Big trees provide shade and improve air quality. But new study insists that they can fight crime as well. Large trees in urban areas are associated with lower crime rates. Conversely, smaller trees around homes were associated with higher crime rates.
The claim comes from a US Forest Service study. Geoffrey Donovan led the research for the US Forest Service's Pacific Northwest and Southern Research Stations. The results have been published in the journal Environment and Behavior.
The study says that large trees make a home seem more cared for, hence its residents seem more vigilant. Smaller trees, on the other hand, provide more places for criminals to seek cover.
From 2005-2007, Forest Service researchers studied 413 reports of burglary, vandalism, and other crimes at 2,813 single-family homes in Portland, Oregon. They also considered landscaping factors, such as whether the front door was covered by vegetation. Nearby businesses, such as bars, were also considered.
“ We wanted to find out whether trees, which provide a range of other benefits, could improve quality of life in Portland by reducing crime, and it was exciting to see that they did,” said Donovan. “Although a burglar alarm may deter criminals, it won’t provide shade on a hot summer day, and it certainly isn’t as nice to look at as a tree.”
Planting trees in high crime areas could have a positive effect on property values and reduce crime, but only if done right, the team concurred. Tree plantings need to avoid blocking lines of sight or providing hiding places. Proper pruning of smaller trees could also reduce crime, by removing places criminals can lurk.
The researchers found that variables that decreased the probability of a criminal being observed or increased the probability that a criminal would encounter a house increased crime occurrence. In contrast, variables that increased the probability of a criminal being observed decreased crime occurrence.
They argue that the results not only demonstrate correlation but also causation. They give three reasons for this. "First, our choice of tree variables was guided by established theories of crime motivation. Second, we controlled for a wide range of other variables that may affect crime occurrence (our choice of covariates was guided by the crime literature and by consultations with local crime-prevention officers).
"Third, our results are consistent with a 2001 study, where researchers studied the effect of trees on crime occurrence in a very different residential environment using different statistical tools. However, it remains possible that our findings resulted from unmeasured third factors correlated with crime as well as the tree variables."
