A growing body of evidence suggests that humans are hard-wired not just to enjoy a pleasant view of nature, but to actually exploit it, much like a drug, to relax and refresh after a stressful experience. Our earliest ancestors, Ulrich theorizes, likely needed a way to swiftly recover from a traumatic experience such as a hunt, a battle or an attack from a wild animal. "You can imagine that those who could look out at the open savannah, seeing its safety and tranquillity, and quickly feel calm but also alert to their environment would likely have a survival benefit over others," Ulrich says.

Scientists have documented this restorative effect in a number of controlled experiments. In the study published in the June issue of the Journal of Environmental Psychology, Dr. Terry Hartig and colleagues at the University of California at Irvine measured markedly different physiological, attentional and mood changes in test subjects exposed to natural or urban settings.

In the experiment, 112 young adults were assigned a variety of stressful tasks, including driving to a site they hadn't visited before. Afterward, the people who sat in a room with tree views and then walked through a nature preserve showed declining blood pressure and substantially more positive change in their feelings than those who sat in a windowless room and then walked in an area of medium-density urban development.

Some of the changes could be measured within minutes of being exposed to the natural settings, says Hartig, now at Uppsala University in Gavle, Sweden. He provides advice to several European cities whose planners are considering expanding so-called urban forests.

James Raimes, 64 years old and retired from publishing, experiences an effect like this when he returns to his modest country home in Chatham, N.Y. "The sounds, the smells, and the sights have an immediate calming effect as soon as I step out of the car," Raimes says.

Many gardeners say they lose track of time while weeding, planting or mulching. "I can and often do garden from sunup to sundown, to the exclusion of many other things in my life," Raimes admits. Indeed, as people who move to fecund environments like Florida's can attest, the biological draw of gardening can be powerfully addictive — though it's clearly a much safer outlet than other addictions.