Changes

:Chromosome number: ''x''= 10, 11;''D. costatus'',''D. elongatus'',''D. kunstleri'',''D. obtusifolius'': 2''n''= 20,''D. baudii'',''D. cornutus'',''D. oblongifolius'': 2''n''= 22,''D. alatus'': 2''n''= 20, 22 == Trade groups ==

'''Trade groups''' Keruing: medium-weight to heavy hardwood, e.g. ''Dipterocarpus baudii'' Korth., ''D. cornutus'' Dyer, ''D. costulatus'' v. Slooten, ''D. crinitus'' Dyer, ''D. verrucosus'' Foxw. ex v. Slooten.

*Keruing: Indonesian gurjun (En). *Keruing, kruen (Fr)

Graveyard tests in Malaysia showed an average service-life of stakes (50 mm × 50 mm × 600 mm) in contact with the ground ranging from 0.8 years for ''D. kerrii'' to 4.1 years for ''D. verrucosus'' . Under temperate conditions, stakes may last 10-15 years. Most keruing wood is classified as moderately durable. The resistance to wood rotting fungi is quite variable, and to dry-wood termites usually poor, except wood of ''D. elongatus'' and ''D. lowii'' . In general, the sapwood is readily susceptible to fungal, borer and dry-wood termite attack and should be rejected. Keruing is fairly resistant to marine borers (mean service life of 6-7 years). Preservatives are absorbed very readily by most keruing species, with the exception of ''D. crinitus'' and ''D. lowii'' . An absorption of 100-130 kg/m³of an equal mixture of creosote and diesel fuel can be obtained when using the open tank method, and 300 kg/m³of copper-chromium-arsenic based preservatives, using the full-cell pressure treatment. Treated keruing can be very durable in exposed conditions, more than 20 years in the tropics.

The resin consists of sesquiterpenoids, and has fungicidal and termiticidal properties, as was demonstrated for ''D. kerrii'' .

*Medium-sized to large, resinous trees of up to 65 m tall; bole usually branchless for as much as 35 m, straight with little taper, with a diameter often exceeding 150 cm with a maximum of 260 cm and usually with small and concave or sometimes tall and straight stout buttresses; bark surface orange-brown bleached by the sun 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 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 in dormant stage, prominent and specifically diagnostic, not much broader than the twigs. *Leaves alternate, simple, leathery, rarely thin, 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; petiole geniculate at the joint with the lamina, stout or slender; stipules paired, large, hastate to lorate, obtuse, more or less succulent, caducous, characteristically carpeting the forest floor in the growing season. *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, or rarely all 5 short; petals large, oblong to narrowly oblong, strongly contorted, loosely cohering at base on falling, 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.

*Heartwood varying from greyish-brown, pink-brown to red-brown, sometimes with a purple tinge, darkening on exposure, sapwood pale with grey tinge, 50-75 mm wide, often but not always clearly demarcated from the heartwood, some species with characteristic white blotches. *Grain straight, interlocked grain rare, fissile. *Texture medium to coarse, even. Growth rings indistinct; vessels medium-sized to moderately large, mostly visible to the naked eye as individual pores, vessel lines long and conspicuous on longitudinal surfaces, varying amounts of tyloses visible; parenchyma absent or sparse; rays .*Rays of two sizes, fine and larger sized ones individually distinct to the naked eye; ripple marks absent. *Axial intercellular canals in short tangential arcs spanning several rays, empty or filled with chalky white or black resin often producing resinous exudation on end surfaces.

*Growth rings indistinct. *Vessels diffuse, 3-10/mm², predominantly solitary (over 95%), a few in pairs, uniformly distributed, tending to oblique arrangement, distinctly oval, average tangential diameter (120-)180-250(-280)μm; perforation plates simple, horizontal and rounded; intervessel pits sparse, loosely alternate, rounded, tending to be horizontally elongated, vestured, pit border diameter approximately 5-7μm; vessel-ray pits simple, rounded, with large apertures of c. 20μm; tyloses varying from sparse to abundant. *Vasicentric tracheids few to common. Fibres 1.7-2.0 mm long, non-septate, walls moderately thick to thick, pits small, distinctly bordered. *Parenchyma paratracheal, partially surrounding pores, to aliform with short wings, diffuse, surrounding axial intercellular canals, in 4-5-celled strands, free from extraneous materials. Rays 6-8/mm, uniseriate and multiseriate, the latter 3-6(-8) cells wide, up to 2.0 mm high, heterocellular with 1-3 rows of square to upright marginal cells (Kribs type heterogeneous III and II, occasionally I), uniseriate rays few, short; sheath cells present. *Silica bodies abundant in ray cells of all species; crystals absent; dark staining material usually abundant. *Horizontal intercellular canals absent; axial gum canals in short tangential series of 2-7 individual canals, (50-)80-120(-170)μm, smaller, as large as, or larger than the vessels, occasionally forming continuous tangential series in ''D. confertus'' and ''D. elongatus'' .

Species studied: ''D. acutangulus'' , ''D. borneensis'' , ''D. caudatus'' , ''D. caudiferus'' , ''D. confertus'', ''D. costatus'' , ''D. costulatus'', ''D. crinitus'', ''D. dyeri,'' , ''D. elongatus'', ''D. eurynchus'' , ''D. geniculatus'' , ''D. globosus'' , ''D. gracilis'', ''D. grandiflorus'', ''D. kunstleri'' , ''D. lowii'', ''D. oblongifolius'' , ''D. palembanicus,'' , ''D. rigidus'' , ''D. verrucosus'' .

The axial gum canals arranged in typically short tangential series of 2-7 canals distinguish ''Dipterocarpus'' from most other ''Dipterocarpaceae.'' . ''Anisoptera'' differs from ''Dipterocarpus'' by the wood lacking pink tints and by the lack of oblique arrangement of the vessels.

Keruing seedlings need shade for optimal growth. For ''D. oblongifolius'' maximum height increment after one year is obtained at about 30% of full daylight, but root weight (more important for transplanting) is maximum at about 60% of full daylight. Seedlings of ''D. hasseltii'' show optimal growth at 50% shading. The average annual height growth and annual diameter growth differ between species. In experiments in Java, ''D. retusus'' had an average height growth of 50 cm/year and an average diameter increment of 0.7 cm/year; for ''D. grandiflorus'' and ''D. tempehes'' the corresponding figures were 58 cm/year and 0.9 cm/year, and 83 cm/year and 0.9 cm/year, respectively. A comparatively large average annual height growth of 160 cm/year was reported for ''D. gracilis'' on Java. Several species may reach large bole diameters in a comparatively short time. The following bole diameters of 40-year-old planted trees have been reached or estimated in Malaysia: ''D. oblongifolius'' 79 cm, ''D. kerrii'' 74 cm, ''D. costulatus'' 73 cm, ''D. baudii'' 65 cm, ''D. cornutus'' 61 cm, ''D. grandiflorus'' 58 cm, ''D. hasseltii'' 52 cm, ''D. chartaceus'' 51 cm, and ''D. crinitus'' 48 cm. Other species appear to grow slowly, e.g. ''D. kunstleri'' and ''D. palembanicus'' , which reportedly reach maximum bole diameters after 40 years of only 24 cm and 20 cm, respectively, and ''D. caudiferus'' which needs over 150 years to reach a diameter of 75 cm (estimated in Sabah).

Some keruing species are reported to flower and fruit annually. Examination of flowering shoots of ''D. oblongifolius'' in Malaysia revealed alternating periods of flowering and vegetative growth; the tree investigated flowered and fruited annually in April - August and sometimes again in October - January. The apical reiteration of primary branches (i.e. starting new copies of its growth model) has been described for ''D. kunstleri'' .

Keruing trees probably need mycorrhizae for optimal growth, but data are lacking. Ectomycorrhizae have been recorded for ''D. cornutus'' and ''D. obtusifolius'' , but the identity of the fungal symbionts is unknown. Self-compatability has been demonstrated for ''D. oblongifolius'' in Malaysia.

The genus ''Dipterocarpus'' is characterized by its bark with warty lenticels, its generally amplexicaul stipule scars, its prominent resting 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'' . ''Dipterocarpus'' has been divided into 5 sections on the basis of characters of the fruit calyx tube, but these do not correlate with other characters and they vary within a species. Natural hybrids between species of the genus have been observed and are mentioned in the subsequent species treatments. The hybrids are generally found in small patches together with the parent trees. ''D. intricatus'' Dyer, ''D. tuberculatus'' Roxb., and ''D. turbinatus'' Gaertner f. supply much of the timber used in Indo-China and Thailand, but they do not occur in Malesia.

Most species grow scattered, but some, such as ''D. elongatus'', ''D. gracilis'' and ''D. obtusifolius'' , frequently occur gregariously. This may be due to their fire-resistance, their high germination rate or to peculiar chemical properties of the soil. Keruing species occur in evergreen forest, semi-evergreen forest or savanna woodland up to 1000(-1400) m altitude. In Thailand ''D. obtusifolius'' (and some other species) is frequently found in association with pines, forming the Pine-Dipterocarp association.

Viability of the seeds is short. In the nursery, seeds should be sown immediately (no later than 7 days after collecting the nuts), preferably under a cover of dry hay, and kept continuously wet. Seeds of ''D. humeratus'' can be successfully stored for up to 8 weeks at half of their initial moisture content and at 15C 15°C in sealed polyethylene bags filled with nitrogen gas. Seeds of ''D. oblongifolius'' survived at 4C 4°C for at least 2 months. The germination rate, however, is often low. Tests in the Philippines showed a germination rate for ''D. grandiflorus'' of 56% and a survival percentage of seedlings of 22%; the comparable figures for ''D. gracilis'' are 16% and 6%, and for ''D. hasseltii'' are 14% and 3%, respectively. Fruits of ''D. crinitus'' seem to be particularly prone to insect attack and viable seeds are difficult to obtain. The weight of a nut of ''D. crinitus'' is approximately 1.5 g, for ''D. gracilis'' about 3 g. Germinated seeds are often immediately put into plastic bags and kept under shade. After one year the seedlings have reached 50 cm in height on average, and can be planted out in the field. It has been recommended to plant ''Paraserianthes'' ''falcataria'' (L.) Nielsen as a source of mycorrhiza and as a shade tree, before transplanting the keruing seedlings.

'''Silviculture and management''' Keruing 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 have been well established (about 120 cm tall) the canopy can be opened up, to speed up growth. Many species regenerate well only in primary forest, and for these species enrichment planting after selective cutting is recommended. In plantations, weeding is necessary during the first 3 years. Thinnings should be carried out after 5, 10, 15 and 25 years. In the first 2-3 years, shade trees are used such as ''Acacia auriculiformis'' Cunn. ex Benth. and ''Paraserianthes falcataria'' .

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. In Peninsular Malaysia the fungus ''Cylindrocladium scoparium'' is pathogenic to seedlings of ''D. grandiflorus'' .

Insects may damage seeds, e.g. ''Alcidodes crassus'' (''(Coleoptera''),'' ''Alcidodes dipterocarpi'' , ''Nanophyes shoreae'' (''(Coleoptera)'' ) and ''Cydia pulverula'' (''(Lepidoptera).'').

''D. kerrii'' appears to be by far the most important species for tapping keruing oil in Malaysia. Other species tapped are ''D. chartaceus, D. cornutus'' and ''D. gracilis'' , and in Thailand also ''D. baudii'' and ''D. costatus'' . Usually the tap consists of an axe-cut hole in the stem, 90-120 cm from the base of the trunk, sloping down to the centre of the bole. The lower part of the notch is often hollowed out to catch the wood oil. The flow of wood oil is stimulated by firing which is spasmodic, depending on the flow of the oil. There have been no studies to test whether tapping does or does not affect timber production, but in Thailand tapping is usually done within 18 months before felling of the tree. It is reported that the maximum quantity of wood oil can be obtained when the bole is tapped on the side which bears the largest branch.

Although keruing is common over large areas, and is often outnumbered only by meranti ( ''Shorea'' sp.), the trees usually occur scattered (e.g. in Thailand with an approximate density of 8 trees/ha). Indiscriminate logging of trees belonging to a genus with so many species may endanger the less common ones. The establishment of reserves of sufficient extent, located in areas with optimal species richness, seems to be the best way to protect genetic diversity.

* Quiniones, S.S., 1980. Notes on the diseases of forest trees in the Philippines. Sylvatrop 5(4): 263-271. | '''10''' | *Smitinand, T., Santisuk, T. & Phengklai, C., 1980. The manual of Dipterocarpaceae of mainland South-East Asia. Thai Forest Bulletin (Botany) 12: 1-110. == Selection of species ==