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Ancient homes for the dead can double as wildlife havens

DAILY SCIENCE

Ancient homes for the dead can double as wildlife havens

Ancient burial mounds create islands of native grasslands in eastern Europe and Asia, pointing to the ecological potential of sacred spaces.
July 26, 2023

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Some 5,000 years ago, a nomadic people spread across the rolling grasslands of eastern Europe and Asia, their expansion fueled in part by their mastery of horse riding, the earliest in the archaeological record.

Today, the path of conquest by the Yamnaya is marked by as many as 600,000 burial mounds which gave the Bronze Age society its name (yamnaya is a Russian adjective meaning “related to pits” that refers to the corpse-holding chambers beneath the mounds).

It turns out these human-made hills are helping to preserve another bit of the region’s legacy—remnants of the native grasslands that once carpeted Eurasia’s vast steppes.

These mounds, known as kurgans, “act as habitat islands in transformed landscapes,” ecologist Balázs Deák of Hungary’s Centre for Ecological Research, wrote in an email. “They are analogous to ‘real’ oceanic islands, just in this case the water is represented by corn fields.”

Much of the region’s grasslands have been plowed under. More than half of Eurasian steppe habitat is now being farmed. In Ukraine less than 10% of the original steppe remains, while in Russia millions of hectares have disappeared.

 

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The kurgans range from small bumps to 100-meter-diameter hills. Their steep sides discourage farming. So does their ancient significance, which helped attract later cultural markers such as churches and graveyards. Though relatively short (typically less than 15 meters from base to summit), the varying orientation, soil and water conditions on different parts of the hillsides help create micro-climates favoring a bounty of grassland species, such as the delicate white-flowered panicled baby’s breath and Siberian sandwort, and the purple dwarf iris. A survey in Bulgaria turned up 1,059 plant species—a quarter of the country’s plants – in 111 kurgans covering roughly the equivalent of the parking lots at 9 Walmart stores.

“Not the size of the kurgan is impressive, but the richness of historical and cultural values and the biodiversity potential,” said Deák.

A group of eastern European researchers including Deák are cataloging these kurgans and trying to call attention to their role as ecological havens. They created a crowd-sourced database of kurgans and their surroundings, the Eurasian Kurgan Database. The collection includes more than 1,000 kurgans from 10 countries ranging from a national park in western Hungary to far eastern Mongolia, a testament to the continent-spanning reach of this ancient society.

Using this database, a team led by Deák sought a broader understanding of how the kurgans fit in the landscape. Relying on a combination of information in the database and maps of grassland coverage, they found that more than half the kurgans surveyed—58% – were covered with grasslands. The most grassland rich mounds were in Bulgaria (90%) and Ukraine (75%) while Russia had the lowest coverage at 27%, they reported July 10 in the journal Conservation Biology.

Culturally significant features such as churches, stone pillars, or a mention in ancient stories appeared to bestow a protective effect on kurgans—67% with such features still were home to grasslands, as were more than 77% with some kind of official landscape protections, such as parks.

But even in unprotected places where the surrounding landscape was devoid of native habitat, nearly 40% of the kurgans remained grassland oases, prompting the authors to declare the mounds “had a great potential to preserve grassland habitats.”

These ancient sacred spaces on the windswept steppes are just one example of accidental wildlife refuges—places that harbor more natural habitats and a smaller human presence as a side-effect of their main uses. Sacred natural spaces more broadly have been found to provide conservation benefits on multiple continents. In Ethiopia, church forests provide islands of green amid arid farmlands. On a less religious front, military bases have turned into havens for rare species. Even some of the world’s most polluted no-go zones, such as the forests surrounding the destroyed Chernobyl nuclear power plant and the desert around the Hanford nuclear weapons complex in eastern Washington, are habitat hotspots.

For the kurgans, some official protections are already in place, though they vary from one country to the next. Hungary is one of the most ambitious, with restoration efforts, legal limits on activities around them and subsidies for farmers who avoid plowing them, said Deák. But even in places with fewer regulations, the cultural value of the kurgans can offer their own shield. The research showed that just the presence of some kind of culturally significant marker increased the chance grassland would be there by 30%.

“This kind of protection is provided by the own willingness of the people (no legislative restrictions are needed), and thus can be maintained in a sustainable way for a long time,” said Deák.

Perhaps that insight can help people find ways to promote habitat protections far from the lands where the Yamnaya once roamed.

Deák, et. al. “Contribution of cultural heritage values to steppe conservation on ancient burial mounds of Eurasia.” Conservation Biology, July 10, 2023.

Photo: courtesy of the Centre for Ecological Research/ Balázs DEÁK

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