The National Park Service was created to protect and preserve the United States’ natural wonders. But what happens when climate change starts to alter these sites?

On Thursday, U.S. Interior Secretary Sally Jewell announced a new report revealing that three-quarters of 276 national parks are experiencing an earlier onset of spring. Half of the parks studied are experiencing “extreme” early springs.

The report authors discovered this by looking at historical data dating back to 1901.

For the parks in the “extreme” category, they found that “the onset of spring is earlier than 95 percent of the historical range,” says Jake Weltzin, an ecologist at the U.S. Geological Survey and one of the authors of the report.

“And we’re talking on the order of weeks.”

Good News for Invasive Species

Jewell made Thursday’s announcement in Shenandoah National Park, Virginia, one of the sites that has experienced an early onset of spring. Weltzin says that, like many parks, Shenandoah is struggling to manage invasive species like kudzu—a scourge that can be exacerbated by earlier springs.

“Biological invasions are a really big deal in the national parks,” he says. In Saguaro National Park, Arizona, near where Weltzin lives, one of the invasive species that park staff struggle with most is buffelgrass.

“The warmer the winter and the warmer the spring, the sooner it can start growing,” Weltzin says of buffelgrass. “And so a lot of the other native plants are sort of sequestered in place.”

Another problem that earlier springs present for parks is a mismatch between plants and pollinators.

“Not every organism is going to respond the same way to an early spring,” Weltzin says. “Some plants might respond a certain way, but the hummingbirds or other pollinators might not be affected in part because of where the migration routes are taking them or when they start migrating.

“So they may be arriving and it may be too late for certain species,” he says.

Looking Ahead

The Park Service’s new report was actually initiated by the National Phenology Network, a science nonprofit of which Weltzin is executive director. For the report, the network used a tool that it had developed to assess the onset of spring in different locations.

“What we’re doing really is producing maps of spring for the entire nation,” he says. “The national parks is just sort of the first application. As we go along, we hope to be able to apply this to the national wildlife refuges and other protected areas.”

The purpose of the current report is to give staff at individual parks a sense of how climate change is affecting their sites, rather than make prescriptions about how parks should deal with this change. Given the diverse ecosystems among the more than 250 parks surveyed, more research is needed to determine the more specific ways in which climate change is affecting particular parks.

“There’s clearly more work to be done,” says Weltzin. “And you know, we’ve got about a century behind us, and there’s a century ahead of us.”