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Part three: The role of Acacia in the rural economy
3.1 Acacia species in the Sahel
3.2 Acacia species in the horn of Africa
3.3 Acacia species in East Africa
3.4 Acacia species in Southern Africa
3.5 Acacia species in North Africa
3.6 Acacia species in the Near and Middle East
3.1 Acacia species in the Sahel
It is claimed by Guinko (1990) that more than 80% of the woody species in the Sahel are Acacia. The communities in which they occur are described below.
Sahel semi-desert grassland (White (1983, mapping unit 54a), occurs on the deep sandy soils of northern Sahel where the annual rainfall is less than 250 mm and the vegetation usually consists an admixture of bushes and bushy trees and extensive areas of grassland. The chief woody species are Acacia ehrenbergiana, A. laeta, A. tortilis, Balanites aegyptiaca, Boscia senegalensis, Commiphora africana and Leptadenia pyrotechnica. They all, apart from Acacia ehrenbergiana and Leptadenis pyrotechnica, also occur in the Southern Sahel.
The northern Sahel is considered too dry for the growing of rain-fed crops except around oases and along water courses. Pastoralism is the only acceptable usage, preferably as the ecologically friendly transhumance grazing, a life style unpopular to governments because of the difficulties in administrating transient populations.
To the south, where the annual rainfall is between 250 and 500 mm, lies the Sahelian Acacia wooded grassland and deciduous bushland (White (1983, mapping unit 43), and is the most widespread vegetation type on the sandy soils of the southern Sahel In West Africa the chief woody species are Acacia laeta, A. tortilis, Adansonia digitata, Balanites aegyptiaca, Boscia senegalensis, Calotropis procera, Combretum aculeatum, C. glutinosum, Commiphora africana, Leptadenia pyrotechnica and Maerua crassifolia; their distribution extends eastwards to the Sudan.
The characteristic tree of the deep sands of the Sudan is the gum acacia, Acacia senegal, often occurring in almost pure stands which are possibly of secondary origin, the result of abandoned mature gum acacia fallows. The pure stands of the shrub Guiera senegalensis may dominate exhausted fallow lands on sandy soils throughout the southern Sahel.
Rain-fed agriculture becomes increasingly more practical with increasing rainfall. Dry season browse and, where available, crop residues, are important sources of food for livestock, especially for those nomadic graziers who utilize the northern Sahel during the rains and migrate southward during the long dry season..
Rocky outcrops and shallow stony soils may support what is termed Sahel deciduous bushland (White, 1983), consisting of dense and ofen impenetrable bushland dominated by Acacia mellifera and Commiphora africana. Other associates include Boscia senegalensis, Dichrostachys cinerea and Euphorbia candelabrum. Such bushland is characteristic of the drier northern and eastern slopes of the Jebel Marra massif in the Sudan.
Acacia mellifera is also often the dominant shrub of the poorly drained, clayey depressions on the leeward side of some of the major rock outcrops (jebels), again often forming practically impenetrable thickets. In the drier parts Acacia tortilis, Balanites aegyptiaca and Commiphora africana are occasional constituents.
The vegetation of the Nile as it traverses the Sahara has been described by Haddid (1976). The silty soils of the lower middle terrace support the trees Acacia nilotica subsp. nilotica, A. seyal and Tamarix nilotica.
Further south in the Nile Valley, where the rainfall is between 400 to 570 mm, the cracking Pleistocene clays supports extensive areas of impenetrable thickets of Acacia mellifera, which alternate with open areas of bare clays or, wherever there is a veneer of sand with Schoenefeldia gracilis. Above 570 mm A. mellifera gives way to A. seyal, the latter often forming pure stands, sometimes in association with Balanites aegyptiaca. Acacia senegal, also occurs on clay soils in areas receiving more than 600 mm, the additional rainfall compensating for the lower available soil moisture, which is in agreement with Smith (1949) who postulates that tree species requiring 2x mm annual rainfall on sandy soils require 3x mm on clay soils.
It is generally accepted that the rural populations are aware that trees are a natural resource which has to be safeguarded. For some rural populations this is a fairly recent acceptance brought about by witnessing the devastation caused by desertification and drought during the past three decades. Other populations have long appreciated the value of certain trees, such as Faidherbia albida and its benefits to both crops and livestock, or Acacia senegal for its gum. On the other hand, the nomadic pastoralists, forced outside their own environment by the years of drought, perhaps tend to be less appreciative of the sustainability of what still must appear to be an abundant resource. Examples of the latter are to be found in Wadi Aribo Basin, Darfur Province, Sudan where, in the late 1960s, the camel-owning tribes left their drought stricken grazing areas for what had previously been a prime cattle wintering area in order to feed their camels on the abundant Faidherbia albida. The new arrivals were both ruthless and wasteful in their severe pollarding of what had formerly been a carefully husbanded fodder resource. Similarly, nomads who had lost all their camels and were forced to settle along the Nile in northern Sudan, cut down all the local trees (chiefly Acacia nilotica and A. tortilis) to sell for fuel. It was only after the resulting dune encroachment threatened their villages that they began to appreciate the role the trees had played in stabilizing the soil and providing shade and shelter (Wickens, in ed.).
The usages of the various Acacia species for food, fodder, fuel, medicine, tannin, etc. are summarized in Table 184.108.40.206.
3.1.1 West Africa
Mauritania is entirely arid and in the western part the Atlantic Coastal Desert (White (1983, mapping unit 68a), forms a narrow strip bordering the Atlantic Ocean. Some 40-50 km wide, in the north it extends from the southern limit of the succulent shrubs at Saguia el Hamra (c.27°N) southwards to the northern limit of the Sahel (c.20°N). It is characterized by a relatively high humidity, lower temperatures and the absence of frost. Among the Sahelian species extending northwards into this Mauritanian coastal desert are Acacia tortilis, Balanites aegyptiaca and Salvadora persica and the grasses Panicum turgidum and Stipacrostis pungens (White, 1983).
Inland lies the Sahara regional transition zone (White, 1983, mapping units 67. 69-73). Here Acacia species are confined to the rocky beds of wadis and the gravelly alluvium of outwash fans, which are generally associated such Sahelian species as Acacia tortilis subsp. raddiana, A. ehrenbergiana, Balanites aegyptiaca Calotropis procera, Capparis decidua, Maerua crassifolia, Salvadora persica and Ziziphus mauritiana together with the grass Panicum turgidum.
The Sahel Acacia wooded grassland and deciduous bushland (White, 1983, mapping unit 43) extends along the Mauritanian border of the Senegal River. Plantations of Acacia senegal, have been established in this area, the gum of which is the property of the Moor landowners and not the farmers.
A number of Acacia species occur abundantly in Senegal. In the northern border with Mauritania, along the Senegal river valley, Acacia nilotica subsp. nilotica used to occur in dense stands of high productivity on the alluvium of the river and benefiting from its floods; natural regeneration readily occurred provided there is no excessive overgrazing and trampling. The Acacia nilotica stands have been largely decimated by the drought spells, except for relatively young stands.
Acacia seyal was abundantly present in the so-called silvopastoral area of the Senegal, a large expanse of over 50000 km2, sandy and rocky towards the east, along with Acacia tortilis subsp. raddiana accompanied by Sclerocarya birrea and Pterocarpus lucens in the east.. It also occurs in patches of pure stands on heavy clays and along the salty flats in central western Senegal and has contributed to the supply of energy to cities like Dakar, Thies and Mhour from the mid forties to mid sixties.
Faidherbia albida is concentrated in the densely populated groundnut basin in the Sere Region. The agricultural practices and traditions of the Serer population encourages natural regeneration of this tree, which is valued for its multipurpose uses (soil fertility/conservation, fodder, production of domestic utensils, etc.). The regeneration of Faidherbia albida has also been encouraged through specific projects and now through community forestry and agroforestry practices.
Other acacias also occur further south, such as Acacia sieberana in the the Sudano-Sahelian areas.
The regeneration of Acacia, especially A. tortilis and A. senegal is largely facilitated after ingestion by livestock. For the other species, regeneration is patchy and very often by sprouting from the root stock.
220.127.116.11 Burkino Faso and Niger
The importance of Acacia for the various ethnic groups inhabiting the thorn savannas and bushlands of Burkino Faso (Gourmantché, Mossi, Peuhl, Samo, Sonraii and Toureg) and Niger (Beriberi, Hausa, Peuhl, Toureg and Zarma) are discussed by Guinko (1991). The essential source of fuelwood for the rural populations of these land-locked countries is inevitably largely from Acacia, especially in the drier regions where the planting of alternative species is either impossible or extremely difficult.
To the south of the Libyan Desert in areas where the annual rainfall ranges from 75 mm to 300 mm, the major vegetation communities consist of semi-desert grasslands with A. tortilis subsp. spirocarpa and Maerua crassifolia desert scrub in the east giving way in the west to A. mellifera and Commiphora africana desert scrub (Harrison and Jackson, 1958). Camel-owning tribes formerly utilized the region during the rainy season, migrating to the south for the dry season. Three decades of low rainfall have destroyed the vegetation and the region is no longer habitable (Asher, 1988).
In Darfur broad stands of Faidherbia albida occur on the alluvial terrace soils of the Wadi Aribo. Such soils are intensively cultivated during the rainy season and heavily browsed by migrant cattle during the dry season. The stands are generally even-aged, mature to over-mature, with little signs of any natural regeneration. As a result of the recent years of below average rainfall, migrant camels have also entered the area during the dry season over the past two to three decades. Many trees have been grossly mutilated by heavy lopping and it is feared that there could be a dramatic deterioration in the F. albida population (Hunting Technical Services, 1977).
Scattered Faidherbia albida is also found on the volcanic ash slopes of the Jebel Marra massif up to c. 2500 m, where they are chiefly valued as a source of dry season browse. Temperature limits the cultivation of sorghum and millet on the massif to 2200 m and below. The enhanced yields associated with cultivation beneath the tree canopy is attributed by the farmers to the dung produced by the browsing livestock. The tree is also utilized for green manure, brushwood fences, fuel, tannin and medicine. Although regenerating well from seeds, coppice regrowth and root suckers, there is a high tree mortality due to excessive lopping, the F. albida populations are becoming increasingly younger but not at present foreseeably endangered. Although live trees are legally protected against felling, such restrictions tend not to be observed on communal lands (Miehe, 1986).
The Acacia senegal, is the source of gum arable, a major export crop of the Sudan. In the past, the rural population of the Sudan "gum belt", which stretches from eastern Darfur to the Nile in eastern Kordofan practiced a tree fallow rotation system. During the fallow period A. senegal, formed practically pure stands, increasing soil fertility and reducing soil erosion while, at the same time, providing a dry-season source of income from the gum harvest. With increasing human and livestock populations and pressure on the cultivatable and grazing lands, the length of the tree fallow was decreased or, in some instances, eliminated. Larger areas were brought into cultivation in order to try and compensate for the decreased yields, albeit with little success. The carrying capacity of the range land has also deteriorated dramatically to the detriment of the livestock industry.
3.2 Acacia species in the horn of Africa
The typical vegetation of much of Somalia is described by White (1983, mapping unit 42) as Somalia-Masai Acacia-Commiphora Deciduous Bushland and Thicket. Characteristically this community is dense, mainly deciduous bushland or impenetrable thicket, 3-5 m tall with scattered emergent trees up to 9 m tall. In those areas of Kenya and Somalia where the rainfall is less than 250 mm, the vegetation is intermediate between bushland and shrubland, consisting of low 2-3 m tall bushes and stunted trees, principally of Acacia reficiens subsp. misera, which forms a thin cover over a ground layer of mainly small shrubs. Pastoralism is the primary occupation.
The role of the Acacia species in the life of the nomadic Somali pastoralists is described by Lawrie (1954), who states that the "many species [of Acacia] play an important, almost vital, part in the lives of the Somali nomads. It might even be said that without these trees nomadic life would be impossible; at least it would be very difficult." They provide browse for the livestock, building material for the portable huts, protective fencing, fuel, fibre, and numerous other necessities (Table 3.2.1).
Although rough tribal grazing areas are recognized, albeit with huge overlaps, there is no tribal or individual ownership and consequently no responsibility for managing the grazing (Lawrie, 1960). The combined effect of desertification, drought and the present civil unrest must have had a dramatic influence on the nomadic way of life. Past attempts at a more rational control of grazing and watering points have been unsuccessful. It will require a very strong government indeed to develop a sustainable livestock industry among the various tribal factions of the Somali nomads.
To the south of Mogadishu, in the Bay region of southern Somalia, the broken, 6-8 m high tree canopy consists of A. bussed, A. mellifera, A. senegal, A. tortilis, Delonix elatoa, Dobera glabra, Cadaba spp., Commiphora spp. and Terminalia spp. Of these, A. bussei is the major source of charcoal for the Mogadishu township, current stocks are estimated to be less than 2 years' supply for Mogadishu, with tree recruitment failing to keep pace with exploitation (Bird and Shepherd, 1989). Charcoal cutting is carried out by a small group of local and migrant labour, for whom it currently provides an important source of income, although future prospects are not very bright. It is interesting to note that Trump (1986), with reference to the Bay region, provides a list of similar usages for A. bussei to that provided by Lawrie (1954), suggesting little change in the nomadic life style. Again, Acacia species rank among the most valued but vulnerable tree species utilized by the rural population.
Livestock production is the major occupation in the Bay region, with cultivation restricted to the heavier textured soils. Current tenurial rights of cultivated land and grazing are ambiguous, compounded of the pre 1960 clan territorial rights for individual farm plots, communal access and common grazing lands followed by the Republic's abolishment of all traditional land-ownership rights and all land vested in the State. Previous tenurial arrangements have to be registered anew with leases up to 50 years. Communal properties are restricted to registered water collecting ponds maintained by the villagers and the range is open to all. In practice the local population continues to recognize their traditional rights. Meanwhile the Ministry of Agriculture remains responsible for the allocation of individual farmland rights while the National Range Agency is responsible for the rangelands, the two agencies acting independently (Bird and Shepherd, 1989).
In the semi-desert grassland and shrublands of Djibouti (White, 1983, mapping unit 54b) Acacia nilotica subsp. tomentosa forms pure or nearly pure stands on silty-clay soils subjected to seasonal inundation, with Ziziphus abyssinica as a minor associate and A. ehrenbergiana in association with thickets of Salvadora persica on drier sites. The ground flora includes the aquatic Aponogeton nudiflorum, patches of Echinochloa corona and patches of Cyperus rotundus. Pastoralism appears to be the sole occupation and where browse is essential for livestock survival.
Some grazing areas may be freely used by the Assayamara tribe throughout the year while other areas are tribal property (derso). The derso lands areas are strictly controlled by the tribe, both as to grazing animal and start of the grazing season although stocking rates are not controlled, nor is the end of the grazing season. However, where certain tree populations within the derso are considered to be of value to the farmer, including A. nilotica, Ficus spp. and Ziziphus mauritiana, they are the property of family groups.
The trees, which are evergreen (provided the interval between two floods or two periods of rain do not exceed 10-12 months), are lopped to provide browse for small ruminants and camels. At least some of the pods are harvested and stored. Lightly crushed, they are fed to milking goats and camels during the dry season. While the camel will eat the entire pod, goats only eat the pod casing and are reported to reject the seed. The ground pods in water are used for treating diabetes and ulcers. Unusually the wood is not used for fuel, even the dead wood from the lopped branches is allowed to rot, despite a shortage of fuelwood in the towns of Djibouti. Possibly there is some fetish associated with practice; it requires investigation since it may influence any future plans for fuel plantations. There are proposals for the re-establishment of degraded grazing areas with A. nilotica at 100 tree per hectare and the planting of the stoloniferous grass Sporobolus helvolus at 625 plants per acre (Audru et al., 1992).
3.3 Acacia species in East Africa
3.3.1 The Pokot
The Pokot homeland (c.1°30'N 35°25'E) in northwestern Kenya lies to the south of Lake Turkana and east and northeast of Mt. Elgon and is part of the Acacia-Commiphora deciduous bushland and thicket (mapping unit 42 of White, 1983). The dominant shrubs are the 8-10 m high Acacia mellifera and A. reficiens subsp. misera. The Pokot are a farming and pastoralist people whose traditional management of the environment continues to ensure their survival. The three Pokot stategies are (1) integration of herding and farming subsistence activities, (2) multiple uses of shrubs and their products, and (3) the active participation of men, women and children in maintaining rangeland quality. The Pokot practice shifting cultivation on the steep slopes of the eastern branch of the Rift Valley escarpment and, on the lowland plains, open-range management of their cattle, sheep, goats, camels and donkeys. The farming and pastoral populations are not entirely separate for there is some exchange between the two through marriage and young men from farming stock taking up livestock in order to earn enough to settle on their own farms. The surplus livestock products of milk, meat, blood, hide and horns, are exchanged for farm surpluses of grain, beans, cucurbits and spices.
The productivity of the lowland range is maintained by mixed grazing where the zebu cattle are outnumbered by goats, often by 5 to 1 or sometimes by an even higher ratio. The goats browse on the Acacia and keep it in check. The extensive use of Acacia branches for fencing (c. 2500 m for a family of 4 adults, 8 children, 40 cattle, 200 goats) and the annual burning of the range also help to maintain a shrub to grass cover of 24 to 34% respectively. The effectiveness of this management can be seen in areas that the Pokot were forced to abandon where within 5 years the ratio changed to 50% and 13%. The smothering effect of the thicket-forming A. mellifera on the ground flora together with the fact that it is one of the last trees to produce leaves and among the first to shed them each year are obvious factors in determing shrub to grass cover.
Various parts of the Acacia are used in local medicines, for fibre and gum. Log beehives are wedged in the upper branches, a variety of birds also roost and nest in the branches. The Acacia thickets serve as refuge for small game and fowl, which are hunted by the Pokot. This is a traditional system of management where the Pokot have maintained their subsistence and exchange system, effectively integrating low-potential lowland grazing areas with higher potential farming areas. So far they have successfully resisted attempts to make them adopt 'more productive' methods, especially in the farming area (Conant, 1989).
3.3.2 The Mbeere
The Mbeere occupy part of Central and Northern Frontier Provinces of northeastern Kenya lying to the west of the Tana River and including the Somalia-Masai Acacia-Commiphora deciduous bushland and thicket and the Zanzibar-Inhambane coastal mosaic vegetation (mapping unit 16a) of White (1983). The latter consists of scrub forest dominated by Diospyros cornii and Manilkara mochistia with edaphic grassland on gray-black cracking clays supporting scattered individuals of Acacia zanzibarica, Hyphaene compressa, Terminalia spinosa and Thespesia danis. The uses of the Acacia species are shown in Table 3.3.2.
Unlike the Pokot subsistence agriculture is predominantly one of land rotation and bush fallow. In the Tana valley cattle and goats are the primary industry. "Vegetation is vitally important, however, to all activities connected to subsistence, whether it is directly or indirectly used for agricultural pursuits" (Riley and Brokensha, 1988, 1:67). Indeed a wide range of plants are or were utilized in the domestic economy of the Mbeere. During the past two decades fuelwood has become increasingly more difficult to obtain. Farms were formerly fenced with thorny branches of Acacia mellifera, A. senegal, A. seyal and A. tortilis, now, because of the shortage of Acacia species, barbed wire is being used in the more intensively farmed areas. Riley and Brokensha (1988) place the blame on an increasing population and associated increased land clearance for farming rather than on excessive cutting. The local resources had also been taken for granted and people had failed to see that they were dwindling until it was too late.
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