eldavojohn writes: PBS's NewsHour interviewed Geoffrey Donovan on his recent research published in the American Journal of Preventative Medicine that noted a correlation between trees (at least the 22 North American ash varieties) and human health: 'Well my basic hypothesis was that trees improve people's health. And if that's true, then killing 100 million of them in 10 years should have an effect. So if we take away these 100 million trees, does the health of humans suffer? We found that it does.' The basis of this research is Agrilus planipennis, the emerald ash borer, which has systematically destroyed 100 million trees in the eastern half of the United States since 2002. After accounting for all variables, the research found that an additional 15,000 people died from cardiovascular disease and 6,000 more from lower respiratory disease in the 15 states infected with the bug compared with uninfected areas of the country. While the exact cause and effect remains unknown, this research appears to be reinforcing data for people who regularly enjoy forest bathing as well as providing evidence that the natural environment provides major public health benefits.