Strewn with mines and bordered with barbed wire, the demilitarized zone between North and South Korea extends in a narrow band about 150 miles long and two and a half miles wide. No permanent structures or settlements exist in the DMZ, and over the past 50 years, only occasional soldiers, observers, and the 225 residents of Daeseong-dong, a little village on the southern border, have been allowed in. Because of this imposed isolation, the politically tense zone is an inadvertent haven for wildlife.

Regions like this, which were once part of a war zone, can ironically sometimes become a no-man's-land where animals and plants flourish free of human interference. Even in countries with no recent conflicts, conservationists are exploring how border zones, which tend to be unpopulated, could be used to preserve wildlife.

In the case of the Korean DMZ, population growth on both sides, as well as land conversion and development, has forced wildlife—including rare species—into the zone. Although the terrain is mostly mountainous, the zone includes the Han River delta and extensive grasslands. White-naped and red-crowned cranes use it seasonally; black-faced spoonbills, swan geese, Angora goats, Amur leopards, and the Asiatic black bear thrive year-round.

Remarkably, a few rare Amur tigers (also known as Siberian tigers) may also hang on in the DMZ. While some still exist in ­eastern Siberia and the Kamchatka peninsula, only about 10 live in South Korea, and there are no data from North Korea. But farmers who live next to the DMZ have seen pug marks, the scratches large cats make to mark their territories, and locals have also reported animals apparently mauled by a large predator. To find tigers in the DMZ would be great news for the future of the species—and not just because of the boost in numbers. In Korea the tiger has such symbolic importance that its presence in the DMZ might prove a compelling counterargument to the myriad plans for joint development in the zone, which include an international trade center, hotels, tourism programs, and housing.

The 1982 Falklands War between Argentina and the United Kingdom over ownership of a group of small islands in the South Atlantic Ocean also had an unexpected ecological benefit. In that brief span of time, Argentine forces created 150 minefields, mostly around the coastal town of Stanley, the capital. Home to about 1,500 of the islands' 2,900 citizens, Stanley also attracts about 40,000 tourists each summer to observe the region's distinctive bird and marine life. After the war, both sides worked together to remove the mines, but an estimated 15,000 to 25,000 remain scattered across 117 minefields. For four species of penguin that use the area for breeding—gentoos, southern rockhoppers, Magellanics, and kings—the mines are a boon. Because the penguins are apparently too light for their footsteps to set off the explosive devices, the birds now congregate in fenced minefields that are off-limits to people and livestock. Their new haven, however, doesn't protect these penguins from the impact of commercial fishing, which harvests the squid and fish they depend upon. As a result of the diminished food supply, local penguins have become less successful at raising chicks. Despite the minefields, the number of penguins at various sites in the Falklands has declined by roughly 84 percent since the war ended.

The paradoxical impact of battle is unmistakable in the regions involved in the Vietnam War. Between 1961 and 1971, U.S. forces dropped an estimated 100,000 tons of herbicides and defoliants on Vietnam, Laos, and Cambodia. In many places, tropical forests were reduced to single-species grasslands. Such devastating simplification of habitat led to marked declines in species, including ­elephants, Javanese rhinos, deer, and wild cats.

Yet the long-running war in Southeast Asia also helped to stave off exploitation of one of the planet's most biologically fascinating areas—the region along the Vietnam-Laos border known as the Annamite Mountains. Called "a Noah's Ark lost in time" by the naturalist George Schaller, this rainy, forested area is a marvelous trove of biodiversity. Although hunters used to prey on its unusual wildlife, during the war they had to skirt battle zones to avoid unexploded land mines, and the trade in wildlife from that region dropped off. In some of those same bomb-strafed forests, the trees are still so filled with metal fragments that the lumber is too dangerous to harvest, which also keeps humans away. Two decades after the war ended, field surveys done there turned up a large number of species unknown to science, including no fewer than five large mammals.

Even in the absence of war, countries often create protected areas along borders, because it makes sense to have uninhabited land in politically sensitive zones. About a tenth of the world's protected wildlife areas are along borders. In a 1999 study, Dorothy Zbicz of Duke University identified 169 clusters of what she calls transfrontier protected area complexes, involving 113 countries—more than half the nations in the world.

Pursuing the creation of cooperative "peace parks" makes a lot of sense for ensuring the security of both wildlife and people. The South Africa–based Peace Parks Foundation, which works to promote jointly managed transborder protected ­areas around the world, has helped establish several such regions in Africa, including a huge park linking Mozambique, South Africa, Swaziland, and Zimbabwe.

The multinational World Conservation Union, headquartered in Switzerland, is coordinating a project to create a massive transborder greenbelt that would eventually extend from the border of Russia and Finland southward through areas once obscured by the iron curtain: the old, rural East and West German border and parts of the former Czechoslovakia, Hungary, Romania, and Bulgaria. Ideally, the belt would then divide into forks to include both Bulgaria's southern border and the adjoining areas of Macedonia and Greece. The greenbelt will provide a series of natural bridges between various national parks and refuges. In Germany, the former iron curtain divide is already an 870-mile-long ecological corridor.

Although the aftermath of war—and even the implicit threat—can aid conservation, war is generally every bit as bad for the environment as it is for people. During the Iran-Iraq war in the 1980s, troop movement and heavy bombing had a serious impact on the two countries' shared fragile desert ecosystem, which is home to such species as sand cats and spiny-tailed lizards. Once the desert crust layer is damaged and the sand underneath blows away, restoration can take many years. Iraqi ecosystems continued to deteriorate with the 1990–1991 Gulf War and the myriad problems in Iraq since.

As with so many conflicts in the world, Iraq's turmoil has produced a tidal wave of refugees—estimated at more than 1.1 million people at the start of the war in 2003—and their mass movement, along with their livestock, poses an additional threat to habitats and wildlife. During the decade-long Soviet-Afghan war in the 1980s, three million refugees, and their voracious goats, fled to western Pakistan, where the animals devastated the region's dry, fragile land.

One positive development in the midst of the relentlessly distressing picture in Iraq is the restoration of the marshlands of Mesopotamia, considered by some to be the location of the biblical Garden of Eden. The regime of Saddam Hussein drained 90 percent of the marshlands of southern Mesopotamia, and as the wildlife fled, so did some 170,000 Marsh Arabs who lived in the region. Now the Canada-Iraq Marshlands Initiative is reviving the habitat. So far, 40 percent of the area has been reflooded, and wildlife is beginning to come back. Among the returning birds are 18 globally threatened species; several of them, like the Basra reed warbler, are found almost nowhere else on Earth.

Some day, there may even be a transboundary peace park covering the full extent of the marshlands of Mesopotamia, a new Garden of Eden shared by Iraq and Iran.