Photograph by Sergei Bogomyakov, Alamy Stock Photo
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A species of mesquite tree from South America is growing like wildfire in Morocco and elsewhere in Africa, but people are fighting back.

Photograph by Sergei Bogomyakov, Alamy Stock Photo

An invasive, thorny tree is taking over Africa—can it be stopped?

Mesquite was introduced on purpose from the New World, but the dream of a helpful tree soon turned into a nightmare.

Mohammed Al-Murawih remembers thinking what a joy it would be if the desert was always green. He wouldn’t have to lead his camels on many mile-long migrations in pursuit of pasture, and he wouldn’t run the risk of losing livestock in lean years. Never again would his family go hungry.

So when, about a decade ago, a host of brilliantly lush shrubs began to protrude from the sand and rocks around his home village in North Kordofan, to the southwest of Khartoum, the Sudanese capital, Murawih was jubilant. At last some proper vegetation, he thought, and at last some major sustenance for his livestock, who’d been looking increasing emaciated after frequent droughts. His fellow herders were similarly enamored of this new arrival. In late 2012, the village mosque even offered a prayer of thanks for their good fortune.

It didn’t take long, though, before the community began to have second thoughts. This shrub—a type of mesquite called Prosopis juliflora—was too prolific, too greedy. Its spiky undergrowth wasn’t as useful as they’d hoped. As the problems mounted and the plants multiplied, Murawih soon wished he’d never clamped eyes on this botanical menace.

“When we first heard about this tree, this tree that can grow anywhere, we thought: good, this will bring shade, this will bring food,” he said. “But really it’s not like that. It’s a devil tree.”

The P. juliflora mesquite was once presented as a solution to some of East Africa’s most pressing problems when it was introduced by development agencies through much of the 20th century, starting in the 1920s. By producing foliage and animal fodder in areas with little of either, it was meant to fortify the region’s crumbling drylands. And by holding the sands at bay with its deep, cloying roots, it was envisaged as a much-needed weapon against desertification. Initially, at least, it proved its worth. Some farmers credit their fields’ continued existence to its sand-stopping properties; others value the mesquite as a ready source of charcoal at a time when states are taking tougher stances on tree cutting.

But, in an almost textbook illustration of the perils of invasive species, the mesquite eventually displayed a crueler side. Slowly at first and then more rapidly of late, it’s sprawled across much of Africa. And as it’s colonized tracts of land, the tree has complicated millions of people’s lives. It’s out-competed weaker, more nutritious species, and poisoned livestock who consume its pods. In doing so, it’s harmed herders, the very people it was supposed to help. Its tentacle-like roots have sponged up water in already thirsty districts. Such is the mesquite’s capacity for wreaking havoc that it’s seemingly even contributed to the spread of malaria.

“If you could potentially manage it better, it might be ok, but you can’t. It’s just a pretty nasty plant,” said Arne Witt, coordinator for invasive species at the Center for Bioscience Agriculture International (CABI), who’s spent decades tracking the plant’s spread. “It’s destroying habitats. It’s creating monocultures. It’s not going to stay where you’ve planted it.” The International Union for the Conservation of Nature (IUCN) lists the Prosopis juliflora, which has also settled swathes of Asia and Australia, as one of the worst invasive species.

The mesquite was originally brought to West Africa from its native South America in the mid-19th century, before bit by bit establishing footholds throughout the continent. The tree’s roots, which can burrow up to 50 meters, enable it to search out water in drylands, and its ability to withstand extreme temperatures has allowed it to prosper where other plants wither. With no natural predators outside of its native habitats, the mesquite has expanded across several million hectares in the last few years alone, according to the IUCN. The spread has been particularly dramatic in East Africa since the fierce El Niño rains of 1997-1998, which distributed the plant’s seeds even farther afield.

Land eater, animal killer

At 9 am on a weekday morning in July, the fields around Dulga in Sudan’s Gezira state should be teeming with life. Instead, with planting season fast approaching, a solitary man roams back and forth with an axe. Hacking away at a particularly stubborn mesquite, he strikes root after root. Only when he’s cleared a full tree, a deeply embedded, six foot-tall sapling, does Mohammed Zain Al-Baseer pause for a restorative cigarette.

“This needs so much work that for most people it’s not worth it,” he said, gesturing at the empty expanses around him. “We will spend more to prepare the land than we’ll earn from the crops. It is a shame what a tree can do.”

Farmers in East Africa thought they knew adversity, but in some badly afflicted areas mesquite has made agriculture all but impossible. It’s forced them to spend time and money they don’t have clearing their fields, while guzzling water that their crops desperately need. A South African study suggests that country loses up to 700 million cubic meters (185 billion gallons) of groundwater to this plant every year, an amount comparable to half of New York City’s annual usage. The situation is particularly trying in countries like Sudan, where a recent fuel crisis has deprived many of the use of mechanized diggers, and Kenya, where most farmers lack access to these tools in the first place.

Those land management troubles are, if anything, even more challenging for herders, who are already reeling from desertification and droughts. In swathes of northern Kenya, mesquite is growing so thick, so fast, and so abundantly that it’s blocking animal migration trails. In Garissa, not far from the Somali border, thick mesquite growth along the river banks has prevented livestock from approaching major watering holes.

Officials in some of Africa’s most arid nations say these plants are robbing them of what meager pasture they have left. “It occupies all the space, so the grazing land disappears,” said Dini Abdullah Omar, director-general of Djibouti’s Ministry of Environment. “We have almost none to start with, so this is a tragedy.”

Then there are the implications for livestock health. Mesquite was supposed to be a source of nourishment for animals in drylands—and eat it they have, but not with the intended consequences. The pods are extremely sweet and stick to animals’ teeth. Cattle are suffering from severe tooth decay; camels are contracting diabetes. The tree itself is so formidable that it’s beaten off most other species. Livestock now have little but the dreaded pods to feed off.

“Ideally this shouldn’t be more than 20 to 25 percent of their diet, but somewhere like Baringo, there’s nothing else,” said George Muthike, a senior research scientist at the Kenya Forestry Research Institute, referring to a particularly hard-hit county in northern Kenya. “It occupies whatever land is in front of it.”

But the worst might be yet to come. By colonizing vital grasslands in Kenya and Ethiopia, extinguishing much of its other vegetation in the process, the mesquite has helped push the endangered Grevy’s zebra to the brink. In a bitter twist, the zebra has been one of the inadvertent architects of its own downfall as its droppings act as fertilizer and its grazing helps the seeds spread. And by providing mosquitos with bountiful nectar, the mesquite might be helping malaria advance into new areas. With flowers that bloom for most of the year, the plant looks to be fostering the disease’s transmission, according to several studies, including one in rural Mali.

Can the mesquite be weeded out?

Still, for all the mesquite’s problems, opinion is divided on what ought to be done. As debilitating as it can be, some farmers have grown dependent on its assets. Mahmoud Jamal, a farmer near the northern Sudanese town of Karima, attributes his property’s continued existence to the plant. While many of his neighbors’ farms have crumbled into the desert, the deep-rooted trees he planted around his land appear to have foiled the sands.

“It’s nasty and eats everything. That’s why I call it the National Congress Party tree,” he joked of the Sudanese dictator’s political party. “But it’s good when it’s on your side!”

In Kenya, where the government has imposed a moratorium on tree cutting due to rampant deforestation, the mesquite has been mooted as an undesirable and prolific alternative to struggling native species. It could bring in up to $300 million worth of charcoal, the ministry of environment and forestry suggests. The tree might have timber and biomass energy potential, too. None of this may be sufficient to balance out the drawbacks, the plan’s advocates acknowledge, but with major mesquite contamination and little cash, they feel it’s the best of a bad bunch of options at their disposal.

“Looking at the budgets, the amount of money that will be needed, it may not be possible to get rid of it,” Muthike said. “So looking at the challenges, we have to utilize it.”

Other scientists, however, inist that eradication must be prioritized. Championing its use will only contribute to its spread, they warn.

One proposed idea is to release natural enemies of the plant, such as the evippe moth. But despite assurances from some scientists officials are worried that the moth could end up being a problem of its own.

In the meantime, conditions are ripe for continued spread of mesquite. More climate change-related extremes, like flooding, could carry its seeds far and wide. The tree, too, may adapt—allowing it to spread even farther. It seems likely it will continue to impact one of the world’s most vulnerable regions.