Restoration of Drylands: ‘Planting’ trees does more harm than good

A native of arid lands in Central and South America, the woody shrub, known locally as mathenge, was promoted by the Kenyan government and the UN Food and Agriculture Organization to help restore degraded drylands. At first, mathenge helped prevent dust storms, supplied ample wood for cooking and construction and provided fodder for animals, said Simon Choge, a researcher with the Kenya Forestry Research Institute in Baringo County. But after the El Niño rains of 1997, things changed. 

Mathenge seeds dispersed widely, and without any local fauna adapted to eat the foreign tree, it spread aggressively. Impenetrable thickets overran grazing pastures, displaced indigenous biodiversity and depleted water sources. The trees’ thorns pierced the hooves of livestock, while its sugary pods caused tooth decay and loss, sometimes leading to starvation among the animals it was meant to nourish. “Now, people have no livelihoods,” Choge said. Large scale tree planting programs have been heralded as an effective way of drawing CO2 from the atmosphere. Yet in the verdant vegetation that has transformed Baringo’s grasslands lies a stark warning: Sometimes, planting trees can do more harm than good. 

Since colonial times, misconceptions about drylands and disregard for indigenous knowledge have led to trees sometimes being planted where they do not naturally occur, devastating endemic ecosystems and livelihoods. And with fresh emphasis on tree planting as a low-tech way of tackling the climate crisis, some experts are concerned these same mistakes will be repeated. 

Drylands cover 40% of the earth’s land surface, mostly in Africa and Asia and include savanna, grassland, shrubland and desert biomes. These are areas characterised by water scarcity, seasonal climatic extremes and unpredictable rainfall. But they are rich in plants and animals uniquely adapted to these extremes. Today, they are home to 2.3 billion people and half the world’s livestock. Nearly half of all cultivated lands are in drylands, and 30% of cultivated plant species are native to them. Over millennia, people have adapted to the extremes of drylands, too. They have done this by learning how to manage risk and harness variability and uncertainty in their favor, said Ced Hesse, an expert on the livelihoods of dryland areas at the London-based International Institute for Environment and Development. From exploiting seasonal variations to maximise food productivity, to selectively breeding animals that can endure challenging conditions, dryland inhabitants “developed incredible indigenous knowledge of how to work with nature to their benefit,” said Hesse. 

In her book “The Arid Lands: History, Power and Knowledge,” Diana K. Davis, an associate professor of history at the University of California, Davis, argues this knowledge has historically been devalued and disregarded because of the colonial-era assumption that drylands were wastelands and mostly treeless due to overgrazing and deforestation by locals. Davis says such assumptions were common across French and British colonies — from Maghreb to Southern Africa and Middle East to India — and used to justify policies that marginalised significant numbers of indigenous people. 

At the same time, these assumptions paved the way for drylands to be appropriated for other land uses, like croplands and conservation, said Susanne Vetter, an associate professor in plant ecology at Rhodes University in South Africa. It was from this context that tree-planting — often with invasive foreign species — emerged as a solution to drylands’ perceived problems. Like the social legacy, the environmental costs of land conversion were high: degradation, salinisation, loss of productivity and biodiversity, spread of invasive species and depleted water sources.