War’s main effect is killing people, sure — but it also kills wildlife. In Africa, the number of large animals like elephants, zebras, and buffalo can decline as much as 90 percent during wartime, according to new research. But the animals that do survive can rebuild their populations, so conservation efforts in war-torn areas are incredibly important.

Researchers looked at thousands of reports about wildlife populations in protected areas in Africa between 1946 and 2010. They found that in peacetime, the number of large herbivores stays largely stable. But even one year of conflict in as little as 20 years causes wildlife to decline, according to the study published today in Nature. The longer the war continues, the steeper the declines: a 15-year civil war in Mozambique, for instance, caused one national park to lose 90 percent of its wildlife.

Previous studies on the effects of war on wildlife were mostly individual case studies, and the results varied. In Kashmir, for example, leopards and bears thrived because poachers avoided combat areas like forests. But often the effects are negative: animals are killed by bombs or chemicals, or hunted to feed soldiers. Wars also make it hard for governments and nonprofit organizations to implement or continue conservation programs. Every country, and every conflict, is different. That’s why today’s study is important: it’s the first to take a comprehensive look at how war affects wildlife over a long period of time all over the African continent.

“We’ve shown for the first time that the overall impact of war on wildlife is a net negative,” says co-author Joshua Daskin, a postdoctoral environmental fellow at Yale University. “It takes very little conflict for wildlife populations to begin declining.”

The idea for the research came to Daskin and Robert Pringle, assistant professor of ecology and evolutionary biology at Princeton, from their work at Gorongosa National Park in Mozambique. Between 1977 and 1992, the country went through a bloody civil war that left thousands dead, and devastated wildlife in Gorongosa. The park lost 90 percent of its large herbivores to poaching, while hyenas, leopards, and wild dogs basically disappeared. But after the war, wildlife populations rebounded, and today the park is thriving, Pringle tells The Verge. There are more waterbuck now than before the war, for instance. So the two ecologists wanted to know how common these massive animal die-offs are in times of war across Africa, and whether there’s any hope of recovery.

Knowing how war shapes wildlife is crucial in Africa, since it’s home to species including elephants and rhinos, which are at risk of extinction. “It’s really the last place on Earth that has extensive, widespread, nearly intact assemblages of this sort of large wildlife,” Daskin tells The Verge. “So from that perspective, it’s a conservation priority.” To see what effects war has on these animals, Daskin and Pringle collected thousands of studies and government reports about the population decline or growth of 36 species in 19 African countries, from 1946 and 2010.

Peacetime had no effect on the populations, but generally as soon as war started, animals took a hit. “As conflict becomes more frequent, populations decline on average more quickly,” Daskin says. In Lake Mburo National Park in Uganda, for instance, impala populations declined by 4.5 percent per year on average between 1982 and 1995, when the country was swept by a series of wars and insurgencies. Hippo populations dropped by 12.5 percent per year during the same time period. And in Zakouma National Park in Chad, elephant populations declined at 44 percent per year between 2006 and 2009, when the country had a civil war.

It’s not clear from the data they used why the animals die, Pringle says. And the study’s limited to large herbivores — so carnivores and plants aren’t measured. “I suspect that these newly documented declines in large herbivore populations are just the tip of the iceberg when it comes to the effects of conflict on the natural environment,” says Kaitlyn Gaynor, a PhD candidate in the Department of Environmental Science, Policy, and Management at the University of California, Berkeley, who was not involved in the study.

Though the results sound pretty bleak, there are reasons to be optimistic, Daskin says. There were few extinctions. And as Gorongosa National Park in Mozambique shows, wildlife can rebound after conflict if conservations strategies are implemented. In Mozambique, for instance, former soldiers on opposite sides of the conflict were put to work together as rangers to protect the country’s wildlife, Pringle says. “The findings of this study show that we should not overlook conservation and restoration opportunities after conflict,” Gaynor writes in an email to The Verge. “War-torn protected areas are not necessarily a lost cause.”

And saving elephants, zebras, and rhinos is a moral imperative for Pringle. “These large animals are an important link, and one of the last links between humans and the wild world that we emerged from,” he says. “It’s important to conserve these species and enable them to persist long enough for our children and grandchildren to have that experience.”