Americans have been visiting national parks and other natural reserves less and less since 1987, new research confirms. Outdoor pursuits, ranging from camping to hunting, have entered a persistent and growing decline.

"Folks are going out into nature much less and decreasingly every year," says conservation ecologist Patricia Zaradic of the Environmental Leadership Program and co-author of the report published in Proceedings of the National Academy of Sciences USA. "It would take 80 million more visits this year to get the per capita number back up to the level it was in 1987."

Zaradic and her colleague conservation biologist Oliver Pergams of the University of Illinois at Chicago analyzed trends in visits to national parks and forests, state parks, surveys on camping and the number of licenses for activities such as hunting or fishing. All peaked between 1981 and 1991 after 50 years of steady increase and have been declining at roughly 1 percent per year since for an overall drop of as much as 25 percent.

Even a slight increase in the frequency of hiking and backpacking trips did nothing to offset the overall decline. "The average American backpacked once every 12.5 years in the past and [is] now backpacking once every 10 years," Zaradic notes. Similar data on park visits in Japan and Spain showed the same trend. "It looks like, clearly from the Japan data, that this may be an international problem," she says.

The conservationists believe that the electronic world has supplanted the natural world as the leading diversion. Their statistical analysis shows that the increase in video games, movie rentals and other electronic entertainment most closely matches the decrease in camping and park visits, as opposed to income, vacation time, park overcrowding, foreign travel or other potential causes.

But Richard Louv, chairman of the Santa Fe, N.Mex.–based Children and Nature Network and author of Last Child in the Woods, ascribes the change more to increasing school and work pressure on children and parents as well as the rising cost of park visits. Plus, he says, there's the fear factor. "You didn't have the concept of stranger danger [in the past]," Louv says. "If you are raising a generation under protective house arrest, will they have a joyful experience in nature?"

Without such an experience, Louv, Pergams and Zaradic agree that the value of nature might be lost on such children and adults. "If we aren't out in nature, we aren't aware of our human footprint in nature. Then it takes natural disasters like Hurricane Katrina to recognize global warming," Zaradic says. "You don't see the subtle signs, you have to wait for something to hit us over the head."

Pergams and Zaradic plan to tackle the fear issue next. "If fear is a factor, what kinds of fear?" Pergams asks. "Fear of the unknown, fear of animals, fear of getting lost, fear of crime, fear of disease, all kinds of different fears that might come into play and to what extent they might play into the decline." In addition, they hope to compare the results of children's exposure to "virtual" nature online or on television with the real thing.

The solution may be as simple as getting kids into the woods or other natural areas in the company of parents, grandparents or other relatives. "This isn't a bitter pill," Louv says. "In order to give kids some semblance of unorganized activity in nature, we're probably going to have to organize a lot of it. It's a paradox we'll have to deal with with a sense of humor."

Biologist Edward O. Wilson argues that humans are hardwired for biophilia, or a love of wild plants and animals, and that putting them back in touch with the environment could resurrect that feeling. "We undervalue the playing in the mud kind of experience," Zaradic says. "Which, it turns out, provides a lot of education."

Putting more nature back into humanity's urban environments might not hurt either. "Green urbanism is about efficiency, saving energy. That's important but ultimately it's kind of boring," Louv says. "Biophilic design is the idea that when we design nature into our cities really interesting things begin to happen."