- In major yam-producing areas such as West Africa and the Caribbean, the tuber is traditionally grown using sticks as scaffolds for vine growth, which are traditionally cut from the forest, causing deforestation.
- Scientists and yam breeders are trialing ways to replace these sticks through agroforestry, introducing living supports that can also improve the soil and provide other benefits to farmers.
- Trials using plants such as pigeon pea and bitter damsel as living yam sticks have shown potential.
- However, conservationists say that entrenched traditional farming methods and a lack of funding to promote more sustainable approaches are preventing living vine sticks from widespread application.
Yams are considered one of the world’s most important crops. A starchy, nutrient-rich root vegetable of the genus Dioscorea, the yam thrives in a tropical belt across West Africa, with outliers in the Caribbean and some Asian countries such as Japan.
In 2023, nearly 90 million metric tons of yam were produced globally, according to data from the Food and Agriculture Organization of the United Nations. But the way in which they’re grown, using traditional “yam sticks,” is now seen as a major cause of deforestation.
“The yam is a climber,” says Eric Owusu Danquah, a research scientist at Ghana’s Council for Scientific and Industrial Research (CSIR), “it has to climb to expose its leaves to the sunlight.” To do this, it depends on “yam sticks,” staves around 2 meters (6.5 feet) long that are often cut from the nearby forests — a practice that conservationists such as Danquah say prevents trees from developing and forests from regenerating. Each stick only lasts two growing seasons at most. As a result, yam breeders, scientists and local forestry groups are looking at alternatives for the vines to climb.
The yam grows as a tuber, with Ghana and Nigeria producing more than 80% of the world’s output, according to Danquah. It’s a demanding crop. As well as staking, it also requires fertile soils, with farmers traditionally moving from field to field each year, so they can leave land fallow and allow nutrients in the soil to recover.
Planting is a labor-intensive job, with seed tubers or slips, a cutting taken from another yam, planted in earth mounds, often with a core of rich organic matter to help kick-start growth.
Each yam needs staking individually, and Danquah has spent the last 15 years looking at climate-smart ways to reduce Ghanaian farmers’ dependence on yam sticks. Trials with rope were successful, he says, and immediately reduced the use of sticks by 50%, without compromising the yields. But the ropes were costly for the farmers, he says, and a cheaper option was needed, which is where his research into a bushy shrub called the pigeon pea (Cajanus cajan) began.
The plant acts as a living yam stick, he says, and as well as reducing the need to cut wood from the forest, the pigeon pea brings other benefits too. Like all leguminous crops, it fixes nitrogen in the soil, and because it’s living, continues to sequester carbon, too. The plant also produces nutritious grains that the farmer can sell. Continuously pruning the shrub encourages it to grow tall and straight, and the cuttings act as a nutrient-rich mulch on top of the yam mounds. This is doubly important, Danquah says, as most of Ghana’s yam production is grown by smallholders, working on less than 2 hectares (5 acres), many of whom struggle to afford artificial inputs.
But despite its many selling points, pigeon pea-supported yam cultivation has yet to make it off the demonstration plot. “We need to upscale,” Danquah says. “As it stands now, the adoption is very low … We need funding to be able to train farmers; [we] need to get into the yam growing communities.”
At the moment, he says, most yam funding goes into disease research and cultivating varieties with more seeds. But Danquah says he would like to see some of this money channeled toward incentivizing farmers, too. “[If] we want farmers to adopt good practices that are good for climate change and resilient crop production, this is something that the farmers needs to be rewarded for,” he says.
Asrat Amele is a yam breeder at the International Institute of Tropical Agriculture (IITA) in Abuja, Nigeria, and has also looked at a range of options to replace the yam stick, both to reduce deforestation and also help yam farmers adjust to the effects of climate change.
Among the alternatives Amele has trialed are plastic stakes, which can last up to four years, but heat up in the sun and harm the vines, which also struggle to gain purchase on the stake’s slippery surface. As in Ghana, Amele has also used ropes, but in “high humidity and heat, they rarely last more than one season,” he says. He’s also looking at new biodegradable netting from Japan, a country where the yam is considered a delicacy, but this is likely to prove too expensive for most yam farmers in Ghana, he adds.
Changing weather patterns are also influencing thinking. The yam is traditionally a crop of the forest, where it thrives on rich soils, plentiful rainfall and humid conditions. But now, Amele says, “the rain is not reliable.” He adds that population growth and an increased demand for yam is also putting pressure on farmers, who can no longer afford to leave fields fallow, which means the soil never fully recovers. “Farmers are being forced to plant in the same land again and again, every year,” Amele says, “so now they are encountering productivity decline.
“These are the changes that drive yam to more open land,” Amele adds, pointing to a transition zone where scrub becomes savanna, and trees are largely absent. “The yam can adapt to different environments,” he says, with more resilient cultivars and climate-smart production allowing it to take advantage of the extra space.
For instance, IITA is developing cultivars such as the dwarf yam, with short vines just a meter (3 ft) high that don’t need support.
By eliminating the need for stakes, these yams not only optimize space but also provide an opportunity for mechanized planting and harvesting, making yam cultivation more efficient and scalable.
Although carried out on a much smaller scale, yam farming in Jamaica is still seen as a factor in the loss of the island’s natural forests. According to Donna Lowe, principal of forest science and technical services at the Jamaican Forestry Department, by harvesting saplings for use as yam sticks, farmers are “affecting the future forest, because these trees will never mature and replace the bigger trees that people [loggers] are already removing.”
“Over time you are degrading the forest, which will eventually lead to deforestation,” she says, adding that a flourishing and often illegal trade has also sprung up around yam sticks, with new mining roads allowing access to previously inaccessible and uncut areas.
“[T]he composition and structure of the forest is annihilated,” Lowe says. “Farmers need a feasible alternative.”
In Cockpit Country, Jamaica’s main yam-growing area, the solution may lie in a native tree species, the bitter damsel (Simarouba glauca), and a move toward agroforestry.
According to Arlette Dunkley-Fullerton, chair of the South East Cockpit Country Local Forest Management Committee Benevolent Society, bitter damsel trees are easy to propagate and require minimal care once they’re established. They also play an important role in maintaining tree cover, which supports wildlife and prevents soil erosion.
Like the pigeon pea in Ghana, the bitter damsel also enriches the soil by adding nitrogen (though through decomposition rather than fixation), reducing the need for chemical fertilizers. Each tree can support up to six vines, Dunkley-Fullerton says, and protects the vines’ leaves from harsh sun and strong winds, while the bitter damsel is also good for intercropping with shade-tolerant crops like ginger.
Normally, farmers “go into the forest and cut the young trees,” Dunkley-Fullerton says. “By using live yam sticks, farmers can reduce pressure on the natural forest, helping to preserve the rich biodiversity [of the region].”
Her committee has calculated that, on average, between 800 and 1,000 yam sticks are needed per acre of farm. Cutting one tree, with a diameter of 3-4 inches (7.5-10 centimeters), can yield four to six yam sticks, which means that to stake one acre, up to 200 trees must be cut, at least every other year. Promoting live yam sticks, Dunkley-Fullerton says, could save between 2,660 and 4,000 trees every year across Cockpit Country.
The roots of the project stretch back to 2000, when local farmer Martin Brown planted 300 bitter damsel seedlings provided by the Forestry Department. He now has a forest of more than 2,000 trees supporting his yams, and helps to promote the scheme to other farmers. He says around 60 have now planted their first damsel seedlings, but the going is slow, and as in West Africa, more needs to be done to encourage farmers to embrace the living yam stick.
“People like to do traditional things,” Dunkley-Fullerton says. “When they see something actually working, that’s when they gravitate to it.”
Banner image:Roots and nodules of a lab-grown yam plant. Image courtesy of Asrat Amele/IITA.
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