A study conducted in Chicago found that apartment buildings with more trees had lower crime. The buildings all belonged to the same housing project, all had the same architecture, and all had residents with similar characteristics. The researchers proposed two possible reasons for the reduction in crime.
Trees deter crime. That is, trees encourage potential criminals to commit a crime somewhere else. In buildings with trees, residents spent more time looking out their windows and sitting outdoors. People are less likely to commit a crime where there are observers.
Trees reduce crime. That is, trees lead potential criminals to not commit a crime at all. Studies show that nature helps us feel better, reducing our aggression and making us less likely to engage in antisocial behavior. People are less likely to commit a crime when they are in a positive mood.
Natural yards, with or without trees, draw our gaze and make us feel good. If the researchers’ theories for why trees reduce crime are correct, then natural yards also reduce crime.