Kenya’s arid north has always stirred the imaginations of those who visit. Its open, scorched bushland distributed over exposed geological formations and crosscut by riverine tentacles never fails to elicit impressions of emptiness and remoteness. To most outsiders, this is a timeless land. It is beautiful but unproductive, so the imaginary goes. It is backward. Its vulnerabilities – drought, famine, conflict, poverty – are inherent. Radical change is needed: a new way of doing things to unlock vast untapped potential and bring prosperity.

This is not a new idea. In Kenya’s north, the idea has been shaped by generations of development workers and policymakers. Its legacy today is diverse, surfacing through transformative large-scale investments and interventions across the private and public sectors. But this vision of prosperity also surfaces in the very earth itself, in the form of an invasive shrub, Prosopis juliflora (recently renamed Neltuma juliflora) or etirae in the local Turkana language.

A kind of mesquite native to South America, Prosopis was first introduced in this part of Kenya in the early 1980s at the height of a catastrophic famine caused by drought. The reason for its introduction, as cited by the NGOs spearheading the planting programmes, was to address a suite of pressing concerns made even more urgent by the protracted drought: fuelwood shortages, soil erosion and a lack of fodder for the livestock of local pastoralists.

These were real problems. But to the organisations who intervened, the issues seemed to suggest that the crisis was not really a product of chaotic environmental shifts or longstanding marginalisation. Instead, catastrophic famine served as evidence of pastoralism’s inherent vulnerability. Confirmation, that is, of a kind of fragility that lay at the heart of local people’s livelihoods and was inconducive to true prosperity. The obligation to respond to immediate hunger – to help – quickly became a desire to change, to improve, to make what was there more ‘sustainable’ or, in the more recent language of development agencies, ‘resilient’. The introduction of Prosopis, then, was part of a wave of interventions that sought to transform pastoralism, setting it on a new path towards a prosperity that is fixed, predictable and under control.

But in the decades since, the shrub has become one of Africa’s worst invasives, strangling rural livelihoods across the continent. Encroaching on farmland, forest and range, it has brought ill-health both to people and their livestock, outcompeting local flora and disrupting longstanding ways of life.

You might think the ideas that led to such a catastrophe would wither with time, but the opposite is true. Like the shrub itself, they’ve grown ever more tenacious, tangling together dissonant things in stubborn sprawling shoots that refuse to offer any resolution. This is a story about the thicket that is left behind, and what it conceals.

The banks of the Kerio river in southern Turkana County, Kenya, covered in dense Prosopis. Photo supplied by the author

For the past 12 years, my research has explored the history of development projects in Kenya’s northwest and the changing course of mobile pastoralism. I’ve interviewed hundreds, perhaps thousands of people, seeking to understand what binds together diverse mobile economies.

When I first began this anthropological work, it was in a thicket of Prosopis on the bank of the Kerio river, which arcs through the plains of Turkana County before draining into Lake Turkana. This is an area, I came to learn, that was once covered in spacious gallery forest, where regular floodwaters washed across cultivation plots laid out on meander scars, depositing in their wake rich alluvial silts. Sorghum, a common grain crop in Turkana, grew here in tall stems and flowed outward from the riverside, carried across plains, hills and scrubland by herders who loaded it into goatskin bags attached to their donkeys. Only in the harshest, cruellest of dry seasons did this resource fail the people of Turkana.

Since the 1980s, the world in which sorghum thrived has mostly been crowded out. The process began when government agencies, supported by NGOs and international donors, first introduced Prosopis to combat desertification. Projects supported by the Kenyan Forestry Department and the UN Food and Agriculture Organisation planted the shrub across riverine areas and rangelands, promoting it as a natural solution to ecological and economic challenges. Before long, Prosopis had invaded native forests and areas cleared for cultivation. Then reports began to emerge of serious gastrointestinal problems and tooth decay in the livestock who ate it. By the early 2000s, farmers and herders across northern Kenya were voicing concern, but it was not until 2008 that the Kenyan government classified the plant as an invasive species.

‘Porridge. People were fat from eating it. I can’t remember the last time we had it here’

When I arrived in Turkana in 2012, the Kerio river was strangled in relentless green. So were the old cultivation plots, which now lay fallow – it had been impossible, for many, to clear them in time for planting. Thick green walls towered over the ghosts of past rhythms and relationships.

Emeri Lowasa, whom I have interviewed on innumerable occasions, and whose family I’ve lived and worked with for many years, began cultivating this land in the 1960s when she was a young woman newly married. Now her home stands like a rocky bluff in a rising tide.

When I interview her about her family’s sorghum farm, she sits delicately in front of it, serene amid a frenetic sea of leaves and thorns. Her grandchildren cut in and out of pathways that disappear down to a river she can no longer see. ‘Porridge,’ she says, waving her hand as though in disbelief, ‘sorghum from the farm mixed with milk poured out from gourds. People were fat from eating it. I can’t remember the last time we had it here.’

It is not porridge that nourishes those settled along the Kerio now, but often a kind of paste called Plumpy’Nut, a peanut-based emergency food made by a French company and distributed sporadically by aid agencies such as UNICEF to treat malnutrition. The world in which packets of Plumpy’Nut circulate – the settlements dotted along the banks of the Kerio in Turkana – is one radically transformed by a host of other interventions, too, all of which have come to be tangled up in the steady invasion of Prosopis.

These settlements now abound with churches, schools,........

© Aeon