What will happen to the natural world when humans disappear?

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Rather than going against our intuition, it is a concept that has been instilled in our minds: humans are like the cancer of the earth, destroying nature wherever they go, but if humans disappear, nature will, in time, regain its original appearance and ecology.

Unfortunately, this stubborn idea in our minds is likely to be wrong, sometimes even outrageously wrong. More and more evidence shows that even if humans disappear from a certain place, the recovery of nature will not happen as we imagine. In fact, when asked what is the "original" picture of nature, scientists believe that most parts of the earth do not have the so-called "original" landscape at all.

When abandonment came, it crept in from the edges. Homes on the edge of town were abandoned first, followed by grocery stores on the periphery. It moved slowly but inexorably inward. Gas stations closed, creepers climbed up pumps and spread across rooftops until they collapsed under the weight. Bus shelters, pharmacies, movie theaters, cafes, and finally schools closed.

Today, one of the few institutions still maintaining human activity in the central Bulgarian village of Tyurkmen is the post office. Dimitrinka Dimcheva, a 56-year-old postal worker, still keeps the post office open two days a week, bringing in goods from outside the city that are no longer available in local shops.

Once a bustling town of more than 1,200 people, Turkmen now has fewer than 200 residents. On a warm spring afternoon, Dimcheva stood in the town's central square. "Weddings used to take place here, as well as folk dances and volleyball matches. There were a lot of young people, and a swimming pool," she said. She looked around, pointing to ruins or now empty areas, recalling buildings that once stood there. There was a small cinema; behind it was the school that burned down, was rebuilt, and then finally closed. "Life was vibrant back then," but now, she said, "village life is dying." Villages like this are everywhere in Bulgaria.

As people flocked to the cities in search of work, many villages were emptied out over the next 30 years until they were completely abandoned. According to the 2021 census, nearly 300 villages in Bulgaria are completely uninhabited, and more than 1,000 have fewer than 30 people—most of whom are elderly. Bulgaria’s population has been declining for decades due to low birth rates and high emigration . Its population has fallen from nearly 9 million in 1989 to less than 6.5 million—one of the worst peacetime population declines in modern history[1].

Bulgaria is at the extreme end of this demographic shift, but the forces reshaping it are everywhere. Over the past half century, the share of the global population living in rural areas has fallen by nearly a third. Agriculture is becoming increasingly industrialized and concentrated. Today, more than half of the population lives in and around cities, a proportion projected to rise to 70% by 2050. In many countries, birth rates are falling steadily. Although the global population is expected to continue growing until 2080, about half of that growth will be driven by fewer than 10 countries[2].

A crane returns to its nest, seen through a dilapidated shed in Turkmen, Bulgaria. © Ivo Danchev

As populations migrate and decrease, long-standing settlements are gradually abandoned. People often leave everything where it is, as if preparing to return one day, but that day often never comes. In Türktor, empty houses still have Christmas balls hanging on curtain rods, slowly covered by cobwebs. In one abandoned house, a china cabinet collapsed into a hole in the rotting floorboards, and the dishes in the cabinet were still neatly stacked, and next to it was a pack of diapers for visiting grandchildren. Sometimes abandonment is sudden, perhaps because of a legal ruling or an emergency evacuation; but more often it is chaotic, slow and unplanned. People just leave.

Since the 1950s, some scholars estimate that around 400 million hectares of land – an area almost the size of the European Union – have been abandoned worldwide.[3] A team of scientists recently calculated[4] that around 30 million hectares of farmland have been abandoned in the contiguous United States since the 1980s. As the climate crisis renders more areas uninhabitable (floods, water shortages and wildfires make it impossible to build homes, and land degradation and drought make it impossible to farm), we can expect more displacement in the future.

This world-changing shift has gone virtually unnoticed. “It’s always been there — but we haven’t really described it,” says He Yin, a professor at Kent State University who is using remote sensing to map abandoned land around the world. “We always talk about expansion,” he says, referring to land development. “Yes, that’s certainly important. But there’s another side — abandonment — that’s rarely talked about.”

An abandoned house in Turkmen. © Georgia Public Broadcasting

Beyond the story of declining populations is another story - about what happens to lands left behind. To preserve a habitable planet, it is vital to protect and expand forests, grasslands, healthy ecosystems and wild areas. Large tracts of abandoned land present both opportunities and questions. It is an unfinished experiment with an unpredictable outcome. Over millennia, humans have drastically altered the places they live, reshaping the face of the planet. So what happens to the natural world when we disappear?

It’s this mystery that has drawn ecologist Gergana Daskalova to Turkmen. On a hot, quiet morning in May, she walks along the main street. The street is deserted, but fences, gates and telephone poles are covered with sheets of paper that flutter in the early summer heat, their staples pulling loose from the wind. In Bulgaria, when a family member dies, it’s tradition to post an obituary. These A4-size sheets of printed paper bear the deceased’s name, photo, date of death and a brief eulogy. Each sheet of paper notes the time since the person died: six months, one year, ten years, twenty-two years. In villages across the country, these obituaries often also mark the end of human habitation.

Obituary from the village of Prestoy. © Ivo Danchev

“If you walk around, it’s like a clock marking when these people are gone,” said Daskalova, who specializes in global change ecology, the study of how large-scale human activities are reshaping the natural world. “From a human perspective, it’s sad. But it’s also marking the end of human impact and the beginning of environmental change that comes with it.”

She is working on an ambitious research project to study 30 villages in the Bulgarian countryside at various stages of abandonment. Together with collaborators and students, she is collecting extensive data: using drones to map forest recovery, conducting plot-by-plot botanical surveys to observe changes in plant species, and installing recording devices on trees to record changes in the density and volume of birdsong. Over time, she hopes to compare the ecology of abandoned villages with those that are still inhabited, to get a comprehensive picture of how nature responds after humans leave.

Daskalova, a researcher at the University of Göttingen in Germany, carries out her work in Bulgaria. © Ivo Danchev

Daskalova is in her early 30s, a warm and talkative woman with a patient knack for popularizing scientific theories, a skill she may have gained from explaining to curious shepherds in remote fields why she tied microphones to trees. She recently had a son, who sometimes sits beside her, watching with a serious expression as she moves through the research plots. Turkmen was not a randomly chosen research site—it’s where she grew up. Like many of her generation, Daskalova was raised primarily by her grandparents as a child while her parents worked in the nearest city. Eventually, she left the village to attend university.

“For 10 years, I became one of those people who left the village and came back occasionally. Each time I came back, my street was populated by fewer people,” she says. When she was younger, Daskalova would track signs of abandonment in the winter, looking to see if there was still smoke coming out of a chimney or lights in a window. “But eventually, one by one, the lights went out.” In the first few years of her career, Daskalova worked in far-flung places, including the Arctic tundra. But she always remembered the massive population decline she had experienced and realized it was part of a wider trend that could reshape the future of thousands of species. Today, she lives and works in her grandparents’ old house in Turkmen. The houses around her are almost all empty. Across the street, a house collapses like an abandoned cardboard box in the rain.

Each study site is a village in its own right, like thousands of others. “But in some ways that’s what makes it special, because the depopulation is happening on a very large scale.” And what happens after abandonment is often very different from what we expect.

To learn that large swathes of our planet are being abandoned is to imagine the Garden of Eden resurrected amid human ruins. Without us, nature will come roaring back. Deer will roam crumbling city streets, vines will tear through concrete, football pitches will become forests. Skies will clear, species will thrive. During the 2020 lockdown, many people saw what semi-abandonment looks like. Wildlife returned to city streets and suburban gardens as humans were forced indoors. “Humans are the virus,” one commentator quipped, and in our absence, “nature is healing.”

An abandoned house in the village of Kreslyuvtsi, Bulgaria. © Ivo Danchev

The view of humans as the bane of the natural world, and of a paradise that will flourish after us, ties in with some of ecology’s oldest ideas. In the late 19th century, botanist Frederick Clements popularized the theory of succession, the idea that any landscape, if undisturbed, will follow a gradual process of development. For example, a patch of cultivated land will first be covered by fast-growing grasses and weeds, then shrubs, and finally trees and forests.

Clements believed that everywhere, through succession, a “top” state of stable equilibrium would be reached. The end result might vary by climate and geography—an Alpine forest would be different from a swamp or a desert—but the basic trajectory was the same: what Clements called a “universal law” that ecosystems “climb” toward the top, just as animals grow from juveniles to adults. The idea gained wide acceptance in the early 20th century, as humanity’s cities, populations, and industries exploded. There was something beautifully simple and elegant about it. It also offered a measure of comfort as people watched human activity transform the planet around them. No matter how drastic the disturbance—whether a glacier retreated or a forest was cleared for farmland—nature’s capacity to return always existed. The ideal top state was like a matrix beneath the soil that would recover, even if the ground was plowed, dug, burned, or paved over, with just time and undisturbed conditions.

Over time, Clements’s broader theories were questioned by fellow botanists. His supposedly stable, permanent climaxes proved elusive: Field studies found that ecosystems undergo unpredictable cycles of collapse, regeneration, divergence, and stagnation. Today, such deterministic theories of succession have been disproven. But Clements’s vision remains entrenched in the public imagination, sometimes to the dismay of ecologists. “Many popular ideas about the environment are based on the belief that nature will maintain its equilibrium if only humans can avoid interfering,” the ecological historian William Cronon wrote in 1995. “These stories are ours, not nature’s. Nature does not spontaneously organize itself into fables.”

In fact, scientists have found that the relationship between humans and the natural world is far more complex than we often assume. This is also a counterintuitive discovery made by Daskalova: not only is human presence not always necessarily in conflict with nature, but it can actually help many species survive. Even more surprising is that complete abandonment can sometimes have worse consequences for biodiversity than leaving humans partially behind.

To illustrate this point, Daskalova takes me to a village buried under vines. Kreslyuvtsi is located in a semi-mountainous area in central Bulgaria. For years, the village was almost completely abandoned. In the genealogy of villages that Daskalova studies, it provides a case study in the near-absolute absence of humans. Standing at the edge of the hillside, Daskalova carefully steps out onto the trail. When her foot lands, it bounces slightly, supported by the thousands of intertwined vines, whose tightly woven resilience creates a kind of elastic buoyancy.

Somewhere down, on a steep slope, a few meters away, is a long-abandoned house in the village of Kreslevtsi. Its shape is slowly disintegrating as its stone walls collapse. Vines have crawled all over the house, leaving only a corner of the roof sticking out like the bow of a sinking ship in its final stages. “They will completely consume this place,” Daskalova said.

Abandoned house in Kreslevtsi covered by vines. © Ivo Danchev

Vines illustrate the first force that land faces after humans leave: when humans leave en masse, emerging dominant species can sweep away other species. The worst infestations are not vines but invasive species. In Poland, where about 12% of farmland has been abandoned, these fields have turned into vast expanses of mustard yellow—covered in the bright pollen of Canada goldenrod. The plant has taken over 75% of the country’s abandoned fields, and where goldenrod grows, other species have little chance of taking root. Scientists studying these abandoned fields have found that wild pollinator populations have fallen by 60%-70%, and bird populations have been cut in half.[5]

In Bulgaria, an emerging threat is Ailanthus altissima, a hardy, fast-growing, disease-resistant tree native to northern China that emits a bitter sap that repels other plants, animals and microorganisms. These monospecific concentrations can form “biological deserts” where only one species survives. The need for diversity is not just an aesthetic preference. Monospecific populations are often associated with soil degradation and nutrient depletion, the extinction of other species, difficult-to-purify water, large-scale wildfires, vulnerability to drought and the rapid spread of disease.

Remains of a stone wall at an abandoned house in Bulgaria. © Gergana Daskalova

In some cases, the dominance of a single species is temporary. Even deadly invasive species can sometimes serve as nursery environments for a variety of plants and organisms that may eventually outgrow them. In other cases, ecosystems can stagnate, failing to recover or diversify. “It is widely assumed that once disturbed, forests can naturally recover from grassland or shrubland within a few decades, and that tree planting can help,” wrote scientists in a 2023 study of plantations in Hong Kong. “ Our study suggests that forest recovery is not as rapid or comprehensive as imagined. ”[6]

Humans are often blamed for the dominance of a single species. But they also play an unexpected, underappreciated role in preventing it. Amid the vines of Kreslevtsi, Daskalova turned and walked carefully back to the path that led up the hill. Once back on the path, she crouched in the grass and began naming the species at her feet: grasses, ivy, but also buttercups, purple-flowering vines, and a tiny yellow orchid. “I can’t imagine many people taking this path, but occasionally someone does,” she said. In the process, they block the spread of the vines, opening up space for this small patch of species to surge with color. The path where Daskalova stood led to an open area in the woods, where grasses and wildflowers grew in a cleared patch of grass. Here again, fragile clusters of flowers emerged, revealing the history of the land. The buttercups and agricultural weeds suggested that humans were here not long ago, and the cleared space suggested that as well. Daskalova points to the dense trees surrounding the clearing, arranged like an amphitheater of spectators, their network of branches already beginning to extend toward the clearing’s precious light source. “They’re right at the edge, ready to move in when the opportunity presents itself. Without grazing or pruning, it could take only five years for this land to be completely submerged in the shadow of the dense canopy.”

A Western Yellow Wagtail in an uncultivated wheat field near Shishmantsi, Bulgaria. © Malkolm Boothroyd

When people imagine ecosystem restoration, this return of forests is often the first thing that comes to mind. But forests represent only a small fraction of possible habitats. For other species, the currency of life is light, and survival is impossible beneath the confined canopy of a forest. The swallow is perfectly adapted to wide open fields: the curves of its wings and the unique forking of its tail are designed to quickly snatch insects flying over meadows. The starling murmuration, which sprinkles pepper on a tablecloth, is an adaptation to open fields: it drives away predators and protects habitat. Numerous species have adapted to and co-evolved with these open places—plants, mammals, insects, herbivores, and wildflowers. The biodiversity of open grasslands may even be richer than that of temperate forests.

Once upon a time, these kinds of environments were created by megafauna. Animals such as mammoths, buffalo, bison, and cave bears were large enough to reshape forests, knocking down trees to create grasslands and even prairies. Scientists estimate that megafauna destroyed around 30% of South America’s forests.[7] However, they became almost extinct, often coinciding with the arrival of humans.[8] In many places, humans are the only creatures left that can continue to transform the landscape in this extreme way, pushing back the shade of trees and giving other creatures a chance to take root.

An abandoned farmhouse near Rijssen, the Netherlands. © Stringer via Getty Images

Across the planet, humans have used fire and tools to clear land for agriculture, gardening, grazing and hunting for thousands of years. In the process, we have created ecological “mosaics” or “patchwork landscapes”: landscapes that contain a variety of habitats, such as meadows, gardens and forests. These places are not designed as nature reserves, but they often host a wide variety of animal life. Research detailed by Sophie Yeo in Nature’s Ghosts[9] shows that hay meadows cultivated for animal husbandry in Europe are actually more successful at protecting a greater number of species than meadows cultivated for biodiversity. Looking back to the early Holocene (which began 11,700 years ago), researchers found that human presence was about as likely to increase biodiversity as it was to decrease it[10]. Not all human-created landscapes are created equally. A neighborhood paved with asphalt and its artificial lawns is very different from a village planted with a diverse array of vegetables and flowers. A traditional hay field is even more different from a soybean plantation drenched in pesticides.

However, scientists continue to find that the old idea of ​​humans versus nature is equally wrong, and the rosy vision of the environment thriving in the absence of humans is more fantasy than reality. "People still imagine that nature is some kind of pristine place that will be saved by humans," said American environmental scientist Erle Ellis. "This is absolutely a misunderstanding."

© CN Traveller

In 2021, Ellis published a new study that looked back 12,000 years. He and his colleagues found that nearly three-quarters of the Earth’s land has been occupied and transformed by human societies. Other researchers have gone even further back. Examining human interactions with biodiversity during the late Pleistocene (up to 120,000 years ago), scientists have concluded that “pristine” landscapes do not exist in most parts of the planet, and in most cases, have not existed for thousands of years.[11] Many landscapes now thought to be untouched, from the savannas of equatorial Africa to the depths of the Amazon rainforest, have actually been profoundly altered by humans. “The critical role that humans play in ecology is so important and has long been overlooked,” Ellis says. “The most biodiverse places on Earth—and this is almost universally true—are inhabited by indigenous peoples.

Why? Because they preserve a lot of biodiversity, and even create it. They maintain this heterogeneous landscape.” There is no doubt that recent human activity — especially the massive clearing of ecosystems and industrial consumption of fossil fuels — has brought ecological disasters. But if nature is to return to some past state, the key question may not be human absence but the form in which human presence can appear.

A shepherd drives his sheep through the Yatürk Gate in Bulgaria. © Malkolm Boothroyd

In small Bulgarian communities that are losing population, traces of modest human activity can sometimes be seen, offering both a path to the future and a glimpse into the past. Off the main street in the village of Turkmen, a dirt road leads to a shrubby meadow. On the day I visited, Slavcho Petkov Stoyanov, 56, was standing there, watching his sheep graze among the bushes. “Years ago, no one would let me graze here,” he said. “It was all for growing vegetables.” He is the last sheep owner in the village, and usually employs shepherds to look after his flock—but lately the young men have left the village, and he has returned to the fields, sitting in the shade to avoid the midday sun.

Stoyanov is one of the few people here, helping to maintain a diverse mosaic of landscapes: some open spaces have expanding tree canopies, but others have been cleared for grazing and dotted with wildflowers. He shows how human activity, far from harming the environment, can actually protect it. As rural areas like Turkmen become depopulated, they become vulnerable to new forms of exploitation: Land prices fall, and with fewer people around, it’s harder to oppose projects like mining and quarrying. “You could see depopulation becoming a springboard for industrialization,” Daskalova told me.

This road in Turkmen village has played an important role in the lives of several generations. © Gergana Daskalova

Stoyanov points to the reservoir down the field. His grandparents had helped dig the reservoir themselves. However, just a few years ago, a company was awarded a cheap contract through the city hall to fish from it. The process followed a brutal short-term logic: they installed pumps, drained the reservoir, and scooped out the fish. Almost everything else died. "They caught about 20 tons of fish," Stoyanov said. The remaining villagers were furious and launched a successful campaign to end the contract. The reservoir has slowly recovered, and the water, fish, and birds have returned. In time, he hopes that parts of the village will recover, too. They now have new opponents, including a project to build a limestone quarry on the edge of the village.

Taking full advantage of the environmental possibilities this massive population exodus presents requires a shift in our conceptions of humanity’s relationship to nature, an understanding that our species can be both beneficial and detrimental to ecosystems. It also requires human intention: neglect alone is not enough. Around Slavcho’s sheep, the backdrop of the Turkmen Gate is changing. Forest plots push outward, vines engulf villas, and invasive shrubs that smell of chemicals take over meadows. Nature’s advance seems unstoppable, but its future remains uncertain, depending on the people who remain: what will they allow to grow? And what will they suppress?

Behind the door of the storage room in the abandoned house, there are dozens of jars of pickles and preserves that have not been opened. © Gergana Daskalova

This uncertainty comes up repeatedly in conversations with scientists who study abandoned land. It takes time for biodiversity to flourish. The same forces that drive people away from a place—epidemics, wars, changing economic trends—can also bring them back. A study by He Yin and a team of scholars found that millions of hectares of abandoned land were brought back to cultivation within a few decades. Their neglect was “too brief” to translate into real gains for nature.[11]

At one of the longest-abandoned sites Daskalova monitors, she sees trees growing strong, undisturbed since the last occupants left. “No one had set foot on that plot for almost half a century,” she says. Yet, just this year, a new set of owners showed up. They planned to build a hotel and turn the isolated plot into a haven for tourists. “The first thing they did was clear every inch of vegetation—they literally bulldozed the whole place,” she says. The forest was cut down and plowed into dirt, leaving only a few invasive weeds on the plot. After clearing the land, the buyers realized their new project wouldn’t be profitable. “They abandoned the hotel plan,” Daskalova says. “Now it’s abandoned again.”

References:

[1]www.researchgate.net/publication/290752133_Bulgaria's_population_implosion

[2]www.theguardian.com/global-development/article/2024/jul/11/global-population-predictions-offer-hopeful-sign-for-planet-un-says?CMP=share_btn_url

[3]www.science.org/doi/10.1126/science.adf1099

[4]iopscience.iop.org/article/10.1088/1748-9326/ad2d12

[5]www.science.org/doi/full/10.1126/science.adi7833

[6]www.kfbg.org/en/press-release/article/KFBG-Study-Finds-That-Trees-Planted-in-Monocultures-Impede-Forest-Recovery

[7]nsojournals.onlinelibrary.wiley.com/doi/epdf/10.1111/ecog.01593

[8]royalsocietypublishing.org/doi/10.1098/rspb.2013.3254

[9]www.cambridge.org/core/journals/environmental-conservation/article/managing-biodiversity-rich-hay-meadows-in-the-eu-a-comparison-of-swedish-and-romanian-grasslands/3FB1EEF21C821CB667CC6D87B9F1A817

[10]www.nature.com/articles/s41559-024-02457-x

[11]pmc.ncbi.nlm.nih.gov/articles/PMC9132457/

By Tess McClure

Translated by tim

Proofreading/tamiya2

original/

www.theguardian.com/news/2024/nov/28/great-abandonment-what-happens-natural-world-people-disappear-bulgaria

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