Plant 323

Senegalia senegal (L.) Britton (Fabaceae)

Gum acacia

Acrimonious, arcane argument in the mid-2000s resulted in all African acacias losing their place in the genus Acacia. However, such scientific name shifts change nothing regarding the ecological, cultural, social and economic importance of these leguminous African trees. Researchers from the Oxford Forestry Institute spent decades investigating the biology and genetic improvement of multipurpose African acacias.

Globally, gum arabic is the most economically important material produced by African acacias. The international gum arabic trade is ancient. Egyptians were trading it from at least 3400 BCE, using it in everything from mummification to cosmetics and inks. By the seventeenth century and eighteenth century, gum arabic trade with Europe had shifted to West Africa.

Between 2014 and 2016, crude gum arabic exports from Africa (primarily Sudan) were worth over US$150 million; the majority was imported by France and India. This polysaccharide-rich gum is the dried sap that leaks from the trunks and branches of two African acacias: Senegalia senegal and Vachellia seyal, of which the former is the most important.

Gum arabic dissolves in water to produce highly concentrated, low-viscosity solutions, with multiple traditional and industrial uses where thickening and stabilisation are necessary. Moreover, it is capable of stabilising oil-in-water emulsions.

Traditionally, in Africa, gum arabic is a famine food, which is also used in medicine and in household activities, such as glue and ink making. Industrially, the main use of gum arabic is in confectionary, for texture improvement, and in beverages, as an emulsifier and flavour enhancer. It also has multiple roles in pharmaceuticals, cosmetics, printing, photography and firework manufacture.

The natural distribution of Senegalia senegal extends in a band from Senegal through sub-Saharan Africa to the Red Sea, south through East Africa to South Africa across Arabia and into India and Pakistan. It grows best in deep, sandy, well-drained soils in warm, sub-desert environments.

Traditional Sudanese gum gardens evolved from bush-fallow systems where cereal crops were planted annually until the soil was exhausted and cereal yields fell. Crop production was shifted, and the area replanted or regenerated with Senegalia. Since Senegalia fixes nitrogen from the atmosphere, soil fertility of the abandoned areas gradually increased, and eventually cropping cycles could be re-established.

Current desertification in sub-Saharan Africa is being ameliorated by planting gum acacia, which brings benefits to people and the environment. Soil fertility and stability is improved, whilst the trees provide fuel wood, animal fodder and income for local communities.

Further reading

Diop S et al. 2018. Combating desertification and improving local livelihoods through the GGWI in the Sahel Region: the example of Senegal. Journal of Resources and Ecology 9: 257-265.

Fagg CW and Allison GE 2004. Acacia senegal and the gum arabic trade. Oxford Forestry Institute.

UNCTAD 2018. Commodities at a glance: special issue on gum arabic. United Nations.

Stephen Harris