From the sea, volcanic Ascension Island looks as if its smouldering. Big mid-Atlantic swell rolling up from the Southern Ocean explodes onto the rugged cinder and sand shoreline, leaving sea spray hanging in the air like steam. Inland, its all black lava and red rubble, a forbidding landscape that once earned the island the tourist-repelling descriptor of hell with the fire put out.

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The mist that collects around the islands highest peak completes the smoky illusion. Rising above a cataclysmic backdrop of dormant craters, pyroclastic deposits and lava domes, 859m-high Green Mountain is a leafy oddity on the charred island: its flourishing cloud forest is testament to both the ingenuity of humans and the resilience of nature.

Planted on a desolate hilltop less than 160 years ago, the forest that began on a whim has started attracting the notice of scientists around the world. Upending traditional ideas of conservation, Green Mountain offers the hopeful idea that man-made ecosystems can improve our environment. As the climate crisis ravages landscapes and leads to catastrophic damage such as the recent bush fires in Australia the thriving jungle on Ascension bolsters the argument that maybe we can regenerate a forest using concepts from this remote and often forgotten place.

Ascension Island erupted from the Atlantic Ocean about a million years ago. Located midway between Angola and Brazil, the island got its name when it was rediscovered by Afonso de Albuquerque on Ascension Day 1503 (it was first spotted by Joo da Nova in 1501). For a long time it was only occupied by nesting seabirds and green turtles that make the 3,000-mile journey from Brazil to breed. Its first human inhabitants came in 1815, when the British Royal Navy set up camp to keep watch on Napoleon, who was imprisoned 700 nautical miles south-east on Saint Helena.

What you see on Green Mountain is something traditional researchers wouldnt have looked twice at

Ascension went on to become a useful stopping point for ships. But during his visit in 1836, Charles Darwin pointed out the islands most obvious flaw: its treeless, naked hideousness made it a tough place to live. Inspired by his friend Darwins theories about turning the arid landscape into a garden, botanist Joseph Hooker came up with a plan: by planting seedlings from around the world, trees could catch the mist and increase rainfall over the scorched island, making it livable.

The plan was a success. In 1860, John Bell, the island's horticulturalist, supervised the planting of some 27,000 trees and shrubs, which resulted in the development of enough soil to grow crops.

It was the opportunity to visit Darwins quirky and little-known forest, along with the mid-ocean promise of fresh raspberries and bananas, that drew my family to Ascension; an island that now has a population of around 900 people made up of American and British military and their civilian contractors.

Leaving our sailboat anchored in Clarence Bay, we drove our rental car out of Georgetown, along Nasa Road and through a blindingly bright lunarscape past the nightclub, the golf course, lava flows and volcanic craters and around the feral donkeys that were foraging in a desert of mesquite and prickly pear.

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Eventually we started up Green Mountain. Here the harsh sunlight was softened by mist and then blotted out by patchy rain. Then the road took us into a casuarina and acacia forest that could have come straight out of Australia. From there we drove into a dense jungle of bananas, ginger, juniper, raspberries, coffee, ferns and figs.

After parking, we set off on a hike. Encountering the occasional feral sheep, we walked along a cool, misty trail. Overgrown with Cape yews and Norfolk pines, descendants of some of the seedlings Hooker advised the British Admiralty to transport to Ascension from botanical gardens around the world, the forest felt deceptively ancient.

According to traditional ecological principles, this hotchpotch of endemic grasses and ferns combined with more than 300 non-indigenous species should never have evolved into a thriving ecosystem. Complex forests are thought to take millions of years of careful self-selection to develop. But the man-made ecosystem on Green Mountain, where introduced species and island plants seem to have evolved together, doesnt fit that paradigm. Its neither garden, nor wilderness.

What you see on Green Mountain is something traditional researchers wouldnt have looked twice at, Dave Wilkinson, ecology professor at the University of Lincoln, UK, told me over the phone, Because its completely dominated by non-native species, it would have been of no interest.

He added: Ecologists have traditionally focused on the natural bits, not the things that arent supposed to be there. Those things were considered bad.

Until recently, conservation meant getting rid of invasive species and allowing a landscape to return to the way it was before people got involved. On isolated and treeless Gough Island, 2,000 nautical miles further south, the English house mouse offers a classic example of what goes wrong when humans mess with the environment. In his book The New Wild, Why Invasive Species Will Be Nature's Salvation, author Fred Pearce describes how house mice got to the island from passing ships and then, over decades of windswept isolation, the mice mutated and turned carnivorous. They now consume a ton of seabirds a day, threatening the local population.

A chance visit to Ascension Island in 2004 got Wilkinson thinking about this natural versus invasive perspective. Most who see the forest say, Well this is very odd, and then go study the turtles or seabirds, he said. But Wilkinson couldnt move on. Green Mountain is a very dramatic example of something quite common: in a lot of the world, non-native species are a functioning part of the ecosystem.

Its a tropical forest on a site that didnt use to have a tropical forest

Wilkinson took the idea further in his controversial 2004 essay for the Journal of Biogeography, The Parable of Green Mountain, challenging the theory that introduced species dont belong and putting forward the argument that man-made ecosystems, like Green Mountain, could play a critical role in our future.

Over the next few years this idea gained traction, and in 2006 the term novel ecosystem was developed by renowned ecologist Richard Hobbs to describe places like Green Mountain that were irreversibly changed by human intervention and may not need to be fixed.

Anna Bckstrm, senior ecologist at the ICON Science Research Group, RMIT University in Australia, says that proponents of a novel-ecosystem approach have a pragmatic view of conservation. The concept offers more flexibility, she explained. Given the realities of climate change, human impact and the small amount of funds usually available for conservation, she says that by accepting the changes humans have made, ecological restoration is more manageable. The landscape doesnt have to revert to what it was, she said. We just want diversity and balance.

This idea, that the service an ecosystem provides such as flood control, carbon sequestration or pollination is more important than a forests pristine condition is becoming embraced more widely. As ecosystems are thrown into chaos through the fires, storms and disease brought on by the climate crisis, its becoming more about resilience than anything.

If a group of plants survive, and some of them are non-indigenous, we dont want to rip them out, Bckstrm said. Diversity in the ecosystem is more important than a plants origin.

Going even further, Wilkinson says that the novel-ecosystem approach allows ecologists to account for some of the forces that might shape the ecosystems of the future. Twenty years ago conservation managers would never consider planting a non-native species, but now we know the value of having a mixture of trees on the site so if a tree pathogen, fire or storm comes through you dont lose absolutely everything, he said. With a novel-ecosystem approach, conservationists have the freedom to rebuild a now-dry flood plane with drought-resistant species or replant a fire-ravaged landscape with plants that thrive in a hotter region.

What this means is the experiment of Green Mountain, where plants were thrown together from different places and then somehow thrived, can perhaps be replicated. It tells us that controversial ideas like Chinas, to plant billions of trees to hold back the desert; or Australias push for people to plant non-indigenous fire retardant plants and trees are worth looking at closely. Darwin and Hookers novel idea tells us when it comes to survival, sometimes its okay to experiment and create something new.

Green Mountain is a very dramatic example of something quite common

The thing that struck me the most when I stood on the misty summit of Green Mountain, looking over the arid lowlands out to the sea, was the awareness that in traditional ecology there should never have been a Green Mountain. Even Hooker came to regret the forest and the damage it did to Ascensions native ecosystem, with the introduced plants eventually outcompeting the sparse growth that was there.

But luckily, there was never that much interest in digging up Green Mountain. And then time went on and longtime Ascension Island conservation officer Stedson Stroud discovered that the once thought-to-be-extinct Ascension Island parsley fern hadnt actually been wiped out by the new plants, and that some of the islands other native plants actually grew better because of the introduced species.

Wilkinson says that in the past five to 10 years, a shift in thinking meant conservationists began to see the accident of Green Mountain as something optimistic, Its a tropical forest on a site that didnt use to have a tropical forest. Were used to seeing the opposite; tropical forests are cleared and then theyre gone.

Wilkinson says while you probably cant build a Green Mountain after every fire, or whenever pests or pathogens destroy a forest, Darwin and Hooker did leave us a few clues for building a more resilient world. We live in a time of accelerating climate change, when disease moves more quickly than evolution. Just look at how Covid-19 sped around the world, he said. Green Mountain shows that you can bring ecosystems back or potentially put them into places where they werent before on a timescale of less than a century.

They wont be as diverse as a tropical forest thats been there for millennia. But theyll exist.

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