Mysterious Terraformed Island Offers New Clues to Life’s Survival

A 150-year-old experiment on the remote Ascension Island may help us green Mars. Can it also help us save Earth?

ASCENSION ISLAND - Touching down on Ascension Island feels like landing on Mars.

Clay-coloured lava rocks form football field-sized craters visible from my aeroplane window. Residences near the airfield are low-slung, white, and identical in shape, just like the space colonies in science fiction. There are 800 or so mostly British and U.S. citizens residing on this 85 square-kilometre island, and very few were born here. Hundreds of satellites pepper the craters, listening to U.S. test missiles, space junk, and things that are classified.

I deboard the military charter plane and walk down the U.S. Air Force’s Wideawake Airfield under a cloudless sky. I am over 1,609 kilometres from any continent. It’s hard to imagine that scientists from another century chose to build the planet’s first artificial ecosystem here.

Naturally treeless, Green Mountain once provided a strategic viewpoint to monitor passing ships. Today, a thick forest of alien trees obscures the view.


Rock and blinding sun overpower my senses. While waiting with two-dozen fellow civilians for passport stamps, Lyndon Smith, an elderly British visitor, points to the tripod slung across my shoulders.

“She once wept here,” he says quietly, pointing toward his wife. “There’s no release from the sun. Are you out here to take pictures?” I nod in response.

Charles Darwin popularised the stigma about Ascension Island that Smith and many others are repeating almost 200 years later. Darwin called the island “hideous.” He stopped here en route to England from the lush Galapagos on his famous voyage on the HMS Beagle. Darwin lamented in his journal that this inhospitable place occupied by the British military should be made into a “productive spot.” Darwin called the landscape “burnt” and “completely destitute of trees.” To be fair, there was one solitary tree.

If Galapagos was Charles Darwin’s Eden, Ascension was his Inferno.

Darwin developed names to describe the island’s inferno-like rock formations: Devil’s Riding School, Devil’s Ashpit, and Broken Tooth. Those names have stuck. I pick up a hand-drawn driving map in the open-air immigration area. I count six roads, forty-four volcanic peaks, and five features still containing the word “devil.”


I walk toward a concrete patio filled with strewn baggage when a sliver of green reaching over 2,000 feet in height catches the corner of my eye. The peak stands in stark contrast to the Mars-like landscape around me. This artificially green mountaintop is the reason I’d come. I’d spent months wondering: What can we learn from this place?

Despite being visited by only a few thousand people each year, this mountain has become the poster child for “human-made” or “novel” ecosystems worldwide. The aptly named Green Mountain is one of the most cited and debated examples for the phenomena of wholly new combinations of species, with no historical equivalent, that assemble through human intervention.

If we indeed want to figure out how to green Mars and settle there, this mountaintop forest surrounded by a volcanic moonscape is our scientific starting point.


Darwin first suggested engineering a new environment on Ascension. But Sir Joseph Hooker, a younger Victorian-era botanist, would take action. He embarked on a fifty-year experiment that would disrupt the island’s landscape and ecology. Archivists would later find in Hooker’s journal that, as an old man, he expressed regret for the whole endeavour. He predicted the tragic impact it would have a century later.

Young Hooker was eager, in 1843, to make his mark on science after years of sleeping with Darwin’s manuscripts under his pillow. He shipped 330 plants from the Royal Botanic Gardens, Kew to Green Mountain before the middle of the century. By 1870, 5,000 more trees had been planted. Anecdotal records report that greater rainfall soon followed these plantings (a point disputed by lack of reliable weather measurement).

Sir Joseph Hooker, the architect of Ascension's transformation

With time, the soil changed, as did the island’s hydrology. The Royal Admiralty, the project’s early financiers, reported conditions more hospitable for its troops stationed on Ascension Island. All thanks to the plants.

I visit Ascension’s famous Dew Pond. By the 1880s, Hooker’s “mist-catching trees” had formed a small pond at the mountain’s summit, the island’s first freshwater water body. Today, bamboo trunks form a 12-metre tall wall around the pond, knocking together harmoniously in the breeze.

A life-sized, plastic crocodile waits half-submerged in the pond with teeth showing. The faux reptile appeared there in the 1990s as a gag. It quickly developed its own mythology among the military residents. Should they remove the item? Or leave it? No one can agree what to do with it now. The same can be said about the artificial ecosystem all around.

Hiking down from the pond, along the ridge of Green Mountain, I notice striking similarities between the lush forest around me and the “natural” cloud forests I’d visited in Costa Rica. Scientists deemed the biological transformation on Ascension’s peak so unprecedented that, in the late 1990s, they borrowed a term from science fiction—terraforming—just to describe what was happening.

Newly digitised letters reveal the remarkable extent of Hooker’s experiment. Sparrows, chaffinches, linnets and several coastal African birds arrived to the island in 1863. Orchards of oranges, lemons, cherimoyers, custard apples, and lychees were planted by 1868. But not everything flourished. The orange trees withered. Hooker’s botanical plantings waned into the 1890s and only the fittest non-native plants survived. The surviving mash-up of flora from Africa and the Americas ran untended for most of the 1900s.

Monkey Rock Cemetery contains the graves of mostly infants and toddlers who did not survive the remote, inhospitable conditions of Ascension Island during the 18th and 19th centuries.

The experiment became a historical footnote. But in the early 2000s, it resurfaced smack in the middle of a new scientific vocabulary around “novel ecosystems.” What long-term value do human-made ecosystems have, whether intentional or accidental? How do they work?


As plans advance for human settlements on Mars, more and more people seek answers from this mountain. For example, in 2004, evolutionary biologist David Wilkinson used Green Mountain to illustrate that snail-speed coevolution is not always necessary for complex ecosystems to build themselves. Sometimes things can happen quickly, chaotically, by just fitting together.

Terraforming Mars may require evolutionary insights like this about random species assembling, competing, and cooperating in strange, new places.

Novel ecosystems are popping up around the globe on terms much more accidental than Green Mountain. One researcher estimated that up to 35 percent of undeveloped lands near cities and farms may soon be covered with these novel systems.

Morning sun lights Green Mountain as viewed from Elliot's Pass, looking south toward the U.S. Air Force buildings at Wideawake Airfield.

In 2008, Dox Sax of Brown University co-authored a paper that found plant diversity had doubled on five remote islands and island chains because of accidental biological invasions. Yet almost no extinctions of local plants and animals had occurred. Sax believes Green Mountain is therefore “at the nexus of issues we’ll all be wrestling with for years to come: novel as opposed to historic communities, the role of non-natives in providing ecosystem services, and what our conservation goals should be.”

Sax believes evolutionary relationships are forming atop Green Mountain that could be wholly different from ones that work on long timelines in “pristine” places. Pristine place is where scientists traditionally flock.

Dan Simberloff of the University of Tennessee says that studying Ascension Island could help us learn not just about Mars, but also how to green Earth’s deserts and feed more people. He and Sax agree that more research is needed on novel ecosystems. Yet neither of the men has managed a research trip to Ascension Island. Non-military travel to the island is expensive. Accommodations are limited. Unlike the Galapagos, where evolutionary biologists arrive in the hundreds each year, visiting scientists are generally a rarity on Green Mountain.


Stedson Stroud, with nothing more than an 8th-grade education, knows more about Ascension’s plant life than anyone today. He picked up where Hooker left off.

Stroud always carries a walking stick and ties his hair back in a long, curly ponytail. Stroud came to this island as a teenager in the early 1960s. He has seen the island change. A descendent of Chinese, African, and Indian labourers, he is a “Saint”—someone born on Ascension’s much-larger sister island of St. Helena. He points to a sign for Old NASA Road on our first drive together to Green Mountain.

Naturalist Stedson Stroud searches for non-native birds species in the invasive African grasses that blanket the high elevations of Green Mountain.

“I was the janitor when they were relaying the first Apollo radio transmissions from this island,” he says. “My job was to keep the coffee supplied throughout the night.” He smiles behind a thick, black moustache.

We stop at the Royal Air Force base for snacks and water. Desalinated water spouts from the fountains and Mars bars pile next to the register. Green Mountain’s orchard and dew pond no longer serve the basic survival needs of residents.

We roar up thirty switchbacks in Stroud’s canvas-top Jeep with a faded decal on the side. It reads: Conservation Department. The air gets noticeably cooler. On average, Green Mountain is 7°C cooler than where resident lives in the lowlands. Wild sheep and bright orange land crabs dart to the banks.

“The sheep look thin,” I comment. “They look healthier than earlier this year,” says Stroud. In addition to being Green Mountain National Park’s only ranger when I visited, Stroud is considered the island’s unofficial veterinarian. I would soon learn that those two jobs are at odds here on Ascension Island.

Ascension Island residents Jeff and Carla Smith raised "Chlow" the sheep as a pet after rescuing it from certain death. They keep the invasive animal away from sensitive areas of the island.

When a wild lamb was found motherless in 2015, Stroud recruited two island residents, Carla and Jeff Smith, to take her in. Chloe is now a grown sheep that lives very much like a dog. She roams inside a fenced yard, drinks filtrated water from a bottle and rides in the back seat of a BMW. Chloe isn’t alone. There is a nascent but growing culture of feral donkey and sheep “adoptions” among the residents as the community and invasive animals try to survive together in this harsh environment. Besides, it’s better that way for the plants found only on Ascension.

I follow Stroud to the restoration site of Euphorbia origanoides, a diminutive shrub on the brink of extinction. It’s miles away and only accessible by foot. We pass sandy beaches pocketed by last night’s laying of turtle eggs. Seawater spouts over 15 feet in the air, like a geyser, through a unique coastal rock formation. I spot a dozen sea turtle heads bobbing in the turquoise surf.

After a mile of barren lowlands, we near a fenced paddock. I spot a handful of tire-sized rock circles on the ground. One is shaped like a heart. At the centre of each is a stump, grazed to an inch from the ground. They are the mourned remains of a once hopeful out-planting of Euphorbia origanoides. Inside the paddock, the plants are still safe from sheep and rabbits.

A masked booby, Sula dactylatra, and chick face each other with White Hill in the background.

Non-native sheep, much like the island’s non-native plants, threaten the things Stroud cares most about: the island’s last surviving endemic plants.

Ten plants discovered by Hooker and colleagues are found only on this island. Three are now thought to be extinct. Outmuscled by Hooker’s plants and sailors’ livestock, the remaining seven are among the most threatened plants in the world. “We’re in a race against time,” says Stroud.


I ask Stroud to show me the place and plant he calls “the loves of my life.” It takes a half hour of sliding on our buttocks down steep banks blanketed by meter-tall African grasses.

Stroud bounds ahead. I and two part-time park volunteers from the U.S. Air Force base slog behind, sore and muddy. Stroud walks to a rocky pinnacle and hands me a fraying nylon rope. We do a repelling-like leap to a ledge that, clearly, no sheep can reach. He points to seven tiny individuals, about the size of a four-leaf clover, of the once-lost Annogramma ascensionis—the Ascension Island parsley fern.

This rocky pinnacle is the site where Stedson Stroud (pictured here) in 2012 rediscovered the endemic Ascension parsley fern, Anogramma ascensionis, not seen since the 19th century.

Stroud made international headlines in 2009 when he rediscovered the last three individuals of this species at this very site. Since then, almost a million dollars has been collectively invested in cultivating and reintroducing a viable population.

“It was better than finding gold,” says Stroud. Biodiversity aside, the plant had political value.

Green Mountain had long been evoked among scientists as a talking point about evolution. History buffs would visit for its historical affiliation with Darwin and terraforming. Finding the extinct Ascension Island parsley fern shifted the conversation about this novel ecosystem towards topics of conservation and renewal.

A team of explorers scans the island for native plants.

Both Hooker and Stroud are conflicted botanists. Hooker predicted—and regretted—the extinction of Ascension’s unique ferns, which he saw as vital keys to our understanding of island evolution. Stroud stewards the terraformed landscape while simultaneously investing in heavy-handed management projects to save the remaining endemic species. He references their cultural value to South Atlantic islanders.

The island has one endemic bird, the Ascension frigatebird, which was saved from near extinction after a multi-million dollar, decade-long effort that eradicated feral cats from the island. I ask Stroud if he favours a similar effort for Green Mountain. Perhaps mow down the forest and focus wholly on traditional conservation of endemics plants.

Stroud pauses, “At this point, I fear we’ve too far gone for [that]. We need to focus on coexistence.”


Green Mountain’s shady slopes have only one residence, a stately concrete mansion reserved for the Londoners who serve term positions as Island Administrator. A bride and groom borrow its manicured grounds for a wedding ceremony my last Saturday there. I watch the groom harvest non-native ginger leaves from the summit and decorate the alter. The wedding photographer poses the newlyweds in the shade with a lush, forested backdrop. Children in bright dresses jump off 200-year-old cannons onto cool Bermuda grass.

Silas "Jim" Reynolds of the U.K.'s South Birmingham University studies Ascension's wildlife.

“How we think about non-native plants has changed in the past decade,” says Sax. “Drastically so.”

Some scientists now say we ought to make peace with the novel ecosystems around us. And better understand what they provide us. Others, of course, push back.

How do we reconcile the norms of traditional conservation and the reality around us? In the minds of Ascension Islanders, there seems to be little controversy.

“If I could snap my fingers and return the mountain to its original state, would I? Probably not,” says Drew Avery, president of the Ascension Island Heritage Society. Avery argues that many island residents have no knowledge that the forested landscape on Green Mountain is not “natural”—the way things were before human beings arrived.

There’s another reason why mowing down Green Mountain’s trees is off the table: some might be capable of rescuing the remaining endemic individuals being obliterated by the expanding forest.

With a population around 800, weddings are rare on Ascension. Here, Tahirra Felton wed Aaron Rogers at the U.K. Administrator's Residence, which sits just below the summit of Green Mountain.

Bullied out of their home rooted in the ground, the plants Pteris adscensionis and Xiphopteris ascensionense have found refuge in the novel ecosystem’s canopy. Thriving in the moist, sponge-like mosses that grow on the branches of the cape yew and white olive trees, a small population of ferns that spent thousands of years on the ground are popping up into the air. Are they actually adapting and thriving? It’s too early to tell.

Stroud has turned traditional conservation on its head by facilitating the fern’s canopy survival hack in the cape yew trees. He’s planting more of the trees once considered so problematic. This strategy is unorthodox but showing promise. It is part of the island’s Biodiversity Action Plan designed in 2012 to reconcile with the changing landscape.

After years as the first and only conservation officer, in 2016, Stroud worked as part of an eleven person, full-time conservation staff. The team includes a younger generation of Saints, like Jolene Sim and Natasha William, who left St. Helena like Stroud to start a life on Ascension. Their traditional knowledge of St. Helena’s plants has found a new, urgent use on this South Atlantic sister island.

“We grew up and are used to the terrain that is here and St. Helena, so it’s quite natural for us to be walking on these [cliffs] and be clambering about,” says Sim, the deputy head of conservation who has been working on a massive repopulation effort of the once-lost Ascension parsley fern. In February of 2015, the clambering paid off.

Sim and a collaborator from Kew Royal Botanical Gardens discovered 170 new sporophytes—the next generation of parsley ferns—on a rocky ledge where they had placed their hopes. She had also placed, with tweezers, seven nursery-reared ferns months earlier.

The land crab Johngarthia lagostoma is restricted to the slopes of Green Mountain, where there is sufficient moisture and vegetation. This crab is found on only four islands in the Southern Atlantic Ocean.

“We were surprised,” Sims recalls. “We didn’t expect such big success from just seven initial plants.”

This kind of reintroduction is a more traditional approach to plant restoration than Stroud’s canopy creation. But both are part of a larger portfolio approach to biodiversity conservation that the on-island staff has spent years developing in collaboration with off-island scientists.

Theirs is a do-what-you-can-and-see-what-works strategy that seems to be helping a conservation landscape where, seemingly, few ecological rules apply.

Together, Sim and Stroud picked out this ledge on a steep, mist-covered cliff where the descendants of nursery-reared parsley ferns now attempt a species come back. Conservation Department staff commonly refer to this spot as Stedson’s Ledge.

“It’s nice to have my name there,” comments Stroud, who was about to turn 70 years old when I visited. “But, really, it will be Jolene and the others who will continue this fight for our endemic plants long after I’m gone.”


On my last day on Ascension Island, the mist that had perpetually covered the summit of Green Mountain momentarily lifts. Five U.S. Air Force airmen and airwomen arrive in casual clothes with a visiting serjeant. They walk down the muddy path to a fenced area where Stroud is waiting, two shovels in hand. To commemorate the serjeant’s visit, Stroud has invited him to plant a ceremonial tree to contribute to this effort of creating a large cape yew canopy, where the last endemic ferns might persist. The serjeant lifts the sapling from the pot and kneels down. Photos are snapped.

Unlike every other peak on Ascension Island, a perpetual cloud seems to hang at the summit of Green Mountain.

To me, it’s a strange sight. The purposeful planting of non-native trees, just like Hooker did, is an act that got us all into this whole novel ecosystem mess centuries ago. Is this the right path forward for Green Mountain—or for other novel ecosystems?

After the planting, Stroud and I are alone. The mist begins to roll back over the mountaintop.

Green Mountain has become a metaphor, parable, and talking point for scientists. Among conservationists, it’s used to debate ethics. But few people ask Stroud, the daily caretaker, what this place teaches him about the future direction of conservation. So I ask.

“I am now extending Hooker’s forest, of large mist-interception trees, as a survival tactic for these ferns to grow on,” he says. “If we stand by and do nothing, then we will be rightly condemned by future generations.”

Stroud picks a few wild but non-native raspberries. He hands them to me as we walk back toward his Jeep. They’re tart and delicious.

I scribble in my notepad on our ride down the mountain: “If you can’t save everything the way it used to be, save what you can the way it is now.”

Header Image: For most of the 1800s and 1900s, Ascension Island's teaming population of seabirds was decimated by the invasion of cats. By the time the cats were eradicated in the 2000s, this colony of sooty terns near the U.S. Air Force's Wideawake Airfield was a rare holdout. PHOTOGRAPH BY CLARE FIESELER, NATIONAL GEOGRAPHIC

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