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Acacia senegal (L.) Willd. |
 
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Leguminosae
Gum-arabic tree, hashab. |
Author: Le Houérou
A-Flowering Branch ; B-Pod ; C-Seed |
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Gum arabic is the main product. A. senegal produces some 90 % of the marketed gum arabic sold in the world. Annual world commercial production varies from 20,000 to 60, 000 tons per annum, averaging 40,000. 80 % of the world trade used to originate in the Rep. of Sudan, particularly in the Kordofan province ; but this has decreased and other countries are developing their own production, as it is an open ended market. Production varies widely and wildly from 10 g to 10 kg per tree / annum. The average may be of the order of 100 g per tree and up to 250 g / tree / annum in the best managed orchards of Kordofan. Bush or small tree, usually 2 -6 m high, occasionally reaching 10 m under optimal conditions, frequently forming thickets. It has a short stem, is usually low branched with many upright twigs, the crown eventually flattened, umbrella-shaped. Bark pale brown to pale grey, smooth in young individuals, brown scaly on the older parts, slash mottled red and white, prickles up to 0.5 cm long, the centre one sharply curved, the other two more or less straight and directed forward. Leaves bipinnate, small, greenish-grey, with 3-6 pairs of pinnulae having 10-20 pairs of leaflets each. Leaflets grey-green, 3-8 x 1-2 mm. Flowers very fragrant, creamy white (red in bud), usually appearing before the leaves in pedunculate spikes 3-10 cm long either solitary or two to three together. Pods 7-10 cm long x 2 cm wide, flat and thin, papery, attenuated at both ends, containing 3-6 flat, round, light-brown to brown-greenish seeds. Both tap roots and lateral roots are very developed ; the latter may spread many metres from the tree, particularly in sandy terrain. The tree is deciduous, drooping its leaves in November in the Sudan. A. senegal is sensitive to frost but is very heat tolerant. Occurring between the 100 and 800 mm of MAR, mainly between 200 and 600 mm. It is extremely drought resistant as it occurs close to the very border of the Sahara and West Asian Deserts. A. senegal is sensitive to water logging. In the drier parts of its area of distribution it tends to be restricted to sandy habitats and dry river beds, but to fine textured soils under the higher rainfalls of the South Sahelian and North Sudanian ecozones., it may also occur on shallow soils and duripan lithosols. The tolerance to pH is quite broad : 5-8 . This is a typical tree / shrub of the Sahel from the Atlantic to the Red Sea, extending to the Southern Arabian Peninsula, to Eastern and Southern Africa arid and semi-arid lands, as a major component, with A. mellifera and A. oerfota, of the widespread Acacia-Commiphora formation. Four botanical geographic varieties have been identified (Brenan, 1959, 1983, Cossalter, 1991, Wickens & al. 1995) : var. senegal in West and East Africa to the Arabian Peninsula and India, var. kerensis in East Africa, var leiorhachis in East and South Africa and var rostrata in East and South Africa, Angola and in Oman. Propagation is made either from direct seeding of treated seeds (8,000-18,000 per kg) or via nursery-grown seedlings in various kinds of containers ; naturally the former is much cheaper and used to be a part of the traditional management of the Acacia bush-fallow production system of Kordofan (Seif el Din; 1965 ; Seif el Din & Mubarak, 1971). The wood is a good fuel and leaves and pods are eaten by herbivores. The leaf fall is mineralized to build up the fertility of sandy soils for ensuing crops of groundnuts, sorghum, bulrush millet and sesame. Strips of bark are slashed from the branches in November, and in January the gum exudate is collected and sold as gum arabic. Camels and goats browse it, but are usually excluded from gum-bearing groves as they browse back the trees and reduce gum production (Skerman, 1966). Human medicine : bark, leaves and gum are used to treat gastritic disorders,, haemorrhage, ophtalmia, colds, diarrhoea, as emollient, astringent ; the gum is considered an aphrodisiac. The flowers are relished by honeybees. Nutritional Quality and Animal Production The average Net Energy value of leaves and twigs is around 5-7 MJ / kg DM ( = 10-14 Mj ME) and the 13-16 % CP, with 0.12-0.15 % P ; pods contain some 20 % CP (15 % digestible) and a NE value of 4-5 MJ/kg on the DM, with 0.12-0.14 % P. Regarding the feed value of pods, see the remarks under Prosopis juliflora.
Seif el Din 1965 ; Catinot 1967 ; Seif el Din & Mubarak 1971 ; Berhaut 1975 ; Giffard 1966 ; Giffard 1975 ; FAO 1971 ; Poupon 1977 ; Delwaulle 1978 ; Delwaulle 1979 ; El Amin 1973 ; El Amin 1990 ; Le Houérou 1980a ; Le Houérou 1980d ; Geerling 1982/88 ; Baumer 1983 ; Von Maydell 1983/86 ; Cossalter 1991 ; Burkill 1995 ; Wickens et al. 1995 ; Vassal 1972 ; Vassal 1998 ; Dommergues et al. 1999. |
