THIES, Senegal — The instructions were clear – farmers should rip out the scrappy Guiera senegalensis shrubs, clearing their fields before the planting season. The humble, hardy, leafy bursts of green somehow thrived in Senegal's semi-arid climate, just below the Sahara Desert, popping up knee-high out of the sandy soil like a green tumbleweed.

They must be competing with crops for water, the logic went.

The policy began under French rule, at least as far back as the 1950s, and continued into the 1970s. The advice to uproot the shrubs has since fallen off the books, though today many farmers clear their fields by burning the shrubs before each planting season.

But now, there's a new attitude among a small but growing contingent of farmers and researchers: Keep the shrubs. Prune them, trim them down to ground level, plant your crops around and even right over them – the deep roots of the shrubs won't mind.

It goes even further: Plant more shrubs in your fields, to the tune of about one per three square feet.

Your enemy turns out to be your friend

The shrubs are not enemies, say American and Senegalese researchers – in fact, they'll draw up more water for your crops, through a process called hydraulic lift, also known as hydraulic redistribution. At night, when photosynthesis stops, excess water drawn up to the surface from their deep roots leaks out, nourishing the soil near the surface.

Guiera senegalensis – and its sister shrub, Piliostigma reticulatum, which is similar but thrives in Senegal's wetter south – are tough plants. Their survival in harsh conditions in Senegal and across West Africa's semi-arid Sahel region has captured the fascination of Senegalese and American researchers, and is now leading to agricultural insights.

When farmers turn to the Sahel's sandy plains to plant their crops during the rainy season, the shrubs – which have been growing here for thousands of years – create "fertility islands" by locking in topsoil, cooling the surroundings and bringing up water to the surface from deep underground beyond other crops' natural reach. Their leaves and branches, if pruned, shredded and spread on the ground, provide fertilizing biomass. Perhaps most important, the plants are indigenous to West Africa, and, when they're trimmed, their small branches don't block the basic horse- or donkey-pulled plows and weeding tools used by small-holder farmers.

"Farmers are faced with soil degradation – very, very low-fertility soils – and climate change, and especially drought," says Ibrahima Diedhiou, a professor at the University of Thiès who has been studying the shrubs for two decades, and now collaborates with American scientists. "They can use [these shrubs] so they can reduce their vulnerability to food insecurity, because the shrubs can improve crop yields, protect the soil and reduce vulnerability to drought, which is the big challenge in our local context."

With this new understanding – years in the making – researchers now understand how and why the shrubs are good for other plants or crops surrounding them. And there's a nascent campaign to bring about widespread use of the shrubs.

It's a critical matter. Weak soils in the semi-arid belt below the Sahara Desert have been degrading for years from heavy fertilizer use and expanding populations that make it difficult to let fields lie fallow so soil can regenerate, agricultural experts say. Amid a changing climate, farmers in countries like Senegal, Burkina Faso and Mali are also facing increasingly erratic rainfall.

"[Using the shrubs] provides farmers with resilience options and adaptation to what's coming, and what's already here" in regards to climate change, especially increasing droughts, says Amanda Davey, CEO of the Agro-Shrub Alliance, a nonprofit spun off from Ohio State University research on the shrubs. "Without these kinds of solutions that are really locally driven, and without resources that are locally available, it's going to be really dire."

He's a shrub lover

Sidy Diakhate is a believer in the power of the shrubs. He's an agricultural consultant and a farmer. His 6 acre farm sits on the flat, sandy plains of Khombole – about 60 miles east of the rapidly expanding capital, Dakar, on the Atlantic Ocean.

His fields are covered with the hardy shrubs. And they're the reason, he says, his plots of peppers, eggplant and cabbage have grown so well this season.

After years of study, people like Diedhiou and Diakhate – who did his Ph.D studying how the shrubs can act as natural pesticides by keeping nematodes at bay – are now trying to move their research out of the classroom and into the hands of farmers.

Last fall, shrub enthusiasts, farmers, and students gathered for a field day put on by the Agro-Shrub Alliance and the University of Thies. In the testing fields, the agriculture attendees were invited to look upon millet – a staple crop in Senegal – grown in shrub-filled fields. The stalks towered over much smaller plots of millet grown apart from the shrubs. Experimental millet plots incorporating shrubs have seen 105% and 128% yield increases when cohabitating with P. reticulatum and G. senegalensis respectively, OSU researcher Richard Dick says. Using shrubs also eliminates the need for expensive and environmentally costly fertilizer.

A new agricultural philosophy

The shrub intercropping method, which researchers call the "Optimized Shrub System," is a turn away from conventional advances in agriculture, which incorporate large-scale, mechanized agriculture practices that rely heavily on fertilizers. In addition to the costs associated with industrial agriculture – out of reach for many smallholder farmers – the land in the Sahel has been under pressure from expanding fields and weakening soils for some time, says Salima Mahamoudou, a research associate for the World Resources Institute who is not involved in the research.

"There was the belief that in order to increase productivity, we needed to reduce all competition on the land, so we needed to cut off trees and shrubs," she says. "And we learned that it actually had the complete opposite effect. ...These areas were no longer able to retain moisture."

Using native shrubs like P. reticulatum and G. senegalensis echoes success seen in other parts of the Sahel that have reintroduced indigenous shrubs into farmers' fields, Mahamoudou says. "These are low-cost practices that farmers can do" to increase yields, increase soil health, regreen the land, and reduce fertilizer runoff.

Managing the shrub

The Agro-Shrub Alliance is currently working on scaling up the reach of OSS across Senegal. But it won't be easy. The shrubs only need to be planted in the fields once. Beyond that, they require upkeep to both protect them from grazing animals and also when it comes to pruning and chopping the leaves and stems for biomass. All of this is added labor for farmers, Diedhiou notes. Specialized mulching machines – like those presented at the field day – could help to mulch the leaves and stems, but the equipment is not widely available. And farmers will need to be guided by agricultural extension agents through the first year as their shrub seedlings mature and they learn how to incorporate them into their farms. All of this will require concerted political will, time and effort, and funding.

Still, success has been seen in other parts of the Sahel where farmers have mixed shrubs and trees into their fields as part of a process known as "farmer managed natural regeneration," notes Mahamoudou. "These were desert valleys that were completely regenerated and [brought] back to productivity by smallholder farmers," she says.

Even if farmers can't manage shrubs on all of their farmland, they could at least do so on one plot, says Davey. "I see this as a kind of insurance. Well, if you can't do all 10 hectares, you do one hectare, and you get food for your family."

For now, Diakhate says his neighbors have been inquisitively examining his vegetable fields. A handful have asked him if they can get in on the method themselves, and he's keen to bring them into the fold.

"They are very curious," Diakhate says. And this natural, bottom-up curiosity and buy-in – combined with state support – is what it's going to take to get more people to adopt these practices and overcome the labor barriers, he says. "I think we can try to build a new future using this type of shrub."

Nick Roll is a freelance journalist based in Dakar.