Producing biomass: Biomass types: Trees: Mallee
The mallee eucalypt is a small, multi-stemmed tree that can be grown on marginal land. It can be harvested every few years and the biomass sold for converting to ethanol or electricity. The tree resprouts, or coppices, from the cut stump.

Evaluating the economics

A case study of mallee eucalypts grown for use as a coppicing woody crop and harvested every 4 years is described in Chapter 9 of Bioenergy in Australia: Status and opportunities, published by Bioenergy Australia in 2012.

It covers the production costs, revenue and the benefits of mallee biomass production systems. Detailed economic modelling of the mallee biomass production system and supply chain is included.

A whole-farm economic analysis by NCCARF and the Future Farm Industries CRC in 2013 found that growing mallees as a biomass tree crop was profitable and easy to integrate into farming systems in southern Australian. The report EverFarm® – Climate adapted perennial-based farming systems for dryland agriculture in southern Australia includes results of the whole-farm studies conducted in:
  • Wagga Wagga, southern New South Wales
  • Hamilton, western Victoria
  • Cunderdin, southern Western Australia
  • Katanning, southern Western Australia
The development potential of the mallee industry in Western Australia is comprehensively described in the 2008 Australian Government publication, Oil mallee industry development plan for Western Australia [PDF, 2.5 MB]. Produced together with the Oil Mallee Association, the Forest Products Commission and the Western Australia state government, the book describes the mallee’s potential uses and products, which include:
  • biofuel
  • wood pellets
  • bio-oil
  • bioelectricity.
Case studies modelling the economics of various mallee production systems are described in Chapter 5.

Harvesting and transport systems and costs are described in Chapter 4.

Mallee eucalypt crops in Victoria have excellent potential to produce a significant amount of energy for the state. This was the finding of the Victorian government when they looked at the value chain of bioenergy from agriculture.

Mallee–crop competition is a significant cost to farmers and must be considered when designing mallee agroforestry systems. This was the finding of CSIRO in a research paper on the productivity and economics of agricultural crops and pastures growing in the competition zone adjacent to mallee crops. The research was done at 15 sites across the Western Australian wheatbelt.

Biofuel produced from mallee biomass has emerged as a potential future fuel source for the aviation industry. Growing mallee biomass for biofuels [PDF, 738 kB] is an initiative of the Future Farm Industries CRC aimed at stimulating new and sustainable industries across regional Australia.

Almost 80% of the energy inputs required to produce mallee biomass occurs in the harvest and transport stages, mainly from the use of fossil fuels.

An energy balance analysis by the Curtin University Centre for Advanced Energy Science and Engineering, Production of mallee biomass in Western Australia: Energy balance analysis, says mallee production strategies should focus on developing and optimising harvest and transport strategies and logistics, as well as improving the fuel efficiency of machinery used for producing mallee biomass.

Benefits of producing mallee biomass

Mallees have formed the basis of a processing industry in Australia for more than 100 years because of their natural abundance of eucalyptus oil.

They can also be integrated into wheat belts to:
  • reduce soil salinity
  • give shade and shelter for animals
  • reduce erosion by acting as windbreaks
  • store carbon.
Once established, the biomass can be harvested every few years. Because the tree resprouts, or coppices, from the underground crown root (lignotuber), there is no need to replant.

Oil mallees benefit on-farm biodiversity [PDF, 652 kB], especially when planted near areas of native bush. This was the finding from a 3-year study by CSIRO and the Future Farm Industries CRC.

Supplying mallee biomass

Sustainable biomass supply chain for the mallee woody crop industry [PDF, 3.1 MB], a report published by RIRDC, compares a mallee woody crop supply chain to the sugar supply chain.

The findings are relevant to farmers in Western Australia and mallee areas in New South Wales, Victoria, South Australia and Queensland.

The report also looks at:
  • crop production and systems for mallee
  • harvesting systems
  • transport and storage systems
  • processing mallee
  • product options from mallee.
A model for producing mallee biomass including harvesting, on-farm haulage, and transporting by road to a central bioenergy plant is described in the Curtin University report: Mallee biomass as a key bioenergy source in Western Australia: Importance of biomass supply chain.

Supply chain options for mallee biomass [PDF, 665 kB] are modelled in Chapter 7 of Developing Options for integrated food-energy systems: Supply chain logistics and economic considerations for short-rotation woody crops in southern Australia.

In pellet form, mallee biomass can be used along with coal for combustion in coal-fired power stations – this is known as co-firing.

Delta Electricity is trialling mallee eucalypts to use as renewable biomass fuel at its Wallerawang power station in New South Wales. 200,000 mallee trees are being planted on 20 farms in the Forbes region. Mallee is one of four viable biomass sources in New South Wales [PDF, 55 kb] that Delta has identified.

Growing mallee eucalypts

Mallee describes the growing habit of certain eucalypt species that grow with multiple stems shooting from an underground crown root (lignotuber), usually to a height of up to 10 metres.

Mallee eucalypts grow in the semi-arid areas of southern Australia in:
  • New South Wales
  • north-western Victoria
  • southern South Australia
  • southern Western Australia.
Growing areas of mallee woodlands and shrublands [PDF, 298 kb] across Australia are listed in an Australian Government report.

Of the 26 species of mallee eucalypt, it says, the most widespread species are:
  • Eucalyptus Dumosa (white mallee)
  • Eucalyptus socialis (red mallee)
  • Eucalyptus gracilis (yorrell)
  • Eucalyptus oleosa (red mallee)
  • Eucalyptus incrassata (ridge-fruited mallee)
  • Eucalyptus diversifolia (soap mallee).
The most diverse range of species occurs across Western Australia and South Australia.
The productivity of mallee agroforestry systems (RIRDC 2012) has extensive information on growing mallee. Estimates on growth efficiency based on rainfall figures are provided in Chapter 1. According to this report, mallee agroforestry is not likely to be economical in 350 mm rainfall areas, but could be in 450+ mm rainfall areas (Chapter 6).

Biomass yield of 10–20 green tonnes per hectare per year can be achieved when mallees are grown in widely spaced two-row belts in alley systems in regions with adequate rainfall and suitable soil types (Section 9.3 of Bioenergy in Australia: Status and opportunities, published by Bioenergy Australia in 2012).

Australia has significant areas of marginal land that may be suitable for planting trees for biomass production, but not for intensive agricultural cropping. Using marginal sites to grow mallee [PDF, 2.4 MB] and tall eucalypts for bioenergy was the subject of a paper presented at the 2012 Australian Forest Growers Conference.

Oil Mallee Australia has published a code of practice and guidance notes for establishing a mallee planting.

Harvesting and transporting

An efficient and economic harvesting system is the key to success in growing a mallee crop, according to the Future Farm Industries CRC. They led the engineering of an oil mallee harvester prototype [PDF, 683 kB] in Western Australia in 2010. The harvester demonstrated how supply chain costs can be reduced, increasing the commercial viability of the mallee industry.

The mallee harvester is the world’s first vertically fed, continuous wood chipper harvester. The design maximises the operational and fuel efficiency of the wood chipper and integrates it with a vehicle.

The harvester simultaneously chops trees and converts them to woodchips in a single pass with no need for separate chipping and transport steps. It is designed to integrate with in-field haulout vehicles and roadside collection and transport, similar to the current supply chain model for sugarcane harvesting.

In 2014, ARENA announced it would fund a project to increase the size of the harvester and upgrade the design to enable it to operate under full-scale commercial conditions.

The $3.5 million project ($2 million from ARENA) is being run by Biosystems Engineering. They aim to collect 15,000 tonnes of chipped mallee at a plantation near Casino in NSW during a 33-day harvester trial. The chips will be used to supplement feedstock to the 30 MW bioenergy power plant at the Broadwater sugar mill in NSW.

The project is scheduled for completion in 2017.



Harvesting and collecting mallee biomass from the field is described in detail in Section 6.3 (‘Short cycle tree crops’) of Bioenergy in Australia: Status and opportunities, published by Bioenergy Australia in 2012, which covers:
  • selecting a harvesting system
  • machinery options
  • relocating the biomass from the plantation (extraction)
  • transporting the biomass
  • processing the raw material into a form that can be used efficiently as fuel (e.g. chipping and chunking)
  • drying the biomass.

Contacts

Geoff Pain

147 David Hill Road, Monbulk, Victoria 3793

geoff.pain@bigpond.com
Dr Xun Hu

Fuel & Energy Technology Institute, Curtin University

Kent St, Bentley WA 6102,
Phone: 08 9266 9679

x.hu@curtin.edu.au
Chris Horner

Program Director, Biomass Cofiring, Delta Electricity

175 Liverpool Street, Sydney NSW 2000
Phone: 0419 696 891

chris.horner@de.com.au
David McFall

Mallee grower and Oil Mallee Association Regional Manager , 26 Jersey St, NARROGIN WA 6312
Phone: 08 9881 5373

templemc@treko.net.au
Simon Dawkins

Director, Oil Mallee Association

FREMANTLE WA 6959,
Phone: 0412 563 388

simon.dawkins@oilmallee.org.au
Brendan George

Tamworth Agricultural Institute / NSW DPI

4 Marsden Park Road, Calala, NSW 2340,
Phone: 02 6763 1238

brendan.george@industry.nsw.gov.au
John Bartle

Manager, Revegetation Unit, Department of Parks and Wildlife, WA

168 St Georges Terrace, PERTH WA 6000,
Phone: 0408 907 762

John.bartle@dpaw.wa.gov.au
Dr Yun Yu

Curtin University of Technology

Kent Street, Bentley, WA 6102,
Phone: 08 9266 9202

Yun.Yu@curtin.edu.au
Prof. Hongwei Wu

Curtin University

Dept. of Chemical Engineering, Curtin University, Perth, WA
Phone: 08 9266 7592

H.Wu@curtin.edu.au