11/09/2023
For more than a century, people around the world have tried to stop “encroaching deserts” by planting “green walls” of trees, sometimes thousands of kilometres 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 marginalised.
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, techno-centric 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 civilisation. 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 organisations 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.
https://science.thewire.in/environment/abandon-the-idea-of-great-green-walls/
Cookswell Energy Saving Jikos Ministry of Agriculture & Livestock Development KALRO University of Nairobi
@ Cookswell Jikos – GRASK/0059
@ Mr. Teddy Kinyanjui - GRASK/0059
