US cities are losing 36 million trees a year. Here's why it matters and how you can stop it

If you're looking for a reason to care about tree loss, this summer's record-breaking heat waves might be it. Trees can lower summer daytime temperatures by as much as 10 degrees Fahrenheit, according to a recent study. 

But tree cover in US cities is shrinking. A study published last year by the US Forest Service found that we lost 36 million trees annually  from urban and rural communities over a five-year period. That's a 1% drop from 2009 to 2014.If we continue on this path, "cities will become warmer, more polluted and generally more unhealthy for inhabitants," said David Nowak, a senior US Forest Service scientist and co-author of the study.Nowak says there are many reasons our tree canopy is declining, including hurricanes, tornadoes, fires, insects and disease. But the one reason for tree loss that humans can control is sensible development.

More than 80% of the US population lives in urban areas, and most Americans live in forested regions along the East and West coasts, Nowak says."Every time we put a road down, we put a building and we cut a tree or add a tree, it not only affects that site, it affects the region."The study placed a value on tree loss based on trees' role in air pollution removal and energy conservation.

The lost value amounted to $96 million a year.