In two studies, newly greened urban areas have been shown to reduce residents' heart rates and help them feel less fear.

A recent University of Pennsylvania School of Medicine study showed that urban residents' heart rates were reduced when they walked by city lots that had been greened up.

Published in the American Journal of Public Health, the study observed people in two Philadelphia neighborhoods who wore heart rate monitors when they went for strolls, and documented a reduction in heart rate when they walked by a lot that had underwent cleaning and debris removal, had grass and trees planted, and a low wooden fence installed.