From an article by the USDA Forest service: "Evidence is increasing from multiple                scientific fields that exposure to the natural environment can                improve human health.              In a new study by the U.S. Forest Service, the presence of trees              was associated with human health.
For Geoffrey Donovan, a research                forester at the Forest Service’s            Pacific Northwest Research Station, and his colleagues, the loss            of 100 million trees in the eastern and midwestern United States            was an unprecedented opportunity to study the impact of a major change            in the natural environment on human health."
 
