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3.4 Acacia species in Southern Africa
The semi-desert vegetation of the Karroo-Namib Region (White) 1983), mapping units 51, 52, 53) represents the drier formations of southern Africa, extending southwards to beyond the Orange River with such scattered small trees and shrubs as Acacia erioloba, A. mellifera subsp. detinens, Boscia albitrunca, B. foetida, Ehretia rigida and Grewia flava. In areas of European settlement commercial ranching (cattle, sheep, goats and ostrich), albeit at low stocking rates, is the major occupation, with more traditional herding systems in the native areas.
Among the species confined to the northern part of the Region are the endemic Brandberg acacia, Acacia montis-usti, A. robynsiana, Adenolobus pechuelii, Commiphora spp., Euphorbia guerichiana and Rhigozum virgatum.
The riparian vegetation includes the widespread and gregarious Acacia karoo, Combretum erythrophyllum, Euclea spp., Pappea capensis, Rhus lancea, R. undulate, Tamarix usneoides and Ziziphus mucronata. In the northern part of the Region the riparian vegetation includes such tropical species as Acacia erioloba, Colophospermum mopane, Combretum apiculatum, Faidherbia albida, Ficus sycomorus and Sterculia africana.
Among the principal trees and shrubs growing on the sands of the Kalahari thornveld (White (1983), mapping units 35s p.p., 44 and 56) are Acacia erioloba, A. fleckii, A. hebeclada, A. luederitzii, A. mellifera, A. tortilis, Boscia albitrunca, Dichrostachys cinerea and Terminalia sericea. Broad-leaved species become increasingly more abundant in the northern parts despite the continued dominance of Acacia spp.
On the stony soils the principal species of the dense bushland is Tarchonanthus camphoratus; associated species include Acacia karroo, A. mellifera, A. tortilis, Boscia albitrunca, Buddleja saligna, Croton gratissimus, Diospyros lycioides, Ehretia rigida, Euclea spp., Grewia flava, Rhigozum spp., Rhus spp., Tarchonanthus minor and Ziziphus mucronata.
In the Windhoek Mountains (White (1983), mapping unit 35c) among the principal trees and. shrubs of the wooded grassland are Acacia hebeclada, A. hereroensis, A. reficiens subsp. reficiens, Albizia anthelmintica, Combretum apiculatum, Dombeya rotundifolia, Ficus spp., and Tarchonanthus camphoratus.
The uses of the Acacia species in the these formations are shown in Table 3.4
3.5 Acacia species in North Africa
The role of Acacia species in the rural economy of North Africa are shown in Table 3.5
The little known endemic Acacia gummifera grows either as a 1-2 m high shrub or 5-6 m high tree with a globose crown. It is allied to A. nilotica from which it differs in having only 1-3 pinnae pairs, 7-12 pairs of leaflets per pinnae and tardily dehiscent pods; A. nilotica is absent from Morocco (Ross 1979).
A. gummifera occurs in the Argania spinosa scrub forest and bushland of the Mediterranean /Sahara regional transition zone (White (1983), mapping unit 49), Acacia gummifera-Ziziphus lotus bushland (White (1983), mapping unit 79 pro parse), and succulent sub-Mediterranean shrubland (White (1983), mapping units 10 pro parse, 49, 55 and 79 pro parse), growing on arid plains of central Morocco, at the base of the mountains to the south of Oum or Rbia and the plains of Haouz, Entifa, Tadla, Rehamna, Djebilet, Sous and Anti Atlas. A small forest of c. 1200 ha exists near El Kalaa, also in the region of Tanent - Beni Mellal in association with Euphorbia resinifera. It is often associated with another endangered Moroccan endemic, Argania spinosa (Sapotaceae). The species is reported to regenerate from seed during years with higher than usual rainfall.
A. gummifera yields abundant gum, known as gomme ammoniaque, which is marketed locally. It is also a source of fuel, charcoal, tool handles and other domestic uses. The trees are often mutilated for browse by horses and sheep; it is also browsed by hares. Indeed, the nomadic pastoralists would be unable to survive in southern Morocco without A. gummifera and its products (Boudy, 1950).
Over much of the area many centuries of firewood collection, cereal cultivation and overgrazing have reduced the former vegetation that included Acacia tortilis subsp. raddiana to the present-day degraded shrub steppe. Relics of this former vegetation occur in the Bou Hedma National Park in southern Tunisia, 80 km northwest of Gabes; the last Acacia near Menzel Habia, 50 km northwest of Gabes was felled some 15 years ago (Aronson et al., 1993). A. tortilis subsp. raddiana in Tunisia is a slow growing albeit long-lived species, attaining a diameter of 40 cm in 125 years and 90 cm in 250-300 years (Boudy, 1950). Due to its slow growth its potential for rehabilitating the former vegetation would, therefore, appear to be limited.
3.6 Acacia species in the Near and Middle East
The recorded uses of Acacia species in the dry regions of the Near East to India are presented in Table 3.6.
3.6.1 Arabian Peninsula
A number of Acacia species from tropical Africa extend into the Near East. In the Arabian peninsula, the arid, 100 km long, 8-20 km wide Ariva Valley, an extension of the Jordanian-Dead Sea Rift, drains into the Dead Sea. In the lower sections occur Acacia tortilis subspp. raddiana and tortilis and Ziziphus spina-christi. In Dhofar A. laeta is at the eastern limits of its range, where it can be found in the dry, north-draining wadis.
Typical coastal vegetation of the Red Sea and Persian Gulf consists of open Acacia-Maerua savanna with Acacia tortilis, Maerua crassifolia and the grasses Lasiurus scindicus and Panicum turgidum (Walter and Breckle, 1986), while the inland plain as far as the foothills supports Acacia ehrenbergiana, Cadaba rotundifolia, Salvadora persica and Tamarix aphylla (syn. T. articulate) (UNESCO, 1977).
In the Acacia-Commiphora deciduous bushland and thicket the woody species of the characteristic dense, 3-5 m tall bushland thicket where the scattered, up to 9 m high, emergent trees include Acacia asak, A. edgeworthii, A. etbaica, A. hamulosa, A. oerfota, together with a number of species of East African origin (White and Léonard, 1991). Pastoralism with some rain-fed and irrigated cultivation in the river valleys are the main occupations.
The subtropical desert vegetation of the Iranian arid coastal region along the eastern coasts of the Persian Gulf and the Gulf of Oman represents an eastern extension of the Arabian Desert. The vegetation consists of a spiny shrub and grass pseudo-steppe and includes among the Saharo-Sindian trees, Acacia nilotica subsp. indica, A. senegal, and A. seyal.
The role of Acacia species in the rural economy for much of Arabia is difficult to assess because of their relative scarcity over much of the terrain, where they are largely restricted to drainage lines. Certainly where they form large enough stands they appear to be appreciated.
In Dhofar A. tortilis subsp. tortilis, the only subspecies present in Oman, holds an important position in the lives of those herders where it forms the staple diet of their herds. Formerly some tribes even forbade the cutting or damage to the tree in any way, while in the more desert areas the lower branches were propped up in order to increase the area of shade (Miller and Morris, 1988).
3.6.2 Thar-Sind Deserts
The human population live in widely scattered hamlets and villages, a large part of the which leading a nomadic or semi-nomadic life with livestock as their main occupation. Much of the area has been degraded by over-grazing and excessive cutting of fuelwood (Bhandari, 1990). In areas of stabilized sands favoured by an accumulation of organic matter, the characteristic species include big, tuft-forming bushes such as Acacia jaquemontii, Calligonum polygonoides, Capparis decidua, Crotalaria burhia, Leptadenia pyrotechnica, Sericostoma pauciflorum and Ziziphus nummularia.
The gravel plains of the Thar-Sind Deserts includes among the more common trees and shrubs of the shrub vegetation Acacia leucophloea, A. nilotica subsp. indica, Capparis decidua, Maytenus emarginata, Prosopis cineraria, Salvadora oleoides and Ziziphus spp. Typical species of the riverine vegetation are Acacia nilotica subsp. indica, Salvadora persica and Tamarix dioica, while Acacia senegal, occurs in the valleys and depressions (Bhandari, 1990).
The uses of the Acacia species are presented in Table 3.6. Special mention should be made of the babul, A. nilotica subsp. indica, which is widely planted for shelter belts and in rainnfed agroforestry and irrigation schemes where the tree is an important source of browse, bark and pods are used for tanning, wood for fuel, building purposes, agricultural implements, etc. as well as being a source of gum (Bhandari, 1990). Some doubt has been cast on its value for agroforestry because of the depressed crop yields from beneath the canopy; this is discussed more fully in section 2.3.6.
On the fringes of the Himalayan foothills from Afghanistan through Pakistan and into India Acacia modesta is a major component of some of the vegetation types. Slow growing, it is much used for hedges as well as being a source of gum (Macmillan, 1954; Agarwal, 1983).
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