Styrax (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Styrax L.

Protologue: Sp. pl.: 444 (1753); Gen pl., ed. 5: 203 (1754).

Family: Styracaceae

Chromosome number: x= 8

Styrax benzoin Dryand., Philos. Trans. 77(2): 308, t. 12 (1787), synonyms:

• Benzoin officinale Hayne (1841),
• Cyrta dealbata Miers (1851),
• Plagiospermum benzoin Pierre (1892).

Styrax paralleloneurum Perkins, Bot. Jahrb. 31: 484 (1902), synonym:

• S. sumatranus J.J.Sm. (1917).

Styrax tonkinensis (Pierre) Craib ex Hartwich, Apoth. Zeit. 28: 698 (1913), synonyms:

• Anthostyrax tonkinense Pierre (1892),
• Styrax macrothyrsus Perkins (1902),
• S. hypoglaucus Perkins (1902).

General:

• benzoin tree (En)
• Indonesia: haminjon (Batak, Sumatra), kemenyan (Java)
• Laos: nha:n.

S. benzoin :

• Sumatra benzoin tree, gum benjamin tree (En)
• Indonesia: kemenyan (general), haminjon durame, menyan (Java)
• Malaysia: kemenyan (Peninsular)
• Laos: kam nha:n (general)
• Thailand: kam yaan (peninsular)
• Vietnam: bồ đề nhự (northern), an tức, kơ ngan (southern).

S. paralleloneurum :

• Sumatra benzoin tree, gum benjamin tree (En)
• Indonesia: kemenyan (general), haminjon toba, kumayan putih (Batak, Sumatra).

S. tonkinensis :

• Siam benzoin tree, Lao benzoin tree (En)
• Laos: nha:n kh'an th'ung, nha:n ngwà, (kôk) ph'ung
• Vietnam: (cây) bồ đề, (cây) nhàn, mu khỏa đeng.

Styrax comprises some 120 species in the tropics, subtropics and temperate zones of Asia, Europe and America. In Malesia 8 species occur.

S. benzoin occurs naturally in India, Burma (Myanmar), Thailand, Cambodia, Laos, Vietnam, Peninsular Malaysia, Borneo, Sumatra and is rare in West Java; it has been cultivated in Sumatra since early the 19th Century, and is also cultivated in Java and West Kalimantan. S. paralleloneurum occurs naturally in Thailand, Sumatra and Peninsular Malaysia and has also been planted in Java. S. tonkinensis occurs naturally in southern China (Guangdong, Guangxi) and in the northern parts of Laos and Vietnam. Vietnam is the only country where it has been planted on a large scale, although not for benzoin but for pulp production; it has been planted experimentally in Java.

Benzoin is a balsam obtained by wounding the stem cambium of several Styrax species. It finds extensive use worldwide as incense and in the flavour, fragrance and pharmaceutical industries. In volume terms, Sumatra benzoin (the product of S. benzoin and S. paralleloneurum) is the most important type of benzoin and it is used for incense in e.g. the Middle East, North Africa, parts of Asia and the Indian sub-continent. Most commonly, small or crushed pieces of the raw benzoin in semi-processed block form are simply placed on an open fire, either in the house or in the place of worship. Sometimes it is mixed with other natural fragrance resins such as frankincense (Boswellia spp.), myrrh (Copaifera spp.) and storax (Liquidambar orientalis Mill.). Extracts of Sumatra benzoin are used to produce fragrances for joss sticks. In Java, benzoin is applied for ritual ceremonies related to death or spirits. Siam and Sumatra benzoin are both used for flavour and fragrance purposes but usually satisfy different parts of the markets. Siam benzoin has a rounder, more vanilla-like odour than Sumatra benzoin, which is harsher to the nose. The better grades of benzoin are extracted for the manufacture of fragrant products. These include personal health care products (e.g. toilet soaps, shampoos, body lotions, creams) and household and other products (e.g. liquid soaps, air fresheners, washing detergents). Although there is occasional overlap in end-use, the pleasant, rounder fragrance of the more expensive Siam benzoin is generally found in fine fragrances (perfumes and colognes) and the more expensive soaps. Although benzoin contributes its own fragrance to the final, formulated product, one of its important functions is to serve as a fixative for the other fragrance materials, increasing the tenacity and preventing loss of the middle and top notes of the more volatile components.

Benzoin's principal role in foods is as a flavouring agent. Sumatra benzoin is used particularly in the manufacture of chocolate flavours for chocolate bars, ice-cream, milk products, syrups and other products. Benzoin is popular in Scandinavia as a flavouring in baked goods containing vanilla or cassia, where it also serves to "fix" the other flavours and increase their spiciness. In Japan benzoin is applied as a chewing gum base. In Central Java (Indonesia) an important outlet for Sumatra benzoin is in flavouring tobacco by mixing it with tobacco when making cigarettes. However, it finds wider application in the production of "Manila" and other types of tobacco flavour. Benzoin is also employed by the tobacco industry in China.

Benzoin is well-known in both allopathic and traditional medicine. Several national pharmacopoeias specify either Siam or Sumatra types, while others include both. In the form of a tincture, benzoin is inhaled with steam for the relief of catarrh, laryngitis, bronchitis and upper respiratory tract disorders. It is also used for the prevention and treatment of cold sores, for the treatment of warts and to freshen and soothe dry skin and ameliorate skin allergies. Benzoin is employed similarly in the form of over-the-counter herbal medicines and in aromatherapy in western societies. Taken internally, benzoin acts as a carminative, expectorant and diuretic.

In Vietnam, S. tonkinensis is planted for pulp production. In the past, matches were made from the wood. In the highlands of Laos the wood is an appreciated source of building material because of its resistance to insects.

Sumatra benzoin is one of the oldest known export items from Indonesia and was traded as early as the 8th Century. Indonesia is the only producer of this type of benzoin, which dominates world trade. It is collected in the Tapanuli region of North Sumatra, mainly in the highlands to the west and south of Lake Toba. Some production is from wild trees but many families plant Styrax as a source of cash income. The large amounts of semi-processed block benzoin exported from Indonesia make it exceedingly difficult to quantify real production of benzoin, as it contains other resins as well. Production estimates vary from over 4000 t for each of the years 1990-1993 in northern Tapanuli, to about 470 t in 1986 of which 420 t was from Tapanuli. It seems probable that production is at least several thousand t per year.

In Palembang, South Sumatra, the benzoin plantations were replaced by para rubber (Hevea brasiliensis (Willd. ex Juss.) Müll.Arg.) in the 1920s. The Tapanuli area around lake Toba, North Sumatra, however, is too high for para rubber and continues to be important for benzoin cultivation and production.

In contrast, annual production of Siam benzoin, mostly in Laos, is around 50 t. Collection takes place in the mountainous northern provinces, where the trees are managed within the shifting cultivation cycle that is widely practised. Although production is relatively small, it provides a welcome source of cash income. Unlike Sumatra benzoin, for which there is a large domestic market (mainly Java), virtually all the benzoin produced in Laos is exported. Vietnam and China are the only other (minor) producers of Siam benzoin. Exports from Vietnam are small (probably around 12 t/year at most) and do not necessarily represent indigenous production - some benzoin enters Vietnam from Laos and is re-exported.

Exports of raw and processed benzoin from Indonesia averaged 1010 t annually in the period 1987-1995, valued at US$ 1-1.6 million. Most of this was shipped to Singapore, where much of the raw benzoin is processed into block form, and re-exported to the major markets in the Middle East, Africa, the Indian sub-continent and Asia. The main Asian market for benzoin is Malaysia. Most Siam benzoin is exported to Europe, principally France; recorded exports from Laos showed an upward trend from 27 t in 1990 to 51 t in 1995.

Recent prices in 1997 in Medan for best quality Sumatra benzoin "almonds" per kg and free-on-board (FOB) have ranged from US$ 8 for large pieces (grade 1) to US$ 2 for dust/small particles (grade 4). The superior sensory properties of Siam benzoin are reflected in the higher prices fetched in 1997 in Marseille by comparable grades of benzoin from Laos per kg and cost and freight: US$ 16 for the top grade to US$ 8-9 for dust/small particles. Prices for semi-processed block Sumatra benzoin in 1997 in Singapore varied per kg and FOB in the range US$ 0.80-4.00.

It is difficult to find reliable data on properties of benzoin. Samples may or may not be representative. For the two best balsam grades of S. benzoin ("red benzoin") and S. paralleloneurum ("white benzoin") the following data are an indication of their chemical content: insolubility in ethanol 1.2-2.8% and 1.3-3.7%, ash content 0.09-0.17% and 0.03-0.07%, cinnamic acid 0% and 24.5-30.6% and benzoic acid 26.2-27.2% and 11.5-12.9%. Sumatra benzoin is usually 75% soluble in ethanol, but when of very high quality it is 95% soluble. As Sumatra benzoin is sold in blocks its quality is variable, partly because it includes pieces and dust of "damar", the exudate from Dipterocarpaceae. The aromatic compounds of the different benzoin species (balsamic acids (i.e. benzoic acids and cinnamic acids), vanillin, cinnamic-, p-coumaryl- and coniferylalcohol) are probably products of an injury-induced change to the lignin metabolism. It is unknown whether sumaresinol acid occurs in the bark or wood of non-injured trees. Unlike many other balsams, benzoin produces negligible amounts of essential oil on distillation.

Paleness and purity (without extraneous matter i.e. high alcohol solubility) are important indicators of quality. A tentative FAO/WHO specification exists for "benzoin gum" as a food additive: for Sumatra benzoin and Siam benzoin the ethanol solubility should be respectively ≥ 75% and ≥ 90% and the acid-insoluble ash should be respectively ≤ 1% and ≤ 0.5%. Pharmaceutical uses of benzoin generally require compliance with national pharmacopoeia specifications and these vary according to the pharmacopoeia and the type of benzoin. Loss on drying should usually be ≤ 10% for both types of benzoin, but alcohol solubility is ≥ 70-80% for Sumatra benzoin and ≥ 90-98% for Siam benzoin. Balsamic acid content is important, and both types of benzoin are usually required to contain a minimum of 25% acids (calculated as cinnamic acid for Sumatra benzoin and benzoic acid for Siam benzoin). Total ash and acid-insoluble ash are also specified in some pharmacopoeias.

The wood is dull red to pale brown with irregular white flecks, grain very coarse, 470-710 kg/m³ at 15% moisture content, rather soft, moderately strong and non-durable to slightly durable.

• Evergreen shrubs or trees, bole usually with small buttresses, excreting a fragrant balsam on being bruised; bark surface smooth to vertically cracked or finely fissured, inner bark soft, brown to deep red, pink or purplish-red, sapwood white.
• Leaves simple, spirally arranged, without stipules; petiole grooved; blade ovate to oblong or lanceolate, margin entire or shallowly serrate-dentate, apex acuminate, secondary veins in 5-13 pairs, underside with white stellate hairs or scales.
• Inflorescence a terminal or axillary raceme or leafy panicle.
• Flowers regular, bisexual, 4-7-merous; calyx campanulate or cup-shaped, free or the base connate to the ovary, truncate or rarely 4-5-dentate, persistent in fruit; corolla connate at the base (1-2 mm) with annular staminal tube, deeply 4-7-lobed, subfleshy; stamens twice the number of petals, in one whorl, basally fused to each other and to the corolla tube, staminal tube up to 4 mm long, anthers splitting lengthwise; ovary superior, imperfectly 3-locular with 1 to few ovules per cell, densely hairy, style filiform, 3-angular, stigma capitate or indistinctly 3-lobed.
• Fruit a globose or depressed globose drupe, dehiscent or indehiscent, pericarp 3-5 mm thick.
• Seeds 1(-2), attached basally; testa with 2 layers, the outer layer thick and stony and the inner one membranous.
• Seedling with epigeal germination; cotyledons subfleshy; hypocotyl with purple flecks; first pair of leaves opposite, subsequent ones alternate to spiral.

S. benzoin.

• Tree, 8-34 m tall, trunk 10-100 cm in diameter, young twigs grey.
• Leaf blade 8-13 cm × 2-5 cm, undersurface with white woolly indumentum of stellate hairs, veins in 7-13 pairs.
• Inflorescence a panicle up to 20 cm long, but usually smaller than the leaves.
• Flowers fragrant, white; pedicel up to 4 mm long; corolla tube 1-2 mm long, lobes 9-12 mm × 2-3.5 mm.
• Fruit 2-3 cm × 2 cm, indehiscent.
• Seed subglobose, 1.5-2 cm in diameter, dull pale brown.

S. paralleloneurum.

• Tree, 5-35 m tall, trunk 23-60 cm in diameter.
• Leaf blade 6-16 cm × 2-7 cm, underside with white stellate hairs and golden-brown stellate scales, veins in 6-8 pairs with distinct transverse veins.
• Inflorescence a panicle, up to 11 cm long, with drooping, violet-scented flowers; pedicel 4-6 mm long; corolla tube 4 mm long, lobes 12 mm × 3 mm.
• Fruit globose, 2-3 cm in diameter with large cupular calyx, indehiscent.
• Seed shiny dark brown.

S. tonkinensis.

• Tree, up to 20 m tall, trunk up to 40 cm in diameter.
• Leaf blade 5-20 cm × 2-12 cm, underside with white stellate hairs, secondary veins in 7-9 pairs with distinct transverse tertiary ones.
• Inflorescence a panicle, up to 18 cm long, with white flowers up to 1.5 cm long; pedicel 3-5 mm long; corolla tube 2.5-3 mm long, lobes 6-8.5 mm × 2-3 mm.
• Fruit ovoid, 1 cm × 0.7 cm, dehiscent with 3 valves.
• Seed orange.

In Peninsular Malaysia S. benzoin flowers annually from November to May, in Sumatra throughout the year. In Indo-China it flowers from February to June and fruits from August to September. In western Malesia, S. paralleloneurum generally flowers from March to July and fruits from July to November. In Indo-China, flowering and fruiting of S. tonkinensis are from April to June and from July to October, respectively. Very peculiar bark galls are found in Styrax , caused by Astegopteryx ( Aphidae ). In S. benzoin the galls are comprised of tubes radiating from a central point. They are flat and only 4-5 cm long. In S. paralleloneurum the tubes, which also radiate from a central point are generally spirally contorted and 15-20 cm long. These tubes contain hundreds of lice in different developmental stages. Styrax fruits are only rarely dispersed by pigs and deer.

The two Malesian species S. benzoin and S. paralleloneurum can be distinguished by their microscopic stellate hairs on the underside of leaves. In the arms of the stellate hairs of the former species the hairs radiate in many planes while in the latter stellate hairs are flattened into scales and the arms radiate in one plane.

The following Styrax species have also occasionally been reported to produce benzoin; at present they are usually more important as ornamentals:

• S. benzoides Craib - tree, 10-15 m tall, occurring in Thailand, Laos and Vietnam; especially formerly an important source of Siam benzoin;
• S. crotonoides Clarke - tree, up to 30 m tall, occurring in Peninsular Malaysia and Vietnam;
• S. japonicum Siebold & Zucc. - shrub, 2-3 m tall, occurring in Japan, northern China, Taiwan and (rarely) in the Philippines;
• S. officinalis L. - shrub or very small tree, occurring in the Mediterranean;
• S. ridleyanum Perkins - tree, 30 m tall, occurring in Burma (Myanmar), Peninsular Malaysia and Sumatra;
• S. serrulatum Roxb. - tree, 6-12 m tall, occurring from India throughout continental South-East Asia to Taiwan.

Styrax prefers mixed primary forest with rich clayey soils. It is less common in dense secondary forest. S. benzoin is found at altitudes of 100-700(-1600) m, outside Malesia it is restricted to 200-500 m. S. paralleloneurum occurs at (575-)800-1700 m altitude. In Laos, S. tonkinensis occurs predominantly at (600-)800-1600 m elevation, while in Vietnam it occurs mostly below 1000 m. S. tonkinensis is a light-demanding species and in open habitats it often occurs in the upper storey. Seedlings cannot survive shade in dense forest. Benzoin trees need well-drained soils, as excessive water leads to dying back. In Styrax’s area of natural distribution the mean annual rainfall is usually 1500-2200 mm, with no distinct dry season (or only a few drier months). However, under cultivation it will thrive in areas with mean annual rainfall of 1300 mm and 3-6 dry months. Mean annual temperature in its natural range is 15-26°C but it can tolerate extremes of -4°C and +45°C for a short period. The success of S. tonkinensis owes much to human activities and to its pioneer characteristics: fire accelerates seed germination and many stands occupy sites previously used in shifting cultivation. Bamboo is one of the most common associates of S. tonkinensis and in natural regeneration in shifting cultivation systems Imperata cylindrica (L.) Raeusch. and Erianthus arundinaceus (Retz.) Jeswiet are common undergrowth.

In Sumatra plantations of benzoin trees are established and regenerated by planting wildlings collected from existing plantations, but direct sowing is also applied on a small scale. S. benzoin has 400-850 dry seeds/kg. The seed can be stored for up to 1 month without loss of viability; at storage from 2-8 months, germination percentage drops to 50-60%. Dry seeds of S. paralleloneurum (750-1150 per kg) can be stored up to 4 months and then have a germination rate of 35%. Vegetative propagation of S. benzoin using shoot cuttings treated with Rootone-F (20 g/l) proved successful in North Sumatra. Young seedlings need partial shade for satisfactory development. In North Sumatra planting or direct sowing is presently done at a spacing of 2 m × 3 m. A wider spacing is undesirable, as this allows too much light for weed development and individuals become too branchy.

In Vietnam over 50 000 ha of S. tonkinensis has been planted for pulp production. Collected seed must be stored properly to maintain viability. Premature germination can be prevented by storing at moisture levels17%. Germination is promoted by soaking in water; alternatively, the seed can be stored in moist sand. Depending on circumstances, seed may be sown directly, or nursery-raised stock may be planted. In the nursery, seeds are sown in well-drained germination beds kept moist. Germinated seeds with fully expanded cotyledons are transplanted into tubes containing forest topsoil. They are protected from full sunlight until the first two leaves appear and are ready for planting after 2 months, when about 15 cm tall. Alternatively, seedlings can be raised in nursery beds for 10-12 months and 1-1.5 m tall. After lifting, the stem is cut off 3-5 cm above the root collar and some lateral roots are trimmed to prepare stumps. Three density regimes are currently used in Vietnam: 1600-2000 stems/ha, when soils are fertile, well drained and not erosion-prone; 2000-2500 stems/ha, when soils are relatively fertile and well drained but erosion-prone; and 2500-3300 stems/ha, when soil fertility is low, drainage is poor or erosion is anticipated.

The forest in Tapanuli region, North Sumatra, consisting mainly of Merkus pine (Pinus merkusii Jungh. & de Vriese), has gradually been modified into a forest with a high density of benzoin trees represented by a wide range of sizes. At an elevation of 1300 m S. paralleloneurum is dominant and, at lower altitudes S. benzoin is prominent. The estimated density of benzoin trees is about 1375/ha of all sizes. Benzoin plantations have also been established by sowing before upland rice is sown. In the early stages benzoin trees need shading. Recently, there have been experiments with planting coffee under large benzoin trees while also maintaining a few benzoin seedlings and saplings.

In Laos, S. tonkinensis is managed with agroforestry techniques within a shifting cultivation system. After clearing regrowth of Styrax forest, upland rice is sown and natural regeneration of the Styrax is allowed to proceed freely. Seed germination is promoted by burning the fields before sowing rice. The trees are distributed irregularly and may be kept at a density of 500-600/ha. After harvesting the rice, the fields are left fallow until the Styrax trees are large enough for tapping. During this period terminal shoots are often cut, to stimulate diameter increment and benzoin production. The fallow period varies considerably but has been reduced in recent years as the pressure on land for rice cultivation has increased. Many stands are now clear-felled after 5-7 years, in which case they are tapped for the last 1-2 years only. Young trees are browsed by cattle, buffaloes and goats.

In Vietnam, nitrogen is given in 3 applications of 20 g per plant within one month of planting S. tonkinensis. Plantations should be kept weed-free in the first two years by regularly removing of ground cover and cultivating the soil in a 50-60 cm radius around each plant. In plantations for pulp production with a rotation of 10 years, two thinnings (at 2 years and 3 years old) are required to achieve a final density of 600-800 stems/ha. Under favourable conditions a mean height of 18-25 m and diameter at breast height of 20-24 cm may be achieved after 10 years.

In North Tapanuli fungal diseases have been recorded in benzoin trees but their importance is minor. An unidentified insect, locally known as "tapponok" often attacks young Styrax shoots.

A defoliator (Fentonia sp., Lepidoptera: Notodontidae) causes damage to thousands of hectares of S. tonkinensis plantations in Vietnam every year. The larval stage has four instars, with the third and fourth instars being most damaging, each larva consuming 6-7 g of leaves per day. Control measures involving chemical sprays have been recommended but Fentonia also has several natural predators, including two ant species (Oecophylla smaragdina and Cremastogaster sp.) and two bees (Anastatus spp.) which need consideration. In Laos young trees are attacked by fungi and various insects (crickets, termites, stemborers), which still need to be identified.

The balsam is only produced when the cambium is wounded, probably in newly formed cells at the end of rays in the xylem. Tapped trees generally exude throughout the year, except during periods of heavy rainfall. Tapping of Sumatra benzoin trees may start when 7 years old. After cleaning and smoothening the bark a piece of bark (2 cm wide and 2-4 cm long) is loosened from the wood with a tapping chisel and the bark is lightly beaten. The tapping wounds are made on two sides of the stem and from its base up to 3-5 m (reached by climbing the tree). Occasionally the balsam exudes so fast that it is necessary to use a container to collect the fluid. When harvesting S. paralleloneurum, the balsam under the loosened piece of bark is cut from the tree and graded into "large almonds" ("mata kasar", "mata besar") and "small almonds" (or "mata halus"). Then the wood of the tapping wounds is exposed, the bark of the borders of the wounds is cut and the balsam is scraped off after a few weeks ("jurus"). Three months later the rest of the balsam is collected ("tahir"). The second and third harvests yield a brownish sticky balsam, used to prepare the trade product. S. paralleloneurum in North Sumatra is tapped from June to September. Once or twice a year the trees are tapped again, making new wounds above the old ones where wood is exposed. Although callus formation is rare, the soft wood is rarely attacked by wood-rotting fungi or wood-boring insects. The balsam of S. benzoin does not harden but remains sticky. It oozes from the wound and forms long threads on the stem, resembling yellow rice straw (hence "haminjan durame"). At the first harvest the bark and sticky balsam are removed ("parung") and generally the threads formed on the stem are added to this grade. The second quality is "longkap" and the third one with many impurities is "jarir". Tapping of planted S. benzoin trees in Java has not been successful.

Traditionally, tapping of S. tonkinensis in Laos may start when trees are about 8 years old, allowing for 4 years or more of production until the fallow period of the shifting cultivation cycle ends and the trees are felled. Trees can be tapped for 6-7 years, then production declines and trees die when about 15 years, irrespective of whether they have been tapped or not. During the fallow period there are about 300 trees per ha, but only 50 are selected for tapping. Tapping entails making cuts into the stem wood and collecting the exuded balsam at a later date after it has dried. In Luang Prabang Province, tapping is carried out at the end of the rainy season, usually around September-October. The balsam remains on the tree during the dry season and is collected before the onset of the rains, usually about March. A series of staggered incisions is made into the stem, starting as near the base as is convenient and extending upwards over a height of 2 m or more. If the tree is tapped the following year, a further 2 m section is cut above the first, or tapping is continued to the first branches. The lower part of the cut bark is allowed to remain attached to the tree and this serves to trap the balsam when it flows from the wound. In this way the balsam is prevented from running down the face of the tree and accumulating dirt and other foreign matter. The hardened balsam forms flat pieces, characteristic of Siam benzoin ("almonds").

The annual balsam yield of a S. benzoin tree is estimated at 0.5-1.3 kg. Even higher yields are reported from Indonesia. During a good year a large tree may yield 0.6-1.9 kg of balsam in 3 months. In one year a vigorous S. paralleloneurum tree can yield up to 0.5 kg of first quality "kasar" benzoin and also 0.5 kg of second quality "barbar" benzoin. The average annual production of 10-year-old S. paralleloneurum trees, 14-24 cm in diameter is 0.3 kg/tree when they are tapped once in three months with 8 tapping positions. Horizontal tapping of 15-20-year old S. paralleloneurum trees with a panel of 4 cm wide and 3 cm high yielded an average of 15.6 g per tap and per panel, which is more than for vertical panels (11.9 g) and triangular panels (8.9 g). Sumatra benzoin yield from S. benzoin and S. paralleloneurum maximizes after about 3 years of tapping and remains at this level up to the age of 17-19 years, when the tree is exhausted and dies. Trees of 5, 7 and 9 years old when tapped for 3 months yielded 49 g, 61 g, and 79 g, respectively, but the difference was not statistically significant.

In Laos, the yield of a S. tonkinensis tree is 2-3 kg of balsam per harvest in regenerating forest and 0.8-1.5 kg in old secondary forest with very high tree-to-tree variation. The per hectare yield is 15-25 kg per year. Trees observed to be poor-yielding in the first year are not tapped in subsequent years. Trees with thick, rough, reddish bark are reputed to give higher yields than those with thin, grey bark but this may simply be a reflection of older, bigger trees yielding more than younger, smaller ones. Climatic factors, altitude and the height on the tree at which tapping is carried out affect yields. Intrinsic, genetic variation between different natural populations is also possible.

In Indonesia, more balsam appears to run down the tree, rather than being trapped between the cut bark and the stem, than is the case in Laos, and this results in a large number of different types and qualities of Sumatra benzoin. Darker, dirtier grades are produced, which do not have equivalents in Laos. After hand cleaning sorting gives the following types of balsam:

• "mata kasar" ("big eye"), first quality

• "mata halus" ("soft eye"), second quality, 1-2 cm, yellowish white

• "jurus/jarir", brown with yellowish white pieces, mixed with bark and other impurities

• "tahir", similar to "jurus" and usually mixed with it

• "barbar/laklak" which is the bark that has been removed from the other grades during cleaning

• "abu", ("dust"), produced from broken "almonds", "jurus" and "tahir".

"Abu" and "barbar" are usually mixed with "jurus" and "tahir" before sale. The best quality whole pieces ("almonds") are graded according to size: grade 1 for the larger pieces and grade 4 for dust/small particles.

In Laos, pieces of bark and other extraneous matter are removed from the benzoin soon after collection. Most is then sorted and graded according to size, using a sequence of sieves, resulting in four grades. Each pile of sieved benzoin is then further cleaned to remove pieces of bark which have escaped earlier cleaning. When an order is received, the cleaned, graded benzoin is re-packed in cotton-lined jute sacks, each sack being put in a plywood box and placed in a larger wooden crate for export.

In contrast to Siam benzoin from Laos, which is sold only in its whole, cleaned form, most Sumatra benzoin enters world trade in a processed form known as "block benzoin". Essentially, block benzoin consists of light-coloured pieces embedded in a much darker matrix. However, the light-coloured pieces of benzoin are present only in the higher grades; in the majority of cases they are pieces of "damar" (resin from Dipterocarpaceae). Damar is considerably cheaper than benzoin and readily available from Indonesia and elsewhere. It acts as a binder to make blocks of benzoin that are easier to transport and handle. Most benzoin intended for incense is traded in this form, and damar improves the burning quality as does the presence of powdered bark, although the scent of damar is inferior. The British Pharmacopoeia specification (which relates to Sumatra benzoin) requires damar to be absent and there is a test to check this. Preparation of block benzoin involves adding damar to low grade benzoin according to a well-tried formula, and cooking it briefly in hot water. The wet mixture is then transferred to shallow wooden boxes lined with cotton, and surplus water is squeezed out. The boxes are set aside to cool so that their content solidifies.

As only planted benzoin trees are tapped there seems to be no risk of genetic erosion. FAO has started a tree improvement programme for S. tonkinensis in Laos.

Currently no improved planting stock is used. A screening programme aiming at the identification of superior material in terms of balsam quality and yield from different wild provenances (e.g. "Toba styrax" from S. paralleloneurum ) could greatly enhance production. Two provenance trials of S. tonkinensis were planted in 1997 in Laos and these indicate clear provenance differences in survival and height growth. It is intended to assess balsam yield and quality when the trees are old enough to be tapped.

Demand for both Sumatra and Siam benzoin appears to be firm and is spread amongst the flavour, fragrance and pharmaceutical industries. Provided international prices do not decline markedly, and the resource base is secure, prospects for benzoin are likely to remain promising. Measures should be taken to ensure that the price paid to the collectors remains economically interesting. Otherwise, they may turn to more profitable activities to generate income.

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D.S.H. Hoesen