ATHERTON OAK - THE QUEEN OF NUTS
SCIENTIFIC NAME: Athertonia diversifolia
FAMILY: Proteaceae
Bernard Murawski has completed a report in November, 1998 on the Atherton Oak, Athertonia diversifolia, which he has submitted as a requirement leading towards the award of Bachelor of Applied Science (Horticultural Technology). The following Paper is the first of two articles to be printed.
Australians are slow to take advantage of what their country has to offer.
We allow other countries to take up this challenge and they are reaping the rewards. The macadamia nut (Macadamia sp.) is a good example of the potential our country has to offer. It was developed by the Hawaiians. The same is happening with the quandong (Santalum acuminatum) with research being carried out in Israel and the USA and the pearl bush (Maireana sedifolia), which is being exported by Israel.
The Atherton Oak (Athertonia diversifolia) is a north Queensland rainforest tree closely related to the macadamia. The tree produces a tasty edible nut which has been a valued food item for the local aborigines for hundreds of years.
The nut has the potential, like the macadamia, to become a viable industry, provided it is accepted by the consumer and is marketed correctly. The tree is a fine specimen and may also be useful in the landscaping industry.
The Atherton Oak can be developed here in Australia and has the potential to become the second Australian indigenous plant (after the macadamia nut) to obtain widespread market acceptance.
Natural Distribution and Habit
The Atherton Oak is endemic to north-east Queensland and is confined to the rainforests of the Mount Spurgeon-Mount Lewis area, south west of Mossman, and Gadgarra-Boonjee area on the western side of Mount Bartle Frere.
It grows in well-developed upland and mountain rain forest on a variety of sites. Rainforest types are Complex Mesophyll Vine Forests Type 1b, Mesophyll Vine Forests Type 2a, Complex Notophyll Vine Forests Type 5a and Simple Notophyll Vine Forests Type 8.
The soils in these areas have developed from a range of parent materials such as basalts, granites, acid volcanics and schists (Irvine, 1985). Altitudes range from 500-1100 metres above sea level. Rainfall is mainly summer incidence with the highest falls occurring between December and April with a mean of 1600-3000 mm per annum with a drier period from September to October. There is the possibility of 1 - 8 frost days per year occurring in the cleared low-lying areas.
Propagation
The seeds of the Atherton Oak can be propagated either with the kernel attached or without, with either way can produce a 100% success rate (Costin, 1998). Taylor (1998) had lower success rates with seed propagation where the success rate was sometimes below 50%. Cuttings will give a success rate of around 50-80% (Costin, 1988). Seedling vigour is highest in seed grown plants.
The best times of the year to obtain the propagating material (i.e. cuttings) is in Spring or Autumn (Costin, 1998).
The use of fresh seed may be a factor in the level of success with germination rates as nuts that have been stored for a period of time have shown a lower level of germination. When propagating from seed it is important to protect the germinating nuts from predation by rats as a significant number can be destroyed (Taylor, 1998). The use of fungicides may stop fungal attack on the germinating nuts thereby reducing losses (Irvine, 1985).
Seeds sown at Atherton in an air-conditioned glasshouse started to germinate in 53 days (early December fruit) and 35 days (February fruit). Most of the seeds that will germinate will start to do so within 14 days of the first fruit germinating (Irvine, 1985).
A young plant propagated from a cutting is ready to be planted out into the field after approximately 12-18 months (Costin, 1998).
This is a general guide only as the plant needs to reach a minimum height of at least 40cm to survive in the field. Irvine (1985) reported that at Atherton, the seedlings were ready to be planted out within 10-12 months of sowing and were 40-90 cm in height.
The use of seed grown plants will give unpredictable results for they will not grow 'true to form'. A tree with superior qualities may be found but mostly the new plants show average qualities. This may be acceptable for the home garden but is inconsistent with the aims of a grower where proven performance is needed.
While a cutting grown tree will grow 'true to form' with the inherent genetic traits of the parent plant, the question needs to be "What are the traits of the parent plant". Have they been trialled and selected for the highest possible yields or disease resistance? Conversely, were the cuttings taken from a tree that was convenient at the time?
This especially important in such a new industry where there have been no variety trials to select superior plants.
Geographical Range
The Atherton Oak is best suited to areas that resemble its natural rainforest habitat such as the hilly coastal areas of Queensland and Northern and Central New South Wales. However, it is adaptable to planting in the open and in drier climates (Irvine, 1985). This contrasts with the advice of Sankowsky (1998) who has claimed that Atherton nut requires a continuously moist environment.
The tree is growing well at a number of sites in Sydney (Costin, 1998) and there are a few small plantings in the Illawarra region, south of Sydney. The limit of the tree's growing area may extend further south than this, though the cooler conditions may affect the commercial yield of the nuts or the incidence of pests and diseases. The tree also grows well around Coffs Harbout (Wrigley and Fagg, 1990) and a tree has been thriving in the grounds of Bellingen hospital for the past 50 years (Robinson, 1998).
The growth rate of the Atherton Oak is slow in the first one or two years, then growth rates of up to one metre per year can be expected (Costin, 1998; Sankowsky, 1998; Taylor, 1998).
The growth rate of Atherton nut can be compared with that of the macadamia tree, but some experts claim it should be 25-50% above that of the macadamia.
Growth rates of two trees planted at the CSIRO facility in Atherton was 0.5 metres per annum in an open environment and 0.75 metres per annum in a site that was initially open but then was shaded. Another tree growing in the State Forestry grounds at Atherton is showing similar behaviour.
XXXA plant grown from a cutting will tend to grow to a smaller height than a seed-grown plant; the former tree will be more bushy. Seed-grown trees have the potential to reach their full height and their growth is more upright, with branches appearing higher up the trunk of the tree.
As the height of the seed-grown tree is taller than that of the macadamia, it may need to be pruned in an orchard environment. The cutting-grown plant may not need pruning due to its more compact growth habit; this may depend on the individual variables of the orchards, such as planting densities.
Frosts
As frosts occur in the Atherton Oak's natural habitat, it does display a level of tolerance of frosts. Trees have been reported to survive frosts as low as -4 deg C (Costin, 1998). A frost such as this will burn the foliage but the tree will survive and produce new growth. The plant is more susceptible to frost damage when young.
Soils
The Atherton Oak has been reported to be a difficult tree to grow, with a tendency for the young plants to 'fall-over' (Robinson, 1998). This may be due, in part, to the wrong choice of soils. The preferred soil type is a salty soil (sodic, Costin, 1998) and this implies that they favour a higher pH (alkaline). The tree also favours a soil that is well-drained (Robinson, 1998) though it is not suitable for growing on sandy soils. The growth of the Atherton Oak may exhibit problems if planted in heavy clays though the liberal addition of organic matter to the soil may be of benefit (Costin, 1998). They also grow successfully on basalt (Irvine, 1995) and red (Kraznozem) soils.
Moisture Requirements
According to Irvine (1985) two trees have been growing in the grounds of the Atherton CSIRO for a number of years with little or no supplementary waterings, except at establishment. Rainfall in this area has a mean average of 1456mm per year with a definite dry period between September and October. Growth through the dry period without supplementary watering may indicate a level of drought tolerance.
The tree does prefer a moist soil in keeping with its rainforest origins. Under cultivation, a suitable watering regime would be similar to that currently used for the macadamia tree. Sankowsky (1998) recommends that as the tree needs a high moisture level, the soil should be continuously moist.
Wind and Light Sensitivity
In its natural habitat, the Atherton Oak spends most of its juvenile phase protected from the wind under a heavy rainforest canopy. The plant has an inherent sensitivity to wind and the juvenile foliage needs to be protected.
As the tree matures, it looses this sensitivity to wind damage. Windbreaks would therefore be necessary in the first couple of years of growth (Sankowsky, 1998; Costin, 1998). Sankowsky (1998) reports that if the juvenile foliage experiences dry westerly winds, the leaves blacken and drop-off.
The rainforest canopy also limits the amount of light that reaches the leaves of the juvenile plant and these have evolved to be highly sensitive to sunlight when young. This makes the juvenile leaves susceptible to scorching when planted in the field. Only plants grown from seed are susceptible, as the plants grown from cuttings already have mature leaves (Costin, XXX
Flowering and Pollination
While the flowers are self compatible, self pollination leads to low levels of successful fertilisation of the flowers' ovaries resulting in a small amount of fruit set. Successful fertilisation and high levels of fruit set requires that the flowers are cross pollinated. It is not known whether they can be artificially pollinated.
The pollen is presented for pollination in the following manner; the anthers dehisce before the flowers open and the stamens roll back with the petals on opening, leaving most of their pollen lodged on the stigma, which then acts as a pollen presenter (Irvine, 1985).
The main pollinators appear to be insects, but fruit bats may also play a role. Among the insects, Hymenoptera species, especially the syrphid flies, appear to be the most important (Irvine, 1985). According to Irvine (1985) two species of syrphid fly have been seen feeding directly on pollen on the stigmatic head. One of the species does this while hovering; the other, a Baccha sp. straddles the flower whilst feeding.
At Atherton in far North Queensland, the Atherton Oak flowers from February to early May with the fruit developing 8-12 months later, between December and February (Irvine, 1985). Around Mareeba, also in far North Queensland, the plant flowers from October to December (Sankowsky, 1988). At Chillingham in Northern NSW the tree flowers from late Winter to early Spring (Costin, 1998) and the fruits are ready to harvest approximately 12 months later.
The plant is opportunistic with respect to rainfall supply and may start to flower after heavy rains (Costin, 1998).
Genetic Improvement
Improvements to the Atherton Oak will undoubtedly be effected by breeders to improve its commercial potential, through selection from a larger nut size or higher yielding crops.
One of the major obstacles will be the time period required between subsequent breeding generations. The growth from seed to an assessable maturity would be approximately 8-10 years. If a new variety is found, this would need to be assessed for another 10 or more years, then grown in a number of different locations to ascertain how it reacts to different climatic conditions. This may take another ten years.
The genetic material, while mostly still intact, may be limited because of the restricted areas of natural stands. Also, according to Costin (1998), the white-tailed rat (Uromys caudimaculatus) is limiting the genetic diversity of the species in its natural habitat through increased levels of predation of the nuts.
Rootstock
While the use of different scion/rootstock combinations is common with macadamias and other plant families, there is no reason to use a different rootstock for the Atherton Oak. The use of cutting-grown material gives a level of dwarfing and the plant's vigour is reduced with different root stocks (Costin, 1998).
The Nut
The shell of the Atherton nut is easy to crack in a suitable device and the nut is easy to remove. There is little wastage, as the nut usually comes away cleanly and the two halves of the nut stay together. The nut itself has a tight coat surrounding it and this needs to be removed before XXX juicy (for a nut). While taste is a subjective issue, it has been described as tasting like a coconut (Costin, 1998) or similar to a macadamia but milder and with a sweeter taste (Sankowsky, 1998).
Storage life may be limited (Robinson, 1998; Costin, 1998; Sankowsky, 1998) probably due to the higher moisture content of the nut with a tendency to dry out relatively quickly. This would most likely be due to the highly permeable endocarp (shell) enclosing the nut which allows a high level of moisture transfer. The storage life may be able to be extended if the exocarp (outer fleshy layer) is allowed to dry on the nut, to form a leathery coating, thus decreasing the amount of moisture that could be lost. Refrigeration may also be another method of maintaining the freshness of the nut.
At present, the nuts are harvested by picking them off the ground by hand but would probably be suited to the same vacuum harvesting techniques used for the macadamia nut. For small growers, a contract nut harvester may be utilised if the farm is close to a macadamia growing area (as has occurred in the cashew industry on the Atherton Tablelands).
The shell could be returned to the grower and placed under the trees as mulch. This system is utilised in the sugar industry with mill mud and bagasse being returned to the farm to increase soil organic matter and soil nutrients.
Yields
The time at which the Atherton Oak will start to produce fruit depends on how it was propagated. For plants raised from seed it will take approximately 8-10 years to hear fruit but a few will start from as early as 5 years (Irvine,1985). For plants raised from cuttings this is reduced to 4-5 years with some plants producing fruit in just 3 years (Costin, 1998).
The Atherton Oak has been criticised for having light and variable yields, especially in its original stands. The reasons for this include predation by native and introduced rats (which prize the nuts); low levels of nutrients; and the need to be cross-pollinated and are only partially self-fertile (Costin, 1998). Many trees have been observed growing in isolation and because their need for cross pollination is not met, they consequently produce only light yields.
Planting two or more trees together will overcome this problem and should give heavier yields. Light yields may also be linked to the amount of nutrients that the tree is receiving. Irvine (1985) observed that a tree left standing in a cattle stockyard on an exposed ridge at Upper Barron (Atherton Tablelands) produced significantly heavier yields than had been previously seen in natural stands.
The trees will take many years before they are producing large volumes of fruit. As the markets need a regular supply of nuts, a co-operative of growers may need to supply the nuts, especially in the early stages of production.
Such an organisation would be of prime importance in a new industry and would also serve as a place of encouragement and information exchange to progress the industry.
Tree Spacing
A seed-grown tree has a larger, more spreading canopy than a cutting-grown plant where the cutting grown plant has a more columnar growth form. This would translate into the cutting grown plant requiring a smaller area in which to grow so such plants could be planted at closer densities (with narrower inter-row spacings) than the seed-grown plant. The columnar growth form may require less pruning also.
Processing
Robinson (1998) claims that the nut cannot be roasted due to its lower oil content, though this is disputed by Sankowsky (1998) who has successfully roasted the nuts on many occasions.
Specimen Tree
Feature plants are a common requirement in landscaping with the Atherton Oak having potential as a specimen tree due to its attractive foliage and form (Irvine, 1985; Wrigley and Fagg, 1990). The tree also has a beautiful scent when in flower, which is similar to the macadamia flower but is stronger and more spicy.
The Atherton Oak would be suitable for planting into parks, home gardens, as an indoor plant, and as a potted specimen as well as for tropical areas and under heavy shade (Wrigley and Fagg, 1990).
References
The author is grateful for the assistance rendered by members of the Atherton Nut Industry.
Cooper, W. and Cooper, W.T. (1994). Fruits of the Rainforest. A Guide to Fruits in Australian Tropical Rainforests, RD Press, Australia.
Fletcher, R. (1998). Personal Communication.
Goldberg, J. (1996). An Investigation into Seed Predation and Caching in a Tropical Rainforest Rodent, Uromys caudimaculatus, the White Tailed Rat. James Cook University Thesis.
Irvine, A.K. (1985) Commercial prospects for edible nuts of Athertonia diversifolia and Elaeocarpus bancroftii in The Food Potential of Seeds from Australian Native Plants.. (Jones, G.P. Ed.) Deakin University Press.
Kermond, P. (1998). Personal Communication.
Mason, R. (1998). Personal Communication.
O'Hare, P., Waite, G. and Mayers, P. (1996). Crop Protection. In The Macadamia, From Seed to the Supermarket, (Kermond, P. and Baumgard, B. Ed.).
Phelps, D.G. (1997). 'Feasibility of a Sustainable Bushfood Industry in Western Queensland'. Rural Ind. Development Corp. Sydney.
Robinson, B. (1998). Personal Communication.
Sankowsky, G. (1998). Personal Communication.
Taylor, R. (1998). Personal Communication.
Wriglye, J.W. and Fagg, M. (1990). Australian Native Plants. Propagation, Cultivation and Use in Landscaping. Angus and Robinson, Sydney.
DATE: February 1999
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