
from Acacia saligna or saltbush. In Africa, roots of Acacia
senegal have been reported at a depth of 32 metres (Deans
1984, cited in van Noordwijk et al. 1996).
Deep rootedness is likely to be a desirable attribute
for Acacia species grown as phase crops on permeable
soils, to maximise their productivity when grown at high
densities, and to maximise their soil drying capacity. Deep
rootedness would usually be preferred for Acacia species
grown in alley layouts, to minimise competition for water
with the adjoining crop. However, if the main aim of
growing woody perennials in belts is to reduce
waterlogging in the alley, or if the site on which they are
grown has shallow soil, then Acacia species with a more
spreading root architecture may be suitable.
Competition for water between annual crops and
adjacent perennial woody crops will be strongly affected
by the perennial crop’s root architecture and water use.
But other factors will also be important, including depth
of soil, existing hydrological conditions, rainfall during
the annual crop’s growing season, and management
strategies such as root ripping, or harvesting the perennial
crop. In very wet areas or in very wet seasons, annual crop
yields may be enhanced if adjacent perennial crops reduce
waterlogging, whereas in dry years or on dry sites, they
are likely to be suppressed by adjacent perennial crops
unless the latter have been harvested recently or their roots
are ripped.
Nitrogen fixation
Being a legume, Acacia can fix nitrogen and could play a
significant role in nitrogen input to agricultural systems,
especially when grown as a phase crop on soils poor in
nitrogen.
Mele and Yunusa (2001) found significant increases
in nitrogen and organic matter in soil at Rutherglen in
Victoria following a six-year period under Acacia. This
was not reflected in greater yield in a subsequent annual
crop, partly because the Acacia phase had exhausted the
soil water supply, and partly due to competition from
weeds. However, modelled results from simulated wheat
crops indicated that yields would be boosted for at least
five years after removal of the Acacia crop, due to high
soil nitrogen, once the soil water in the crop root zone
had been replenished (by one wet year in this simulation).
Other researchers have investigated the effect of a
leguminous crop on subsequent non-leguminous crops.
Acacia
species as large-scale crops in the Western Australian wheatbelt
103
For example, using annual leguminous plants in rotation
with maize on acid soils in the humid tropics, van
Noordwijk et al. (1995) recorded an average increase in
maize grain yield of 0.5-1 tonne per hectare following
the legume rotation, compared to maize following a grass-
weed fallow. The efficiency of using biomass N was found
to be about 0.8 times that of applying urea in two split
applications.
It appears likely that nitrogen fixed by an Acacia phase
crop could provide a direct economic benefit by reducing
the need to add N fertiliser to subsequent crops. However,
to maximise this benefit, new farming systems should be
developed based on optimised site selection, crop rotation
sequences and integrated management.
Soil rejuvenation
In addition to producing salinity benefits by dewatering
soil profiles, a range of other beneficial soil effects has
been proposed for woody plants grown in rotation with
annual crops. They include, ‘nutrient pumping’ to relocate
plant nutrients from deep in the soil to the surface,
‘hydraulic lift’ in which dry topsoil is rehydrated with water
drawn by plant roots from deep in the soil profile, thereby
enabling nutrient uptake to continue in surface soils during
dry seasons and droughts (van Noordwijk et al. 1996),
and the provision of new root channels to improve soil
porosity and facilitate root development in subsequent
crops, a topic reviewed by Cresswell and Kirkegaard
(1995). However, little information is available on these
postulated influences of tree roots on soil physical
properties (Ong 1996).
Acacias grown as phase crops could provide extensive
soil rejuvenation that would benefit subsequent crops,
through better soil aeration, reduced surface waterlogging,
and easier access for roots. Working at the Rutherglen site
described above, Yunusa et al. (2001) examined the soil
under a wheat crop planted on land that had been occupied
by Acacia for six years. In the second year after the Acacia
harvest, the duplex soil (shallow sandy to clay loam surface
over a fine sandy clay loam B horizon) contained a greater
number of large pores and had a higher air-filled porosity
than adjacent continuously cropped soil. Soil porosity
increased between the first year after Acacia and the second
year, as the Acacia roots decomposed. The wheat crop
grown on the ‘acacia soil’ had higher root dry matter and
higher root length compared to the adjacent wheat crop
grown on ‘annually cropped soil’. Further investigation
of the effect of Acacia phase crops on soil physical structure
and the productivity of subsequent crops is required.
Seed size and ease of harvest and
establishment
Acacia carries its seed in pods, the seed size is large and,
in southern Australian species, the seed is generally
produced annually in a well-defined season. These
attributes mean that the cost of seed collection should be
relatively low and that plants can be established by direct
sowing rather than by seedling production in a nursery.
The treatments required to break hard-seeded
dormancy in many Acacia species are now well understood
within the nursery trade and among companies and
organisations involved in land rehabilitation and
revegetation. Similar techniques are likely to be successful
for new species developed as crops or, as mentioned above,
it may be possible to breed forms with reduced hard-
seededness, to lower long-term weed risk, while
simultaneously improving ease of establishment.
Vegetative regeneration
Some Acacia species can regenerate vegetatively after the
stem is cut and this could make them suitable for use in
‘permanent’ belts in alley farming systems. The ability to
resprout from the cut stump (coppicing) appears to be
restricted to certain species or, in some cases, provenances
or variants within species. Further research is needed to
understand the coppicing behaviour of potential
commercial species, including variation within species,
reliability of coppicing, conditions that favour successful
coppicing, and the robustness of successive coppice
regrowth from the same rootstock.
Root suckering, also a feature of some Acacia species,
is likely to be a disadvantage in species that sucker
indiscriminately but could be useful in those that sucker
more strategically, after a trigger such as death or removal
of the main stem. Again, more research is needed to
determine the suckering propensity of different species
and provenances within species, as well as the
environmental conditions that might favour or discourage
suckering, so that appropriate farming systems and
management techniques can be developed.
Some preliminary information on the coppicing and
suckering ability of various Acacia species is given in
Table 4.
Assessment of individual species
Acacia species that occur naturally in the south-west of
Western Australia were assessed in 2000 and 2001for their
suitability to be developed as biomass crop plants. The
boundaries of the study area were the regions defined in
the Interim Biogeographic Regionalisation of Australia
(Thackway and Cresswell 1995) as Geraldton Sandplains,
Avon Wheatbelt, Mallee and Esperance Plains.
Species considered to be most suited to further
investigation are listed in Table 4, along with attributes
that may affect their commercial prospects. ‘Plant form
and growth rate’ determine the amount of biomass
produced and its ease of harvest, and have a strong effect
on profitability, while ‘other features’ affect each species’
potential suitability as a crop plant, the type of farming
systems with which it would be compatible, its
management requirements, and its potential primary uses
(influenced by wood density) and secondary products
(such as seed, fodder, tannin and gum).
This assessment was carried out by Bruce Maslin from
the Western Australian Herbarium, in association with the
Search Project.
104 John Bartle
et al
TABLE 4
Preliminary assessment of some Western Australian
Acacia
with potential for crop development.
SPECIES AND PLANT FORM2 AND GROWTH RATE OTHER FEATURES3
DISTRIBUTION1
A. acuminata
Tall shrub or tree 2-7 (-10) m tall. + Low to moderate salt tolerance
Widespread (wheatbelt) Multi-stemmed from ground level, or with a fairly straight + Drought and frost tolerant
bole 0.3-1.5 (-2) m long and 10-30 (-45) cm dbh.Stems - Susceptible to waterlogging, fire
and main branches fairly straight. ± Unlikely to sucker, can coppice from rootstock
Pendulous forms occur occasionally in parts of the range. + Genetically diverse- Seed yields unreliable
Growth rate: moderate ± Wood density: high (1 plant, 7 cm stem)
A. anthochaera
Tall shrub 2-4 m tall, occasionally maturing to bushy + Moderately salt tolerant
Northern wheatbelt tree to 8 m. ± Not known to sucker (unlikely to coppice)
Multi-stemmed from or near ground level. Each stem + Edible seed (large reliable crops)
6-10 cm in diameter at its base and 4-8 cm dbh. ± Wood density: high (1 plant, 8 cm stem)
May be single-stemmed to about 1 m above ground level
and reach 30 cm in diameter at the base (10-20 cm dbh).
Slightly crooked trunks and main branches.
Growth rate: moderate to fast
A. conniana
Dense, bushy shrub or small tree 1.5–6 m tall. ± Unlikely to sucker, coppicing ability unknown
South coast Sparingly divided at the base or up to ± Wood density: medium (3 plants, 5-7 cm stems)
(geographically 1 m above the ground
restricted) Stems sub-straight and 5-8 cm dbh.
Growth rate: low to moderate
A. cyclops
Spreading shrub (1-4 m tall) or small tree (to 7 m tall). + Salt tolerant
Coastal
Single-stemmed to about 1 m or sparingly divided at + Some provenances grow in waterlogged clays
ground level into a few sub-straight or rather crooked ± Rarely coppices, but may sometimes sucker
main stems (dbh often 10-15 cm, rarely over 20 cm). - Weed potential
Growth rate: moderate ± Wood density: medium (4 plants, 5-11 cm
stems)
A. jennerae
Shrub or small tree, often with ‘mallee-like’ form, + Tolerant of fire, frost, salt, drought
Arid zone 1.5-4 (-6) m tall.Sometimes single-stemmed but more ± Strong root suckering and coppicing
commonly dividing at ground level into 2 or more, + Edible seed
straight, rather slender stems.
Often suckering to form clonal thickets.
Growth rate: moderate
A. jibberdingensis
Shrub or small tree 2-4 m tall, occasionally 7 m tall. + Appears to be adaptable to a variety of
Widespread (wheatbelt) Single-stemmed to 1.5 m or sparingly dividing just above habitats
ground level. ± Unlikely to sucker, coppicing ability unknown,
Stems up to 25 cm diameter at the base ( to 15 cm dbh). but probably poor- Variable seed set
Stems and main branches can be rather crooked.
May be spindly when growing in dense scrub.
Growth rate: moderate
A. lasiocalyx
Spreading shrub or tree commonly 2-5 m tall, dbh 13-15 cm.± Unlikely to sucker, coppicing ability unknown
Widespread (wheatbelt) Often an erect tree around the base of granite rocks, - Phyllodes contain relatively high concentrations
reaching 10-15 m tall, dbh 30-50 cm, with fairly of cyanogenic glucoside
straight trunk. ± Wood density: medium (15 plants, 4-12 cm
Usually single-stemmed or sparingly divided at the base. stems)
Growth rate: fast?
A. microbotrya
Bushy, tall shrub or small tree 2-4 m tall + Slight to moderate salt tolerance?
Widespread (wheatbelt) (Dandaragan variant is a tree to 7 m tall). + Drought and frost tolerant± Suckers readily, and
except south-east Single trunk to about 1 m before branching probably coppices- Taxonomically complex (under
(about 11 cm diameter at base), or dividing at ground review)
level into 2-4 main trunks (6-9 cm dbh). + Many related species that may also warrant
Often forming dense clonal clumps by root suckers. investigation+ Edible seed, possibly gum, tannin,
Growth rate: fast fodder± Wood density: medium (42 plants,
4-10 cm stems)
A. murrayana
Large shrub or tree 2-6 (-8) m. - Salt sensitive
Arid zone Single- or multi-stemmed from the base. + Tolerant of fire (coppices) and drought
Stems straight or sometimes rather crooked, dbh to 15 cm.± Suckers and coppices
Commonly suckering to form clonal thickets. - Potential weed
Growth rate: fast + Edible seed, possibly gum
± Wood density: low (3 plants, 8-9 cm stems)
Acacia
species as large-scale crops in the Western Australian wheatbelt
105
SPECIES AND PLANT FORM2 AND GROWTH RATE OTHER FEATURES3
DISTRIBUTION1
A. prainii
Dense, spreading shrub 1.5-3 (-5) m tall. + Hardy
Widespread (wheatbelt) Branching at or just above ground level into a number ± Unlikely to sucker, coppicing ability unknown
of erect to ascending stems. ± Wood density: high (1 plant, 5 cm stem)
Main stems and branches rather straight (4-6 cm dbh).
Growth rate: moderately fast
A. aff. redolens
Small tree 4-7 m tall, may reach 10 m on good sites. + Moderately tolerant of salinity?
Restricted distribution Dividing at 0.5-1.8 m above ground level into 2 or 3 + Grows in waterlogged clays
(Esperance) main stems (9-20 cm dbh). ± Unlikely to sucker or coppice?
Stems and main branches sub-straight. + Thin bark± Wood density: medium (5 plants,
Growth rate: unknown 5-10 cm stems)
A. resinimarginea
Tree 4-7 m tall.
Northern wheatbelt Single-stemmed or branched into 2-5 stems near base. - Low tolerance to salt?
Trunks fairly straight, generally erect, reaching 20 cm dbh. + Suited to Wodjil sands
Growth rate: slow ± Unlikely to sucker, coppicing ability unknown
± Wood density: high (3 plants, 5-11 cm stems)
A. rostelliferaCoastal
Dense shrub or tree commonly 2-5 m tall. + Suited to light soil
Branching near ground level, with main stems usually 5- + Root suckers, probably coppices
10 cm dbh, although some specimens considerably larger. + Many related species
Usually clonal. Spindly when growing within dense clonal - Difficult to get seed
thickets, with stems about 2-3 cm dbh. ± Wood density: medium (13 plants, 4-12 cm
Growth rate: fast stems)
A. saligna
Bushy shrub or tree 2-6 (-10) m tall. - Susceptible to various insects and diseases
Widespread (wheatbelt) Either single- or multi-stemmed, mature trunks ± Root suckers and coppices (all forms?)
20–40 cm dbh. + Variable growth forms
Sometimes forming thickets due to root suckering. ± Genetically variable (currently under review)
Variable growth form. The largest, tree form occurs on + Edible seed, gum, tannin, fodder, yellow dye-
the Swan Coastal Plain. Weed potential?
Growth rate: fast ± Wood density: low (34 plants, 3-15 cm stems)
A. victoriae
Arid zone Spreading, often straggly shrub or small tree + Tolerant of salt, lime, fire (when young), frost and
1.5-5 (-6) m tall. clay soils- Sensitive to severe drought
Main stems commonly about 6 cm dbh but reaching + Coppices and suckers readily
12-14 (-18) cm. + Edible seed, charcoal, fodder- Quite prickly
Readily root suckering and sometimes forming thickets.
Growth rate: fast ± Wood density: medium (2 plants, 4-8 cm stems)
1. Distribution refers to the south-west of Western Australia.
2. Some heights and diameters are given for the normal range, with unusually large sizes in brackets. For example: height 2-7 (-10) m tall.
’dbh’ refers to diameter at breast height (1.3 m above ground).
3. Wood density was calculated from wood cores taken from some species. Sampling was biased towards small trees. The number of
plants sampled and their stem diameter at the sampling height (usually waist height or below) are included. Quoted densities are ‘basic
density’ (oven-dry weight divided by green volume, expressed in kg per cubic metre). Density categories used in this table are: Low: less
than 650, Medium: 650 to 850, High: over 850 kg per cubic metre.
4. Symbols in column 3: + advantageous attribute; - disadvantageous attribute; ± advantageous or disadvantageous attribute depending on
circumstances.
Table adapted from Maslin (2001).
TABLE 4 (continued)
106 John Bartle
et al
CONCLUSION
Large-scale revegetation for salinity management is likely
to occur only if commercial perennial crops are developed.
Acacia is a prospective genus for crop development in
southern Australia due to the large number of species
occurring naturally in Australia, their favourable breeding
biology, and their diversity. Many have suitable growth
rates and form, and the potential to produce commercially
attractive products such as wood, fibre, gums, tannins and
seeds.
Acacia species could be suited to each of the perennial
woody crop types described in this paper. For example,
species with good tree form and good wood quality may
be suitable for long-rotation cropping, while species with
the ability to sprout reliably from the stump after harvest
could be used as short-rotation coppice crops. Obligate
seeders might be particularly suitable for use as phase crops.
Each crop type could fill a quite different role in
agricultural systems.
The economic analysis discussed in this paper shows
that Acacia species are most likely to be profitable if
developed as short-rotation crops, producing low-cost
woody biomass. These crop types are best able to utilise
the biological potential of Acacia to improve water balance
and sustainability in southern Australian wheatbelt
agricultural systems. Large-seeded Acacia species are
especially suitable for development, because low-cost
establishment using direct seeding has a large, positive
effect on profitability, net debt load, and time to break
even.
Detailed evaluation will be required to identify taxa
with the best commercial prospects. The extent to which
Acacia crops may be developed will depend on the size of
markets for low-cost biomass feedstocks, and criteria for
commercial success such as:
• adequate feedstock quality for processing,
• ability to provide feedstock material for more than one
product,
• low cost of production relative to competing
feedstocks.
The potential of Acacia is being investigated in a current
project in Western Australia sponsored by the Natural
Heritage Trust. Known as the Search Project it is
conducting systematic screening of the native flora of the
Western Australian wheatbelt to identify species with the
potential to be developed into large-scale crop plants.
ACKNOWLEDGMENTS
The support of the Natural Heritage Trust for Project
Number 973849 has helped generate many of the ideas
presented in this paper. The Rural Industries R&D
Corporation has been a keen proponent of the Search
Project concept and provided support for projects. The
support of Bruce Maslin is also gratefully acknowledged.
REFERENCES
Anderson, D.M.W. and Wang Weiping (1990). Acacia
gum exudates from Somalia and Tanzania: the Acacia
senegal complex. Biochemical Systematics and Ecology
18, 6, 413-418.
Barbour, L. (2000). Tannin and Fuel Wood from
Plantation grown Bipinnate Acacias. A report for the
RIRDC/LWRRDC/FWPRDC Joint Venture
Agroforestry Program, RIRDC publication no. 00/
47. Rural Industries Research and Development
Corporation, Canberra.
Barrett-Lennard, E.G. (2001). General principles of
salinity and waterlogging tolerance plant adaptations
and water use. In. Proceedings of Workshop, Revegetation
of Saline and Waterlogged Land, 13 December 2001,
Bentley Technology Park. Centre for Land
Rehabilitation, University of Western Australia.
Bartle, J.R. (1999a). The new hydrology: new challenges
for landcare and tree crops. In Proceedings Western
Australian Bankwest Landcare Conference: Where
Community Counts, Esperance Civic Centre, W.A., 8-
10 September 1999, pp. 52-63.
Bartle, J.R. (1999b). Why oil mallee? In Proceedings: The
Oil Mallee Profitable Landcare Seminar, 18 March
1999, pp. 4-10. Oil Mallee Association, Perth.
Bartle, J.R. (2001). New perennial crops: mallee eucalypts,
a model large-scale perennial crop for the wheatbelt.
In Managing Agricultural Resources 3 Proceedings, 27
February-1 March 2001, National Convention Centre,
Canberra, pp. 117-128. Outlook Conference 2001,
ABARE, Canberra.
Bowman, S. and Ruprecht, J. (2000). Blackwood River
Catchment Flood Risk Study. Surface Water Hydrology
Report Series, Report no. SHW 29. Water and River
Commission, Perth.
Brouwer, R. (1963). Some aspects of the equilibrium
between overground and underground plant parts.
Jaarboek IBS Wageningen 1963, pp. 31-39.
Brown, A.G. and Ho Chin Ko (eds) (1997). Black Wattle
and its Utilisation. RIRDC publication no. 97/72.
Rural Industries Research and Development
Corporation, Canberra.
Chegwidden, A., Harrison, D. and Weir, P. (2000). Mallee
eucalypts for electricity, activated carbon and oil, a new
regional industry. In Proceedings Bioenergy 2000:
Making a Business from Renewable Energy for Society
and the Environment, Gold Coast, Queensland.
Bioenergy Australia, Sydney http://
www.users.bigpond.net.au/bioenergyaustralia/
Cresswell, H.P. and Kirkegaard, J.A. (1995). Subsoil
amelioration by plant roots – the process and the
evidence. Australian Journal of Soil Research 33, 221-
239.
Acacia
species as large-scale crops in the Western Australian wheatbelt
107
CSIRO Land and Water, CSIRO Forestry and Forest
Products, Australian National University Department
of Forestry, Rural Industries Research and
Development Corporation, Olsen and Vickery, and
Hester Gascoigne and Associates (2001). The
Contribution of mid to low Rainfall Forestry and
Agroforestry to Greenhouse and Natural Resource
Management Outcomes: Overview and Analysis of
Opportunities. Prepared for the Australian Greenhouse
Office and the Murray-Darling Basin Commission.
Australian Greenhouse Office, Canberra.
Deans, J.D. (1984). Deep beneath the trees in Senegal.
In Institute of Terrestrial Ecology Annual Report, pp.
12-14. Natural Environment Research Council,
Swindon.
Devitt, J. (1992). Acacias: a traditional aboriginal food
source in central Australia. In Australian Dry-zone
Acacias for Human Food (A.P.N.House and
C.E.Harwood, eds), pp. 37-53. Proceedings of a
workshop held at Glen Helen, Northern Territory,
Australia, 7-10 August 1991. CSIRO Division of
Forestry, Canberra.
Dumancic, D. and Le Houerou, H.N. (1981). Acacia
cyanophylla Lindl. as supplementary feed for small stock
in Libya. Journal of Arid Environments 4, 161-167.
El-Lakany, M.H. (1987). Use of Australian acacias in north
Africa. In Australian Acacias in Developing Countries
(J.W.Turnbull, ed), pp. 116-117. Proceedings of an
international workshop held at the Forestry Training
Centre, Gympie, Queensland, 4-7 August 1986.
ACIAR Proceedings no. 16, Australian Centre for
International Agricultural Research, Canberra.
Enecon (2001). Integrated Tree Processing of Mallee
Eucalypts. A report for the Joint Venture Agroforestry
Program. Publication number 01/160, Project OIL-
3A. Rural Industries Research and Development
Corporation, Canberra.
Foran, B. and Mardon, C. (1999). Beyond 2025:
transitions to a biomass-alcohol fuel economy using
ethanol and methanol. Report to the National Dryland
Salinity Program, Working paper series 99/07. CSIRO
Wildlife and Ecology, Canberra.
George, R.J., Nulsen, R.A., Ferdowsian, R. and Raper,
G.P. (1999). Interactions between trees and
groundwaters in recharge and discharge areas – a survey
of Western Australian sites. Agricultural Water
Management 39, 91–113.
Hairiah, K., van Noordwijk, M., Santoso, B. and
Syekhfani, M.S. (1992). Biomass production and root
distribution of eight trees and their potential for
hedgerow intercropping on an ultisol in Lampung.
AGRIVITA 15, 54-68.
Harper, R.J., Hatton, T.J., Crombie, D.S., Dawes, W.R.,
Abbott, L.K., Challen, R.P. and House, C. (2000).
Phase Farming with Trees: a Scoping Study of its
Potential for Salinity Control, Soil Quality
Enhancement and Farm Income Improvement in
Dryland Areas of southern Australia. RIRDC
Publication no. 00/48, Rural Industries Research and
Development Corporation, Canberra
www.rirdc.gov.au/reports/AFT/00-48.pdf
Harwood, C.E. (1994). Human food potential of the
seeds of some Australian dry-zone Acacia species.
Journal of Arid Environments 27, 27-35.
Hatton, T.J. and Nulsen, R.A. (1999), Towards achieving
functional ecosystem mimicry with respect to water
cycling in southern Australian agriculture. Agroforestry
Systems 45 (1-3), 203-214
Kerfoot, O. (1963). The root system of tropical forest
trees. Empire Forestry Review 42, 19-26.
Knight, A., Blott, K., Portelli, M. and Hignett, C (2002).
Use of tree and shrub belts to control leakage in three
dryland cropping environments. Australian Journal
of Agricultural Research 53, 571-586.
Lefroy, E.C., Dann, P.R., Wildin, J.H., Wesley-Smith,
R.N. and McGowan, A.A. (1992). Trees and shrubs
as sources of fodder in Australia. Agroforestry Systems
20, 117-139. Kluwer Academic Publishers.
Maslin, B.R. (2001). Preliminary Assessment of South-west
Western Australian Acacias for Potential in Farm
Forestry. Unpublished report to the Search Project,
Farm Forestry Unit, Department of Conservation and
Land Management.
Maslin, B.R., Thomson, L.A.J., McDonald, M.W. and
Hamilton-Brown, S. (1998). Edible Wattle Seeds of
Southern Australia: a Review of Species for Semi-arid
Regions of Southern Australia. Forestry and Forest
Products, Australian Tree Seed Centre, CSIRO,
Canberra.
Mele, P.M. and Yunusa, I.A.M. (2001). Cereal yields
associated with changes in soil characteristics following
six years of Acacia. Presented at the 10th Australian
Agronomy Conference, Hobart 2001 Available at
http://www.regional.org.au/asa/2001/
Moore, R.M. (2001). Eucalypts for High-grade Timber in
the Medium Rainfall Zone of WA: a Feasibility Study
for a New Industry. Forest Products Commission,
Department of Conservation & Land Management,
and the Water & Rivers Commission, Perth
Murray Darling Basin Ministerial Council (2000). Draft
Basin Salinity Management Strategy 2001-2015.
MDBC Ministerial Council, Canberra. http://
www.mdbc.gov.au/naturalresources/
policies_strategies/projectscreens/
salinity_manage_strategy.htm#salmenu
National Farm Forestry Roundtable (2000). National
Strategy for Low Rainfall Farm Forestry in Australia.
Farm Forestry Program, Department of Agriculture
Forestry and Fisheries, Canberra.
National Land and Water Resources Audit (2000).
Australian Dryland Salinity Assessment 2000: Extent,
Impacts, Processes, Monitoring and Management
Options. Natural Heritage Trust, Canberra.
108 John Bartle
et al
Ong, C.K. (1996). A framework for quantifying the
various effects of tree-crop interactions. In Tree-Crop
Interactions: a Physiological Approach (C.K.Ong and
P.Huxley, eds), pp. 1-23. CAB International in
association with the International Centre for Research
in Agroforestry, University Press, Cambridge.
Pannell, D.J. (2000). Salinity Policy: A Tale of Fallacies,
Misconceptions and Hidden Assumptions Sustainability
and Economics in Agriculture Working Paper 00/08.
Grains R&D Corporation project UWA 251 http://
www.general.uwa.edu.au/u/dpannell/dpap0008.htm
Simpson, S. and Chudleigh, P. (2001). Wattle Seed
Production in Low Rainfall Areas. A report for the
RIRDC/Land and Water Australia/FWPRDC Joint
Venture Agroforestry Program. RIRDC publication
no. 01/08. Rural Industries Research and
Development Corporation, Canberra.
State Salinity Council (2000). Natural Resources
Management in W.A.: the Salinity Strategy.
Government of Western Australia http://
www.salinity.org.au/content/
index.cfm?childID=35&council=true
State Salinity Council (2002). A Salinity Investment
Framework. Government of Western Australia. http:/
/www.salinity.org.au/publications/publications.cfm
Stirzaker, R.J., Lefroy, E.C., Keating, B. and Williams, J.
(2000), A Revolution in Land Use: emerging Land Use
Systems for managing Dryland Salinity. A report
prepared for the Murray Darling Basin Commission
by CSIRO Land and Water, Canberra.
Thackway, R. and Cresswell, I.D. (1995). An Interim
Biogeographic Regionalisation for Australia: a
Framework for establishing the National System of
Reserves, version 4.0. Australian Nature Conservation
Agency, Canberra.
Turley, I. (2000). Common law implications of dryland
salinity. Proceedings of the National Dryland Salinity
Conference: Salinity Stocktake – Present and future,
Bendigo, 14-17 November 2000.
van Noordwijk, M., Lawson, G., Soumare, A., Groot,
J.J.R. and Hairiah, K. (1996). Root distribution of
trees and crops: competition and/or complementarity.
In Tree-Crop Interactions: a Physiological Approach
(C.K.Ong and P.Huxley eds.), pp. 319-364. CAB
International in association with the International
Centre for Research in Agroforestry, University Press,
Cambridge.
van Noordwijk, M., Sitompul, S.M., Hairiah, K.,
Listyarini, E. and Syekhfani, Ms. (1995). Nitrogen
supply from rotational or spatially zoned inclusion of
Leguminosae for sustainable maize production on an
acid soil in Indonesia. In Plant Soil Interactions at Low
pH (R.A.Date et al., eds), pp. 779-794. Kluwer
Academic Publishers.
van Noordwijk, M. and de Willigen, P. (1991). Root
functions in agricultural systems. In Plant Roots and
Their Environment (H.Persson and B.L.McMichael,
eds), pp. 381-395. Elsevier, Amsterdam.
White, D.A., Dunin, F.X., Turner, N.C., Ward, B.H. and
Galbraith, J.H. (2002). Water use by contour planted
belts of trees comprised of four Eucalyptus species.
Agricultural Water Management 53, 133-152.
Yunusa, I., Mele P. and Haines, P. (2001). Increased root
growth associated with ‘plant-priming’ of subsoil
structure. 3rd International Land Degradation
Conference, Rio de Janeiro, Brazil, 17-21 September
2001. Symposium no. VI.
