5. 9 Crime & Vegetation
Figure 5.9: At top are results of a two-year study in the late 1990s on the connection between crime and vegetation at the Ida B.Wells homes (after Kuo and Sullivan 2001a). Crime is lower in areas of high vegetation. At bottom left, more people engage in social activities in vegetated areas at the Ida B. Wells homes in Chicago (after Sullivan et al. 2004). At bottom right, vegetation provides a calming effect, reducing the levels of violence against a partner and children (after Kuo and Sullivan 2001b).
Results of recent studies show that vegetation played a role in residents’ lives at the Ida B. Wells public housing development. The values reported in Figure 5.9 are incidents per building over a two-year period, with 4 to 20 apartments per building, having an average occupancy rate per building of 7.8, ranging from 0.5 to 15. In particular, the reduction in crime between buildings with high and low levels of vegetation measures one incident for every two occupied apartments over a period of two years. Vigilance likely drives this correlation: People use greener spaces more often, and this use increases vigilance and deters crime. In this vein, another study tested whether residents preferred vegetated areas. Connecting measures of vegetation status to people’s revealed preferences, lo and behold, showed that people—with the exception of teenagers—preferred green locations over barren ones. Social activities between women, like eating and talking in a group, nearly doubled in green spaces compared with barren ones. If vegetation promotes social activities, then, perhaps, the additional social activity provides protection against violence. A fine line apparently exists between people feeling afraid of vegetated areas (Figure 5.4) and feeling drawn to socialize in them.
Residents also experienced high levels of domestic violence: 61% reported aggression against their partner at least once in their lives, and 56% reported hitting a child, levels four times higher than the national average. Results here indicate a correlation between a “green” environment and lower rates of domestic violence against a partner, while only “psychologically aggressive tactics” changed significantly between vegetation levels considering violence against children.
What mechanism connects domestic violence and vegetation? One hypothesis, called attention restoration theory, proposes that all the stimuli in natural spaces — birds, bugs, flowers, the wind blowing leaves, and so on — involuntarily grab a person’s attention, providing relief to the exhaustion of directed, voluntary attention. This diverted attention, so it proposes, provides a calming effect. One supporting point comes from pulling out the dependence of violence on attention abilities. Removing the correlation between more violent incidents and the interviewees’ poorer performance on attention measures makes the link between vegetation and aggression disappear.
In dollar terms, the average loss stemming from all 23,440,720 U.S. crimes in 2005 was just $726, with personal crimes averaging $257 and property crimes $866. Making no adjustments for inflation or family income, increased vegetation via reduced crime runs a few hundred dollars per occupied apartment per year, or about $2,900 per building. These crimes add up in a 124-building complex with almost 6,000 people. It seems that city leaders must balance additional police patrols with promoting more enjoyable spaces for watchful good people.
Several important features complicate the connection between crime rates and vegetation. For example, vacancy rate had no effect on crime rates, though the number of units per building was an important factor. Further, although crime rate increased and vegetation decreased with increasing building height, decreasing crime rates remained correlated with increasing vegetation after correction.
Sullivan et al. (2004) study social interactions and their dependence on vegetation levels at the Ida B. Wells buildings. Five landscape architecture and horticulture students determined each of 59 locations’ “greenness,” classifying 27 locations as barren and 32 as green. Next, researchers working with two residents of a different housing complex, presumably minimizing the impact from observations, observed each of the 59 locations three times on weekdays between 3:30 and 6:15 PM, and once on Sunday between 12:15 and 5:15 PM. Observers coded people’s behaviors like sitting, talking, or eating with a group of people as social activities, and activities like reading a book as nonsocial activities. In all, 90% more people used greenspaces than barren spaces, and 83% more engaged in social activities in green spaces compared to barren spaces. I transformed the reported standard deviations into standard deviations of the means.
Kuo and Sullivan (2001b) report studies of domestic violence in the Robert Taylor Homes development. Independent from the reported incidents of violence, 22 horticultural students, both undergraduates and graduate students, rated a building’s “greenness” on a scale from 0 (not at all green) to 4 (very green).
Taylor et al. (2002) describe attention restoration theory and cite a number of studies that confirm the idea.
Although valuing crime reduction in economic terms seems vaguely disturbing, the U.S. Department of Justice attempts it, with economic costs of crime summarized in Table 82, Personal and property crimes, 2005, from the Bureau of Justice Statistics, U.S. Department of Justice. As might be expected, the Justice Department finds a rather minimal total, direct economic loss to crime victims. One statistic, in particular, points out the absurdity of estimating the effects of crime in economic terms: The average economic loss to rape victims was $183. Certainly, everyone, including the Department of Justice, understands the devastation that the crime of rape imposes on its victims, but the crime causes lasting devastation to a nonmarket good, the victim’s sense of well-being. Further along these lines, environmental economists at the EPA summarized studies from 1976 to 1991 that used contingent valuation to estimate the “statistical value” of a life (Dockins et al. 2004). Values, in 2002 dollars, range from $0.9 million to $20.9 million. The EPA has used values ranging from $5.5 to $6.2 million.
An approach called Crime Prevention Through Environmental Design (CPTED) was developed along these lines. Internet searches yield much information on the topic, but peer-reviewed studies appear to be scant.