DISTRIBUTION
The tree is widespread in semiarid areas of Africa on a wide range of soil types and within varying climates and habitats. Mean annual temperatures range from 15 to 25 degrees C, but are usually over 20 degrees C. It prefers semiarid, alluvial, riverine zones and depressions with water present below the surface (Forest Division 1984). A. albida is found in Kilimanjaro, Arusha, Tanga, Mbeya, Iringa, Dodoma, Tabora, and Ruvuma. Prefers drier areas with a high water table (Teel 1984).
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Minimum Altitude (m): |
0 |
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Maximum Altitude (m): |
2000 |
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Minimum Rainfall (mm): |
250 |
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Maximum Rainfall (mm): |
1800 |
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Rain Months: |
6-9 |
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Minimum Temperature (C): |
6 |
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Maximum Temperature (C): |
42 |
REQUIREMENTS
Soil Requirements: Favours coarse-textured, alluvial soils (loamy, sandy) and well-drained soils. Avoids heavy clays (FAO 1988). It tolerates a range of soils, seasonal waterlogging, and slight salinity.
Light Requirements: Strongly demanding.
Influential Factors: Develops a massive root system with a deep tap root, allowing good growth in areas with rainfall as low as 300 mm if roots have access to the water table. For optimal growth and biomass production it requires a high water table. Teel (1984) reports that in Kenya without a water table closer than 7 m to the surface it is not worth planting. It is slightly tender to frost (Palmer and Pitman 1972).
PROPAGATION
Means of Propagation: Direct sowing of pretreated seed, or nursery seedlings Coppicing.
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Seeds per kg: |
15000 |
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Germination Rate (%): |
90 |
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Germination Length: |
14-28 days treated |
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Seed Sources: |
1500 TSH per kg - Tanzania National Seed Centre 1991/92. |
Seed Treatments: A large tree in a good year bears about 1 tonne of pods (Palmer and Pitman, 1972). Pods are large and twisted, about 10 × 2.5 cm, and do not burst open. They can be collected directly from the tree or from the ground.
Seeds ripen in January. Remove seeds from the pod and winnow. Seed stores well and may be kept almost indefinitely in a cool insect free place. Pretreatment is needed to break dormancy. These methods are recommended: soaking in hot water for 24 hours, soaking in concentrated sulphuric acid for 20 minutes (Nwoboshi 1982), or scarifying or nicking the hull. Plant directly after treatment. Germination is good and initial growth is quite fast (Teel 1984).
Seedling Management: Seedlings cannot be dug up and transplanted from the wild because of the long tap root. Success has been reported by sowing seed directly into the soil (Nwoboshi 1982). Direct sowing can be used by putting 3 to 4 seeds in well-cultivated spots at the start of the rains, on a well protected site. Planted seedlings tend to have higher survival rates. Since the tap root establishes rapidly, seedlings should be planted in large pots closed at the base and be transplanted while young, between 10 and 14 weeks after sowing (FAO 1988). Root pruning may be necessary before planting. Von Maydell (1986) suggests that seedlings should be transplanted to the final destination 3 to 7 months after sowing.
SILVICULTURE
Planting Types: A. albida is a deciduous tree, and drops its leaves at the onset of the rainy season. The leaves rapidly decompose to release nutrients at the time when young plants most need them. The tree remains leafless and does not cast enough shade to adversely affect crop grown beneath (Forest Division 1984). It is appropriate for dry land agroforestry in regions of 650 mm annual rainfall or 300 mm if deep ground water is available (FAO, 1988). In Muvumi division 30 km south of Dodoma, A. albida, Adansonia digitata, and Acacia tortilis form an essential component of the farming system.
It is recommended for the interior lowland zone as an alternative to Leucaena leucocephala for maintaining soil fertility in maize fields. In the semiarid zone it is recommended as a suitable tree in valleys with food crops. Livestock also can feed on the foliage and fruit in the dry season (Forest Division 1984).
Growth Factors: Slow initial growth but accelerates once taproot reaches ground water (Forest Division 1984).
Growth Cycle: In 8 to 10 years it can exceed 10 m in height and 10 cm in diameter dbh (Forest Division 1984). Its lifespan is between 80 and 100 years.
Management Systems: Wide spacing of at least 5×5 m, up to 10×10 m, is recommended to allow for intercropping with agricultural crops such as sorghum, cowpeas, or millet at a density of 100 trees per hectare. Pruning in the second year, to about half the tree's height may be needed to control low wide horizontal branching (Forest Division 1988).
Young trees need to be protected from livestock for the first 5 to 8 years. Leaves can be susceptible to various insects, caterpillars, and locusts.
It coppices readily, but may become invasive. When generated by coppicing, height growth is considerably more vigorous than after seeding. Natural regeneration by seed is possible but requires protection against livestock (Von Maydell 1986). Transplanting of wildlings is not recommended because of long roots.
IMPORTANT USES
Use #1: FODDER
Leaves and pods are used as fodder during the rainy season, a time when few other sources of browse are available. It is reported that cattle carrying capacity can double on land with numerous A. albida trees. Since leaves are retained during the hot season it provides valuable shade. It is estimated that a mature tree can supply up to 135 kg per year of seed pods (Watkins 1960).
Use #2: MEDICINE
A decoction of the bark or root is used for coughing, fever, and diarrhoea and the gum, bark, and leaves are used for diarrhoea, haemorrhage, and colds. Fruits are eaten to control diarrhoea. The bark is sometimes used to clean teeth and is believed to contain fluorine (FAO 1988).
Use #3: LAND IMPROVEMENT
In parts of Dodoma region A. albida, Adansonia digitata, and Acacia tortilis are important parts of the farming system. A. albida is important as a source of nitrogen, and fallen leaves are important sources of humus. It is a good species to use in agroforestry for its ability to improve the soil because it drops its leaves at the beginning of the rainy season, providing nutrients to newly established crops. Since it is leafless at this time, shading of crops is not a problem.
OTHER USES: The fairly dense wood is frequently attacked by fungus, borers, and termites sod is not as highly valued as that of other Acacias, even though the wood is used for housing construction and fence posts. It is also used for firewood and charcoal, though in some areas it is not highly regarded. The wood has a calorific value of 4700 kcal per kg dry wood (Webb 1984).
