A new study should give city officials new incentive to plant and preserve more trees in urban areas:

Children who live in tree-lined streets have lower rates of asthma, a New York-based study suggests.

Columbia University researchers found that asthma rates among children aged four and five fell by 25% for every extra 343 trees per square kilometre.

They believe more trees may aid air quality or simply encourage children to play outside, although they say the true reason for the finding is unclear.

The study appears in the Journal of Epidemiology and Community Health.

Hat tip to Natasha Chart, who put up a link to this article at Open Left.