Give Invasive Species a Job
Wild horses could play a role in preventing wildfires, if we only gave them a chance.
Updated at 1:40 p.m. on August 19, 2023
In 2014, William Simpson II was in his cabin in the Soda Mountain Wilderness area, near the California-Oregon border, when he heard a mountain lion screaming in the night. He got a flashlight and went outside. “I saw these big blue eyeballs seven feet off the ground,” he told me. Only once his eyes adjusted did he realize three black stallions were out there, staring right at him.
Simpson had spent time with domestic horses—he had grown up on a ranch, before studying science and working in forest management and logging—but he had not known that wild horses spent their nights avoiding predators. He began closely observing the horses. Now, after more than 15,000 hours studying them, he has become an expert in wild horses, which many people consider little more than a nuisance. “I’m close enough to know what they smell like, what their feet look like, what parasites they have,” he said. He’s also gotten close enough to believe that the horses have a beneficial impact on the landscape, especially when it comes to wildfire. In America, wild horses have long been a problem to be managed; instead, they might be an important part of a healthy ecosystem.
Though North America once had native wild horses, they went extinct about 10,000 years ago. A short 9,500 years later, in the 16th century, Europeans brought domesticated horses with them to this continent, and the equines multiplied. Today some wild-horse-advocacy groups think of wild horses as a reintroduced native species; other groups cast them, more negatively, as feral animals, domesticates that escaped their bonds. The Bureau of Land Management (BLM) actively manages the some 64,000 horses on its lands, through birth control and occasional but controversial culls, which some say are done to balance the needs of ranchers who pay to graze their livestock where wild horses graze. No matter what you call them, the horses will remain part of the Western landscape, thanks to a 1971 bill that gives the BLM the difficult task of both protecting and controlling the animals.
Back in the Pleistocene, large animals like those ancient horses ruled the landscape and its metabolism, Erick Lundgren, a postdoc at Aarhus University, in Denmark, told me. In drier places, as a rule of thumb, grass, shrubs, and other biomass get either eaten by herbivores or burned. When the large herbivores went extinct from most continents some 12,000 years ago, fires increased dramatically; restoring large grazers to these ecosystems, conversely, could reduce fires now. “Wild horses were in North America for 35 million years, disappeared for a heartbeat, and now they’re back,” Lundgren said.
Simpson believes he’s already seen the horses lessen the impact of fires, and the organization he founded, Wild Horse Fire Brigade, advocates for relocating horses to wilderness areas where they can live freely and do what they do best. When the 2018 Klamathon Fire began approaching his property but didn’t burn it, he thanked the wild horses. “I saw how the trees the horses used for shelter year-round survived the fire, because they grazed the fuel under the tree and broke off the low branches,” Simpson said. “The trees the horses didn’t use became matchsticks.” Fire-response teams parked their equipment in grazing areas the horses preferred because there wasn’t enough fuel to burn. The horses protected Simpson from the fire.
Right now “there are no livestock-grazing programs designed primarily for the prevention of fire in the Forest Service,” John Winn, a press officer for the agency, told me. (Some individuals do use hungry goats to reduce flammable biomass, he added.) For a start, Simpson advocates for releasing large herds of horses into forests grown for timber production. He wants to take them off the rangelands, where they’re hated for competing with cattle for forage: “Put them in areas where they actually belong and can benefit the forest.” There, the horses can be left to do what they do best: eat weeds such as flammable cheatgrass and scratch themselves against trees, knocking off lower branches that can spread fire up into the treetops. In Maui, where drought and flammable non-native grasses combined to create some of the conditions that led to this month’s devastating fire, managed grazing (perhaps putting the island’s destructive feral-goat population to work) could have reduced the amount of fuel available.
Although many conservationists would prefer that native species play such roles in restoring an ecosystem, other invasive, feral, or domestic species could take up niches left by extinct or threatened species. Australian saltwater crocodiles that were nearly extinct in the 1970s are now considered a species of “least concern,” thanks in part to the feral pigs they’ve come to feast on. Florida’s endangered snail kites, birds that were harmed by shrinking wetlands, are recovering because of an invasive snail. These pest animals can do more than become dinner too. In Australia, which is overrun with feral and invasive animals, studies have found that feral water buffalo improved the growth rate of young trees in wooded savannas and lowered tree-mortality rates after fires. Hippopotamuses left to roam after being released from Pablo Escobar’s personal zoo in Colombia (referred to in the media as “cocaine hippos”) are undoubtedly having some kind of effect on the local ecosystem, though there’s controversy over whether it’s beneficial or not. In their native range, hippos are considered “ecosystem engineers” for the ways in which they reshape waterways and move nutrients from land into the water.
In the U.S., animal grazing would only ever be a small part of the overall plan for fire management. But with a requested fire-prevention budget of $4.3 billion for 2024, a small part could still be significant. In Europe, the goal of fire reduction has joined with the popular idea of “rewilding” human-disturbed landscapes, even if that means working with domesticated or feral animals to make a wilder world. Natural grazing—whoever is doing it—results in a better and higher diversity of plants, bushes, and trees, for instance. “When you don’t have grazing, you have one species taking over everything,” Deli Saavedra, the head of landscapes for Rewilding Europe, told me. In Portugal, where Rewilding Europe is moving herds of wild horses around the landscape to reduce flammable biomass, the group is seeing big changes with small herds of animals. “There’s no doubt large herbivores are reducing the fire risk,” Saavedra said. “The question is what the management system should be.” Releasing some donkeys, water buffalo, or horses into the landscape may not be enough; people may have to become stewards of the land with these species—understanding the benefits and drawbacks of their effects on the ecology and moving them accordingly.
This is not a new idea. Many of the areas that we consider “wilderness” today were ecologies created in concert with Native people who pruned plants and watched over prescribed burns, among other activities. Nature, as long as we’ve known it, has been a place shaped by humanity. We may not be able to live without making footprints on the land, but we can become custodians of those changes instead of fighters against them.
“There’s a huge amount of stigma toward wild and introduced organisms in general,” Lundgren said. He pointed out that a lot of research on these species still looks at how bad they are for the environment. But that’s not the only possibility. “We’re changing the planet quickly and then refusing to let the living beings on it change with it,” Lundgren said. Avoiding this impulse might mean not killing barred owls just because they are outcompeting threatened spotted owls. Or it might mean allowing opossums to move northward out of their native range, into Canada. It might mean realizing that feral or invasive animals—which are next to impossible to remove once established—could fill an important ecological niche.
Lundgren has been studying feral donkeys in the Sonoran and Mojave Deserts and found that they often dig wells that increase water availability for all species, and even promote the growth of riparian trees. “People will protest that a species doesn’t belong here,” Lundgren said. “But the word belong isn’t science; it’s nativism.” Take away the issue of belonging, and what we’re left with is a wilder and more diverse world.