Prota 7(1): Timbers/Bois d’œuvre 1
Trans. Linn. Soc. London 26: 127 (1868).
2n = 72
Oxytenanthera macrothyrsus K.Schum. (1895), Oxytenanthera braunii Pilg. (1907), Oxytenanthera borzii Mattei (1909).
Savanna bamboo, Bindura bamboo, West African bamboo (En). Bambu africano (Po). Mwanzi (Sw).
Origin and geographic distribution
Oxytenanthera abyssinica is distributed throughout tropical Africa outside the humid forest zone, from Senegal east to Eritrea, and south to Angola, Mozambique and northern South Africa. It is often planted.
The stems are widely used for construction, fencing, furniture and fish-traps. They are also used for stakes, trellises, tool handles, household implements and arrow shafts. The use of dry stems as fuel is widespread and they are sometimes made into charcoal. The stems have some potential as raw material for paper making. Split stems are used for basketry. Sap from the plant is collected for wine making in Tanzania and Malawi, the fresh or dried leaves are used as fodder, and the seeds and young shoots as famine food. Oxytenanthera abyssinica is used in shelterbelts and windbreaks, and as a complementary crop in plantations of Cordia africana Lam., Eucalyptus microtheca F.Muell. and Khaya senegalensis A.Juss. in Sudan, for erosion control in land rehabilitation in Sudan and Tanzania, and as an ornamental plant.
The rhizome is used in the treatment of dysentery and the leaves are marketed for treating diabetes, colic and rheumatism. In Ethiopia the root is applied in the treatment of skin diseases on the head. In Senegal leaf decoctions are taken to treat polyuria, oedema and albuminuria.
Production and international trade
Only limited production information is available and most estimates of the amount of bamboo produced in Africa do not separate Oxytenanthera abyssinica from other species. Oxytenanthera abyssinica populations extend over 850,000 ha in western Ethiopia, over 44,000 ha in Tanzania, at least 10,000 ha in Malawi, and 20,000 ha in Senegal. Ethiopian Oxytenanthera abyssinica stands possibly constitute over half the total area under bamboo in Africa. These stands reportedly comprise approximately 5300 living stems (and 2700 dead stems) per ha. It has been calculated that the Ethiopian standing crop (dry weight above-ground for living stems) is 16.6 million t, and that there is potential for sustainably exploiting 5.5 million t annually. There is no export trade in Oxytenanthera abyssinica and it is used mostly near where it grows. In the past, however, there has been transportation of stems over long distances from southern Sudan to supply demand in Khartoum, and formal commercialization of harvests in Senegal. Price information for Oxytenanthera abyssinica materials, or products derived from them, is not available.
The air-dry density of the stem wall is 0.7–0.9 g/cm³. At 47% moisture content, the modulus of rupture is 82 N/mm², modulus of elasticity 14,600 N/mm², compression parallel to grain 49 N/mm² and shear (split stem) 11 N/mm². Dried stems and fences made from the stems are susceptible to termite and borer attacks.
The stem contains approximately: holocellulose 53–60%, pentosans 12–33%, lignin 15–27% and ash 1–4%. Solubilities are 6.5% in hot water, 2.7% in alcohol-benzene and 27.6% in 1% NaOH. Stem fibre cells of Oxytenanthera abyssinica have an average length of 2.0–2.8 mm, an average diameter of 12–17 μm, a lumen width of 3–5 μm and a cell wall thickness of 5 μm. In trials with different alkaline pulping methods, chlorine-free bleached pulps were obtained of 82% ISO brightness and suitable for writing and printing paper grades. The Oxytenanthera abyssinica pulps were similar to hardwood kraft pulp.
Leaves and twigs contain per 100 g dry material: crude protein 12.8–14.2 g, ether extract 2.8–3.0 g, crude fibre 28.0 g, N-free extract 36.4 –40.0 g, ash 14.6–18.6 g, P 0.11–0.13 g, K 0.60–0.66 g, Ca 0.25–0.40 g and Mg 0.32–0.35 g. Digestible protein and net energy levels are estimated, respectively, at 8.2 g and 3.7 MJ per kg dry matter. The fodder quality is low, due to low energy value and high silica content.
Clump-forming bamboo with a robust rhizome up to 10 cm in diameter; clump dense, typically consisting of 20–100 stems; stems (culms) erect, ascending or leaning outwards, 5–10(–15) m tall and 3–8(–10) cm in diameter, internodes 15–30(–40) cm long, the basal ones solid, the distal ones thick-walled, glabrous at maturity; young shoots grey-green, densely silky hairy. Leaves alternate, simple; sheath up to 15 cm long, with 2–5 mm long bristles at top; ligule short, c. 0.5 mm long; blade linear-lanceolate to oblong, 5–20(–26) cm × 1–5 cm, base tapering into a short false petiole, apex long-acuminate and pungent, somewhat glaucous, with numerous longitudinal veins. Inflorescence a dense star-shaped cluster 4–9 cm in diameter, with 10–20 spikelets. Spikelets sessile, narrowly lanceolate, 1.5–4.5 cm long, pungent, 1–4-flowered with upper floret bisexual and lower florets male or sterile; lower glume 5–8 mm long, upper glume 8–10 mm long, lemma narrowly lanceolate, the lowest 12–20 mm long, the uppermost about as long as spikelet, tapering into a rigid spine up to 7 mm long, palea narrowly lanceolate, somewhat shorter than lemma; floret with 6 stamens, filaments united into a tube, and a glabrous ovary extending into a hollow style terminating in 3 stigmas. Fruit a spindle-shaped caryopsis (grain) 10–15 mm long. Seedling with a short mesocotyl and a loose coleoptile, the first leaves without lamina; primary root a pale taproot bearing short lateral roots.
Other botanical information
The delimitation of Oxytenanthera is unclear. Sometimes it is considered to comprise a single species, but some authors include up to 15 species, most of them described from tropical Asia. It has also been stated that Oxytenanthera abyssinica together with another African bamboo, Oreobambos buchwaldii K.Schum., should be transferred to Dendrocalamus, a large Asian genus.
Growth and development
A single shoot, which may reach 1 m in height, is produced in the first year from a rhizome. From the third season onwards, several shoots are produced annually. Rhizomes penetrate 30 cm in 3 years. Stems reach 1.2 cm in diameter and 1.8–3.0 m in height within a few years of germination, reaching full height and diameter in 4–8 years. New stems break through the soil surface in the rainy season. Extension growth slows down after 3–4 weeks, and ceases after 2–4 months. Branches develop from the upper nodes from about the fifth week of active stem growth. Foliage is mostly shed in the late dry season. The stems mature in 3 years and may survive for 8 years, but they are over-mature and unsuitable for harvesting from 6 years of age onwards. Clump diameters range from 1 m to 8 m, and clumps may contain 20–100 (exceptionally up to 200) stems. New shoots appear at the peripheries of clumps. A clump longevity of 30 years has been estimated for Oxytenanthera abyssinica in Sudan, but is less when mass flowering occurs and rhizomes die with the stems. Mass flowering of Oxytenanthera abyssinica occurs every 7 years (Uganda), 14 years (Zambia) or 20–21 years (Malawi), while sporadic flowering has been widely and frequently noted. Both subsequent death of entire clumps (Chad, DR Congo) and regeneration of shoots from surviving rhizomes (Uganda) have been recorded. The fruit is dispersed as a larger propagule (25–30 mm × 3–4 mm) including several glumes; it is dislodged by animals and adheres to fur.
Oxytenanthera abyssinica is a lowland bamboo, occurring from sea-level up to 2000 m altitude, but mainly at 300–1500 m. It occurs in savanna woodland subject to a climate with an average annual rainfall of over 800 mm and 3–7 dry months (average rainfall less than 50 mm). It is absent from closed forest and extends little into semi-arid wooded grassland and thicket. Prevailing average annual temperatures are 20–27°C, with monthly average daily maxima of 30–36°C and daily minima of 7–17°C. Locally occasional frost may occur; if severe, this may scorch leaves.
Oxytenanthera abyssinica grows on soils from various types of parent rock, but over much of its distributional range parent rock belongs to the old crystalline basement complex. Soil fertility is not a major influence. Oxytenanthera abyssinica is associated with impoverished acrisols and ferralsols, moderately fertile luvisols, and younger relatively nutrient-rich cambisols and nitisols. The species is essentially absent from arenosols that have poor moisture retention and gleysols having poor drainage. Key site factors are good drainage combined with access to a reliable water supply. Characteristic habitats are areas along rivers and drainage lines, termite mounds and rocky slopes. Typical rocky slope microhabitats are well-illuminated gullies with deep soil accumulated between boulders. Saline conditions are unfavourable.
Propagation and planting
Oxytenanthera abyssinica is usually raised from seed. The weight of 1000 grains is 70–110 g. They remain viable for 6–18 months if stored at ambient temperatures under dry and pest-proof conditions. Storage for some months before use has been advised. Germination percentages vary from 30% to 80% and germination periods from 11 days in warm moist conditions to 4 months in cool dry conditions. Seeds are sown in nurseries when the mean daily temperature is 20°C or higher. The nursery period may last 8–24 months. Transfer to field sites is done in the early part of the rainy season, suitable plants having two shoots, the larger one at least 30 cm long.
Where flowering is infrequent, rhizome division is a realistic option for establishing new clumps and it is used traditionally to establish clumps in farmland. It has also been used by the forestry service in Uganda. Early in the rainy season, rhizome sections 12–30 cm long bearing healthy buds, or the lowest 45 cm of a stem, are excavated and transplanted without delay. Oxytenanthera abyssinica can also be propagated by stem cuttings.
Oxytenanthera abyssinica is rarely managed systematically, but weeding of newly established clumps, and removal of overhead shade, is recommended. Spacing of nursery raised seedlings has been 3.8 m × 3.8 m or 5 m × 5 m in experiments and in arboreta. In mixed plantations with hardwood trees the spacing is 6 m × 6 m. Clumps take up to 6 years (from rhizome offsets) or 8 years (from seedlings) to reach the stem harvesting stage. From the third year, thinning (50% of shoots from previous years) appeared justified in a planted stand in Kenya, because individual stems were smaller when stem numbers were high. Clumps for sap (‘wine’) production are typically established within areas cropped for maize, potatoes, pyrethrum or wheat. These clumps are thinned from the second year onwards to prevent stem congestion, while pruning branches to around 2 m favours access, and loosening peripheral soil promotes rhizome extension and unhindered shoot emergence.
A pure stand of Oxytenanthera abyssinica contains up to 750 clumps and 30,000 stems per ha.
Diseases and pests
Leaf rust caused by the fungus Kweilingia divina (synonym: Dasturella divina) has been recorded.
Harvesting of clumps starts when they contain 4-year-old stems; it continues at intervals of 1–3 years, with 4–6-year-old stems being cut. In a management system designed to improve the productivity of natural stands with well-established clumps, rotational harvesting is practised during the first 4 years. Each year shoots of all ages in one quadrant are cut; this treatment progresses round the clump year by year. Stems older than 6 years are used as fuel, those 4–6 years old as building material, and those 2–3 years old may have value for weaving. After the initial phase, 4-year-old stems can be harvested annually or, for stems that are 4 or more years old, at 2-year or 3-year intervals. Apart from culling dead or deformed stems, it is usual to leave unharvested stems which are 3 years old or younger, although clump congestion, or demand for supple material, may justify exploiting some of these.
To collect wine in Tanzania, the tips of young shoots are cut off, and the stem is bruised twice a day during a week. The exudate from the bruises is collected and left to ferment for 2 days. The resulting wine (‘ulanzi’) contains 5–5.5% alcohol.
Yield estimates for natural vegetation where Oxytenanthera abyssinica is abundant are 10–33 t dry stems per ha per year in Senegal. Experimental dry stem yields have been reported equivalent to 8–11 t per ha per year from DR Congo, and 14–28 t per ha per year from Kenya. After a clump has reached an age of 6 years such yields are sustainable under appropriate harvesting.
An equatorial disjunction and intervals east of Lake Chad and south of Ethiopia separate units of the range of Oxytenanthera abyssinica. There are contrasting reports of annual flowering cycles in some places and monocarpic clumps flowering at long intervals elsewhere, which could reflect genetic differences. This fact coupled with the fragmentation and wide range of the species, suggest that there is appreciable genetic variation, prompting suggestions of subspecific taxa. There are no indications that Oxytenanthera abyssinica is currently threatened, but declines in abundance have been reported, e.g. in Senegal and Uganda. Oxytenanthera abyssinica has been excluded, so far, from consideration by the FAO Panel of Experts on Forest Gene Resources although it is included in FAO’s REFORGEN information system, which signifies endangered status in Guinea. In response to over-exploitation, bamboo forest reserves have been gazetted in Uganda. The species has been grown in a number of arboreta, but not as an explicit conservation initiative.
For savanna regions in Africa Oxytenanthera abyssinica has major attractions as a natural product amenable to sustainable management. Straight, strong, light construction materials can be generated in as little as 3 years, and more items can be produced by splitting stems with simple household tools. Undemanding propagation options are available. Community bamboo stands established and harvested following protocols optimizing product quality and quantity can be combined with land rehabilitation. Nevertheless, despite wide rural significance, Oxytenanthera abyssinica remained neglected in the forestry and agricultural sectors until the International Network for Bamboo and Rattan (INBAR) recently included this species among 38 priority bamboos of economic importance. Through INBAR there have now been appraisals of bamboos in several African countries. Prospects for cross-border management collaboration have resulted. Certain key areas of study are relevant to continent-wide initiatives to secure and improve Africa’s savanna bamboo resource, increasing its rural significance and value. One is clarification of geographic variation in features of utility interest, particularly stem size at maturity, a second one flowering cycles and their interaction with clump survival, and a third is clarification of the conservation status. Fourthly, using knowledge of the distribution to decide which geographic areas should be represented, reciprocally planted, range-wide provenance trials monitoring growth and reproduction should be undertaken with the aim of identifying superior germplasm sources for various ecological conditions.
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Correct citation of this article:
Inada, T. & Hall, J.B., 2008. Oxytenanthera abyssinica (A.Rich.) Munro. In: Louppe, D., Oteng-Amoako, A.A. & Brink, M. (Editors). Prota 7(1): Timbers/Bois d’œuvre 1. [CD-Rom]. PROTA, Wageningen, Netherlands.
1, piece of stem; 2, flowering branchlets; 3, spikelet.
Redrawn and adapted by Achmad Satiri Nurhaman
dried flowering branch
huts made of Oxytenanthera abyssinica stems, Ethiopia