Faidherbia albida (PROTA)
|Geographic coverage Africa|
|Geographic coverage World|
|Cereal / pulse|
|Forage / feed|
Faidherbia albida (Delile) A.Chev.
- Protologue: Rev. Int. Bot. Appl. Agric. Trop. 14: 876 (1934).
- Family: Mimosaceae (Leguminosae - Mimosoideae)
- Chromosome number: 2n = 26
- Acacia albida Delile (1813).
- Apple-ring acacia, winter-thorn, white-thorn, ana-tree (En).
- Arbre blanc, cad, faidherbier (Fr).
- Espinheiro de Angola (Po).
- Mgunga, mkababu (Sw).
Origin and geographic distribution
The origin of Faidherbia albida is unclear. It has been postulated that it originated in the Sahara before desertification, but also that it was originally a riverine tree of eastern and southern Africa that was introduced through pastoralism and agriculture into western Africa, where it is only found on cultivated or previously cultivated land. It has long been preserved and protected on croplands by African farmers. However, this practice has become much less common in recent years. Faidherbia albida occurs all across the African continent, encircling the central African forest massif, from the Atlantic coast (Senegal, Gambia) to the Red Sea (Egypt, Sudan, Eritrea and Somalia) and from there to South Africa, Lesotho, Namibia and Angola. Its northern limit is not well defined because it occurs along watercourses and in areas where groundwater is present (e.g. in south-western Morocco, mountain massifs in the Sahara, and along the Nile in Egypt). Elsewhere, Faidherbia albida occurs in Yemen, Saudi Arabia, Israel, Jordan, Lebanon, Syria and Iran, and has been introduced into Ascension Island, the Cape Verde Islands, Cyprus, India, Pakistan and Peru.
Faidherbia albida is an ideal multipurpose agroforestry tree that is widely retained or planted in dry, densely populated areas of West and East Africa where fallow periods have become very short or have disappeared. Its ‘inverted phenology’ (leafless during the rainy season and in leaf during the dry season), and ability to fix nitrogen and draw water and nutrients from deep soil layers, has a beneficial effect on the microclimate, soil fertility and soil moisture for associated crops. It is therefore commonly intercropped with annual crops, especially pearl millet and groundnuts. Leaves and pods are an excellent fodder in the dry season. Branches are pruned more or less intensely by herdsmen for use as fodder. Pods are sometimes also used as fodder for domestic animals.
The wood is commonly used for handicraft and implements, and for the construction of houses, barns and grain stores. It is not long lasting and is sometimes soaked in water for several months to remove the sap and make it more resistant to insect attack. It is an excellent firewood and can be converted into high quality charcoal. The spiny branches are used for fencing fields.
Bark and roots, alone or mixed with other components, are common ingredients of traditional medicinal preparations for external or internal usage. These preparations are prescribed for respiratory infections, sterility, digestive problems, dysentery, backache, malaria, fever, heart and circulatory problems, dental infections and deafness. The bark is also used for making beehives, for stuffing saddles and in hut construction. Soap is made from the wood ash, which also has depilatory action. Pods can be used as fish bait. Seeds are eaten during famine but require long and elaborate preparation. Faidherbia albida has religious significance amongst some tribes, e.g. as a graveyard tree.
The nutritional value of leaves, flowers and pods is excellent and they constitute a fodder supplement rich in phosphorus, digestible proteins and carotene. The net energy value is 6–7 MJ/kg dry matter for leaves and pods with 12–15% of digestible proteins in leaves on a dry weight basis, and 6–11% in pods. The mineral content of the pods and leaves is satisfactory except for a deficiency of sodium and the trace elements copper and zinc. The pods also lack manganese. The bark is rich in tannins, ca. 28%, but pods contain only 5%. An oil can be extracted from the seeds, with a yield of 3–10%. Faidherbia albida extracts did not show antibiotic activity in pharmacological tests.
The wood is a medium-weight hardwood. At 12% moisture content, the density is 580–710 kg/m³, modulus of elasticity 8600–9400 N/mm², compression parallel to grain 41-54 N/mm², shear 6.4 N/mm², cleavage 16–21N/mm tangential and Janka side hardness 3500–5200 N. The rates of shrinkage from green to oven dry are 3.7–4.6% radial and 8.4–8.6% tangential, which can be rated as average. The wood glues well and has excellent nailing properties. It is possible to produce bleached chemical pulp from the wood for the paper industry, but the quality is poor and the yields low. The energy value of the wood is about 19,750 kJ/kg, which is considered excellent for use as firewood.
- Medium-sized to fairly large tree up to 20(–30) m tall, with bole up to 100(–150) cm in diameter; bark smooth when young but becoming fissured and flaky with age, brown to whitish-grey; branches with paired stipular, straight spines up to 3 cm long.
- Leaves alternate, bipinnately compound; petiole 0.5–3.5 cm long, eglandular; rachis 3-7.5 cm long, with 2–12 pairs of pinnae with a gland at the junction of each pinna pair; pinna rachis 2.5–5.5 cm long, with 6–23 pairs of leaflets; leaflets oblong, 2.5–12 mm × 0.7–5 mm, glabrous to pubescent.
- Inflorescence a dense axillary spike 3.5–16 cm long, with a peduncle 2–4 cm long.
- Flowers bisexual, 5-merous, successively white, cream and then yellow, sessile or with a pedicel up to 2 mm long; calyx up to 2 mm long; petals up to 3.5 mm long; stamens numerous (usually 40–50), 4–6 mm long, connate for about 1 mm at base; ovary superior, 1-celled, pubescent, style filiform.
- Fruit an indehiscent, falcate or coiled pod 6–25(–35) cm × 2–3.5(–6) cm, bright orange to reddish-brown, septate, 10–30-seeded.
- Seeds ellipsoid-lenticular, 9–11 mm × 6–8 mm, dark brown and shiny, with large central areole.
Other botanical information
Faidherbia albida is often included in the genus Acacia. It is distinct in having an eglandular petiole, basally connate filaments, eglandular anthers, and peculiar pods. The separation into the monotypic genus Faidherbia is also supported by its pollen structure and by its phenology: leafless in the wet season and leafy in the dry season. The existence of two forms (‘races’) of Faidherbia albida has been recorded for East Africa, differing mainly in the degree of pubescence. However, numerous intermediate forms can be found in several regions. Populations in Ethiopia show more similarity with those in West Africa than with those in nearby East Africa.
Wood-anatomical description (IAWA hardwood codes):
- Growth rings: 2: growth ring boundaries indistinct or absent.
- 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); 26: intervessel pits medium (7–10 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; (70: fibres very thick-walled).
- Axial parenchyma: 85: axial parenchyma bands more than three cells wide; 91: two cells per parenchyma strand; 92: four (3–4) cells per parenchyma strand. Rays: (96: rays exclusively uniseriate); (97: ray width 1–3 cells); 104: all ray cells procumbent; 116: ≥ 12 rays per mm.
- Storied structure: (118: all rays storied); 120: axial parenchyma and/or vessel elements storied; 121: fibres storied.
- Mineral inclusions: 136: prismatic crystals present; (141: prismatic crystals in non-chambered axial parenchyma cells); 142: prismatic crystals in chambered axial parenchyma cells.
Growth and development
The seedling first develops a taproot which can grow down very deeply until it reaches an adequate supply of water. Only then does the young stem start to grow. After 90 days, the taproot may attain a depth of 90 cm and the stem a height of 30 cm. Humid zone provenances develop more extensive lateral rooting near the soil surface, whereas trees in dry zones develop a more prominent taproot. In good conditions, annual growth in height of young trees may be 1–1.5 m. The width of growth rings varies from 1 mm to more than 20 mm.
The tree sheds its leaves at the beginning of the rainy season and comes into leaf again in the dry season. The physiology controlling this process is not yet understood. Flowering starts around the seventh year. The inflorescences appear about 2 months after the leaves. The fruits mature about 3 months after flowering. They are relished by livestock and game, including elephants, which may disperse the seeds. The seed coat is tough, waterproof and leathery, and maintains seed viability for many years. The total lifespan of the tree is generally 70–90 years.
Faidherbia albida forms root nodules and fixes nitrogen with slow-growing Bradyrhizobium spp. Nodulating bacteria and nodules have been found at great depth. Under experimental conditions root nodules have also been found with Rhizobium spp. Mineral nutrition is enhanced by symbiosis with endomycorrhizal fungi such as Glomus spp. and Gigaspora spp. Symbiotic mycelia have been found up to 30 m deep in the soil, enabling recycling of nutrients from such depths. A relationship between infection by root-knot nematodes, Bradyrhizobium and endomycorrhizal fungi resulting in stimulation of the formation of N-fixing nodules has been found, but this observation needs further investigation.
Faidherbia albida occurs in a wide range of habitats from deciduous forest (as in the Guinea zone), riparian forest, savanna woodland to sand dunes and depressions in the desert where its roots can reach ground water. It grows in a wide range of climatic conditions, but it needs a long and distinct dry season and access to permanent ground water. Under natural conditions, it is found particularly in association with water, e.g. along rivers and in gullies and ravines. Its prefers an annual rainfall of 500–800(––1000) mm, but in Mediterranean climates with winter rains 100–400 mm are sufficient. In more humid habitats it cannot compete with other vegetation. It occurs from sea level to 2000(–2500) m altitude. Faidherbia albida prefers deep, light sandy to moderately heavy soils, but also occurs on heavier soils, even clay soils. It tolerates waterlogging or flooding for several months, as occurs along the Nile and in rice fields in Senegal.
Propagation and planting
Under natural conditions, reproduction is by seed and root suckers. In some regions (e.g. western and southern Africa) propagation by seed is the rule, whereas in other regions (e.g. in the Middle East) suckers prevail. In Sudan, trees reproduce equally well by seed or suckers.
Seeds can best be collected from nearly ripe fruits while still on the tree, as the fruits are eaten by game and livestock almost as fast as they fall to the ground. Moreover, completely ripe seeds are often infested with insects such as Bruchid beetles. Fruits are mechanically hulled. Faidherbia albida has orthodox seeds. Green seeds do not store well and must be sown at once, but ripe seeds can be stored after drying and treatment against insects either at ambient temperature (for at least 3 years) or at 1–4°C (many years). Green seeds do not need treatment before sowing, but ripe or stored seeds should be treated with sulphuric acid, immersed in boiling water or scarified, after which germination rates of 75–100% after 30 days have been obtained. In the nursery, seeds are planted in polythene bags (30 cm high and 8 cm in diameter). Watering 2 times a day is recommended. After 3–4 months, seedlings are 15–30 cm tall and can be planted in the field. Spacing is usually 10 m × 10 m.
Tests in Burkina Faso have shown that vegetative propagation of Faidherbia albida by cuttings is feasible, with a success rate of about 50% for coppice shoots and root cuttings. In Mali, however, trials with cuttings showed little success. Micropropagation is still at an experimental stage.
Faidherbia albida often occurs in a park-like vegetation named ‘Faidherbia parks’, especially in West Africa, where it is widely intercropped with annual crops. Studies on the microclimate under Faidherbia albida trees demonstrated the beneficial effects of this on cropping. In densities of 20–30 trees/ha, the potential evapotranspiration decreases by 50% during the dry season and 10% during the wet season compared with cropping without trees. The soil dries out more slowly. Faidherbia albida slightly improves the internal cohesion and porosity of the soil, while soil organic and biological characteristics are strongly improved. In Senegal, increases in total carbon (62%), mineralizable carbon (73%), humus (40–47%) and total nitrogen (50%) have been demonstrated under a Faidherbia albida canopy. Soil conductivity, pH, and cation reserves were higher but the difference was not significant. However, the exchange capacity, the assimilated phosphorus, and the biological activity of the soil were significantly increased. The litter is of good quality.
It has been demonstrated that 45% of total nitrogen in the stem of young plants is the result of nitrogen fixation.
Yields of millet are much higher under a Faidherbia albida canopy; increases of 50-150% have been recorded. Results for sorghum, cotton, groundnut and maize are variable and either positive or negative, depending on the study. The effect may depend on soil fertility; when this is high, Faidherbia albida competes with the crops.
The main causes of mortality during the first year are accidental cutting during weeding of the associated crops, and the failure to control browsing by goats and sheep after crop harvesting. Protection against browsing is essential for at least the first 2 years after planting, while the use of marker stakes may reduce damage during weeding. Two weedings a year are essential for a period of 3 years to prevent young trees from being overtopped by weeds. Later, pruning is necessary so that crop cultivation beneath the trees is easier.
Diseases and pests
In Niger and Burkina Faso, the nematodes Meloidogyne javanica and Meloidogyne incognita attack young plants in the nursery; older plants are resistant. Cochineal insects may also cause damage in the nursery; treatment with parathion is effective. Defoliating caterpillars (notably Crypsotidia conifera) are the main pest of adult trees, defoliating trees in Nigeria and Zimbabwe by up to 50%. Infestation of seeds is mainly due to larvae of Bruchid beetles. Parasitic plants, such as Agelanthus dodoneifolius (DC.) Polhill & Wiens, and strangler figs, such as Ficus thonningii Blume, may infect the trees, but cause little damage.
Average annual production of organic matter, measured under some large trees in Senegal, was about 100 kg/tree of leaves, 45 kg/tree of bark and small wood, and 125 kg/tree of fruits. Regular lopping reduces fruit production. The yield of fuelwood in adult trees is about 0.1 m³/year.
Faidherbia albida was a priority species within the FAO project 'Genetic resources of trees for the improvement of life in arid and semi-arid zones' (1979-1985) concerning exploration, evaluation and conservation of genetic resources of dry zone species in 16 countries in the Sahel and northern Sudan zones. Seed collection and provenance trials have been carried out in many of these countries. The most comprehensive collection of germplasm is at Centre National de Semences Forestières, Ouagadougou, Burkina Faso, with 48 accessions.
In many parts of Africa, farmers have used Faidherbia albida in agroforestry systems for a very long time, highly appreciating this truly multipurpose tree. However, in many areas traditional knowledge of the benefits of this species has faded, and its use is neglected. A new impetus is needed to maintain or restore the use of Faidherbia albida in farming systems in the drier zones of tropical Africa, where it can help soil productivity and enable more intensive land use, especially where increasing population density is dangerously shortening fallow periods. More research is needed on genetic improvement to provide farmers with good planting material. Trials are needed to determine preferred spacings in agroforestry.
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Correct citation of this article
Bernard, C., 2002. Faidherbia albida (Delile) A.Chev. [Internet] Record from PROTA4U. Oyen, L.P.A. & Lemmens, R.H.M.J. (Editors). PROTA (Plant Resources of Tropical Africa / Ressources végétales de l’Afrique tropicale), Wageningen, Netherlands. <http://www.prota4u.org/search.asp>.
Accessed 12 November 2020.
- See the Prota4U database.