Terminalia sericea - Northern Namibia's hardy pioneer

Naturally regenerating, pure stands of Terminalia sericea Burch. ex. DC. grow along the once devastated Namibian - Zambian border line. As agressive, indigenous and easy to establish Terminalia sericea is recommended for reforestation and agroforestry in Owambo, Kavango and Caprivi, northern Namibia, to provide fuel, poles and multipurpose products. Pioneer characteristics, good adaptability to drought and moderate adaptability to saline soils render Terminalia sericea a potential candidate for reforestation, erosion control and agroforestry in other African countries with climate similar to Namibia.

Terminalia sericea Burch. ex DC., Silverleaf (Breitenbach 1968), Silver terminalia (Palgrave 1990) is a semi-deciduous, 3-13 meters tall pioneer species, which grows abundantly in less populated areas of Northern Namibia, as well as around the Kalahari desert. As long as it is not subject to heavy competition on light, it thrives practically everywhere in Caprivi, Kavango and Owambo districts, irrespective of soil composition, moisture and drainage conditions.

Terminalia sericea has low, spreadingly branched habit on badly drained and dry sites. On more favourable sites it grows into taller tree with cylindrical stem and rounded, flat-topped crown. Normally it occurs as scattered on open woodlands, or as dominant or co-dominant in mixed deciduous forests.  It seldom makes pure stands in late successional stages.

Terminalia sericea is an aggressive colonizer which forms dense pioneer thickets on new alluvial or eroded soils as well as on soils which are already partly devastated and deteriorated. Where Terminalia thicket has succeeded in improving sites by draining water-logged soils, or by enriching impoverished soils, or by shading out moisture-competing weeds, climax species can later move in. Terminalia sericea is normally found as single trees still in the later stages of succession, also in mature northern Namibian forests, from where it is ready seeding and regenerating as open sites become available. Only the densest formations of the Zambesi teak (Baikiaea plurijuga Harms) and mopane (Colophospermum mopane Kirk ex. J. Leonard) can exclude Terminalia sericea.

The wood of Terminalia sericea is yellow, grained, hard, heavy and very tough. The heartwood is durable, both termite- and borer-proof. The most common use of Terminalia sericea is for house and compound yard fencing (fencing of Namibian "kraals") (Rodin 1985). For that purpose the timber is as good as the most commonly used mopane.

Terminalia sericea is also harvested for its bark; the strong bark is torn into strips and used to tie together frames of houses and in other construction. A decoction of its roots, which has a bitter taste, is taken to cure diarrhoea and applied as an eyewash. The hot infusion of the outer roots is used for treating pneumonia. The silky, silvery leaf hairs are used by Tswana potters for glazing their wares. A glucoside, nerifolin, has been isolated from parts of the plant and this has been found to have an effect on the heart and pulse rate.

In summary, Terminalia sericea is an indigenous pioneer species, a local multipurpose tree, the potential of which as a reforestation, agroforestry and multipurpose species should be taken into consideration as the independent Namibia is building her reforestation programme in the deforested northern areas.

Occurrence on the Zambia - Namibia border

In the Eastern Caprivi there is a border zone of 100 meters wide and 90 km long between the territories of Namibia and Zambia. During the war period (1970s) the border zone was kept free of vegetation, mainly mechanically but periodically also with herbicides. The bush clearance was stopped in 1978. After 12 years, Terminalia sericea has spread over the devegetated zone, freely through abundant natural regeneration. The zone is in places fully stocked with 5 meters high monoculture of Terminalia sericea.  The soil is seemingly well restored and the tree growth is vigorous.

Potential and research directions

The occurrence of naturally regenerated Terminalia sericea thickets on the Namibian - Zambian border line holds a promise for the future reforestation programme of Namibia. In so many African countries it is predictable that indigenous trees tend to disappear from the silviculture. On one hand this is due to deforestation and lack of suitable indigenous species with limited  availability of reproductive material. On the other hand there often is an easy access to exotic plantation species which are easy to establish as plantations. A typical example is Ethiopia with its long history of deforestation, and introduction of fast-growing exotics already at the end of the 1800's. As the local flora does not provide suitable pioneer species for reforestation the country's reforestation plans rely heavily on exotics, mainly on Eucalyptus globulus (Pohjonen and Pukkala 1990). A similar situation prevails in many countries of East Africa.

It is a remarkable asset for Namibian forestry that a local indigenous pioneer tree species like Terminalia sericea is available. It is readily known by the local people. Reforesting with it is unlikely to involve large, unexpected problems. Reforestation research and development have a potential to progress rapidly. Terminalia sericea has a good tolerance to drought and moderate tolerance to saline soils. Based on its good natural regeneration properties and cultural acceptability (use), Terminalia sericea is a valuable indigenous tree for woodlot and agroforestry applications in Namibia. The growth potential of the species should now be evaluated and its silviculture thoroughly studied for practical applications.

The ecology and silviculture of Terminalia sericea is not yet properly known. There are limited information for instance on flowering and seeding, seed availability, storage possibilities and pretreatments needed. These subjects should now be put under systematic research.

Terminalia sericea is such a potentially valuable reforestation species that it should be studied also in the neighboring countries. It is indigenous in the SADCC-countries of Botswana, Angola and Zambia. Besides, the genus Terminalia is widely spread over Eastern Africa. Terminalia sericea might be useful in other African countries with similar ecological conditions: rather hot arid climate, waterlogged and even salty clay soils, like in parts of Kenya and Ethiopia. Provenance research is one of the first research topics.

Further reading

Breitenbach, F. von. 1968. Long-term plan of forestry development in the Eastern Caprivi zipfel. Department of Forestry, Saasveld Branch Library. 164 p.

Palgrave, K.C. 1990. Trees of Southern Africa. Struik Publishers. Cape Town. 959 p. ISBN 0-86977-081-0.

Pohjonen, V. & Pukkala, T. 1990. Eucalyptus globulus in Ethiopian forestry. For. Ecol. Manage., 36:19-31.

Rodin, R.J. 1985. The ethnobotany of the Kwanyama Ovambos. Monographs in systematic botany from the Missouri Botanical Garden :1-165. ISSN 06161-1542.

Veli Pohjonen

Käsikirjoitus - Manuscript 22.10.1991. Julkaistu lyhennettynä - Published as shortened:

Pohjonen, V. 1992. Terminalia sericea. Northern Namibia's hardy pioneer. Agroforestry today. 4(1):11.