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Part five: Multipurpose management of Acacia formations: A short review
5.1 Future prospects
5.2 Research requirements
In the Sahel, North Africa and Near East the former Acacia communities have either deteriorated to almost beyond recovery or have even disappeared, especially in North Africa. Demands for fuel are undoubtedly the major cause of the loss of trees. Overgrazing resulting in the stunting of tree growth and prevention of regeneration, together with large-scale agricultural projects are additional factors. For example, in the Sudan even the large stands of A. mellifera which dominate much of the clay soils of the Nile and its tributaries are threatened. In the Nile Valley large areas which had supplied charcoal for Khartoum have been clear felled for irrigation, while to the west fuel supplies for El Obeid are making ever increasing inroads into the stands at the El Ain Forest Reserve where annual incremental growth is less than the present rate of extraction. The management plan for the El Ain Forest Reserve, which also includes non-wood forest products, can only provide a sustainable fuel supply for the local villages but not El Obeid town (Vogt, 1994). There is a similar situation in Nigeria where some of the fuelwood for Kano has to be transported for 600 km.
It is clear that fuel demands of the urban populations must have a large impact on the tree resources of the rural areas, affecting not only the rural population but also the environment, wildlife refuge, etc. It is possible that a wider implementation of agroforestry practices supplemented by selective thinnings for fuel and timber from communal shelterbelts could meet the requirements of the rural agrarian communities. For such developments the cooperation of the rural populations is essential; numerous local schemes as being developed now, are consequently likely to prove more effective than non private or non community based projects.
The demands of the herdsmen have also to be met. This includes not only the sustainable availability of herbage and browse for the livestock but also the tree requirements for fuel and fencing by the herdsmen. Much of the rangelands are state owned and it would require very unpopular draconian measures to ensure that the livestock populations were kept below the carrying capacity of the range, i.e. the stocking rate must be regulated to permit natural regeneration and improvement. Without such measures deterioration of the range will continue to take place. The large scale reseeding and reafforestation of rangelands is not an economic proposition when considered in the purely economic terms of carrying capacity and return from offtake. The growing of fodder banks as part of the agroforestry rotation can help carry the livestock through the difficult dry season period. Livestock watering points must be so distributed and regulated that overgrazing in the immediate vicinity are minimized, preferably by rotation. Ideally the dryland ranges should be used primarily for stock rearing with finishing on crop residues and biproducts in regions of higher rainfall or irrigated crops.
This is an idealized system for managing the Acacia communities for the benefit of the rural population in order to meet their needs for fuel, fodder, medicine, etc. as well as maintain the environment and its associated wildlife. But what of the urban populations? A large and probably unknown percentage are refugees from famine and strife. Many would probably return to their farms once stability is ensured. Forestry alone cannot meet all the fuel requirements of the major urban areas of the drylands of Africa and the Near East; it can, however, largely contribute if remaining natural stands (including of Acacia, especially the pure Acacia seyal and/or Acacia nilotica formations) are properly managed and their regeneration secured. Trees must be managed for sustainable production.
However, it must be stressed that the most important role of Acacia and other tree and shrub species is to stabilize the environment and thus prevent desertification, a role that safeguards both the national and rural economy. Any future afforestation schemes should be designed for maximum protection against desertification.
5.1 Future prospects
Desertification, the consequences of over-cultivation, over-grazing and deforestation, is an insidious process. The results are a degradation of the environment. To reverse the process, to return the land to its predesertified condition, is considered an impossible task. The task is not only aggravated, especially in the Sahel, by decades of lower than average rainfall, the rapid increase in human and livestock populations have created additional pressures which are unlikely to be controlled until too late. There is a finite, environmental limit to the carrying capacities of the drier regions in terms of human and livestock sustainability, even with fertilizer and irrigation inputs. The prospect of a climate change (Parry, 1990) casts additional gloom on future prospects.
The enormous scale of environmental degradation in recent decades makes the economics of remedial works beyond even international financial aid unless efficient, low cost and participatory modes of rehabilitation are promoted. The strategy should now be to prevent further desertification by concentrating on protecting the higher rainfall regions and later attempt reclamation by working from the protected area into the area of desertification. This does not mean that essential aid to the decertified regions should stop, rather that more thought should be given to preventative rather than remedial measures.
5.2 Research requirements
Many of the attributes of the Acacia species given in this report are based on a very few observations and varying, unqualified degrees of merit. The usefulness of a species depends very much on availability in terms of abundance and, as a food and fodder resource, seasonal availability, as well as the relative merits of other alternatives. References in the literature to preferred species are often ambiguous. People adapt, when one resource is lost or in short supply, a substitute may be used. The preferred species may have been that which is lost but, in time, becomes that which has been substituted. Contradicting statements regarding, for example, fuel and fodder preferences are invariably found to be merely relative. Such relativity makes it extremely difficult to draw any firm conclusions.
It is possible that the various attributes of the A. tortilis complex, a polyploid series are somewhat similar, so that the various subspecies are more or less interchangeable as regard products but not for ecological requirements, consequently information based on only the species name has therefore not been considered a serious problem. Problems in interpreting data do occur with A. nilotica if the relevant subspecies is not mentioned. This species also forms a polyploid complex of subspecies and, while subsp. nilotica and subsp. tomentosa occur in riverine habitats subjected to seasonal flooding and are often semi-evergreen or even evergreen, subsp. adstringens, subsp. leiocarpa occur in wooded grassland and dry scrub while subsp. kraussiana prefers dry grassland and river valleys away from flooding; all three are deciduous (Sahni, 1968; Fagg and Barnes, 1990). The tannin content is believed to vary considerably between the subspecies and possibly within a subspecies, and this affects not only the usefulness for tanning but also suitability for browse and palatability.
Possible seasonal variations and provenance in the African acacias have not been investigated, neither has the presence of condensed tannins and gallotannins in browse been investigated. It is also recognized that the phyllodous acacias are high in tannin and consequently relatively unplatable to livestock, never-the-less they are a valuable dry season browse; provenance selection may result in species suitable for growing in the Sahel. Comparative trials for growth, yield and seasonable availability are also suggested.
Although the seeds of some African acacias are known to be eaten, very little work has been done on their potential in the human diet, whereas work on a number of Australian species has shown them to be richer in proteins and dietary amino acids than the cereals. What little work is available for African species is based on a very few samples, further analyses are required.
Despite being a major item of commerce for some seven decades very little is known about the production of gum although there appears to have been some interest in recent years in the physiochemical and macromolecular field of gum production (Fenyo et al., 1991). This is an essential field of research for without knowledge of how gum is produced it is not possible to manage trees for gum production.
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