Trees on streets and boulevards reduce crime. Do we know the how or why of this particular correlation, nope. But we do know that trees on private lots also tend to reduce criminal activity, with the proviso that they are over 42 feet high. The studies linked are quite fascinating and most definitely worth a read.
But recent research suggests the opposite: trees don’t give burglars and highwaymen a place to hide, rather they may reduce crime in a neighbourhood.
One piece of research from 2001 focused on a public housing project in Chicago, where some buildings had trees out front, others did not. The research found that buildings with fewer trees or barren yards had more crime reports, while buildings with trees had fewer crimes. Because residents of the project were randomly assigned to various apartments, the differences in crime couldn’t be attributed to factors like income.
A more recently published article in the journal Landscape and Urban Planning focused on Cincinnati. The city’s trees were being killed by the Emerald Ash Borer beetle. Researchers took advantage of the spread of the beetle to study the relationship between trees and crime. They found that when a tree is killed and removed, crime in the area tends to go up.