Beauty leaf tree (BLT; Calophyllum inophyllum L.) is a wild native species of Australia. It mostly grows in the eastern, northern and north-western coastal areas of tropical Australia.

This species also occurs in many islands of the north Pacific Ocean such as Indonesia and Papua New Guinea. The tree can grow up to 30m tall with a stem diameter of two metres and a canopy diameter of up to 50 metres.

The BLT bears dark green, glossy and attractive leaves and hence the name beauty leaf tree. In Australia, it flowers twice a year, bearing round fruits that resemble those of macadamia. The outer skin of the fruit is usually eaten by bats which drop the seed on the ground.

Most fruits fall on the ground within a week or two of maturity (twice a year), although continuous bearing can be seen in trees that are irrigated regularly. The seed contains a soft skin with an underlining of spongy tissues. The round kernel is embedded within the spongy tissues. The cream-coloured kernel turns brown after drying. The dried seed contains 30% to 70% non-edible oil.

The kernel oil is composed of palmitic acid, oleic acid, stearic acid, linoleic acid and linolenic acid. The cold pressed oil has been used for centuries as a medicinal oil under the names ‘Domba oil’, or ‘Tamanu oil’. The BLT oil is also used in cosmetics but not as an edible oil due to presence of toxic chemicals. This is the reason why its kernels were used in the manufacturing of rat poison.

Beauty leaf tree grows well in infertile soils such as sand dunes, waterlogged sites and skeletal soils. It is relatively easy to grow as it thrives well on marginal soils.

Each tree can produce up to 10,000 seeds, so if established in plantations it has the potential to yield up to 4000 litres of oil per hectare in a year. This oil can be converted into biodiesel at 95% conversion efficiency. At the end of its life, BLT can produce substantial quantity of hardwood timber. These features – its ability to grow in marginal soils and produce oil-rich seeds qualifies it to be listed on top of all biofuel tree crops.

Central Queensland University researchers have carried out numerous studies to explore its biofuel potential. The studies include genetic variability amongst trees located in different agro-climatic regions (Rockhampton to Darwin), tree to tree variability in kernel oil content and phenological behaviour and provenance variations for stress tolerance.

The techniques of extracting the oil from the kernel, oil refining, and converting the oil into biodiesel have been optimised. The nature and properties of the biodiesel generated from BLT have been studied, along with engine performance and emission characteristics. These results show that the BLT diesel performs almost on par with petro-diesel.

The significance of BLT biodiesel is that it significantly reduces engine emissions such as carbon monoxide and hydrocarbon. This feature of BLT biodiesel is found extremely attractive for its use in densely populated cities to run city buses, taxies and emergency electricity generators.

Converting the BLT kernel oil into biodiesel involves various steps, such as oil extraction, refining, esterification, transesterification and biodiesel purification. These steps can often be time consuming and costly.

Hence, direct use of the BLT fruit to produce biofuels such as biooil, biochar and syngas have been optimised, and the production of electricity via the use of a microturbine that runs on bio-oil or syngas is currently being trialled.

The pyrolysis process generates by-products such as biochar and bioliquor. The use of these products in synthesising fertilisers to improve soil health, and the use of bioliquor as plant growth promotor or pesticide is also being explored.

CQU’s extensive research on BLT clearly demonstrates various benefits of growing BLT in the coastal areas of tropical Australia. Firstly, establishment of BLT plantations at strategic positions in the landscape can help capture excess water and nutrients that flow from the farmlands into the Great Barrier Reef.

Secondly, establishment of BLT plantations in marginal lands can generate much needed fuel without entering into a ‘food vs fuel' argument. This process also contributes to re-greening of the land that has been cleared and degraded land over the past 200 years.

On one hand, BLT biodiesel reduces greenhouse gas emission; on the other, it sequesters carbon and captures nutrients via tree growth, and fruit and timber production. The continuous use of its fruits for biofuel production will help facilitate carbon recycling.

As a result, establishment of BLT plantations for biofuel production can contribute to Australia achieving a ‘net zero emission’ target. This could also help protect Great Barrier Reef from nutrient contamination.

An assessment of the resources used in the urban and semiurban areas of Australia reveal the following: These regions produce huge quantities of wastewater and organic waste. The city and shire councils will also have waste land (landfills, low lying areas) which are not suitable for housing.

In addition, there are extensive areas of road and rail verges. These areas may be used to grow BLT and other potential biodiesel crops. These crops can be irrigated with city wastewater, and they can also be fertilised with the compost obtained from the city waste.

Under these circumstances, BLT stands out as the pioneering species for biofuel production. In return, the BLT can provide feedstock for biofuel production, and this feedstock could be used to fuel city vehicles to reduce air pollution in the city.

Since there are many benefits of establishing BLT plantations on marginal soils, the process of establishing plantations and generating biofuel could commence immediately. However, one should realise that this process will take more than five years to generate income.

But once commenced, the income generation process could continue for up to 500 years. As a result, the use of BLT for biofuel and timber production should be treated as the superannuation for the children and grandchildren of the person who establishes BLT plantations.

It is possible that the need for biofuel may not arise, if alternative ways of generating power (solar, wind, tide or nuclear) become cost effective. Since BLT produces hardwood timber and it can grow well on marginal soils, BLT would still prove to be beneficial under these scenarios.

BLT can produce substantial quantities of non-edible oil. If this oil is not used for biofuel production, then a suitable technology may be developed to remove the toxic component of the oil so the resulting oil could be used in human and animal consumption.

Owing to the presence of attractive foliage and profuse flowering, BLT has been used as an avenue tree in Yeppoon, Mackay, Townsville, Cairns, Cook Town and Darwin. This tree is known to help protect the cities from cyclones and tsunamis (e.g. Darwin).

The BLT can also be used as an indoor pot plant, as it thrives well in diffused light. The twigs bearing mature leaves can also be used in cut flower industry, as their vase life ranges from 6–10 weeks.

In summary, beauty leaf tree offers many benefits to the community (biofuel, medicinal value, revegetation, hydraulic barrier, carbon and nutrient sequester, indoor pot plant), in addition to providing an excellent habitat for wildlife (bats, bees, butterflies).

Therefore, BLT can be used in all walks of life ranging from the cut flower industry, as an avenue tree and land rehabilitation; to the establishment of large-scale plantations for biofuel and timber production.

Written by Nanjappa Ashwath - associate professor at the School of Medical and Applied Sciences, Institute for Future Farming Systems, Centre for Intelligent Systems, Central Queensland University, Rockhampton, QLD 4701. Email: n.ashwath@cqu.edu.au