The average visitor to some of the nation’s parks and wilderness areas is getting grayer, prompting a new emphasis on getting young people to unplug and head outdoors.

USA Today reported that without “a generation of kids who have had good experiences with national parks, then in a very short amount of time, we may not have enough people who care about national parks to keep them going,” says John Hayes of the Dunes Learning Center at Indiana Dunes National Lakeshore.

For the National Park Service (NPS), developing life-long connections between the public and parks — especially for young people — is a priority from now until its 2016 centennial.

That could be a challenge: A 2010 Kaiser Family Foundation study found that people ages 8 to 18 spent an average of 7½ hours a day on digital media. Last month, a study in the Journal of Personality and Social Psychology found that three times as many Millennials — born in the 1980s and ’90s — as Baby Boomers said they made no personal effort to help the environment.

A “big concern” of the National Park Service “is maintaining 21st-century relevance,” says James Gramann, a Texas A&M professor writing a book on people-park links. Visitors ages 16-24 are most under-represented, he says.

The aging of visitors affects wild places across the USA:

•The average age of a visitor to Minnesota’s Boundary Waters Canoe Area was 26 in 1969, 36 in 1991 and 45 in 2007, says a March report by the U.S. Forest Service. “It’s the same people. They got attached, and they keep going back,” says co-author Bob Dvorak, a Central Michigan University professor.

•The average age of out-of-state visitors to Glacier and Yellowstone national parks in 2011 was 54, says the University of Montana’s Institute for Tourism and Recreation Research.

•At California’s Death Valley National Park, 49% of spring visitors in 2010 were 46 to 65 years old.

Overall visits to national parks fell in 2011 for the second year in a row. The National Park Service counted 278.9 million visits in 2011, down about 1% from 2010.

Some parks have plenty of young visitors. The Lincoln Home National Historic Site in Springfield, Ill., attracts about 10,000 students a year, Superintendent Dale Phillips says. “It’s important that we teach them early,” he says.