科学美国人60秒 SSS 行善应先对社区进行调查（在线收听）

This is Scientific American — 60-Second Science. I'm Jason Goldman.

Trees in cities do measurable good for biodiversity and for human health. They scrub pollution from the air. They provide habitat for wildlife. They make streets look nicer. And they even reduce stress and have been linked to reductions in crime.

Back in 2015 a group of Toronto-based researchers discovered that planting just eleven more trees per city block would reduce heart-related conditions by the same amount as if everybody living on that block became a year and a half younger.

But in Detroit between 2011 and 2014 a quarter of eligible homeowners t??urned down an offer from a local nonprofit for free street trees. Ironic, considering Detroit's nickname was once the City of Trees.

"It was actually over 1,800 trees that were rejected out of an eligible 7,425. So it was a big enough issue at that point where it warranted further investigation."

Forestry researcher Christine Carmichael, who did the research at Michigan State and has since moved to the University of Vermont.

The nonprofit created an education campaign to get more residents to accept the free trees. The assumption being that if people had all the facts, they'd be more likely to take the trees. But when Carmichael talked to residents, she found that they understood the benefits of trees. Their unease was about trust.

"Basically what I found was that opposition in Detroit to tree planting among some of these residents resulted primarily from negative past experiences with street trees, particularly in low-income neighborhoods that were grappling with blight from vacant properties, which created an additional burden of care for their neighborhood."

In the last half-century or so, more than half a million Detroit trees died from disease and neglect. At the same time, the city underwent dramatic demographic shifts. By 2016, Detroit was 82 percent African-American and had the highest percentage of low-income residents in the country. As a result, it was primarily low-income African-American communities who were forced to deal with the consequences and the hazards, like falling limbs, posed by dead trees.

In speaking with residents, Carmichael found that they would be more willing to accept free trees if they could be more involved in the decision-making process. Locals wanted input on tree size and whether they produced flowers. They also very reasonably wanted to avoid trees that could drop rotting fruits or sap on cars and sidewalks. The findings by Carmichael and Maureen McDonough are in the journal Society and Natural Resources.

"It's important to provide a space for people's stories to be heard, about what their experience of community change has been. And let them know that you understand and respect their experience. I think that would open people up more to trusting the intentions of organizations that come into a neighborhood to do good."

Thanks for listening for Scientific American — 60-Second Science. I'm Jason Goldman.