Dipterocarpus (PROSEA Exudates)
- Protologue: Fruct. 3: 50 (1805).
- Family: Dipterocarpaceae
- Chromosome number: x= 10, 11;D. alatus: 2n= 20, 22
Major species and synonyms
Dipterocarpus alatus Roxb. ex G.Don, Gen. Syst. 1: 813 (1831), synonym:
- D. philippinensis Foxw. (1911).
Dipterocarpus gracilis Blume, Bijdr. fl. Ned. Ind. 5: 224 (1825), synonyms:
- D. pilosus Roxb. (1832),
- D. marginatus Korth. (1841),
- D. vernicifluus (Blanco) Blanco (1845).
Dipterocarpus grandiflorus (Blanco) Blanco, Fl. Filip., ed. 2: 314 (1845), synonyms:
- D. griffithii Miq. (1864),
- D. pterygocalyx Scheff. (1870).
Dipterocarpus kerrii King, Journ. As. Soc. Beng. 62(2): 93 (1893), synonyms:
- D. obconicus Foxw. (1913),
- D. cuneatus Foxw. (1918),
- D. perturbinatus Foxw. (1918).
- Keruing (general timber trade group of Dipterocarpus ).
- Philippines: hairy-leaved apitong (general), apinau (Tagalog), ayamban (Iloko)
- Burma (Myanmar): kanyin-byu
- Cambodia: chhë: ti:ël bângku:ëy, chhë: ti:ël ba:y, chhë: ti:ël tük
- Laos: (maiz) nha:ng, nha:ng kha:w
- Thailand: yang-na
- Vietnam: dầu rái.
- Brunei: keruing kesat
- Indonesia: keruing keladan (general), wuluk bulan (Java), damar kacawai (southern Sumatra)
- Malaysia: keruing kesat (general), keruing kesugoi (Sabah)
- Philippines: panau (general), agan-an (Bikol), lalian (Tagalog)
- Burma (Myanmar): kanyin, kanyin-ni
- Thailand: yang-sian (general), yang-daeng (south-eastern), yung-hua-waen (peninsular).
- Indonesia: aput (South Kalimantan), tempudau tunden (East Kalimantan), lagan beras (Sumatra)
- Malaysia: keruing belimbing (Peninsular, Sabah), keruing pekat (Peninsular)
- Philippines: apitong (general), dauen (Ibanag), hapitong (Tagalog)
- Burma (Myanmar): kanyin-byan
- Thailand: yang-yung (general), yang-tang, yung-krabueang (peninsular)
- Vietnam: dầu dọt tím.
- Indonesia: lagan beras (northern Sumatra)
- Malaysia: keruing gondol (Peninsular, Sabah), keruing chair, damar minyak (Peninsular)
- Philippines: malapanau (general), panalsalan (Bikol)
- Burma (Myanmar): see-bin
- Thailand: yang-manmu, yang-man-khon, yang-wat (peninsular).
Origin and geographic distribution
Dipterocarpus consists of some 70 species and is distributed from Sri Lanka, India and Burma (Myanmar), through Indo-China, southern China and Thailand towards western Malesia. It does not cross the Wallace line (an important biogeographical barrier) between Borneo and Sulawesi, except between Bali and Sumbawa. The oldest fossil records are from the Miocene.
D. alatus occurs naturally in Burma (Myanmar), Thailand, Laos, Cambodia, Vietnam and the Philippines (Luzon) and D. gracilis in Bangladesh, Burma (Myanmar), Thailand, Peninsular Malaysia, Sumatra, West Java, Borneo and the Philippines. D. grandiflorus is found in the Andaman Islands, Burma (Myanmar), Thailand, Vietnam, Peninsular Malaysia, Sumatra, Borneo and the Philippines and D. kerrii in the Andaman Islands, peninsular Burma (Myanmar), peninsular Thailand, Peninsular Malaysia, northern Sumatra, Sabah and the Philippines.
The oleoresin ("wood-oil") obtained from the sapwood of Dipterocarpus is known as "minyak keruing", "damar minyak", "minyak lagan" or "balau". The essential oil obtained from the oleoresin is the well-known "gurjun balsam". This is not a balsam in the strict sense, as it does not contain any cinnamic or benzoic acid. It is used as a fixative in perfumery, particularly soap perfumes. It is a cheaper substitute for "patchouli oil" obtained from Pogostemon cablin (Blanco) Benth. The oleoresin is still traditionally used for illumination, to caulk boats, to make baskets watertight and to treat timber which is exposed to the weather. It is now used for interior varnishing, and in medicine as disinfectant, laxative, diuretic, mild stimulant, and in analgesic liniments.
Keruing timber from Dipterocarpus spp. is an important export commodity. It is a lightweight to heavy timber used for general, medium and heavy construction, especially railway sleepers. The timber of the major exudate-yielding species is usually too heavy and often too oily for first class sawmill and peeler logs.
In Thailand, D. alatus is planted as a roadside tree.
Production and international trade
D. gracilis and D. grandiflorus are the 2 principal sources of "balau" in the Philippines, but exact export figures are wanting. In the 1920s southern Vietnam produced about 1 000 t of oleoresin annually, all obtained from D. alatus. In Peninsular Malaysia the price for D. kerrii oleoresin rose significantly during the 1970s from M$7 to M$50 per 15 litre tin. The demand for and the value of Dipterocarpus oleoresins fluctuate with the availability and price of the preferred patchouli oil. In Samar, the Philippines, tappers sell 15 litre tins of balau at US$ 6, i.e. US$ 0.4/litre. In 1998, tappers in Laos earned US$ 0.28/litre D. alatus oleoresin whereas the export company sold the filtered oleoresin at US$ 1-1.40/litre. The price is probably lower than that of D. kerrii oil.
The oleoresin exuded by D. gracilis and D. grandiflorus is a white sticky fluid when fresh, darkening upon exposure. When freshly collected oleoresin from D. grandiflorus is distilled with water it yields 38-40% of a yellowish essential oil. Fresh exudate from D. gracilis contains 35% essential oil, 25% water and 40% solid residue. Direct distillation at 255°C of the oleoresin of D. alatus yields 70% reddish essential oil and 30% resin. Water distillation of the oleoresin of D. kerrii yields 80% essential oil with a pleasantly "balsamic" odour. The essential oils from Dipterocarpus are composed almost exclusively of sesquiterpene hydrocarbons. As such they resemble "copaiva balsam" from South American Copaifera spp. and have been known as "East Indian copaiva balsam" as well.
The essential oil from the oleoresin from D. kerrii harvested by the "bark chipping" method contains the following compounds: 79%α-gurjunene, 5.3% allo-aromadendrene, 1.1% β-caryophyllene, 0.8% β-gurjunene, 0.3% α-humulene and 3.7% other non-identified sesquiterpenes. The essential oil from traditionally harvested oleoresin contain 58%α-gurjunene and 4.1% allo-aromadendrene. The essential oil of D. grandiflorus is soluble in common solvents except ethanol. It has the following properties: specific gravity d30300.9228, refractive index n30D1.493, congealing point -3°C, acid value 0.8, saponification value 16.4, and iodine value 200. The oil contains 50-95% allo-aromadendrene, 3-20% α-gurjunene, 0-10% β-gurjunene, 0.34% β-elemene, trace-4% caryophyllene, trace-20% α-humulene, 0.14% copaene, 0.67% germacrene D and 0.43% γ-gurjunene. The oil from D. gracilis is composed of 75%β-caryophyllene and 25%α-humulene. The compoundsα-gurjunene, allo-aromadendrene, humulene and caryophyllene have termiticidal properties. D. kerrii oil also has fungicidal properties, but these have not been attributed to any particular compound.
The resinous fraction of the oleoresin contains 10-40% dipterocarpol, a triterpenoid. As a natural varnish it produces a brilliant, tough, and durable coating, but it is slow-drying and becomes brittle over time.
- Medium-sized to large, resinous trees up to 65 m tall and up to 180 cm in diameter, usually with small and concave or sometimes tall and straight, stout buttresses; bark surface orange-brown to greyish, usually scaly and warty-lenticelled, rarely fissured or scaly-fissured, outer bark dark rust-brown, inner bark pale yellow-brown to dark rust-brown, homogeneous; resin produced on freshly cut wood surfaces; crown usually relatively narrow, even or irregular (not cauliflower-shaped), dome-shaped, frequently rather flat, open, with a few large, strongly ascending, twisted branches; twigs variable in tomentum and appearance, with distinct, usually swollen and pale, amplexicaul stipule scars; buds prominent in dormant stage and specifically diagnostic, not much broader than the twigs.
- Leaves alternate, simple, leathery, rarely thin; stipules paired, large, hastate to lorate, obtuse, reasonably succulent, caducous, characteristically carpeting the forest floor in the growing season; petiole geniculate at the joint with the lamina, stout or slender; blade very variable in size and tomentum, pinnately veined, with a sinuate or straight margin, plicate in bud and corrugated on opening; secondary veins prominent beneath, straight, curved only near the margins.
- Inflorescence simple or branched, racemose, short, stout, zig-zag, few-flowered; bracts as the stipules but smaller, fugaceous.
- Flowers large, actinomorphic, bisexual, scented, nodding; calyx persistent, 5-merous, united round the ovary into a tube, but not fused to it, with valvate lobes, two of them long, oblong to spatulate, more or less distinctly 3-veined, and 3 short, (rarely, all 5 short); petals large, oblong to narrowly oblong, strongly contorted, loosely cohering at base after shedding, cream-white with a prominent pink, red or purple stripe down the centre; stamens 15-40, persistent at first in a ring round the ovary after the petals fall, filaments of variable length, broad, compressed, connate at base, tapering apically, connective prolonged into a short, sharp or blunt point or a long awn; ovary 3-celled with 2(-3) ovules in each locule, the base enclosed in the calyx tube, the apex ovoid to conical, shortly tomentose, stylopodium present, shortly tomentose, narrowed gradually into a filiform glabrous style, stigma small, simple.
- Fruit a nut, surrounded by the calyx, comparatively large; fruit calyx tube woody, becoming more or less distinctly constricted into a distal neck as the nut expands, smooth, pustulate, tubercled, ridged, winged or plicate, fruiting calyx lobes developed into 2 large wings and 3 ear-shaped lobes or rarely vestigial.
- Nut ovoid, with a woody pericarp, tomentose, with a short acute apical style remnant.
- Seedling with epigeal (cryptocotylar) germination; first two leaves opposite, subsequent leaves arranged spirally.
- Leaf bud lanceolate, yellow pubescent; stipules greyish-yellow pubescent; petiole 2.5-4.5 cm long: blade narrowly ovate to ovate to elliptical-oblong, 9-25 cm × 3.5-15 cm, base cuneate to rounded, apex acute or shortly indistinctly acuminate, secondary veins 11-18(-20) pairs, sparsely pubescent above, beneath densely persistently pubescent.
- Fruit calyx tube glabrous, subglobose, with 5 wings to 8 mm broad, 2 larger fruit calyx lobes up to 14 cm × 3 cm, 3 shorter ones up to 12 mm × 14 mm.
- Leaf bud narrowly conical, scabrid rufous tomentose; stipules narrowly lanceolate, outside persistently rufous tomentose; petiole 2-2.5 cm long; blade elliptical to ovate, 8-15 cm × 4-10 cm, base obtuse, apex shortly acuminate, with 12-20 pairs of secondary veins.
- Stamens about 30.
- Fruit calyx tube spherical, glabrous, smooth, 2 larger fruit calyx lobes up to 14 cm × 2.5 cm, 3 shorter ones up to 2 cm × 1 cm.
- Leaf bud ovoid, pale buff pubescent; stipules oblong-lanceolate, subacute, outside densely buff pubescent; petiole 3-9 cm long; blade ovate, 10-18 cm × 5-12 cm, base obtuse or subcordate, acumen up to 1 cm long, secondary veins 15-17 pairs, glabrous.
- Stamens 30.
- Fruit calyx tube ellipsoidal, glabrous, with 5 prominent wings continuous from base to apex, 2 larger fruit calyx lobes up to 22 cm × 3 cm, 3 shorter ones up to 2 cm × 1.5 cm.
- Leaf bud lanceolate-falcate, glabrous; stipules linear-lanceolate, subacute, inside silky tomentose; petiole 2-3 cm long; blade broadly elliptical, 8-13 cm × 3.3-7 cm, base cuneate, acumen up to 5 mm long, secondary veins (7-)9-11 pairs, ascending, glabrous.
- Stamens about 30.
- Fruit calyx tube globose to subturbinate, smooth, 2 larger fruit calyx lobes up to 14 cm × 3 cm, 3 shorter ones up to 1 cm × 1 cm.
Growth and development
In natural forest in Thailand D. alatus flowers early in December and fruits are mature in mid-February. Viable Dipterocarpus fruits start to germinate a few days to a few weeks after they have fallen on the ground. Twigs and petioles of seedlings are usually hairier than those of the mature trees, leaves are considerably larger, frequently more prominently acuminate and have proportionately shorter petioles. Dipterocarpus seedlings need shade for optimal growth. In experiments in Java, D. grandiflorus had an average annual increment of 58 cm in height and 0.9 cm in diameter. A comparatively large average height increment of 160 cm/year was reported for D. gracilis in Java. In a 40-year-old plantation maximum diameters of 74 cm for D. kerrii and 58 cm for D. grandiflorus have been observed. Dipterocarpus probably needs mycorrhizae for optimal growth. In experiments conducted in Thailand ectomycorrhizae have been observed in D. alatus seedlings. These seedlings developed best in association with Russula spp.
Other botanical information
Dipterocarpus is characterized by its bark with warty lenticels, its generally amplexicaul stipule scars, its prominent dormant buds, the leathery, plicate, corrugated leaves with swollen petioles at their base, and its type of venation. It belongs to the tribe Dipterocarpeae which is characterized by the fruit calyx lobes being valvate at the base, and a basic chromosome number of 11. Within the tribe Dipterocarpeae the genus is most closely related to Anisoptera Korth.
In 1993 it was discovered that D. alatus and D. philippinensis are conspecific. Another important species yielding gurjun balsam is D. tuberculatus Roxb. from Bangladesh, Burma (Myanmar), Indo-China and Thailand. Many other Dipterocarpus spp. are known to yield an oleoresin, but at present these are only exploited on a local scale.
D. alatus occurs gregariously along rivers in Indo-China and Thailand up to 500 m altitude. It is a rapid colonizer of alluvial soils where it is often found in relatively pure populations. In the Philippines it is rare, occurring in mixed dipterocarp forest in seasonal areas at low and medium altitudes. D. gracilis is widespread, often occurring gregariously in seasonal semi-evergreen or evergreen dipterocarp forest on red soils, becoming scattered, rare, and confined to fertile red soils in the humid zones, up to 800 m altitude. D. grandiflorus is common and sometimes semi-gregarious on clay-rich soils and grows in primary semi-evergreen or evergreen forest up to 600 m altitude. D. kerrii is locally common in semi-evergreen and evergreen lowland dipterocarp forest and occurs near the coast or less frequently inland on flat land or hills up to 400 m altitude.
Propagation and planting
Seeds of dipterocarps are generally collected from the ground because of the difficulty of climbing the tall trees and picking the fruits from the branches. Normally, a mature or fully developed fruit has dried greenish-yellow to brownish wings and the endosperm is full and firm. Viability of the seed is short and it is generally recommended to sow seeds within a week after collection. Seeds of D. grandiflorus can be stored at 8°C if treated with fungicides and maintain a germination rate of 28% or even 48% for some weeks; after 50 days of storage, however, viability is lost completely. Tests in the Philippines using fresh seed showed a germination rate for D. grandiflorus of 56%; the comparable figures for D. gracilis are 16% and 6%. In a test in South Kalimantan, however, D. grandiflorus had a germination rate of only 13%. Seeds are sown directly in polybags and put under shade. The apex of the dewinged fruits should point downward which facilitates the radicle to establish as soon as it emerges. For optimal development, seedlings raised in nurseries probably need to be infected with mycorrhizae, either in the nursery or in the field by the presence of mature trees. After one year the seedlings have reached 50 cm in height on average, and can be planted out in the field. Wildlings can also be used as planting stock. In the Philippines air layering of D. grandiflorus resulted in only 10% of the branches developing roots. Cuttings from 2-month old coppice did not develop any roots, even with different rooting hormone treatments.
Dipterocarpus seedlings and saplings can persist in the forest for years under heavy shade. In the first 2 years, major openings in the canopy are not tolerated, but after the seedlings are well established (about 120 cm tall) the canopy can be opened up, to speed up growth. Many species regenerate well only in primary forest. When Dipterocarpus seedlings are planted in open areas shade trees are used, such as Acacia auriculiformis Cunn. ex Benth. and Paraserianthes falcataria (L.) Nielsen.
Diseases and pests
Diseases reported for D. grandiflorus in the Philippines are "wildling blight" caused by Botryodiplodia theobromae and "apitong wilt" for which the most frequently associated organism is a Polyporus sp. A serious attack of bark beetles (Dryocoetiops laevis) killed many D. grandiflorus trees in central Luzon in 1993-1994. In Peninsular Malaysia the fungus Cylindrocladium scoparium is pathogenic to seedlings of D. grandiflorus. In the Philippines sooty mould caused by Asterinella dipterocarpi affects D. gracilis seedlings.
The technique for harvesting of the oleoresin from Dipterocarpus is similar throughout South-East Asia and has not evolved much in the last 100 years. Tapping involves cutting a hole in the stem, with its base sloping down towards the centre of the stem. This process is known as "boxing". Occasionally a scaffold is constructed to be able to reach above the buttresses of large trees. D. alatus trees are only tapped when their diameter is over 50 cm, as smaller trees are not sufficiently productive. The hole is usually triangular and may extend halfway through the stem. It is made on the side of the trunk where the canopy has the largest concentration of branches and leaves. Boxing is confined to the lower 2-3 m of the stem and a tree with a diameter of 75 cm usually has 2(-3) holes. Generally, the oleoresin starts to flow within an hour and collects inside the hole. It is removed once every 7-8 days. After collection, the remaining hardened coat of oleoresin is set on fire to prevent clogging and to stimulate further flow. The burning takes 20 seconds to 2 minutes, exceptionally up to 20 minutes. After the fire has been extinguished the burnt resin is scraped off the inner wall of the hole and the oleoresin is left to flow again. When a hole becomes unproductive it is abandoned. The use of ethrel instead of firing to stimulate oleoresin exudation has been investigated, but did not prove to be much more efficient or less damaging to the tree. Tapping is done throughout the year, and although the oleoresin flow is more abundant in the rainy season, the availability of labour then limits harvesting frequency. In Peninsular Malaysia, D. kerrii is not tapped in the months November-January due to abundant rain. When trees are carefully tapped, especially with regard to the burning of the holes, they may be tapped for 25 years. Laotian tappers claim that D. alatus trees are productive for 50-80 years. Tappers exert user rights over individual trees and these rights are inherited. Gregariously growing trees usually have a single owner. Once the tapping of a tree is abandoned, the tapper loses his rights over that tree.
In Peninsular Malaysia a refined technique has been developed which gives a somewhat better product with a higher essential oil content. The "bark chipping" method involves removing the outer bark, after which a strip of inner bark 2.5 cm wide is removed to expose the wood. This streak is about 1 m long and directed upward at an angle of 30°to the horizontal. An apron and gutter system is fixed just below the streak and a cup is installed at its bottom. Sulphuric acid is sprayed on the exposed wood; in 4 experimental trees a concentration of 10% proved best, giving a daily yield of 78-320 g. A polythene sheet is fixed to cover the apron and gutter system and prevent rain and dirt from contaminating the exuding oleoresin. Without the application of a stimulant, oleoresin production is negligible. It is doubtful whether this technique will replace the traditional tapping technique, as it involves much extra work for little extra gain.
The annual production of D. alatus trees in Laos is estimated at 22.5-31 l/tree. In Peninsular Malaysia, the weekly harvest of D. kerrii oleoresin is (10-)150-280(-800) ml/tree, which implies an annual harvest (9 months harvesting) of (0.4-)6-11(-31) l/tree.
Handling after harvest
In Peninsular Malaysia the harvested oleoresin of Dipterocarpus is filtered by means of gunny sacks and flour sacks, which are firmly fixed to wooden frames. The essential oil fraction drips through, while the more viscous fraction settles inside the sacks. During this process, some of the essential oil evaporates and probably not all essential oil is separated from the resinous fraction. Distillation with water gives a higher essential oil yield.
Genetic resources and breeding
Like other dipterocarp species D. kerrii in Peninsular Malaysia has fast dwindled due to logging. Several natural hybrids are known, like the one between D. gracilis and D. costatus Gaertn.f. (Thailand, Peninsular Malaysia) and between D. grandiflorus and D. baudii Korth. (Burma (Myanmar)). There are no germplasm collections or breeding programmes for Dipterocarpus exudates.
Although oleoresins from Dipterocarpus are undoubtedly of great economic importance, the prospects for commercial tapping of their exudates are not promising. At present there are only very few large and mature individuals that can be tapped because dipterocarp forest areas have been reduced in size tremendously. Only saplings and small individuals are now a common sight in most regenerating forest, especially in the Philippines. Scientific research on tapping techniques that could sustain supply of the oleoresin and prolong the life of tapped trees should be promoted.
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E.G. Aragones Jr and A.B. Ella