"Just five minutes of exercise in a "green space" such as a park can boost mental health, researchers claim. There is growing evidence that combining activities such as walking or cycling with nature boosts well-being. In the latest analysis, UK researchers looked at evidence from 1,250 people in 10 studies and found fast improvements in mood and self-esteem."
'Green' exercise quickly 'boosts mental health'
BBC News Website, Published: Saturday, 1 May 2010 00:01 UK

"'Forest therapy' taking root For stressed-out workers, this may someday be a doctor's prescription: Walk around in the woods.

Scientists in Japan have been learning a lot in recent years about the relaxing effects of forests and trees on mental and physical health. Based on their findings, some local governments are promoting "forest therapy."
Experience shows that the scents of trees, the sounds of brooks and the feel of sunshine through forest leaves can have a calming effect, and the conventional wisdom is right, said Yoshifumi Miyazaki, director of the Center for Environment Health and Field Sciences at Chiba University.
"Humans had lived in nature for 5 million years. We were made to fit a natural environment. So we feel stress in an urban area," Miyazaki said. "When we are exposed to nature, our bodies go back to how they should be."

Taking a walk in a forest, or "forest bathing" as it is sometimes called, can strengthen the immune system, according to Li Qing, a senior assistant professor of forest medicine at Nippon Medical School in Tokyo."
'Forest therapy' taking root'
The Japan Times Online, Akemi Nakamura, Published: Friday, 2 May 2008