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ACACIA TORTILIS*

DISTRIBUTION

Wide ranging in arid and semiarid areas of Africa. It is reported in most parts of Tanzania, but is more frequent in the north (RSCU 1992). It is common in dry savannahs and bushland, on sandy soils, and where rainfall is low. The preferred temperature is 20 to 25 degrees C with over 500 mm rainfall.

Minimum Altitude (m):

0

Maximum Altitude (m):

1500

Minimum Rainfall (mm):

100

Maximum Rainfall (mm):

1000

Minimum Temperature (C):

20

Maximum Temperature (C):

50

REQUIREMENTS

Soil Requirements: Accepts a wide range of soils if well-drained and non-saline. Prefers deep alkaline loams (RSCU 1992). It is also found on shallow soils and has colonized saline and gypseous soils (NFTA 1991).

Influential Factors: An extremely drought resistant species which can tolerate long erratic dry seasons, with very high daily temperatures. It can survive climates with less than 100 mm annual rainfall. Avoid seasonally waterlogged locations and those where inundations occur. It forms a very deep tap root in sandy soils (NFTA 1991). It also has extensive, long, lateral, shallow roots and may be blown over by strong winds. Young trees are susceptible to damage from frost and by grazing animals, although older trees can withstand frosts and light grass fires (NFTA 1991). Trees are susceptible to attack by caterpillars, beetles and blight diseases (Parkash 1991). Bruchid beetles can destroy over 90% of seeds produced in a year.

PROPAGATION

Means of Propagation: Seedlings, wildlings, but primarily by seed. Coppices vigorously and tolerates lopping of large limbs. Abundant distribution though animal dung.

Seeds per kg:

10000-50000 (half after winnowing)

Germination Rate (%):

40 to 65

Germination Length:

40 days

Seed Sources:

1800 TSH per kg - Tanzania National Seed Centre 1991.

Seed Treatments: Pods are small and very twisted. Collect pods by picking or shaking from healthy trees before they open. Remove seeds from dry pods by trampling, or allow them to open during dry storage. Seeds should be cold stored in a dry, sealed container. It will remain viable for long periods. For even and high germination success, seeds need pretreatment. Pretreatment can be done by soaking in water at room temperature for 24 hours; soaking in H2SO4 1 to 2 hours followed by washing and then drying in the shade; or by soaking in hot (80 to 100 degrees C) water overnight. Teel (1984) reports that seeds are difficult to pretreat, being both hard to nick and responding poorly to soaking.

Germination in the nursery averages 25% and survival 50% (Parkash 1991). Once germinated, it grows and transplants well from the nursery (Teel 1984).

Seedling Management: Seed may be sown directly on site in mulched lines 5 m apart, or in patches (Parkash 1991). It is better to plant nursery-raised seedlings in containers in areas of erratic rainfall (Parkash 1991). For containerized seedlings, sow 2 seeds per pot. Young seedlings are sensitive to hot winds.

SILVICULTURE

Planting Types: A. tortilis is a good shade tree for people and for silvipastoral agroforestry uses in arid areas. It is not good for intercropping or near farmland due to wide, shallow roots (Teel 1984). Useful for sand dune stabilization, shelterbelts along canals and roads, and in sandy arid areas. It is recommended for semiarid areas on sandy soils with low rainfall, for fuelwood production (Forest Division 1984). It is considered a promising species in Dodoma. Plantations have been established in India.

Growth Factors: Initially slow growth generally. The growth is relatively fast if planted with good seeds on good sites that are well-managed.

Growth Cycle: Pods ready for livestock at the end of the dry season. For the production of seed, fuel, and fodder, a rotation age of about 10 years is recommended by Parkash (1991). It lives 100 to 150 years.

Limitations to Planting: Can become a weed and should be introduced with caution. Usually not planted near houses since it is very thorny.

Management Systems: Containerized seedlings may be planted at about 10 months when 0.5 m to 1 m tall, in pits 60 cm3. Recommended spacing is 3×3 m to 5×5 m, on sites with deep, sandy soil (Parkash 1991). Young plants in plantations as well as natural regeneration require protection from browsing for 3 to 5 years. Mature plants tolerate heavy browsing. Suppression of weed competition is essential initially (don Maydell 1986).

IMPORTANT USES

Use #1: FUEL
Produces high quality firewood and charcoal (4400 kcal per kg) (Webb 1984). It is rarely used for building or timber as it warps upon drying and is often infected with borers.

Use #2: FODDER
It is an excellent source of fodder and plants can survive heavy grazing. Pods are high in protein (15 to 20%) and are eaten from the ground by livestock and wildlife. Fruits are 19% protein and are readily consumed (Forest Division 1984). Leaves, new shoots, and seedlings are also browsed.

Use #3: FENCING
Branches have 2 types of thorns, short brown ones and long white ones. Both thorny branches and posts are used as fencing material.

OTHER USES: The thorns are also used as needles and inner bark fibre is used for rope.

NOTES

In Indian field trials, it was found to be the fastest growing of the Acacias. Twelve year old plantations at 3×3 m yielded 54 tonnes of fuelwood per hectare and produced 900 kgs of fodder per hectare per year (Forest Division 1984).


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