Why trees could bring water back to the Sahel

Here stands the Great Green Wall: Part 2

Vegetation in the Sahel region is composed of mainly stunted and scattered trees, shrubs, bushes and grasses. Daniel Tiveau, Flickr
23 October 2019
Natasha Vizcarra
23 October 2019
Natasha Vizcarra

The story is the second of a three-part Landscape News series on the Great Green Wall.

“I must confess, I’m more optimistic about the Sahel now than I was 40 years ago when I started working in the region,” says Chris Reij, a Dutch geographer and senior fellow at the World Resources Institute (WRI).

Reij has decades of experience in the restoration of degraded land in Africa’s semi-arid regions where the Great Green Wall initiative (GGW) has been ongoing since 2007. To combat climate change and prepare for a future in which the continent will need to support a population more than double what it is today, the GGW aims to create a mosaic of green and productive landscapes stretching 15 kilometers wide and 7,775 kilometers across the Sahel and Horn of Africa.

“Forty years ago, we didn’t know what to do and how to do it,” he says. “Now we do, and there are many big and small sustainable land management successes in the Sahel, which was not the case 40 years ago.”

When Reij began working in the Sahel in 1978, the region was reeling from a long drought that began in 1968 and would last through the 1970s and ‘80s. Rainfall over most of the Sahel had decreased by 30 percent. Scientists describe it as “the most dramatic drought in any region of this large an extent observed in the 20th century.” Over 100,000 people died from food and water shortages.

Yet, a farmer in Burkina Faso and a staff member of Oxfam International were meanwhile experimenting with traditional farming techniques to restore degraded land. In time, these techniques would inspire many successful restoration projects in the western Sahel.

Mathieu Ouédraogo, who then worked for an Oxfam-funded agroforestry project, built water catchments by laying lines of small stones on contours across fields. Slowing down water flow gave the dry, degraded earth more time to soak in the rain. The accumulated silt also served as perfect nurseries from which to sprout seeds.

Burkinabe farmer Yacouba Sawadogo, meanwhile, figured out how to improve the traditional practice of digging zaï holes for planting not only by making them bigger and deeper but also by filling the pits with manure to provide nutrients for the plants. He grew sorghum, corn and millet this way, yielding crops aplenty. But he also planted the zaï holes with seeds for species more unexpected in these arid agricultural landscapes: trees.

And all of this in the midst of uncontrollable drought.

This interplanting of crops and trees was later studied by researchers and dubbed farmer-managed natural regeneration, or FMNR, a form of agroforestry that involves famers in protecting and managing the growth of trees and shrubs that regenerate naturally from root stock or from seeds dispersed in animal manure. It’s an easy, low-cost way for farmers to increase the number of trees in the fields.

Sawadogo had generously shared his techniques with other farmers in his region and international visitors, organizing zaï trade fairs that started small but steadily grew. The markets featured presentations of plant varieties and tools that worked well with the zaï technique. There were also talks about local issues and new developments in agriculture. To this day, farmers and nongovernmental organizations credit Sawadogo’s technique as integral to the restoration of tens of thousands of hectares of degraded land in Burkina Faso and Niger.

“Yacouba’s impact on restoration in the Sahel has been greater than that of all national and international experts taken together,” Reij said in 2018 when Sawadogo received an international award for his work.

A method of field irrigation in the dry Tigray region of northern Ethiopia. Ake Mamo, World Agroforestry

The Sahelian water’s keepers

Now, the mixture of trees and crops, known as agroforestry, is a widespread concept, with conglomerates such as Nestlé and Mars Inc. incorporating it into their production of global commodities like coffee and chocolate. And it’s a crucial component of creating the GGW.

But at the time of the drought, and before Sawadogo’s successes, on-farm trees were largely regarded as a nuisance in the Sahel. This is in part due to the belief that trees divert water away from crops. However, recent studies have suggested that trees in fact provide more benefits that disadvantages to agricultural landscapes, especially in the Sahel’s arid landscapes.

For example, a 2014 study suggests that the replenishing of groundwater improves with increasing proximity to trees on farmland. The researchers also found that leaf litter, the presence and movement of soil organisms such as worms and insects, and cooler microclimates near and under trees promote better water and air flow within the soil. 

In a more recent study, researchers compared soil water drainage totals in an agroforestry parkland in Saponé, Burkina Faso, and found that under high rainfall intensities, daily soil water drainage was 13 times higher in areas with tighter tree cover compared to more open areas. The study suggests that tree cover increases soil and groundwater recharge and thus can slow down land degradation.

“We know trees provide many benefits, and there has been some widespread misunderstanding of the role of trees in influencing how a landscape interacts with water,” says Douglas Sheil from the Norwegian University of Life Sciences and a senior associate with the Center for International Forestry Research. “When used in a suitable way, trees can help a landscape capture and store more water than otherwise.”

“We also see that trees facilitate larger scale moisture recycling,” says Sheil. “Most rain that falls in Africa derives from moisture that has evaporated off the land, not the ocean, and much of it was taken up and transpired by trees. So this rainfall is very sensitive to land-use choices.”

Faidherbia, a type of acacia tree here shown in Mali, helps improve crop growth by helping maintain levels of nitrogen in the soil. Ake Mamo, World Agroforestry

Law of the trees

Another reason Sahelian farmers kept trees out of their farms was an old law – a relic of Africa’s colonial past – that declared all trees and other natural resources belonged to the state.

Related to this, a social perception arose that a farmer was considered modern if he was cultivating his crop on land without trees.

“There were programs that tried to convince farmers to remove trees from their fields,” says Reij. “So it was a little bit like trying to copy agriculture in temperate West Europe and introduce the same principles in the Sahel.” The sentiment was that you needed to get trees out of the way if you wanted to use tractors for plowing your fields.

But beginning around 1985, with the government of Niger preoccupied with a series of inner crises demanding its attention, farmers in Niger began to have more freedom, cultivating the perception of their on-farm trees as property. This motivated them to invest in the protection and management of trees – especially as these assets were regenerating naturally on their land. Niger’s Forestry Service is now developing a proposal that should create more clarity in existing forest legislation that farmers have ownership rights to their on-farm trees.

“The change in thinking that was necessary was that trees are part of an agricultural production system,” says Reij. “Farmers do not protect on-farm trees for environmental beauty or to sequester carbon. They protect and they increase the number of on-farm trees in order to be able to intensify agriculture. By doing so, they are building more complex farming systems.”

The adoption of FMNR and positive developments in Niger’s forest law has contributed to the regreening of more than 5 million hectares in Niger’s regions of Maradi, Zinder and areas in the south.

Beyond Niger, on-farm trees have increased in Mali’s Seno Plain, and farmers in Malawi have also started to invest in on-farm trees.

“Niger for decades has been the second-poorest country in the world,” says Reij. “But it is also, according to the U.N. Development Programme, the country with the biggest positive environmental transformation in Africa. It’s amazing what has taken place. Every time I go to Niger, I have to pinch my arm.”

A traditional healer in Burkina Faso relies on specific fruit trees on his farm to make medicines to treat diseases such as malaria in his community. Ollivier Girard, CIFOR

Preparing for battle

These success stories and new ways of restoring degraded lands in the Sahel give countries and communities hope that the GGW isn’t just a quixotic dream. However, Reij feels that the program’s larger organizing bodies have not yet done enough to learn lessons from existing successes in the Sahel, and they have not replicated success stories to the degree warranted by the Sahel’s urgent realities.

“The only way to win the battle against land degradation in the Sahel is to mobilize and motivate millions of land users to invest in on-farm and off-farm trees,” says Reij. “This will only happen if land users and their communities perceive a clear right to trees. Forest laws in most countries do not yet give them rights to trees.”

Reij strongly recommends quickly increasing the scale of existing successes in the region. “If you look at the rates of demographic growth and the current state of the environment in most countries,” he says, “and if you look at the rate of degradation, then the one thing that should be done is to try to achieve scale in your interventions.

“And unfortunately neither donor agencies nor the different countries have given adequate thought to scaling strategies.”

Who makes the decision about scale in GGW programs? And why hasn’t scale been an important part of the program’s 12-year history? The answer might be found in the way the GGW is set up.

Next: Will the Great Green Wall’s architecture support its future?
Previous: As the Sahel dries, the Sahara advances


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