By Mark Hillsdon
Yams are regarded as one of the globe's most crucial crops. This tuberous, nutrient-packed root belongs to the genus. Dioscorea The yam flourishes within the tropical zone of West Africa, with exceptions found in the Caribbean region and certain Asian nations like Japan.
In 2023, approximately 90 million metric tons of yams were cultivated worldwide. according to data From the Food and Agriculture Organization of the United Nations, yet their cultivation method utilizing conventional "yam sticks" is currently viewed as a significant contributor to deforestation.
"The yam is a vine," explains Eric Owusu Danquah, a researcher with Ghana’s Council for Scientific and Industrial Research (CSIR). "It needs to grow upwards to allow its leaves access to sunlight." This process relies heavily on "yam stakes" which are typically about 2 meters (approximately 6.5 feet) tall and frequently sourced from surrounding woodlands—a habit that environmental advocates like Danquah argue hinders tree growth and forest regeneration. These stakes have an operational lifespan of just one or two planting cycles. Consequently, those involved in cultivating yams, along with researchers and community-based forestry organizations, are exploring alternative methods for these climbing plants to ascend.
A yam farm located in northern Ghana features wooden stakes that help support the growing yam plants. These "yam sticks" are typically sourced from nearby forests. The image was captured by Attah Mohammed and shared on Wikimedia Commons under the license CC BY-SA 4.0.
The yam develops as a tuber, with Ghana and Nigeria accounting for over 80% of global production, based on information from Danquah. Cultivating this crop is quite challenging. Besides needing stakes, it demands rich soils; hence, farmers typically shift fields annually, enabling them to let lands rest and permitting nutrient levels in the earth to replenish.
Growing plants requires substantial manual effort; you plant seed tubers or slips—cuttings obtained from other yams—in soil heaps that typically contain a center of nutrient-rich compost to facilitate initial development.
Each yam requires individual support through staking, and over the past 15 years, Danquah has been exploring climate-resilient methods to decrease Ghanaian farmers' reliance on traditional yam stakes. He reports that trials using ropes proved effective, cutting down stick usage by half without affecting crop output. However, these ropes turned out to be expensive for local farmers, so finding an affordable alternative became necessary. This led him to investigate a leafy plant known as the pigeon pea. Cajanus cajan ) began.
Yams are harvested by farmers in Nigeria. The image is provided courtesy of Asrat Amele/IITA.
He explains that the plant functions like a live yam stake. Besides eliminating the necessity for cutting firewood from forests, the pigeon pea offers additional advantages. Similar to other legumes, this crop enriches the soil with nitrogen and continuously captures carbon due to its living nature. Additionally, the plant yields nourishing seeds that farmers can market. Regularly trimming the bush promotes its growth into a tall, upright form, while the pruned sections serve as rich-nutrient mulch atop the yam hills. Danquah highlights that this practice is crucial since much of Ghana's yam cultivation—primarily managed by small-scale farmers operating on under two hectares (about five acres)—relies heavily on affordable natural resources rather than costly synthetic additives.
However, even with numerous advantages, cultivating yams supported by pigeon peas hasn’t moved beyond the demonstration stage. "Scaling up is essential," states Danquah. "Currently, the uptake remains quite minimal... We require funds to educate farmers; we must engage directly with yam-growing communities."
Currently, much of the yam funding is directed towards disease research and developing seed-rich variants. However, Danquah believes that part of these funds should also go towards motivating farmers. He states, “In order to encourage farmers to embrace beneficial practices for combating climate change and producing robust crops, they must receive incentives for their efforts.”
Plants from the yam family cultivated with pigeon peas used as supports in Ghana. Image provided by Eric Owusu Danquah/CSOR.
Asrat Amele works as a yam breeder at the International Institute of Tropical Agriculture (IITA) located in Abuja, Nigeria. Additionally, she has explored various alternatives to the traditional yam stick with aims to curb deforestation and assist yam growers adapt to climate change impacts.
Amele has experimented with various options including plastic stakes, known for their durability of up to four years; however, these tend to warm up under sunlight and damage the vines. Additionally, the vines find it difficult to attach themselves due to the slickness of the stakes. Similar to practices in Ghana, Amele has utilized ropes as well. However, owing to high levels of moisture and temperature, these ropes usually do not survive beyond a single growing period according to him. Furthermore, he is considering an innovative biodegradable mesh imported from Japan —a nation that highly values yams— yet he notes that such material might be cost-prohibitive for many Yam growers within Ghana.
Shifting weather patterns are also altering perspectives. Traditionally, the yam is a crop suited for forests, thriving in fertile soils with abundant rainfall and high humidity. However, according to Amele, "the rain has become unpredictable." Additionally, he notes that population expansion and higher demand for yams are exerting stress on farmers, making it unaffordable for them to let fields lie uncultivated—a practice necessary for restoring soil health. As Amele explains, "Farmers must continuously cultivate the same plots each year," leading to diminished yields due to depleted soil fertility.
"These transformations push yams into more open areas," Amele explains, gesturing towards an area where shrubland turns into savanna, with few trees present. "Yams have the ability to adjust to various habitats," he continues, noting that hardier varieties along with climate-resilient farming practices enable them to thrive in these expanded zones.
For example, IITA is working on varieties like the dwarf yam, which has vines measuring only about a meter (3 ft) tall and does not require staking for support.
By removing the requirement for stakes, these yams can enhance spatial usage and offer possibilities for mechanized planting and harvesting, leading to greater efficiency and scalability in yam farming.
The International Institute of Tropical Agriculture (IITA) is exploring methods to enhance the sustainability of yam farming. The image is provided courtesy of Asrat Amele/IITA.
Even though it occurs on a smaller scale, yam cultivation in Jamaica continues to contribute to the depletion of the nation's natural woodlands. As per Donna Lowe, who heads forest science and technical services at the Jamaican Forestry Department, farmers using young saplings as yam stakes "are impacting the potential growth of the forest," since these immature trees won’t reach maturity and replenish the larger ones being cut down by loggers.
She explains that over time, the degradation of the forest will ultimately result in deforestation," She further mentions that an active but frequently illicit trading activity involving yam sticks has emerged as well. This surge is facilitated by newly constructed mining roads providing entry into formerly remote and untouched regions.
[T]he makeup and architecture of the forest are completely destroyed," Lowe states. "Farmers require a practical alternative.
In Cockpit Country, where Jamaica primarily grows yams, the answer might be found in a local tree species known as the bitter damsel. Simarouba glauca ) and a shift towards agroforestry.
As per Arlette Dunkley-Fullerton, who chairs the South East Cockpit Country Local Forest Management Committee Benevolent Society, bitter damsel trees are simple to cultivate and demand little maintenance after being well-established. Additionally, these trees significantly contribute to sustaining forest coverage, thereby aiding wildlife conservation and preventing soil degradation.
Similar to how the pigeon pea enhances soils in Ghana by contributing nitrogen, the bitter damsel improves the ground by decomposing and providing nutrients, thus decreasing reliance on synthetic fertilizers. According to Dunkley-Fullerton, each tree can accommodate as many as six vines, shielding their foliage from intense sunlight and powerful gusts of wind. Additionally, the bitter damsel serves well when planted alongside shade-loving plants such as ginger.
The bitter damsel (Simarouba glauca) is a flowering tree indigenous to the Caribbean region. The image was provided by Ajtjohnsingh through Wikimedia Commons under the CC BY-SA 4.0 license.
Typically, farmers "enter the forest and fell the saplings," according to Dunkley-Fullerton. "Utilizing living yam stakes allows farmers to lessen the strain on the natural woodland, aiding in the conservation of the area’s abundant biodiversity."
Her panel has determined that approximately 800 to 1,000 yam sticks are required per acre of farmland on average. A single tree with a trunk width of 3-4 inches (7.5-10 centimeters) can produce anywhere from four to six yam sticks, indicating that as many as 200 trees may need to be felled annually—every alternate year—to support cultivation over an acre. According to Dunkley-Fullerton, advocating for living yam stakes instead might conserve between 2,660 and 4,000 trees each year throughout Cockpit Country.
The origins of this initiative date back to the year 2000 when local farmer Martin Brown cultivated 300 bitter damson saplings with support from the Forestry Department. Today, he boasts over 2,000 trees forming a woodland that aids in growing his yams and encourages others to join in. According to him, about 60 farmers have started planting these initial damson seedlings; however, progress remains gradual. Similar to efforts in West Africa, additional measures must be taken to motivate more farmers to adopt the live yam sticks method.
Dunkley-Fullerton states, "Individuals have a penchant for adhering to conventional practices. Once they observe these methods functioning effectively, they tend to be drawn towards them."
Banner image: The roots and nodules of a laboratory-cultivated yam plant. The image is provided courtesy of Asrat Amele/IITA.
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