Study after study shows the beneficial effects of spending time in nature: People who reside near green areas live longer, healthier lives than people who don’t, even when adjusting for income. Walking in nature has been shown to have more benefits than taking the same walk in a city. People living under a flight path are at a higher risk for stress and disease. Children who regularly spend time in nature have fewer behavioral disorders than those who don’t.

This is not good news, because the trajectory of human life has been moving inexorably away from “the round ocean and the living air” extolled by Wordsworth. In 2008, for the first time, more people in the world lived in cities than in rural areas, Williams writes. Traffic on U.S. roads tripled between 1970 and 2007, the number of passenger flights has increased 25 percent in the past 15 years and 83 percent of land in the lower 48 states is close enough to a road that you can hear it.

Still, nearly everywhere, some modicum of nature can be found. And if you’re willing to put up with sketchy trails and the roar of jet planes, the Washington area abounds with it.