Sometimes an unfortunate event yields interesting information. The emerald ash borer has killed over 100 million trees in the United States over the last few decades. The US Forest Service Pacific Northwest Research Station saw this as an opportunity to investigate a possible link between trees and human health.
As municipal planting schemes usually involve using one tree species to line streets, entire neighbourhood landscapes have radically changed. Looking at records between 1990 and 2007 in 15 states, researchers found 21,000 more deaths from lower respiratory and cardiovascular diseases in areas affected by ash tree loss. The results were controlled for other variables such as income and education.
This adds to other studies that have found a link between green environments and better human health. Exactly why greenery is so important to us is still undetermined, but probably this gives us another reason to try to preserve the natural landscape, for our own sakes.