- Recent population surveys show continued decline in two desert-adapted succulent tree aloe species, with conservationists fearing for the state of an understudied third species.
- A years-long drought has accelerated spreading dust-bowl conditions following decades of mining and heavy grazing, with grave consequences for endemic succulents.
- A conservation triage should prioritize cultivating at-risk species in nurseries and botanical gardens, many of which are unlikely to survive reintroduction into their natural habitats.
Sometimes words fall hopelessly short. This might explain the silences between the two botanists as their vehicle crunches over a gravelly Richtersveld moonscape, a desert that straddles the South African and Namibian border along the Orange River. “We’ve just arrived in the Namaskluft,” says Wendy Foden, recording her observations in a tone that’s oddly neutral, given the circumstances.
“We’re driving through an avenue of mostly dead Aloidendron ramosissimum,” she goes on above the growl of her pickup truck’s diesel engine. “Never seen anything like this.”
Later, she will say it was like driving through a graveyard.
Each dead tree is a tombstone, marking where the bushy aloe once thrived. Each is a sun-cured skeleton, long having shed the fleshy canopy of olive-green leaves that were reservoirs of water.
Like any graveyard, some of the tombstones have toppled.
“There’s a live one … But there’s literally hundreds of dead … This is insane.”
Fading hope
For two decades, Foden, a specialist climate scientist at SANParks, South Africa’s national conservation authority, has been tracking the common quiver tree, Aloidendron dichotomum, a species listed as vulnerable on the IUCN Red List.
Foden’s study of these succulents (from the same family as aloe vera) was prompted by reports of the plants dying off in great numbers in Namibia. She’s spent the intervening years visiting sites across the species’ full range, from the Brandberg Mountains in Namibia down to the South African town of Nieuwoudtville, about 1,400 kilometers (870 miles) south.
When she started her surveys to monitor growth, survival rates and seeding success, she expected to find the usual culprits causing harm: damage from domestic livestock herds or wildlife such as porcupines or baboons, or disease.
What her data showed, though, was that something else was at play. The highest numbers of deaths were in the hotter, far northern parts of the species’ range. Mature trees and seedlings in the cooler south were thriving.
At the time, ecologists theorized that species would likely move poleward as their climatic envelopes changed in response to carbon pollution and rising global temperatures. There were already a few examples of animal species doing this in the Northern Hemisphere, such as the red fox moving into the Arctic fox’s territory in Canada, and some European birds shifting in a similar direction.
“[This] was one of the first examples of a plant globally [responding in this way], and certainly the first in Africa and in an arid system,” says Foden, who is also an adjunct professor at Stellenbosch University in South Africa. “One of the key questions that came out of that is: would the tree be able to track its range as parts of the range were lost on the hotter edges?”
Twenty years on, an answer is emerging. Foden and doctoral researcher Kayleigh Murray’s most recent survey numbers have yet to be published, but their first sweep of the data shows that the trend evident in previous years’ studies continues: the trees are dying on their hotter northern edge, and the head count is looking increasingly grave. In the early 2000s, Foden didn’t need a category for “deaths between 75 percent and 100 percent”.
Now she does. “We’re seeing even more die-off in the hotter range edges.”
They’re exploding in their cooler southern reaches where conditions are becoming warmer and more favorable for their survival. But while existing quiver tree forests are growing more abundantly, the trees aren’t claiming new ground. “We’d hoped to see them shift further south, and some colonization in newly suitable areas, but sadly, we see no evidence of that. We’re still increasingly losing populations and range up north, and we’re not expanding south.”
And there are worrying signs that vital portions of the quiver trees’ habitat may not hold up to a changing climate.
On that early September 2024 morning, Foden and Murray are headed to do a run-of-the-mill population survey at Namaskluft. The last time she was here, in 2003, the population of a closely related species, the maiden’s quiver tree (A. ramosissimum), was in good shape.
This time, the scene floors them.
Ignition point
Foden and Murray are among several research teams that travelled into the Richtersveld area between 2022 and 2024 to study the fallout of the drought that gripped Southern Africa between 2015 and 2021.
They’re finding catastrophic die-offs of three sister species of quiver tree, an alarming warning of pressures that are killing off vegetation across an arid but once-verdant area. Plant life used to be so abundant here, mostly shin-height dwarf succulents, that it drew wild herds of gemsbok (Oryx gazella) and springbok (Antidorcas marsupialis), among others, and their hunters, and domestic animals tended by Indigenous shepherds, and more recently commercial farmers.
The quiver trees, named after their branches, which hunter-gatherers used to hollow out and close off with animal hide so they could carry their arrows, are the charismatic personalities that most attract the photographic trophy hunters.
But today, decades of aggressive mining and heavy grazing have left much of the region threadbare; rising temperatures and the recent extreme drought have tipped much of the region toward dust bowl conditions that may be irreversible in places.
Plant poaching has been the final straw for some. Conservationists say there’s no time to lose, as they consider an ecological triage for the most at-risk species here.
Johanna von Holdt first noted something was amiss in 2020. An environmental scientist from the University of Cape Town who specializes in air quality, Von Holdt was studying satellite images taken over Northern Cape province when she noted a dramatic increase in sand plumes.
From high altitude, these look like smoke rising from a chimney stack, although the plumes lie on the ground, starting as if from a single ignition point, fanning out over the landscape and heading west, out to sea.
It starts with a small nick in the ground, one that breaks the cap that binds the land in place. A few too many hungry sheep shear the succulent shrubs whose plump leaves hold precious water in an otherwise parched landscape. Cloven hooves trampling the ground around a dwindling number of watering holes. A miner’s front-end loader scooping out another industrial-sized load of gravel and sand to sift for diamonds. A dump truck’s tires cutting out a path as it carts more tailings to a growing mound of mining waste.
The sand loses its moorings and is picked up by winds that can reach speeds of 40 km/h (25 mph).
“You really can’t do much to prevent sand grains [once they’re mobile], which act like sandpaper on plants,” says Timm Hoffman, professor emeritus of botany at the University of Cape Town, who has studied a giant quiver tree (A. pillansii) population at a site near Foden’s location for two decades.
These sandstorms may be short-lived, but lethal, even to desert-adapted plants that have evolved many ways to survive sandblasting. Too much exposure to the razor-edged particles carried in the high-velocity air will destroy plants’ leaves and stems, or smother them, leaving them unable to breathe.
Hoffman also found astonishing changes to study sites he knows well on a November 2024 trip to the Richtersveld. “[Sand] abrades not only the seedlings, because of the way in which sand particles move over the surface, but it also kills the adult plants. It covers all the leaves so they can’t transpire. They can’t open their stomata.”
In 2022, Von Holdt lead a team of arid-systems ecologists and others on a trip to the region. Not only did they confirm what the high-altitude photographs are saying about the intensity of the offshore sand plumes. They also found evidence that onshore winds from the coast are sending sand into the interior.
In many places, the ground had lost the physical mechanisms that bind this sensitive landscape in place — succulent plants and the crusty layers that form a natural cap on the ground — leaving many areas vulnerable to winds that strip away any nutrient-rich organic material and the lighter sand and dust. In places, they found wind erosion down to the dorbank, a cement-like dry-pan layer.
People in the region report an increase in high winds and sandstorms, but sifting through data recording wind speeds and direction, the team found no changes in those patterns.
By Hoffman’s estimation, this is a “runaway train” that may be irreversible in parts of the Richtersveld.
Triage for survival
Foden’s work on the common quiver tree started in the early 2000s. The maiden’s quiver tree hasn’t been studied as closely over time, but conservationists are reporting significant die-offs of this species as well, just like the one Foden encountered in the Namaskluft last September.
Elsabe Swart, senior manager with the Northern Cape Department of Agriculture, Environmental Affairs, Rural Development and Land Reform, is also one of the plant specialists who knows the region best. She’s also seen unsettling die-backs in maiden’s quiver tree populations. “One of the spots where you visually observe high mortality is within the Richtersveld National Park.”
Conservationists are calling for an immediate rescue mission in the region, to support species’ survival in this beleaguered desert.
Despite 30 years of negotiations, carbon emissions continue — historically, this has overwhelmingly come from the United States and Europe, and now with China taking over the baton, though South Africa is Africa’s leading greenhouse gas emitter in its own right — driving temperatures above lethal levels.
Cutting emissions now will only deliver gains in generations to come, but there are “very active conservation approaches” that can be taken now, Foden says.
“The most important thing we can do is to reduce other threats on these species, to make sure that the pressure of land transformation, for agriculture, for mining, overgrazing, and, of course, succulent plant poaching, all of these disrupt those systems and really reduce the resilience and the opportunities they have to adapt on their own. We can take some very active conservation approaches.”
At least two species of endemic succulents are now regarded as extinct in the wild — Lithops herrei and Cyanella marlothii — mostly pushed over the brink by poaching. The only remaining known specimens are in a SANParks botanical garden in the Richtersveld.
Swart says this kind of ex-situ conservation will top the triage list for at-risk species like this. “A key thing is to have people cultivating a plant in gardens, and having some of the seeds in the Millennium Seed Bank.”
Trying to reestablish populations in the wild is probably not feasible, she says, “because of all the pressures we observe: sandblasting, dune movements and the increased [animal] stocking rates.”
While the slow process of conservation research ticks over — researchers like Foden plan to put more effort into studying the maiden’s quiver tree now — the horse may have already bolted as much of the region may have tipped into irreversible and more extreme desert conditions.
The spreading dust bowl is a sign that even this desert-adapted plant community has reached a breaking point from which it may not recover. It’s a trend whose toll will first be counted in lost plant species, followed by the livelihoods of those who depend on the succulent plants that once made this place so unique.
Banner image: Common quiver tree, Namaqualand, South Africa. Image by Leonie Joubert for Mongabay.
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