​​​Along the Polish-Belarusian border, a​​ kaleidoscope of golden, yellow and orange leaves hangs from magnificent, centuries-old trees. Lush moss carpets the ground of the Bialowieza Forest, which took root after the Earth's last ice age 12,000 years ago. 

"It is a truly unique place," said Mateusz Szymura, who grew up in the area and is now head of nature conservation for ​Poland's ​Bialowieza National Park that lies within the forest. "It has a beauty that can't be bought."

But the forest — a 140,000-hectare (346,000-acre) UNESCO World Heritage site that is home to European bison, lynx, pygmy owls and 10,000 varieties of fungi — is on the frontlines of a geopolitical battle and migration crisis.

​​In July 2022, Poland completed the construction of a 186-kilometer (116-mile) fence along its border with Belarus and through the transboundary forest.​

The 5.5-meter metal barrier topped with barbed wire and security cameras was erected to prevent migrants — many from the Middle East and increasingly the Horn of Africa — from entering Poland as a gateway into the European Union.

​Katarzyna Zdanowicz, a spokesperson for Poland's border patrol​​, told DW there are as many as 3,000 guards and soldiers policing the so-called "green border" in an effort to block potential asylum seekers from entering the country. She said about 30,000 attempts to cross the frontier were logged by authorities in 2024. 

Analysts say​ migrants are being weaponized in a "hybrid" war ​​by pro-Russian Belarusian president Alexander Lukashenko in retaliation for EU sanctions against his country.​​​     ​​

The barrier's impact on biodiversity​

The erection of a physical border through Bialowieza​​, which previously had minimal human presence,​​ "is a very significant trauma," said Katarzyna Nowak, a scientist at the Mammal Research Institute of the Polish Academy of Sciences. "It was here before humans. Parts of the forest were untouched for centuries, until now."

A year after the barrier was built, Nowak and a team of dozens of Polish and international scientists began an independent study over 18 months to assess its impact on Bialowieza's animals and plants.

Using methods and tools such as camera traps, sound sampling, temperature and light monitors, as well as snow tracking, they found the fortification of the border has led to numerous animal deaths, including reptiles, birds and ​​bison being killed on roads. 

Their report, which was released in March, found the fence and barbed wire were injuring animals and preventing species like deer, moose and wolves from crossing between the two countries. Nowak said Eurasian ​lynx on the Polish side that are unable to hunt, feed or breed on the larger Belarusian side are at risk of local extinction.

Though the barrier was built with gates for animals to pass, they have never been opened due to concerns among authorities that migrants would use them to cross into EU territory.

Human presence is affecting natural behavior

The scientists also observed fewer animals near the border than elsewhere, and a negative impact of loud sounds, such as vehicles and ​gunshots, on birdlife along the barrier.

In addition, the findings point to changes to Bialowieza's ancient ecosystem as a result of activity around the fence, including the introduction of 13 plant species with "​​invasion potential." Nowak says some were likely brought in during the barrier's construction, when there was a lot of vehicle movement. 

In October, the International Union for Conservation of Nature (IUCN) declared Bialowieza's conservation status to be "critical." The environmental organization said the border and related security activities were significantly increasing habitat fragmentation and pressure on wildlife.

Growing number of borders worldwide

The forest fence is just one example of the growing militarization of international frontiers. Research suggests there are currently over 60 physical border walls in the world and further militarized boundaries, which is a sharp increase on the six that existed after the fall of the Berlin Wall in 1989. 

These frontiers regularly impact local wildlife. At the US-Mexico border, white-tailed deer, American black bear, and mountain lions are being blocked by more than 1,000-kilometers of walls and barriers.​ 

​In the case of Poland's fence, which also passes through five other EU-protected Natura 2000 areas, scientists say they don't know enough about its impact. This is in part because the Polish government sanctioned its construction without an environmental impact assessment. 

In a written statement to DW, the national park, which began monitoring wildlife deaths last year, said "the number of mammals harmed by the fence is very low, and fatalities occur extremely rarely."

But Michal Zmihorski, head of the ​​​​Mammal Research Institute, questions the effectiveness of official efforts.

"The most important thing is good data, but we don't have enough. Only then can we make data-based solutions," he said, adding that the government should be funding the monitoring he and his team are doing. 

"We have had to take on the responsibility," he said in reference to the independent financing his institute sourced for its 18-month research project.

Poland's Ministry of Climate and Environment did not respond to Zmihorski's claim but said in a statement that it was the responsibility of park authorities to implement "preventive measures," and that data on incidents involving animals is submitted to the ministry every two weeks. It did not, however, respond to a request for such data.

Can conservation help build bridges?

Though the national park says it has taught some 4,000 soldiers about the "exceptional value" of the forest, the institute says the efforts don't go far enough to raise ​environm​ental ​​awareness among soldiers and border guards, who have been seen littering, feeding stray cats and exercising off-duty in the forest. 

Scientists from the Mammal Research Institute are also requesting better access,​​ including ​​permission to take samples at border posts to track zoonotic disease risk amid rising human-wildlife contact. Racoon dogs, which carry coronaviruses, are in the forest.

Meanwhile, h​umanitarian groups argue that safe, legal routes should be available to migrants, meaning they wouldn't need to cross the forest.

Zmihorski hopes "conservation diplomacy" ​​— using cross-border conservation to improve diplomatic relations —​​​ ​can build bridges with Belarus and protect the Bialowieza Forest.

In 2022, the Slovenian government began to remove the 194 kilometers of fence and barbed wire it had erected along its border with Croatia seven years earlier to stop irregular border crossings, conceding that security "cannot be ensured by a fence at the border."

​​Poland, meanwhile, has banned its scientists from collaborating with their Belarusian counterparts. An IUCN spokesperson said the nations "urgently" need to take joint action. The IUCN and UNESCO have offered to moderate talks.

"The wall could be removed eventually," said Zmihorski. "It's possible. It's realistic. But it depends on geopolitics."

Edited by: Tamsin Walker