Dyera (PROSEA Exudates)

Plant Resources of South-East Asia Introduction

List of species

Dyera Hook.f.

Protologue: Journ. Linn. Soc., Bot. 19: 293 (1882).

Family: Apocynaceae

Chromosome number: x= unknown; 2n= unknown

Major species and synonyms

Dyera costulata (Miq.) Hook.f. Journ. Linn. Soc., Bot. 19: 293 (1882), synonyms:

• Alstonia costulata Miq. (1861),
• Dyera laxiflora Hook.f. (1882).

Dyera polyphylla (Miq.) Steenis, Blumea 14: 316 (1966), synonyms:

• Alstonia polyphylla Miq. (1861),
• Dyera lowii Hook.f. (1882),
• D. borneensis Baill. (1898).

Vernacular names

General:

• jelutong (En)
• Indonesia: jelutung.

D. costulata :

• Hill jelutong (En)
• Indonesia: jelutung bukit (general), melabuai (Sumatra), pantung gunung (Kalimantan)
• Malaysia: jelutong bukit (general), jelutong pipit, jelutong daun lebar (Peninsular)
• Thailand: teen-pet daeng, ye-luu-tong, luu-tong (peninsular).

D. polyphylla :

• Swamp jelutong (En)
• Indonesia: jelutung paya (general), gapuk (Sumatra), pantung (Kalimantan)
• Malaysia: jelutong paya (Sabah, Sarawak).

Origin and geographic distribution

Dyera consists of only 2 species, namely, D. costulata which is found in peninsular Thailand, Peninsular Malaysia, Singapore, Sumatra and Borneo, and D. polyphylla which occurs in Sumatra and Borneo.

Uses

Early in the 20th Century jelutong (or "Pontianac" or "dead Borneo"), the coagulated latex of the inner bark of Dyera , was used for the manufacture of inferior rubber intended for uses where elasticity was not of prime importance. Up to the 1920s production declined due to the higher-yielding para rubber (Hevea brasiliensis (Willd. ex Juss.) Müll.Arg.). In 1922, however, demand from the United States sharply increased again for use in the manufacture of chewing gum because supply of the coagulated latex of Manilkara zapota (L.) P.Royen ("chicle") was dwindling and jelutong was found to be a suitable substitute due to its tastelessness and consistency. Today, the use of its latex in chewing gum is still the main application.

Dyera is more important as a timber tree.

Production and international trade

Export of jelutong from Indonesia averaged 3600 t annually over the period 1988-1993, but annual exports fluctuated widely, between 1200-6500 t. Kalimantan has always been the main area of supply. Around 1910 annual export from Indonesia was estimated to be 35 000 t; thereafter annual world production fell sharply, to 2700 t in 1922. When jelutong was found to be suitable in the manufacture of chewing gum, exports rose again. Imports by the United States averaged 7500 t annually between 1926-1930. The average annual export from 1973-1983 from Indonesia was 3550 t valued at US$ 3 million. The average free-on-board (FOB) export values for raw, pressed and refined Indonesian jelutong were down to US$ 720-750/t in 1993, from a high of US$ 980-1060/t in 1991. The processed Indonesian jelutong is exported "pressed", "refined" or "other" to Singapore from where it is re-exported, mainly to the United States.

Properties

Jelutong contains about 20% of thermoplastic polyisoprene and about 80% resin on a moisture-free basis. A very low concentration of soluble iron (1/20 000) in the latex causes the jelutong to oxidize completely in about 3 months, making it brittle, which is undesirable. Fresh Dyera latex has a specific gravity of 1.012-1.015 at 28°C, the pH is 7 and when left standing the pH falls to 5.5 after 24 hours and to 5.0 after 48 hours. D. costulata appears to produce a better quality latex than D. polyphylla. Latex traces are commonly present in the wood; they are lens-shaped in tangential surface and up to 1 cm high.

The compound dimethylmyoinositol isolated from the latex of D. costulata is reported to inhibit allergic passive cutaneous anaphylaxis reactions in guinea pigs.

Description

• Large to very large deciduous trees, up to 50(-65) m tall; bole straight, columnar, branchless for up to 30 m, up to 250 cm in diameter, without buttresses, sometimes with pneumatophores; bark surface smooth, with small squarish scales leaving dippled patches, inner bark mottled, pale brown to whitish, with copious latex; crown monopodial at first, with whorled branches; branchlets 5-8-angled.
• Leaves verticillate, (5-)7(-8) in a whorl, glabrous.
• Flowers in a slender axillary panicle, 5-merous, small, fragrant; calyx lobes rounded, margin frilled, with glands at the base inside; corolla with a short slightly angled tube, with a ring of hairs inside, white, fragrant, the lobes overlapping to the right; stamens inserted on the tube above the ring of hairs, the connective prolonged into a fleshy appendage; ovary semi-inferior, pubescent, style single, short.
• Fruit a pair of large woody spreading follicles, dehiscing along a dorsal suture.
• Seeds 12-24 in each follicle, flat, ellipsoidal, glabrous, surrounded by a membranous wing.
• Seedling with epigeal germination, cotyledons leafy, hypocotyl elongated; first few pairs of leaves opposite, later leaves whorled.

D. costulata:

• Tree up to 65 m tall, bole branchless for up to 30 m, up to 250 cm in diameter, bark blackish.
• Leaves elliptical to obovate or narrowly so, rounded to subcordate at base, short acuminate to rounded at apex, secondary veins well-spaced.

D. polyphylla:

• Tree up to 35 m tall, bole straight, columnar, up to 95 cm in diameter, bark whitish.
• Leaves spatulate-elliptical, cuneate at base and decurrent on the petiole, rounded to slightly emarginate at apex, secondary veins close-set.

Growth and development

Early growth of Dyera is rather slow, but after the establishment of a well developed root system growth becomes more vigorous. Annual diameter increment of D. costulata in plantations may be 1.5 cm, whereas that of trees in an unmanaged plantation is about 1 cm. The average diameter of planted D. polyphylla 17 years after planting is about 19 cm.

In Peninsular Malaysia D. costulata trees are usually deciduous once a year. They are leafless for a few days and all the trees in a certain area tend to change their leaves at the same time. Flowering occurs from July to December, whereas flowers start to develop simultaneously with the young leaves. They open during the night or early in the morning and the corollas are shed before 9 a.m. Fruits ripen in 8-9 months after anthesis. The flat winged seeds are distributed by wind.

Other botanical information

Dyera is closely related to Alstonia R.Br. ("pulai") and may be confused with it. Dyera can be recognized by its massive columnar bole, its massive spreading follicles containing seeds with a membranous wing all around, and the short style. Alstonia species have a fluted or buttressed bole, slender, drooping follicles with comose or ciliate seeds, and a longer slender style.

Ecology

Both Dyera species are scattered emergent trees of primary (often dipterocarp) evergreen rain forest, but favour different habitats. D. costulata occurs in primary lowland or hill forest in well-drained locations, up to 300 m altitude, whereas D. polyphylla is found in swamp forest, peat-swamp forest, and on podzols in kerangas, at low altitudes.

Propagation and planting

Dyera may be propagated by seed or by stumps made from 2-3 year-old wildlings. Seed weight varies greatly, with 7500-20 000 seeds of D. costulata per kg. Fruits should be collected from the tree when they are just beginning to split, as they do not drop until all seeds have been released. Because the trees are so tall, however, it is difficult to judge when the fruits are ready for collection, and the trees are hard to climb.

About 90% of the fresh seed of D. costulata germinates in 14-28 days, although a period of up to 4 months has also been reported. The viability of seed stored for 8 months at 22-24°C and a relative humidity of 60% (in an air-conditioned room) is still 70%. Storage temperatures below 10°C are detrimental. Seed of D. polyphylla germinates in 5-12 days.

Seeds are sown flat and should be pressed into the soil in nursery beds. To enhance germination, they should be soaked in water for about 2 hours. When the seed has germinated and the seedling has emerged, it should not be allowed to dry out and harden, because then the cotyledons and the plumule risk becoming trapped inside the seed-coat. Seedlings should be grown under shade, as full sunlight adversely affects their growth. Optimal development of seedlings was obtained under experimental conditions with about 33% relative light intensity. Seedlings of D. polyphylla are ready for planting in the field when they are 1 year old.

Management

Natural regeneration of Dyera is generally fairly abundant, but sometimes it is noticeably absent in secondary forest. Growth is vigorous when light is abundant. D. costulata demands plenty of light and once a young tree has established well in full light, it tends to spread its crown and develop into a pronounced "wolf tree". Rapid opening of the canopy encourages it to out-compete other tree species.

D. costulata coppices readily, is extremely resistant to girdling and tapping panels readily recover when the cambium has not been cut.

Diseases and pests

In Peninsular Malaysia, a large longhorn beetle (Batocera rufomaculata) is a secondary parasite of D. costulata. It is a wound parasite of the latex-tapping panels, but in old and weak trees infestation may extend over the entire stem. Eggs are laid on dead bark or where the bark has been completely removed; if they were to attack living bark, the larvae would be trapped by the copious stream of latex. Two small ambrosia beetles (Diapus pusillimus and D. quinquespinatus) are other wound parasites, often occurring in association with Batocera rufomaculata. They cause degrade of the timber by producing numerous "pinholes" and associated stain. Another ambrosia beetle (Platypus vethi) occurs frequently in fallen trees of D. costulata or in trees injured or weakened by unskilled tapping or by Batocera rufomaculata. In a survey of tapped D. costulata trees in Peninsular Malaysia, the following Coleoptera were found: Batocera rufomaculata in 86% of the trees, Platypus vethi in 44%, Schizotrachelus cameratus in 20% and Acicnemis vehemens in 15%.

Harvesting

D. costulata trees should have a diameter of at least 60-80 cm, whereas the somewhat smaller D. polyphylla should reach 50 cm diameter before tapping can start. Tapping of plantation-grown D. polyphylla may start 30-35 years after planting, when trees reach a diameter of about 35 cm. Generally, tapping of smaller trees is uneconomic. In Borneo, tapping of Dyera is traditionally done by making 4-6 vertical tapping panels of about 10 cm wide which are widened every 8 days by some 3 cm on either side until the panels touch each other. Horizontal tapping panels which are enlarged by cutting 3-5 cm of the bark on the upper side of the panel have also been used. The latex is collected on the same day by scraping it off with a wooden spatula. A more sophisticated way of tapping, the herring-bone method, is generally applied in Peninsular Malaysia. With this method a V shape is cut in the bark at 1.5 m height with its legs at an angle of about 45°with the vertical and covering about half of the circumference of the tree. From the base of the V cut a channel is made to a bamboo receptacle in which the latex is collected. The tapping panel is enlarged every 2-3 days by cutting a narrow strip of bark on both sides of the V. At first a turbid, watery fluid exudes, but soon turns into a chalky-white latex, gradually acquiring a fairly viscid consistency with a tendency to congeal in the channel. In all cases only the bark should be cut, with the cambium and the sapwood remaining intact to promote bark recovery and to prevent attack of wood-boring insects. Tapped panels may be retapped after a resting period of 2 years, as bark recovery is generally good. Many D. costulata trees in Peninsular Malaysia, however, have reportedly produced lumps and burs on the old tapping panels, which renders retapping impossible. To prevent the latex becoming contaminated with iron salts, rusty tapping knives, gouges or latex receptacles should never be used.

Tapping is restricted to several months per year, in the case of D. polyphylla this is because the swamp forest is inaccessible in certain seasons. In Sarawak in the 1950s, there were restrictions on the felling of D. costulata and D. polyphylla because of the value of the latex. Prolonged tapping of the latex invariably leads to the death of the trees, but careful tapping of D. polyphylla may continue for 12 years.

Yield

A single Dyera tree may yield up to 30(-50) l of latex per year, but high yields generally kill the trees rapidly. However, during the tapping season average monthly yield for large trees is 12 l of latex, which results in about 3.6 kg jelutong. The latex yield from D. costulata is higher than that of D. polyphylla .

Handling after harvest

The daily tapped latex of Dyera is processed on the day of collection, in the temporary settlement in the forest. The fresh latex is first strained through a fine-mesh sieve, which should not be made of copper or iron. Formerly all kinds of coagulants were used (kerosine, sago flour, sap of Ixonanthes icosandra Jack, methylated spirit, alum, creosote, sulphuric acid, urine), but today acetic acid and phosphoric acid are used for this purpose. Phosphoric acid is preferred, because any iron in the latex will precipitate as iron phosphate and very small quantities of iron make the jelutong brittle. With the "cold method" a 10% solution of phosphoric acid or acetic acid is added to the latex at 5 ml/l and the latex completely coagulates in 3 days. During this process it is important not to break the surface film, as anaerobic conditions improve the yield of the coagulum. The coagulum after cold coagulation still contains about 80% moisture, which is reduced to 35-45% by subsequent pressing and moulding. By the "hot method" acid is added at a rate of only 1 ml/l latex, the mixture is heated, stirred and after 2-3 minutes of boiling the latex coagulates. The hot method not only needs much less coagulant and gives a higher yield but the resulting coagulum is also less susceptible to drying out and is therefore preferred. The moisture content of the coagulum after hot coagulation is about 35%. The coagulum subsequently needs refinement, which is sometimes done in the forest but more generally in a factory. Refining the coagulum consists of repeated boiling in clean water to remove all soluble acids and sugars. If this process is not carefully performed the product is susceptible to oxidation, rendering the jelutong brittle and promoting development of brownish-black moulds. The product is then kneaded, pressed into blocks and stored in running water before shipment.

Genetic resources

Dyera occurs scattered and there is a risk of over-exploitation for timber and latex. However, it often regenerates readily in logged-over forest and grows fast, which may reduce this risk. Although the production of jelutong from Peninsular Malaysia fell to zero in the 1930s, possibly due to poor tapping techniques, trees have not been killed as the timber export from this area is still considerable.

Breeding

Judging from differences in growth rates it seems that genetic variation in Dyera is large. Breeding for higher latex yield, however, is not economically feasible.

Prospects

With the advent of synthetic products it is unlikely that the use of jelutong will increase. At present, Dyera is much more important for timber production.

Literature

• Browne, F.G. & Foenander, E.C., 1937. An entomological survey of tapped jelutong trees. Malayan Forester 9(4): 240-254.
• Burkill, I.H., 1966. A dictionary of the economic products of the Malay Peninsula. 2nd Edition. Vol. 1. Ministry of Agriculture and Co-operatives, Kuala Lumpur, Malaysia. pp. 889-897.
• Coppen, J.J.W., 1995. Gums, resins and latexes of plant origin. Non-wood forest products 6. Food and Agriculture Organization of the United Nations, Rome, Italy. pp. 118-121.
• Heyne, K., 1927. De nuttige planten van Nederlands-Indië [The useful plants of the Dutch East Indies]. 2nd Edition, 3 volumes. Departement van Landbouw, Nijverheid en Handel in Nederlandsch-Indië. pp. 1279-1283. (3rd Edition, 1950. W. van Hoeve, 's-Gravenhage, the Netherlands / Bandung, Indonesia. 1660 pp.).
• Kalima, T., Jafarsidik, Y. & Pratiwi, 1987. Jenis-jenis tumbuhan penghasil minyak astiri, getah dan resin [Plant species yielding essential oils, gutta and resin]. In: Soemarna, K. et al. (Editors): Prosiding diskusi pemanfaatan kayu kurang dikenal, 13-14 Januari 1987, Cisarua, Bogor. Badan Penelitian dan Pengembangan Kehutanan, Bogor, Indonesia. pp. 157-184.
• Meijer Drees, E., 1939. Herkomst, gebruik en bestemming der voornaamste boschbijprodukten van Nederlands-Indië [Origin, use and destination of the major non-timber forest products of the Dutch East Indies]. Tectona 32: 920-1017.
• Rudjiman, Martawidjaya, A. & Tonanon, N., 1995. Dyera Hook.f. In: Lemmens, R.H.M.J., Soerianegara, I. & Wong, W.C. (Editors): Plant resources of South-East Asia No 5(2). Timber trees: minor commercial timbers. Backhuys Publishers, Leiden, the Netherlands. pp. 225-230.
• van Wijk, C.L., 1950. Enkele aantekeningen over de verjonging van djelutung (Dyera lowii Hook.f.) [Some notes on the regeneration of jelutong (Dyera lowii Hook.f.)]. Tectona 40(2): 167-173.
• Walton, A.B., 1937. Jelutong tapping. Malayan Forester 6(1): 17-21.
• Williams, L., 1963. Laticiferous plants of economic importance IV: Jelutong (Dyera spp.). Economic Botany 17(2): 110-126.

Authors

E. Boer