Isoberlinia doka (PROTA)
|Geographic coverage Africa|
|Geographic coverage World|
|Forage / feed|
Isoberlinia doka Craib & Stapf
- Protologue: Bull. Misc. Inform. Kew, Add. Ser. 9: 267 (1911).
- Family: Caesalpiniaceae (Leguminosae - Caesalpinioideae)
Doka (En). Doka, sau (Fr).
Origin and geographic distribution
Isoberlinia doka occurs in a wide, more or less continuous belt from Mali and Guinea eastward to northern DR Congo, Sudan and Uganda; its range does not extend south of the equator. Isoberlinia doka woodlands are estimated to cover close to 20 million ha in West Africa.
The wood of Isoberlinia doka, called ‘abogo’ or ‘sau’ in trade, is used for joinery, furniture and cabinet work. Traditionally, it is also used for posts, poles, handicrafts and agricultural implements. It is suitable for light construction, flooring, panelling, moulding, ship building, railway sleepers, boxes, crates, veneer and pulpwood. As there are no physical differences between the heartwood and the very wide sapwood, the latter can be used just like the heartwood after treatment with preservatives. The wood is widely used for fuel or made into charcoal.
Wood ash is used in soap making. The inside of the fruits is used to scour earthenware pots. Several parts of the tree have traditional medicinal uses. In Benin a decoction of young leafy shoots enters into a potion or bath against convulsions; gum from branches is used to treat abscesses and purulent infections. In Côte d’Ivoire the bark is used to treat fever including malaria, as well as body pain; in Ghana a bark decoction is used to clean skin wounds. The bark is also used as vermifuge. In Mali a leaf decoction is used as a wash by women against infertility. A preparation from the roots and leaves is used against jaundice.
Isoberlinia doka is a host of wild silk worms, especially of the butterflies Anaphe moloneyi and Gastroplakaeis rufescens, and its flowers are visited by honey bees. In northern Ghana the leaves are used as fixative when dyeing nails with henna.
Production and international trade
The wood of Isoberlinia doka is mainly used and traded locally. The silk of Anaphe moloneyi is of high quality and considerable quantities have been exported from Nigeria before 1940.
The heartwood is pinkish brown to reddish, mottled with irregular grey-purple veins; it is distinctly demarcated from the greyish to silvery or white sapwood, which is 3–7 cm wide and makes up about 40% of the bole volume. The grain is often distinctly interlocked and uneven, texture moderately coarse.
The wood is medium-weight to fairly heavy, with a density of 690–850 kg/m³ at 12% moisture content. Drying of the wood is difficult and should be done with great care. In southern Côte d’Ivoire, boards of 3.5 cm thick and with an initial moisture content of 71% took nearly 5 months to air dry under cover to stabilize at 16% moisture content. Drying defects include end splitting or longitudinal cracks over the total length of flat-sawn boards, as well as surface checking and case hardening. The shrinkage rates are moderate, from green to oven dry 3.5–4% radial and 7.5% tangential. Once dry, the wood is moderately stable in service.
At 12% moisture content, the modulus of rupture is 80–118 N/mm², modulus of elasticity 7060–9900 N/mm², compression parallel to grain 36–57 N/mm², shear 7.5 N/mm², cleavage 16–24 N/mm and Chalais-Meudon side hardness 3.8. The wood is brittle. It is fairly easy to work with hand or machine tools. In planing and turnery, some picking up is observed due to the interlocked grain, but the wood can get an attractive surface after sanding. It nails and screws well, but there is a tendency to split. It glues well.
The heartwood is moderately resistant to termites, pinhole borers and marine borers. The sapwood is easily attacked by fungi causing blue stain and by borers. The heartwood is resistant to impregnation with preservatives, the sapwood moderately resistant.
Young shoots and leaves of Isoberlinia doka constitute part of the food of antelopes, but are not palatable to cattle.
Adulterations and substitutes
The wood of Isoberlinia doka is similar in characteristics to the wood of ‘melegba’ (Berlinia confusa Hoyle) and ‘pocouli’ (Berlinia occidentalis Keay) and might be commercialized in mixed consignments with these two species.
Small to medium-sized tree up to 25 m tall; bole branchless for up to 12 m but more often only for 4–6 m, straight and cylindrical or twisted, up to 75 cm in diameter, sometimes more; bark surface smooth in young trees, later flaking off in large scales, inner bark red; crown fairly narrow and open; twigs grey-brown hairy, becoming glabrous. Leaves alternate, paripinnately compound with (2–)3(–4) pairs of leaflets; stipules c. 2.5 cm × 2 cm, more or less fused at base, usually caducous; petiole 6–12 cm long, rachis 10–25 cm long; petiolules c. 1 cm long; leaflets opposite, ovate-elliptical, slightly asymmetrical, 6–25 cm × 3–13 cm, base usually rounded, apex obtuse to short-acuminate, leathery, glabrous, pinnately veined with 6–17 pairs of lateral veins. Inflorescence a terminal or axillary panicle 10–18(–30) cm long, soon glabrous, many-flowered. Flowers bisexual, nearly regular, 5-merous, whitish; pedicel up to 2 mm long, with 2 thick bracteoles c. 1 cm long, finely hairy on both sides; sepals narrowly triangular, 6–7 mm long; petals nearly equal but one slightly broader, oblong, 7–13 mm long; stamens 10, free, c. 2 cm long; ovary superior, hairy, with stipe, 1-celled, style slender, longer than stamens. Fruit an oblong pod 15–30 cm × 5–8 cm, brown, with fine transverse streaks, initially short-hairy but becoming glabrous, dehiscent with 2 woody valves, c. 4-seeded. Seeds rounded, flat.
Other botanical information
Isoberlinia comprises 5 species and occurs in the Sudanian and Zambezian woodlands, but one species in rainforest in eastern Tanzania.
Isoberlinia tomentosa (Harms) Craib & Stapf (synonym: Isoberlinia dalzielii Craib & Stapf) is a small to medium-sized tree up to 18 m tall with bole up to 80 cm in diameter, occurring from Guinea and Mali eastward to Sudan in wooded savanna together with Isoberlinia doka, and southward to Tanzania, Malawi and Zambia in Brachystegia woodland. Its wood resembles that of Isoberlinia doka and used for similar purposes, e.g. for posts, planks, joinery and furniture. In Burkina Faso the leaves are eaten as vegetable and in various sauces, whereas the bark is used in the treatment of sores. The bark also enters into medicines against stomach problems and is used in Nigeria in the preparation of arrow poison.
Wood-anatomical description (IAWA hardwood codes):
Growth rings: 1: growth ring boundaries distinct. Vessels: 5: wood diffuse-porous; 13: simple perforation plates; 22: intervessel pits alternate; 23: shape of alternate pits polygonal; 25: intervessel pits small (4–7 μm); 29: vestured pits; 30: vessel-ray pits with distinct borders; similar to intervessel pits in size and shape throughout the ray cell; 42: mean tangential diameter of vessel lumina 100–200 μm; 46: ≤ 5 vessels per square millimetre; (47: 5–20 vessels per square millimetre). Tracheids and fibres: 61: fibres with simple to minutely bordered pits; 66: non-septate fibres present; 69: fibres thin- to thick-walled. Axial parenchyma: 79: axial parenchyma vasicentric; 80: axial parenchyma aliform; 81: axial parenchyma lozenge-aliform; 83: axial parenchyma confluent; 86: axial parenchyma in narrow bands or lines up to three cells wide; 89: axial parenchyma in marginal or in seemingly marginal bands; 92: four (3–4) cells per parenchyma strand. Rays: 96: rays exclusively uniseriate; 106: body ray cells procumbent with one row of upright and/or square marginal cells; 115: 4–12 rays per mm; 116: ≥ 12 rays per mm. Mineral inclusions: 136: prismatic crystals present; 142: prismatic crystals in chambered axial parenchyma cells.
(F.D. Kamala, P.E. Gasson & E.A. Wheeler)
Growth and development
Isoberlinia doka trees may first flower when they are 2–3 m tall. Flowering occurs in the dry season, in Côte d’Ivoire and Nigeria in January–February(–March), and the fruits dehisce around July. Seeds are dispersed by the explosive opening of the fruit and most of them germinate close to the mother tree. Germination starts quickly. A taproot of 25–30 cm quickly develops together with the sprouting of the very slow-growing plumule. After 6 months the stem is only about 5 cm long and has a single pair of leaves, and one year later it is 10–15 cm long. In case of fire at this juvenile stage, a new shoot immediately replaces the one that has been destroyed. When seedlings are 100–200 cm tall, they become resistant to the passage of light fires. Only about 1% of the seedlings reach this stage. Damaged stems do not fully recover and develop mouldy spots up to 2–3 m above the ground. The development of a bole takes several years. After disturbances, trees produce numerous suckers.
In plantations Isoberlinia doka also has slow initial growth. In Côte d’Ivoire 4.5-year-old plants were on average only 130 cm tall and elsewhere plantation trees reached a height of 2 m after 6 years. The first years after planting seem to be little more than an establishment phase, but later growth is faster and in mature populations the increment in bole diameter can reach up to 1 cm per year. In Nigeria it has been observed that, although the tree keeps its leaves during the dry season, the bole does not continue to grow in diameter and even that it may slightly shrink.
Isoberlinia doka grows in a zone receiving on average 900–1500 mm annual rainfall, at altitudes of 100–1200 m. It is a gregarious pioneer species that occurs in clumps or in large groups, in pure stands or mixed with other leguminous trees; it never occurs dispersed. Isoberlinia doka woodlands are the northern equivalent of the miombo woodlands of the Zambezian region in southern Africa. While Isoberlinia doka is the characteristic species of these formations, it is often associated with Uapaca togoensis Pax, Daniellia oliveri (Rolfe) Hutch. & Dalziel, Burkea africana Hook., Erythrophleum africanum (Welw. ex Benth.) Harms, Diospyros mespiliformis Hochst. ex A.DC., Monotes kerstingii Gilg and Prosopis africana (Guill. & Perr.) Taub. In this vegetation, the woody cover represents in general over 50% of the vegetation, and the herbaceous cover is dominated by tall, more or less shade-tolerant, perennial grasses, such as Andropogon tectorum Schumach. & Thonn. and Pennisetum unisetum (Nees) Benth. Intact woodlands of this type have unfortunately become increasingly rare as a result of clearing for agriculture.
Isoberlinia doka is a hardy, undemanding species colonizing all types of soil, except hard pans, crusted soils, rocky outcrops and areas subject to flooding. The roots have difficulty in penetrating hardened ferruginous horizons, which leads to superficial rooting, but the roots can penetrate compact gravelly horizons. Isoberlinia doka may grow in very poor sites and may survive fires, land clearing and erosion due to abundant suckering. In the Central African Republic it prefers well-drained, red or ochre, ferralitic soils, whereas it is replaced by Monotes kerstingii on rocky soils. In northern Côte d’Ivoire and Nigeria, it has been reported that seeds germinate readily in well-drained loamy soils, but not in shallow sandy soils on clay where Terminalia avicennioides Guill. & Perr. grows, which may explain the strict segregation of the two species. Isoberlinia doka is associated with several species of ectomycorrhizae, including Scleroderma spp.
Propagation and planting
The seeds of Isoberlinia doka, about 400 per kg, are recalcitrant; they germinate soon after dispersal or lose viability. In a test in Burkina Faso seeds lost 40% of their viability after 3 weeks, and they lost viability completely within 5 weeks of storage at ambient temperature of 30°C. In Togo regeneration of Isoberlinia doka and Isoberlinia tomentosa takes place through seedlings (32% of the observed cases), by coppice shoots (11%) or by suckers (57%). Most suckers are concentrated under the crown of the tree, but some may appear at more than 10 m distance. Suckering is the main mode of regeneration in cultivated areas, whereas seedlings are predominant in undisturbed forest.
In Nigeria it has been observed that bush fires early in the dry season strongly reduced the regeneration of Isoberlinia doka, whereas late fires led to rapid degeneration of the whole vegetation. However, deep ploughing after felling strongly increased regeneration, mainly by suckers. In Côte d’Ivoire, after protecting an Isoberlinia woodland (480 stems per ha with more than 7 cm diameter of which 141 Isoberlinia stems) for 3 years against fires, 105 Isoberlinia seedlings and 905 coppice shoots per ha were counted, including those on stumps with less than 1 cm diameter derived from seedlings or suckers damaged by previous fires. Three years after clear felling, 250 seedlings, 1590 coppice shoots and 570 suckers were counted per ha.
The growing of young plants in the nursery is a delicate process, because the roots have to be trimmed regularly. Transplanting is easy with a high rate of success, but the establishment period in the field is long, the young trees only measuring about 15 cm tall after 20 months.
The young trees are easily cut during weeding operations in the plantation. Isoberlinia doka is well adapted to coppicing.
Diseases and pests
The deformations caused by fires in young trees become apparent in adult trees as a wet rot of the heartwood, sometimes over a length of 2–3 m.
Boles of Isoberlinia doka studied in Côte d’Ivoire were fairly straight, without ridges or buttresses. They are in general without knots, but often have more or less pronounced flat spots and an excentric heart in the upper part of the bole. At felling, a blood-like liquid exudes from between the sapwood and the heartwood, which disappears during drying. The presence of bands of traumatic gum channels of variable width has often been noted.
In Benin a minimum bole diameter of 55 cm for felling Isoberlinia doka trees is recommended; this allows the recovery of 30% of the felled area in 15 years. Isoberlinia doka is the most abundant timber tree in northern Côte d’Ivoire. Forestry development plans recommend its harvesting with a cutting cycle of 80 years, whereas the minimum age for felling is estimated at 60 years with a minimum bole diameter of 40 cm.
In Bahr el Ghazal, South Sudan, 42 m³/ha of marketable wood (roundwood, poles, small sawn wood) was harvested by felling boles with a diameter above 30 cm in a dense dry Isoberlinia doka forest. In Benin mature Isoberlinia woodlands have a ground surface varying from 7.5 to 36.5 m²/ha depending on soil fertility. In Côte d’Ivoire on average 4.4 trees with a bole diameter of more than 40 cm have been counted per ha, representing for Isoberlinia alone a volume of 4.1 m³/ha of logs and 6.8 m³/ha of fuelwood and service wood. Wood volume tables in Côte d’Ivoire showed that a tree with a diameter at breast height of 40 cm and a total height of 17 m represents on average a wood volume of 1.4 m³ of which 0.6 m³ of log wood; a tree with a diameter of 50 cm and a height of 20 m has a wood volume of 2.6 m³ of which 0.9 m³ of log wood; a tree with a diameter of 70 cm and a height of 23 m represents a wood volume of 5.2 m³ of which 1.6 m³ of log wood.
An abandoned field in Nigeria completely protected from fire for 10 years led to trees 3–4.5 m tall; after subsequent use of bush fires in the early dry season for 10 years a dense stand of Isoberlinia doka developed, with trees 9–10.5 m tall and 13–25 cm in bole diameter, interspersed with some trees of Khaya senegalensis (Desr.) A.Juss. of comparable size. The harvestable volume of fuelwood was estimated at 60 m³ per ha or 3 m³ per ha per year.
The wood yield at sawing after removal of the bark is about 52% of the bole volume including the sapwood and 31% for the heartwood alone.
Handling after harvest
The main problem of felled trees is discoloration of the sapwood by blue stain, caused by fungi of the genus Lasiodiplodia. Black spots, caused by ambrosia beetles are also a common problem. To protect the logs against fungi and insects attacking the sapwood after felling, it is necessary to treat them with a preservative without delay, to avoid the removal of bark and to minimize the period between felling and sawing. It is recommended to treat sawn wood immediately with an fungicidal and insecticidal solution. Rapid and thorough drying will also help to reduce the deterioration caused by fungi.
Although Isoberlinia doka forests are increasingly cleared for agriculture, they remain common. Isoberlinia doka occurs, for example, in many sacred forests in northern Côte d’Ivoire, where it is one of the dominant species, if not the single dominant one. The abundant regeneration of the species ensures that the genetic diversity is not endangered.
To date, not a single study of the genetic diversity seems to have been done.
Well-managed Isoberlinia woodlands can have a bright economic future and may contribute to increased income for the local population. It is imperative to suppress bush fires in order to facilitate abundant regeneration by coppice shoots, suckers and seedlings, and to avoid that young plants are damaged by the fire and become unable to yield later high-quality timber due to bole damage and subsequent wet rot of the heartwood.
Research on the silviculture of natural stands and plantations is warranted because Isoberlinia doka is the most common timber species in its native range, representing considerable economic and ecological interests. It is equally important to know its genetic diversity and to undertake selection and breeding for rapid juvenile growth and for straight and long boles, in order to provide the local markets with timber. The pharmacology of the species would also deserve to be better documented.
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Correct citation of this article
Louppe, D., 2012. Isoberlinia doka Craib & Stapf. [Internet] Record from PROTA4U. Lemmens, R.H.M.J., Louppe, D. & Oteng-Amoako, A.A. (Editors). PROTA (Plant Resources of Tropical Africa / Ressources végétales de l’Afrique tropicale), Wageningen, Netherlands. Accessed 14 February 2019.
- See the Prota4U database.