Why did nearly one-quarter of eligible residents in Detroit turn down free street trees? That's the mystery researchers solve in one of the first studies to explore opposition to city tree planting programs. As cities from New York to L.A. embark on tree planting initiatives, the research helps to explain why more than 1,800 of 7,425 eligible Detroit residents — roughly 25 percent — submitted 'no-tree requests' between 2011 and 2014 alone.