Araucaria A.L. Juss.
- Protologue: Gen. pl. 413 (1789).
- Family: Araucariaceae
- Chromosome number: x= 13; A. cunninghamiiand many other species: 2n= 26
Araucaria: lightweight softwood, Araucaria cunninghamii Aiton ex D. Don, A. hunsteinii K. Schumann.
- Papua New Guinea: araucaria
- Thailand: son-nam (Bangkok)
Origin and geographic distribution
Araucaria consists of 19 species and has a disjunct distribution composed of New Guinea (2 species), eastern Australia (2 species), Norfolk Island (1 species), New Caledonia (13 species), southern and central Chile and adjacent Argentina (1 species) and southern Brazil (1 species). The present disjunct distribution is thought to be related to the breaking up of Gondwanaland. In Jurassic times an important centre of diversity was situated in the India-Australia-Antarctic region, from which species spread to the Cape Province and South America. The oldest find of Araucaria fossils is from India and dates back to the Triassic (190 million years ago). The present occurrence is looked upon as the remnant of a once much wider distribution.
Plantations of Malesian Araucaria species have been established in Papua New Guinea, Irian Jaya, Australia and South Africa, and trial plots have been laid out in Malaysia, Thailand and the Philippines.
Araucaria yields an excellent timber which is used for all kinds of light construction and interior work including mouldings, linings, panelling, domestic flooring, shelves, cupboards, general joinery, furniture and cabinet work. Special applications are matches, match boxes, broom handles, battery separators, chopsticks, agricultural implements, aircraft frames, cask heads and laminated fixed-pitch propellers.
A high-quality plywood can be manufactured from Araucaria. Plantation material yields a premium grade pulp which is useful in mixtures with hardwood pulp. Within the Malesian area, several species are used as ornamentals and Christmas trees. The seeds of A. cunninghamii and several other species from outside Malesia are reported as edible.
Production and international trade
Araucaria timber is commercially important, although mainly locally. Araucaria plywood was a major export item from Papua New Guinea until 1980, but declining supplies of logs from the natural forests resulted in a decline in plywood production; the plywood is now mainly for the domestic market. In Papua New Guinea approximately 8000 ha of both A. cunninghamii and A. hunsteinii have been planted, the oldest plantations being established in 1949-1950. This is much less than the plantation area in Australia, which amounts to 44 500 ha (A. cunninghamii) with an annual timber production of 211 000 m3in 1988-1989 and 248 000 m3in 1989-1990. The export of Araucaria logs from Papua New Guinea has been banned to obtain added value from the processed product.
The wood is lightweight and soft. The heartwood is pale yellowish-brown, occasionally with a pinkish tinge and not sharply demarcated from the straw-coloured sapwood which may be up to 150 mm thick. The wood has a natural sheen and lustre. The density is 450-530(-570) kg/m3 at 12% moisture content. The grain is typically straight, texture outstandingly fine and even.
At 12% moisture content the modulus of rupture is 77-90 N/mm2, modulus of elasticity 11 900-13 000 N/mm2, compression parallel to grain 44-49 N/mm2, compression perpendicular to grain about 4.5 N/mm2, shear 9-9.5 N/mm2, cleavage 38-39 N/mm radial and 54-56 N/mm tangential, Janka side hardness 2380-3490 N and Janka end hardness 3940-5430 N. The rates of shrinkage are small to moderate, from green to 12% moisture content 2.2-2.5% radial and 3.8-4.0% tangential. The timber seasons satisfactorily with little or no degrade, although precautions must be taken to prevent blue stain. The recommended temperatures for kiln drying 25 mm thick boards from green to 15% moisture content are dry bulb 80-90°C and wet bulb 55-65°C.
Araucaria wood is easy to work with hand and machine tools, it finishes well and takes paint, stains, varnishes and lacquers uniformly without requiring the use of a filler. The attractive colour makes the wood particularly suitable for the application of clear finishes. The wood nails and glues well, and it is easy to peel, making excellent veneer and plywood. Compression wood is sometimes troublesome in A. cunninghamii grown in plantations.
The wood is considered to be non-durable in contact with the ground and is susceptible to termite, pinhole borer and marine borer attack. It is, however, resistant to Lyctus attack. A. hunsteinii is relatively easy to penetrate with preservatives but A. cunninghamii is reported to be variable in its resistance to impregnation; the heartwood is often moderately resistant to impregnation.
Although the basic density is slightly lower in A. hunsteinii, the wood of A. cunninghamii and A. hunsteinii is almost identical. However, A. hunsteinii wood can be differentiated by applying a few drops of concentrated hydrochloric acid which produces an intense green colour.
- Large or very large, monoecious or sometimes dioecious, evergreen trees up to 60(-90) m tall; bole straight, cylindrical, often branchless for a considerable height, up to 200 cm in diameter, with a cylindrical base; bark almost black, dark brown or reddish-brown, transversely wrinkled, fissured, ridged or plate-like, peeling either horizontally or in slabs; branches in whorls of 4 or 8, horizontally displayed with the apex turned upwards.
- Leaves simple, entire, spirally arranged, sessile and broadly attached, crowded, broad and flattened to needle-shaped, many-veined, heteromorphic, changing in form with the age of the tree, tips often pungent.
- Pollen cones solitary, terminal or lateral, on branches separate from the seed cones, subtended by a cluster of reduced sterile bracts.
- Seed cones large, disintegrating when mature, terminal on a shoot with modified leaves; fertile bracts closely packed, broad and often extended laterally into membranous wings, the apex with a prominent spur; seed-bearing scale 1-ovuled, partly fused with the associated bract, the apex free and acute. Seed-coat fused with its scale.
- Seedlings with hypogeal (section Araucaria : A. hunsteinii) or epigeal (section Eutacta Endl.: A. cunninghamii) germination.
A. cunninghamii :
- Sapwood straw-coloured or pale yellow-brown, heartwood a little darker with a slight pinkish tinge.
- Grain straight.
- Texture fine and uniform; persistent leaf traces often produce a mottled or dimpled pattern on longitudinal faces; bands of compression wood often present, sometimes showing up as yellow or brown streaks on longitudinal faces.
- Growth rings often just visible, seldom distinct, earlywood forming most of the ring and transition to latewood very gradual.
- Rays barely visible to the naked eye, usually pale and not very prominent on the radial surface.
A. hunsteinii sometimes differs in having pale purplish streaks. Growth rings generally indistinct and figure not marked.
A. cunninghamii :
- Tracheids rounded to square, irregular in outline, 25-55μm in diameter, thicker walled in the latewood and poorly aligned in radial rows, 3.5-6 mm long, with little resin; intertracheid pits alternate in 1-2(-3) rows, mainly in radial walls, more frequent near tracheid ends, rounded in outline when solitary, tending to hexagonal when in groups, with rounded apertures; pits on tangential walls rare, small and solitary; crossfield pits 2-8 per cell, half-bordered, circular or slightly distorted when crowded, apertures lens-shaped.
- Rays 6-8/mm, almost exclusively uniseriate, sometimes biseriate, up to 20 cells high (up to 15 cells high in A. hunsteinii).
- Resin more frequently found in cells of A. hunsteinii.
Species studied: A. cunninghamii, A. hunsteinii.
Wood of Araucaria spp. and Agathis spp. can be distinguished from all other conifers by their characteristic alternate intertracheid pitting. Agathis wood never has the very small pin knots usually seen in Araucaria ; ray height in Araucaria is often greater than in Agathis, but anatomically it is very difficult to distinguish the two genera.
Growth and development
Trees usually start bearing cones at 15-25 years of age. Cones of A. cunninghamii and A. hunsteinii take 21-27 months to ripen after pollination. The mature cones fragment, and the seeds, having membraneous wings, are dispersed by wind. Seeds of A. hunsteinii are reported to be dispersed over 5 km from the mother tree, although this distance is questionable. During germination, the thick radicle penetrates the litter and soil, and the cotyledons gradually emerge from the seed-coat. The growth and development of seedlings depend on the amount of available sunlight and the density of the canopy.
Juvenile growth of A. cunninghamii is generally slow, but trees in Queensland reached a height of 33 m and an average diameter of 42 cm in 34 years and in Peninsular Malaysia the same height was reached after 30 years. Young trees of A. hunsteinii grow slower, but they outgrow those of A. cunninghamii when maturing, and their form is better.
Other botanical information
Together with the genus Agathis Salisb., Araucaria constitutes the family Araucariaceae. Araucaria is much more heteromorphic than Agathis and is often regarded as the more primitive genus. Araucaria is divided into two sections, section Araucaria (4 spp.) and section Eutacta Endl. (15 spp.), which differ in the pollen cones being lateral or terminal and the juvenile leaves being flattened or acicular, respectively. Several other sections have been proposed in the past but are now considered as synonyms of the two mentioned. The occurrence of glaucous forms within A. cunninghamii and A. hunsteinii deserves attention and needs further study. A. angustifolia (Bert.) O. Kuntze yields an important timber in South America, particularly Brazil, and the timber of A. bidwillii W.J. Hooker is used in Australia.
The Malesian species of Araucaria are tall emergent trees of lowland but more often submontane or montane rain forest. They are regarded as pioneer species, regeneration taking place in disturbed habitats. They are often dominant in the forests where they occur and are distributed from sea-level up to 2750(-4000) m altitude. In the areas they occur, the annual precipitation is 1000-4000 mm, and there may or may not be several dry months.
A. cunninghamii is more common above 1000 m altitude in areas with high rainfall and a temperature range of 9-26°C. It occurs on a variety of rain forest soils and may grow on very nutrient-poor, severely leached and podzolized soils with a pH of less than 5.0 and a thick layer of semi-decomposed litter, although it shows poor growth on such soils in plantations. In Papua New Guinea it is commonly associated with Castanopsis acuminatissima (Blume) A.DC., Cinnamomum sp., Podocarpus neriifolius D. Don, Prumnopitys amara (Blume) de Laubenf. and Schizomeria sp.
A. hunsteinii is mainly distributed between 700 m and 1000 m altitude in areas with high rainfall and where the temperature in the coldest month ranges between 10-28°C, the lower temperature occurring only a few times in a season. It is not resistant to frost and occurs especially on alluvial and volcanic, heavily textured, clayey or loamy soils with a pH of 5.5-6.5. It is commonly associated with Acmena acuminatissima (Blume) Merr. & Perry, Elmerillia tsiampacca (L.) Dandy, Ficus sp., Flindersia amboinensis Poir., F. pimenteliana F. v. Mueller, Pometia pinnata J.R. Forster & J.G. Forster and Xanthophyllum papuanum Whitm. & v.d. Meijden.
Propagation and planting
Araucaria can be propagated by seeds sown in beds of well-rotted sawdust or friable sandy loam, under 70-90% shade. Pre-germination and tubing as well as direct sowing may be feasible. Fresh seeds give up to 90% germination. Viability of seed of A. hunsteinii drops to zero after 4 months when stored at 25°C, but when stored in airtight containers at a constant temperature of 3.5°C, viability can be maintained for at least 6 months and sometimes up to 18 months. However, seeds of this species cannot be safely dried to below 30% moisture content without damage. Furthermore, viability of seed drops rapidly when removed from storage at 3.5°C. A cunninghamii seeds can be dried to 2% moisture content without damage, and can be kept at temperatures of -18°C or lower; seeds may be stored for 6 years. To obtain the seeds, cones are collected before they disintegrate on the trees. Cones that do not disintegrate within 10 days of harvesting are immature. Cone maturity can also be determined by sampling the length of the embryo, which should be 16 mm long for A. hunsteinii, and the endosperm, which should be well-developed and hard. Often, less than 1% of the seeds collected from a tree are viable. Filled and unfilled seeds may be separated by flotation, but the appropriate liquid mixture varies according to the clone.
Cuttings of 6-7 cm long (with a whorl of branches) taken from leaders of 3-year-old seedlings of A. hunsteinii show up to 90% rooting. Lateral shoots root well but remain plagiotropic. Rooted cuttings outgrow seedlings of the same age.
In vitro propagation can be practised successfully. Stem segments with 3-5 leaf axils, excised from the upper portion of the main stem of 2-year-old seedlings of A. cunninghamii, produce orthotropic buds from the concealed axillary meristems when cultured on a medium of half-strength Murashige and Skoog inorganic salts. This procedure is also successful with A. hunsteinii. Up to 80% rooting is obtained, and after 2 weeks the plantlets are transferred to a mixture of peat and perlite and maintained at a relative humidity of 90-95%. The young plants are subsequently transferred to normal greenhouse conditions and then to the field, with less than 5% mortality.
Mycorrhiza inoculation is necessary. Seedlings reach plantable size in 18-24 months. When planted into the field, spacing is usually 2.5(-3) m × 2.8(-3) m, but wider spacings of up to 7 m × 7 m have also been practised.
Silviculture and management
The main form of planting is in monoculture plantations. Underplanting in Pinus plantations has been tried with varying results in Papua New Guinea and Australia, but should be tested further. Enrichment planting has been tried on a large scale in Papua New Guinea, but was not considered economically viable because of management problems. However, the system should be tried again and adjusted on a pilot trial basis. For successful establishment in this situation, the objective is to release the striplines as soon as possible.
A. cunninghamii has shown good regeneration under the parent canopy and within gaps, and is regarded as a shade-tolerant species.
In plantations, weed control during juvenile stages is essential and the plants respond well to fertilizers. Pruning is usually first done when the trees are about 6 years old. In 35-year-old plantations, about 100 stems per ha are maintained.
Diseases and pests
Seeds of A. cunninghamii and A. hunsteinii imported from Papua New Guinea into Malaysia show poor germinative capacity and high seedling mortality, mainly as a result of transport difficulties. During storage, seeds are often infested by Penicillium fungi (in A. hunsteinii up to 75% of the seeds). Seedlings may be infested by Fusarium fungi. Treating seeds and seedlings with fungicides such as Demosan does reduce mortality somewhat. Seedlings are susceptible to damping-off and root rot.
The most significant disease of plantation-grown A. cunninghamii in Papua New Guinea and Australia is root and heart rot caused by Phellinus noxius . Seedlings of A. hunsteinii are very susceptible to bud dieback associated with Colletotrichum derridis. In Papua New Guinea the most serious pests of plantation-grown A. cunninghamii are the branchlet-mining Hylurdrectonus araucariae (Scolytidae, Coleoptera) and the weevil Vanapa oberthuri (Curculionidae, Coleoptera). Trees of 2.5-12 years old are most susceptible to Hylurdrectonus attack. Minor pests include the termite Coptotermes elisae and a caterpillar defoliator Millonia isodoxa. No serious pests of A. hunsteinii have been recorded and only Coptotermes elisae has been of any consequence.
The principal termite pests in Peninsular Malaysia in Araucaria plantations are subterranean species of the genus Coptotermes, particularly C. curvignathus. They can be controlled by chemical soil treatment with aldrin, dieldrin or heptachlor and by immediate removal of felled trees and stumps and they are one of the reasons why Araucaria has not been planted more extensively in Malaysia.
After fire, trees are much more susceptible to termite attack, and also to attack by ambrosia beetles (mainly Diapus pusillimus and Xyleborus perforans). Araucaria is intolerant to fire.
In Irian Jaya Araucaria trees are logged selectively with a diameter limit of 60 cm at breast height. Care must be taken to prevent damage to trees selected for retention during thinning operations, as removal of bark will result in rapid colonization by insects and decay fungi. The timber is prone to blue stain infection and should be treated with fungicides and removed rapidly from the logging areas.
Total production of 34-year-old plantations of A. cunninghamii in Queensland (Australia) was 977 m3/ha, i.e. 29 m3/ha annually. A stand in Papua New Guinea of 55 years old had produced 835 m3/ha, of which 707 m3 sawn timber logs. Generally, the average annual volume increment is 11-14 m3/ha, but in successful plantations 20-30(-35) m3/ha may be reached.
Genetic resources and breeding
Maiden stands of both species in New Guinea have been and are being exploited heavily for their high-quality timber (particularly for the plywood industry) and are endangered in parts of their natural range. Areas with once large stands, such as Bulolo (Papua New Guinea), are already exhausted. A large number of very small stands, on a wide range of ecological habitats, still exists in Papua New Guinea.
Extensive genetic improvement research is being conducted on A. cunninghamii in eastern Australia and a research programme on A. cunninghamii and A. hunsteinii has been established in Papua New Guinea. Brazil has established a similar research project on A. angustifolia. The research projects encompass provenance and progeny trials. Provenance hybrid trials and clonal seed orchards have been established in eastern Australia and Papua New Guinea. It appears that the better stem quality and overall growth of the southern provenances can be combined with the more rapid early growth of northern ones into superior hybrids.
By comparison with many other timber species, much is known about propagation and silviculture of Araucaria . Extensive plantations have already been established and they produce large amounts of timber, especially in Australia. In New Guinea natural stands are no longer being logged on a large scale, and the plantation area is still comparatively small. Protection of natural stands and extension of plantation establishment of this useful and comparatively fast-growing timber is desirable.
- Arentz, F., 1980. Some factors affecting the viability of Klinkii pine (Araucaria hunsteinii) in storage. Seed Science and Technology 8: 277-282.
- Burrows, G.E., Doley, D.D., Haines, R.J. & Nikles, D.G., 1988. In vitro propagation of Araucaria cunninghamii and other species of the Araucariaceae via axillary meristems. Australian Journal of Botany 36: 665-676.
- Darus, H.A., Ng, F.S.P. & Sabariah, A., 1982. Vegetative propagation of Araucaria hunsteinii by cutting. Malaysian Forester 45: 81-83.
- Godlee, J.L.R. & White, K.J., 1976. Enrichment planting with Araucaria hunsteinii K. Schum. Tropical Forestry Research Note, Papua New Guinea No SR. 33. 5 pp.
- Havel, J.J., 1971. The Araucaria forests of New Guinea and their regenerative capacity. Journal of Ecology 59: 203-214.
- Hong, L.T., 1974. Germination and seedling survival of Araucaria with Demosan (chloroneb: 1,4-dichloro-2,5-dimethoxy benzene) treatment. Malaysian Forester 37: 54-60.
- Howcroft, N.H.S., 1978. Exploration and provenance seed collections in Papua New Guinea 1976/77: Araucaria cunninghamii Lamb. and A. hunsteinii K. Schum. Forest Genetic Resources Information No 8. Forestry Occasional Paper 1978/2. FAO, Rome. pp. 5-11.
- Ntima, O.O., 1968. The Araucarias. Fast growing timber trees of the lowland tropics No 3. Commonwealth Forestry Institute, Department of Forestry, Oxford. pp. 1-14, 24-59.
- Tompsett, P.B., 1984. Desiccation studies in relation to the storage of Araucaria seed. Annals of Applied Biology 105: 581-586.
- Wylie, F.R., 1982. Insect problems of Araucaria plantations in Papua New Guinea and Australia. Australian Forestry 45: 125-131.
Selection of species
- F. Arentz (general part, selection of species),
- W.G. Keating (properties),
- J. Ilic (wood anatomy)