Session 5 Social and Development Issues

Session Papers

Faidherbia albida in Zimbabwe

J. Clarke¹

Abstract

Faidherbia albida lias a limited distribution in Zimbabwe, occurring along riverbanks in remote, sparsely populated zones of the country. It is an important source of fodder for both wild and domestic animals and is retained in fields. Trials started in 1985 have shown that eastern and southern African provenances have larger seed, greater nodulation at the seedling stage, and faster growth up to 43 months in comparison with western African provenances. Performance of even the best provenances has been poor in comparison to rates achieved on favorable sites elsewhere in Africa. Further testing on more suitable sites is required in order to assess its potential outside its natural range. Within its range, opportunities for protection and further planting should be assessed. In the rest of the country, farmers consider acacia species to be weeds and always remove them from fields. There are several valuable indigenous tree species in Zimbabwe that are more widely known than F. albida and these should be given priority in forestry trials.

Natural Distribution and Ecology

In Zimbabwe, Faidherbia albida is a riparian species found along the Zambezi River and its tributaries in the north, and along the Limpopo River and its tributaries in the south. It is confined to recently deposited alluvial soils at an altitude of 900 m and below (Guy 1977). F. albida is a primary colonizer of sandy river banks, where it is able to withstand prolonged waterlogging. This has been attributed to its characteristic leaf shedding and dormancy in the wet season (Dunham 1989b). Where alluvial terraces exist, the species forms a high open woodland, at a density that results in approximately 25% canopy cover (Dunham 1989a).

As a result of its limited distribution, F. albida is currently only of limited importance on a national scale. In its natural range the species plays an important role both in communal areas and in National Parks.

More effort is needed to protect existing stands, encourage natural regeneration, and plant more seedlings of F. albida in areas where it occurs naturally. It is already known and appreciated by traditional occupants of the land, the Tonga people, who grind and eat the seeds as porridge in times of severe drought (Scudder 1971). A survey of Tonga farmers in southern Zambia revealed many were interested in planting more F. albida seedlings in their fields (Sturmheit 1988). Awareness about the role and importance of the species among new settlers should be assessed and further promoted.

In National Parks, the species is protected from cutting, but not from elephants. Although elephants inflict a lot of damage mature trees do not usually die. In the 1960s there was concern that many old trees at Mana Pools appeared to be dying without regeneration. A subsequent study revealed that while there is no regeneration under mature stands, new sandbanks close to the rivers are continually being colonized by seedlings (Dunham 1989b).

The potential for promoting the species outside its existing range is less promising than in areas where it is already well known and appreciated. In the higher rainfall areas of the country, farmers generally dislike acacias, and F. albida is likely to fall into this category. In Shurugwi, a medium-potential cropping area, farmers consider acacias to be weeds and are not interested in planting more of them (McGregor 1990). In Zvishavane district, indigenous acacias are considered by farmers to have a negative effect on crops and are always removed from fields (Wilson 1987). In the low-potential areas of the country, where cropping is marginal, acacia species make an important contribution to livestock nutrition and are appreciated for this. There is likely to be potential for encouraging planting of F. albida as a fodder species in these areas.

Provenance Trials

Trials to test the potential of the species outside its natural range in Zimbabwe have been initiated (Sniezko and Stewart 1989) but their results are disappointing. So far, despite intensive management, performance of even the best provenances on the best trial site has been mediocre. It may be necessary to further test the best provenances from these trials on a much wider range of sites, taking care to select those that meet the species' requirements. If the species is found to perform adequately in such trials, it should then be introduced and tested in small-scale farming areas, particularly those in low rainfall areas.

Because of its restricted range in Zimbabwe, F. albida is therefore not known or appreciated across most of the country. Ethnobotanical studies have identified a number of valuable indigenous tree species that are deliberately retained in croplands and protected by farmers (Wilson 1987; McGregor 1990). As these species are already well known and play an important role in farming systems, they should be given priority in species selection and breeding trials.

References

Dunham, K.M. 1989a. Litter fall, nutrient fall and production in an Acacia albida woodland in Zimbabwe. Journal of Tropical Ecology 5:227-238.

Dunham, K.M. 1989b. Long term changes in Zambezi riparian woodlands, as revealed by photo-panoramas. African Journal of Ecology 27:263-275.

Guy, P. 1977. Notes on the vegetation types of the Zambezi valley between Kariba and Mpata gorge. Kirkia 10(2):543-547.

McGregor, J. 1990. Trees and their uses: notes from the Shurugwi Area. Zimbabwe Forestry Commission. (Limited distribution.)

Scudder, T.S. 1971. Gathering among African woodland savanna cultivators. Zambian Papers No. 5. Manchester, UK: Manchester University Press.

Sniezko, R.A., and Stewart, H.T.L. 1989. Range-wide provenance variation in growth and nutrition of Acacia albida seedlings propagated in Zimbabwe. Forest Ecology and Management 27:179-197.

Sturmheit, P. 1988. Evaluation of a soil conservation and agroforestry needs assessment study conducted in Mazabuka District of Zambia. Presented to the CTA seminar on' The efficiency of trees in African agrrarian production and rural landscapes,' 11-16 Jun 1988, Kigali. Wageningen, Netherlands: Centre technique de cooperation agricole et rurale.

Wilson, K. 1987. The ecology and use of indigenous tree species in Southern Zimbabwe. Unpublished report. Zimbabwe: ENDA.

Footnote__________

1 Forestry Research Centre (FRC), Zimbabwe Forestry Commission, Harare, Zimbabwe.

Clarke, J. 1992. Faidherbia albida in Zimbabwe. Pages 181-182 in Faidherbia albida in the West African semi-arid tropics: proceedings of a workshop, 22-26 Apr 1991, Niamey, Niger (Vandenbeldt, R.J., ed.). Patancheru, A.P. 502 324, India: International Crops Research Institute for the Semi-Arid Tropics; and Nairobi, Kenya: International Centre for Research in Agroforestry.