Ken Cordell, a leading recreation researcher in the Forest Service's Southern Research Station in Georgia, also sees that the tastes of Americans are shifting, even as people continue to enjoy the outdoors. Based on telephone surveys, Cordell reports that from 2001 to 2009 "nature appreciation" activities -- like watching or photographing birds and other wildlife -- grew more rapidly than backcountry hiking, hunting and fishing. We're still pursuing wildlife, but now we're more likely to use digital cameras and binoculars. And recreation fads like kayaking and orienteering have some of the highest growth rates. Cordell and his research team also found that "walking for pleasure" and "family gatherings outdoors" are today's most popular activities, enjoyed by about 85 percent and 74 percent of Americans, respectively.

Interpreting statistics is a complicated task, and the recent numbers indicate many different story lines. Late last year, the U.S. Fish and Wildlife service reported that from 2006 to 2011, the number of hunters actually increased 9 percent -- the first increase since 1975. However, well over half of hunters used private land exclusively -- a worrisome trend for those concerned about public support for the concept of public lands.

Those rebounds don't surprise Cordell, who believes recreation generally follows the economy's ups and downs. Looking ahead, over the next 50 years, his studies predict an overall increase in outdoor recreation, with some activities growing more than others. Per capita participation in "visiting primitive areas," hunting and fishing, off-road driving and snowmobiling will all decline, he predicts, while downhill skiing, snowboarding and climbing will have faster growth rates. "What people choose to do is going to continue to change," says Cordell. "I think that's a major point, because a lot of our management folks have been pretty much focused on some of the traditional activities."

As politicians and advertisers are aware, the country is undergoing a significant demographic upheaval, and no one knows if the next wave of recreationalists will embrace public land. For one, baby boomers are aging into a less active demographic. "They're still very interested in hiking, but they want it to be easier distances," says Frayer. "They like to go on interpretive hikes and (most) importantly they like to be back by 6 o'clock for martinis."

And most people recreating on public land are still white males, a shrinking percentage of the total population. That's why some land managers are working to encourage more kinds of visitors, installing yurts for busy urbanites and making camping and picnic sites larger to attract Latino families on multi-generational outings.

Today, there's a whole ecosystem of options for outdoor recreation, some more intensely connected with nature than others, offering ever more entry points into the outdoors. If a greater variety of people in coming generations do start venturing onto public land,  they're likely to have a good time. Last year, the Forest Service's National Visitor Use Monitoring program found that only about 3 percent of national forest and grassland visitors reported dissatisfaction, while 94 percent were satisfied (77 percent were very satisfied).

The challenge in the future will be keeping those numbers high, as recreation tastes and the public itself evolve. "We need to be able to change with the times," says Frayer. "If we don't, people will be going other places, and we gauge our success by use. If there's nobody coming, then why the heck are we doing this?"

Sarah Jane Keller is a High Country News intern whose home base is Bozeman, Mont. There are few things that can keep her away from public land, and writing about science and sometimes yurts are at the top of that list.