Redwood City (left side) has significantly less tree cover than its comparatively wealthier neighbor, Menlo Park (center right).

Is the oak tree outside your home the next Superman? New research suggests that it may be more protective than it appears. Geoffrey Donovan conducted a study in Portland, Oregon, which showed a negative correlation between tree size and crime rates. The larger the crown area of trees, the lower the crime rates.

Well-established trees may deter potential burglars by creating the impression that an area is well cared for, and subject to effective authority. Donovan's study controlled for a number of factors, including the ethnic makeup of the neighborhoods and the value of homes. However, Donovan also admits that areas with larger trees were probably historically well maintained, which resulted in lower crime rates. 

This makes sense, as there is also a strong correlation between tree cover and income level. According to a study on the demand for urban forests, for every 1 percent increase in per capita income, there was a 1.76 percent increase in demand for forest cover. When income dropped by the same amount, demand for forest cover dropped by 1.26 percent. You can see this inequality from space (or Google maps). 

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