After dusk, the forests of the Caribbean island of Puerto Rico fill with the cry of the native frog called the coquí. “Ko-kee,” the male frogs croak over and over, long into the night. Hence their name. Researchers believe the first half of the call threatens other males, while the second half attracts females. Whatever, after a few drinks, the local islanders reply: “Soy de aquí como el coquí” (I’m as Puerto Rican as a coquí). The common coquí (Eleutherodactylus coqui) is the unofficial symbol of the island. It turns up in folklore and pop songs and appears on T-shirts and coffee mugs. A few decades ago, as the island’s natural forests were replaced by sugar and coffee plantations, naturalists regarded the endemic inch-long tree frog as being at serious risk. Now the frog is back. But it no longer croaks in the few surviving scraps of native forest, where it has succumbed to a fungal disease. Most of its song comes instead from new woodlands dominated by foreign trees, like the African tulip.

The coquí seems happy there, in what ecologists are starting to term “novel ecosystems” —composed of new combinations of native species and species introduced by humans, but where the system itself does not depend on humans to keep it going. Is this sacrilege, or is this the future? Is it an ecological abomination doomed to self-destruct, or a model for protecting species and reviving nature in the modern world?

The frog has the unusual distinction of being on the IUCN Red List of threatened species and on the same body’s list of 100 most dangerous invasive species.

Puerto Rico has a singular history. When Europeans arrived at the end of the fifteenth century, it was thinly populated by a native seafaring people called the Taino and still almost entirely forested. Spanish colonists changed that, farming sugar in the lowlands and coffee and tobacco in the mountains. The plantations spread further after the United States wrested control of the island during the Spanish-American War of 1898. Sugar production peaked in the 1940s, by which time only six percent of the native forests remained. The island’s environment was a mess. With the trees gone, it suffered massive soil erosion, and its rivers clogged with sediment. A series of big hurricanes added to the mayhem. The coquí and many other species went onto endangered lists. The island’s growing human population was blamed and, fearing a Malthusian apocalypse on the island, US doctors began oral contraception trials and started sterilizing the island’s women.

But another future awaited. Export markets for sugar and other commodities declined. Smallholder farming also faltered as rural people moved to towns to work in US-owned factories. The island experienced economic boom but agricultural collapse. The forests began to grow back into abandoned fields. Between 1959 and 1974, land devoted to agriculture halved while forest cover rose tenfold to 60 percent. It was “proportionately, the largest event of forest recovery anywhere in the world during the second half of the twentieth century,” says Thomas Rudel, who studies land use at Rutgers University.

But it wasn’t the native Caribbean trees that raced to plant their roots in the former sugar fields. Native species balked at returning to the infertile, compacted, and sun-baked soils on crumbling hillsides that the farmers had left behind. Instead, the trees that colonized the former farms were mostly from the island’s stock of introduced species. There were more than a hundred of them, the majority imported by Europeans for forestry and agriculture or as ornamental garden plants. Suddenly the abandoned fields were full of mangoes and grapefruit, avocados, rose apple, and, most prominent of all, the African tulip tree (Spathodea campanulata). Introduced to the island about a century before as an ornamental tree, it now spread its orange and crimson flowers across the new wild lands.

One man charted the transformation—Ariel Lugo, a local forester and the long-time director of the US Department of Agriculture’s International Institute of Tropical Forestry in Puerto Rico. In his sixties now and with a white beard, he has seen the island change hugely. It was, he says, extraordinary, apparently unique and definitely not in the textbooks of either foresters or ecologists. Conservationists were horrified, as their hopes of a natural reforestation were dashed. Instead they saw an alien takeover. There was, says Lugo, talk of eliminating the aliens and starting afresh. But he stood up for them. His research showed that they were not freezing out the natives but actually paving the way for their return. The invader trees repaired soils and restored biodiversity. Some provided homes for birds, both native and alien, that subsequently speared the seeds of native plants. With time, many of the more slothful native trees joined the thrusting invaders in the new forests, often now germinated by non-native insects and birds.
He sees Puerto Rico’s new forests as a model for the future in many tropical countries. “Our history of land use means we are ahead of most countries in the cycle of deforestation, degradation, and abandonment of land.”

The African tulip tree proved a vital colonist, taking over abandoned floodplains in particular. It is now the most common tree on the island. But it is a friendly giant. It is home to the coquí. It allows light to penetrate to the forest floor. Native species, including reptiles and birds, make up 80 percent of animal life in the tulip-dominated forests. Seven out of the 60 native bird species were lost during the period of extensive deforestation, but the new forests should prevent further disappearances. Three native finches have been joined by 17 alien finch species, spreading seeds in the novel habitats. Parakeets and parrots from other Caribbean islands happily add to the mix. The blue-and-gold macaw is fully established in Puerto Rico, whereas it is on the verge of extinction in its native Paraguay.

Not all natives have revived, it should be said. The two formerly dominant native trees, Manilkara bidentata and Pterocarpus officinalis, have not so far come back. But without the aliens, says Lugo, forests may not have returned at all. Instead, two-thirds of the island’s forests today contain alien species, but few are dominated by them. The invaders have ended up helping produce what Lugo calls “beautifully functioning” new forests, with greater biodiversity than the old forests. Eradicating them would be “fraught with ecological risk.”
Lugo has taken a lot of flak for telling this story of ecological redemption. “I have been scolded, yelled at, and abused by the conservation priests. Whenever I talk at a conference and give our latest results, I’m met by absolute silence and then, often, hostility from the old guard,” he told journalist Gaia Vince. People don’t personally hate him, he told me, but “they are very resistant to accepting the idea of nature’s resilience.”

Lugo is unrepentant. A founding member of the US Society for Ecological Restoration, he sees Puerto Rico’s new forests as a model for the future in many tropical countries. “Our history of land use means we are ahead of most countries in the cycle of deforestation, degradation, and abandonment of land,” he says. Old ecosystems will not work in new times, with new climates and new landscapes. Puerto Rico’s forests are “the harbingers of how biota might respond elsewhere to rapidly changing environmental conditions.” He challenges conservationists to encourage their development rather than to try to reinstate what was once there. This, he says, is the new wild.

Conservationists remain confused. Their treatment of the coquí shows this only too well. The frog has the unusual distinction of being on the International Union for the Conservation of Nature “Red List” of threatened species and on the same body’s list of 100 most dangerous invasive species. It is regarded as at risk because—despite its widespread colonization of the new forests across the island—its only “native” habitat is a small fragment of old Puerto Rican forest, where a fungus is wiping it out. And it is regarded officially as a pest, worthy of eradication, in the other place where its population is growing fast—in Hawaii, where it was accidentally introduced in the 1980s.

Ecologists are tying themselves in knots because they refuse to recognize that these novel, hybrid ecosystems are desirable habitats for anything. But as the sun sets across the island, the people of Puerto Rico can simply cherish their new forests. And they can once again carouse with the common coquí.

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Fred Pearce is an author and journalist based in London. He has reported on environment, popular science, and development issues from 64 countries over the past 20 years. Currently the environment consultant of New Scientist magazine and a regular contributor to British newspapers, he is the author of more than 15 books.This article is excerpted from his latest book, The New Wild: Why Invasive Species Will Be Nature’s Salvation.

Header Image: Coqui ©Jomme