The African walnut: An ‘unconventional liana’ full of promise

Daisy Ouya

This strong, rambling vine originates in the humid tropical forests of West and Central Africa. Its seeds are rich in fat, nearly eighty percent of it polyunsaturated ‘good fat’ with proven cholesterol-lowering properties. Its bark and leaves are used in traditional medicine to ease dysentery and other diseases, and in Nigeria, its seeds are reportedly used to treat male infertility. Demand in the sub-region is strong for the African walnut, Tetracarpidium conophorum, and the findings of a new survey in Cameroon reveal its huge potential to bring socio-economic and environmental gains. The survey also reveals areas needing research and intervention, such as seedling production, storage, processing and marketing.

The African walnut is well known in West and Central Africa, where it goes by many different names—conophor nut, ukpa, asala kaso, and ngak to name a few. Besides its nutritious seeds which can be eaten raw or cooked or sold for cash, cocoa farmers grow the vine for the partial shade its high canopy provides to their cocoa orchards, protecting them from full sun. Another attraction is that, being a climber, the vine takes up no extra land on their farms.

“The natural habitat of the vine is the forest, but since nowadays it is not that easy to harvest inside the forest; smallholder farmers have therefore decided to integrate the vine into their cocoa agroforests, where they can see it, guard it and control the harvest of its valuable products,” says botanist René Jiofack, a doctorate student at the University of Kinshasa.

Jiofack coordinated an agroforestry and socioeconomic survey of the liana in six villages in Bafia and Kiiki districts in Central Cameroon, involving 35 smallholder farmers, 29 of them men. The collaborative research, whose findings were recently published in the journal Bois et Forêts des Tropiques, had partners from the World Agroforestry Centre (ICRAF), the University of Yaounde, Université Libre de Bruxelles and Cameroon’s Natural History Museum. The work was funded by the International Foundation for Science, Sweden.

The researchers found that farmers typically grew the walnut vines within diverse cocoa agroforestry systems. Because mature vines of the walnut are heavy—fully grown plants can attain a diameter of up to 17 cm— mango and African plum trees were used as hosts to support the climber. The walnut was abundant in the area surveyed, with about 14 plants per hectare, second only to mango at 19 trees per hectare.

All 93 retailers and wholesalers interviewed in Yaoundé city and its surroundings said they wished the supply of the African walnut was more steady, as there was a strong and ready market in the entire sub-region. “A 15-kg bucket of raw, unshelled nuts costs anywhere from 7,000 to 12,000 FCFA (US$10–18), depending on season and where it is bought. Around harvest time, small lots of 8 to 10 boiled seeds are sold for 100 CFA (around 15 US cents) but when supply goes down, the same 100 CFA will get you only 4-5 seeds,” says Jiofack.

A major hindrance to improved production of the African walnut, the researchers found, was the unavailability of planting material of the walnut; not a single nursery in the survey area sold its seedlings, and the only way farmers could obtain them was from neighbors who had germinated them from seeds.

“There are many improved techniques for grafting and seed germination that farmers and nursery owners can learn and apply to the African walnut,” says Dr. Zac Tchoundjeu, the Regional Coordinator for ICRAF-West and Central Africa, and Co-leader of the Centre's Global Research Project on Tree Domestication and Agroforestry Germplasm. “Research can also allow us to develop high-yielding varieties with the qualities the market desires. Furthermore, modern plant propagation methods, including tissue culture, could allow the rapid multiplication of uniform seedlings for farmers to plant on their fields,” he adds.

Tchoundjeu is keen to bring the African walnut into research that will unlock its potential to raise the incomes for farmers and communities. His two decades of work in West and Central Africa saw him awarded the 2012 National Geographic Society/Buffett Award for a lifetime contribution to conservation in Cameroon, specifically recognizing Tchoundjeu’s work on the participatory domestication of traditionally important forest tree species that were fast-disappearing. The work has allowed such trees to be grown on smallholder farms and bring nutritional, livelihood, and environmental benefits.

Already, more than 10,000 famers in West and Central African region are making a good living from the activities related to participatory tree domestication, with bush mango (Irvingia gabonensis), njansang (Ricinodendron heudelotii), bitter kola (Garcinia kola), kola nut, and the African plum tree (Dacryodes edulis) as some of the priority species. In Cameroon many Rural Resources Centers—where farmers receive training in agroforestry, nursery management, tree domestication, use of microfinance and community infrastructure improvements—have annual incomes from the sale of improved indigenous fruit trees ranging from $20,000 to 30,000, indicating that tree domestication is a powerful tool for alleviating poverty in rural areas.

Tchoundjeu says value chain development work is needed that will allow farmers to reap just livelihood benefits from cultivating the vine. In addition, research into better processing and storage methods will allow a more steady supply and even pricing.

Although the African walnut is already contributing to the wellbeing of some households in parts of West and Central Africa, the new research represents a first step towards domestication of the ‘unconventional liana.’ This will open the way to the walnut’s serving as a true cash crop that contributes to the wellbeing of households, communities and the environment.



Link to the journal article: Agroforestry and socioeconomic potential of a non-conventional liana: Tetracarpidium conophorum (Müll. Arg.) Hutch. & Dalz. in Cameroon



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