Abandon the idea of ‘great green walls’

For more than a century, people around the world have tried to stop “encroaching deserts” by planting “green walls” of trees, sometimes thousands of kilometers long. These efforts have failed. Tree survival rates are often less than 30 percent, biodiversity has decreased, water tables have dropped, local livelihoods have been disrupted, and already-poor people have been further marginalized.

Despite this problematic history, the vision of a green wall of trees to hold back the desert remains very popular, with billions of dollars pledged and spent in China on the Three Norths Shelterbelt Program, and in Africa on the Great Green Wall Initiative.

As ecologists and geographers who have worked in the drylands of Africa and Asia for decades, we argue that the idea of “green walls” is not only misguided but dangerous. Bound to fail for both social and ecological reasons, the green wall idea reinforces false assumptions about the nature of environmental change in the world’s drylands — lending powerful support to misguided notions that top-down, technocentric interventions are the best. We should abandon the idea to make room for more realistic, evidence-based and effective interventions.

Scientists today define desertification as the degradation of arid lands caused by local human mismanagement. This is different from aridification, which is the loss of vegetation due to climate change. We now know that desertification doesn’t cause the edges of deserts to march forwards; rather, desertification happens in patches, in areas of high and more persistent land pressure from grazing, farming and firewood collection. There’s no need to stop the forward march of desertification — because there isn’t one. Although some desert boundaries might be expanding due to aridification from climate change, water-hungry trees do little to combat that. In other words, a wall of trees isn’t suited to fix either issue.

Green wall programs are fed by an erroneous belief that planting trees anywhere will always improve climates, water supplies and biodiversity, while preventing erosion and mitigating climate change. This tree-centric belief has its origins in 18th century Europe; by the 19th century it attained the level of ideology, with forest cover equated with civilization. The concept was used by Western powers to justify a wide variety of colonial and imperial projects in inappropriate environments around the globe.

A tree-focused worldview that equates ecological improvement with tree cover, although valid for some ecosystems, does not translate well to dryland ecologies that were not originally covered with forests but rather with steppes, grasslands or savannas. Their replacement with rows of trees, often all of the same species, is generally not an ecological improvement.

Research has shown that trees at higher densities can compete with native vegetation, which can lead to reductions in moisture availability, biodiversity and groundcover protection from erosion, with limited climate change mitigation benefits. In China, where more than a quarter of the nation was targeted for tree planting from 1952 to 2008, surprisingly little evidence has been found for a positive impact of planting efforts on changes in vegetative cover or dust storms. More comprehensive assessments of the ecological effects of mass tree-planting efforts remain elusive, given the limited data collected or shared by the governments and organizations that support these programs.

Green walls are problematic not only ecologically but also socially. Promoters often give the impression that these dryland areas are basically empty. The reality is that they are almost always populated by people who make good use of their drylands and, understandably, often resist the replacement of their fields or rangelands with tree plantations and fences.

Green wall projects also provide an opportunity for the powerful to control and exclude the most vulnerable through the guise of environmental rehabilitation. In Niger, for example, local elites have used green wall programs as an opportunity to take over (and profit from) formerly public lands. In Algeria, the Green Dam program was used by the government to reduce and control pastoralism — the practice of moving with livestock over large areas, which has been administratively burdensome and erroneously seen as “primitive.” In China, too, the Three Norths Shelterbelt Program has, in combination with other programs, removed pastoralists from their rangelands and employed them in tree-planting instead.

Pastoralism has been long misunderstood and devalued. Ecologists now recognize that mobile livestock husbandry promotes social and ecological resilience in the face of climate change. Acting against it does a disservice to dryland communities.

Policymakers must recognize that drylands are homes to people who do not usually degrade the landscapes upon which they depend. Development programs led by local people to meet local needs show greater promise than top-down technocratic efforts. Such programs may include technical interventions like rangeland protection, irrigation or even tree-planting, if focused on the protection and planting of native trees. Such interventions must respect and support local livelihoods to be successful, as is illustrated by a water program in Chad that has begun to accept the importance of pastoral mobility in its highly variable drylands.

The funding of green wall programs has at times helped to support effective interventions. But their success has come not because of their ties to the “great green wall,” but in spite of it.

The myth of green walls holding back the desert continues to garner strong public interest and generous funding despite being discredited by contemporary ecological science. It should be discarded. Instead, we need to move forward with alternative dryland conservation and development efforts that are more ecologically appropriate, and that support local sustainable livelihood strategies in the face of global climate change.