In English legend, the highwayman rides out from behind the cover of trees and threatens honest travelers. This traditional view of nature’s role in promoting wrongdoing is now being re-examined. Two recent studies provide evidence that trees and grass around public housing sites can reduce some aggression and deter crime. Researchers Frances Kuo and William Sullivan (University of Illinois) studied two Chicago public housing sites. At one site, the researchers recruited and trained fellow residents to ask women questions about the amount of violence and aggression (verbal, psychological, and physical) they had engaged in. Another study at a separate complex looked at police reports over a two-year period.
“Buildings with high levels of vegetation had 52% fewer total crimes, 48% fewer property crimes, and 56% fewer violent crimes than the buildings with low levels of vegetation.”1
Lower aggression
Using the information from the interviews, the researchers found that the women reported fewer aggressive acts against partners over the last year if residents lived in “green” vs. “barren” surroundings. There was no connection between aggression against their children in the last year and greenness.
The researchers also found less lifetime violence against partners in greener buildings—a finding that may reflect the residents’ long-term occupancy in the same apartment, or a bias toward remembering and reporting more recent events.
Less mental fatigue
The researchers then tested the women’s mental fatigue, and found that women who reported more violence showed greater mental fatigue. The amount of mental fatigue even explained the results more accurately than the buildings’ greenness level. This supports the argument that greenness helps mitigate violence by easing mental fatigue—a result found in other studies.
Lower Crime
Turning to crime statistics, the researchers looked at two years of crime reports from a large public housing complex. The vegetation around 98 selected buildings was quantified into three levels: low, medium, and high. The crime reports showed that levels of all crimes, including property and violent crimes, were lower in the greener surroundings.
There was a significant difference between crime reported in the low vegetation buildings vs. the medium-vegetation buildings, as well as the low- vs. high-vegetation buildings. This result was true even when other factors such as vacancy rate and building height were examined.
The percentage decrease in total crimes between medium- and low-vegetation buildings was 42%, and between high- and low-vegetation buildings, 52%; for property crimes, the decreases were 40% and 48%; and for violent crimes, 44% and 56% respectively.
The green spaces around each building were rated from photographs on a scale from 0 (no trees or grass) to 4 (complete tree canopy), with the building front, back, and side ratings averaged to provide a vegetation level. Low-vegetation buildings rated from 0 to 0.9; medium-vegetation buildings from 1.0 to 1.9; and high-vegetation buildings, 2.0 and above. These ratings suggest that very modest increases in greenness may pay big dividends.
Underlying reasons
The researchers believe that increased vegetation may deter crime by:
- Encouraging residents to be “out and about,” thereby increasing casual surveillance, or the perception of such surveillance.
- Sending a signal to trespassers that a space is owned and cared for, and thus the tended green area is hostile “territory.”
- Providing a relief from mental fatigue, which might prevent irrational and impulsive actions.
Plants that block views and provide hiding places may increase fear and crime, but in these studies, the vegetation was primarily trees and grass. Vegetation can clearly influence aggression and crime, whether committed by legendary English highwaymen or modern lawbreakers.
*Note that because of the way the data were grouped for analysis, there is not a one to one relationship between the percentage decrease in aggression scores, and the percentage degrease in aggressive acts.
Originally published in Issue 3, 2004.
1. Kuo, F. and W. Sullivan. 2001. Environment and crime in the inner city: Does vegetation reduce crime? Environment and Behavior, vol. 33 no. 3 (May), pp. 343–67.
Kuo, F. and W. Sullivan. 2001. Aggression and violence in the inner city: Effects of environment via mental fatigue. Environment and Behavior, vol. 33 no. 4 (July), pp. 543–71.