West Oakland
West Oakland

Piedmont, California (enclave of Oakland)

by Tim de Chant / May 24, 2012

“I wrote about how urban trees—or the lack thereof—can reveal income inequality. After writing that article, I was curious, could I actually see income inequality from space? It turned out to be easier than I expected.


Rio de Janeiro

Rocinha, Rio de Janeiro

Zona Sul, Rio de Janeiro
Zona Sul



Fourth Ward, Houston
Fourth Ward

River Oaks, Houston
River Oaks




Hyde Park, Chicago
Hyde Park



Fengtai, Beijing

Chaoyang, Beijing


Boston metro area, Massachusetts

Somerville, Massachusetts
Ball Square, Somerville

Cambridge, Massachusetts
West Cambridge

Above are satellite images from Google Earth that show two neighborhoods from a selection of cities around the world. In case it isn’t obvious, the first image is the less well-off neighborhood, the second the wealthier one.”

by Tim de Chant / May 17, 2012

“Wealthy cities seem to have it all. Expansive, well-manicured parks. Fine dining. Renowned orchestras and theaters. More trees. Wait, trees? I’m afraid so. Research published a few years ago shows a tight relationship between per capita income and forest cover. The study’s authors tallied total forest cover for 210 cities over 100,000 people in the contiguous United States using the U.S. Department of Agriculture’s natural resource inventory and satellite imagery. They also gathered economic data, including income, land prices, and disposable income They found that for every 1 percent increase in per capita income, demand for forest cover increased by 1.76 percent. But when income dropped by the same amount, demand decreased by 1.26 percent. That’s a pretty tight correlation. The researchers reason that wealthier cities can afford more trees, both on private and public property. The well-to-do can afford larger lots, which in turn can support more trees. On the public side, cities with larger tax bases can afford to plant and maintain more trees. Given the recent problems New York City has had with its aging trees dropping limbs on unsuspecting passers-by—and the lawsuits that result—it’s no surprise that poorer cities would keep lean tree inventories.

What disturbs me is that the study’s authors say the demand curve they see for tree cover is more typical of demand for luxury goods than necessities. That’s too bad. It’s easy to see trees as a luxury when a city can barely keep its roads and sewers in working order, but that glosses over the many benefits urban trees provide. They shade houses in the summer, reducing cooling bills. They scrub the air of pollution, especially of the particulate variety, which in many poor neighborhoods is responsible for increased asthma rates and other health problems. They also reduce stress, which has its own health benefits. Large, established trees can even fight crime.

Fortunately, many cities understand the value trees bring to their cities. New York City is aiming to double the number of trees it has to 1 million. Chicago has planted over 600,000 in the last twenty years. And London has been working to get 20,000 new trees in the ground before it hosts the Olympics.

But those cities are relatively wealthy. It’s the poorer ones that probably need trees the most but are the least able to plant and maintain them. The Arbor Day Foundation is a great resource in those cases, but like many non-profits, it is stretched too thin. Compounding the inequality is the fact that most tree planting programs are local. Urban forestry has sailed largely under the federal government’s radar. The U.S. Forest Service does have a urban and community forestry program, but is woefully underfunded, having only $900,000 to disperse in grants. Bolstering that program could help struggling cities plant the trees they need. After all, trees and the benefits they provide are more than just a luxury.

Source: Zhu, P., & Zhang, Y. (2008). Demand for urban forests in United States cities Landscape and Urban Planning, 84 (3-4), 293-300 DOI: 10.1016/j.landurbplan.2007.09.005

Geoffrey Donovan researches trees and crime
by Joe Eaton, Ron Sullivan  /  May 29, 2011

“People have an intuitive sense that trees are good things,” Geoffrey Donovan said. “Being a soulless economist, I like to quantify things. ‘Trees are nice’ isn’t a very useful statement. You need to know how nice and in what sorts of circumstances.” Donovan, who works for the U.S. Forest Service in Portland, Ore., is trying to measure how urban trees affect the quality of life. He has looked for correlations between tree-canopy cover and the risk of premature births, and is studying the role of trees in managing storm-water runoff. The article that has received the most attention, though, deals with the effect of trees on crime in Portland. Co-authored with Forest Service colleague Jeffrey Prestemon, it was published last fall in the journal Environment and Behavior.

This was one of the first attempts to relate the presence and size of city trees to crime statistics. According to Donovan, most previous studies focused on the perceived risk of crime in planted areas: “People were shown pictures of different types of vegetation and asked how it made them feel.” It’s often assumed that trees or shrubs obscure sight lines in public spaces and provide hiding places for miscreants. “To some designers, vegetation is always a bad thing,” Donovan said. “They’d like you sitting on a concrete pad with a spotlight on you.” We’ve encountered that mind-set ourselves, most recently when restored riparian vegetation in a Richmond park was cleared to deter crime. In fact, a previously published study found an inverse association between crime and greenery. Frances Kuo and William Sullivan reported in 2001 that shrubbery and grass had “a systematic, negative relationship with property crimes, violent crime, and total crimes” in Chicago’s Ida B. Wells public-housing development, which was demolished in 2008. They also wrote that Wells “residents living in greener surroundings reported lower levels of fear, fewer incivilities and less aggressive and violent behavior.”

3 years of data
Donovan and Prestemon used three years of crime data from one of Portland’s five police precincts – the one in which Donovan happened to live. He described the area as middle-class and ethnically homogeneous. Its crime rates, he said, were probably in the middle range for the city. The researchers used seven crime categories as indicators of property crime and violent crime. Through street-level surveys and aerial photography, they measured the size and placement of street and yard trees, and collected data on other neighborhood characteristics that might relate to crime incidence, including the presence or absence of neighborhood-watch signs, dogs and window bars. “Two crime-prevention officers walked around the neighborhood with us and pointed out things we might have missed otherwise,” Donovan said.

Large trees, less crime
When he and Prestemon analyzed the relationships among all the variables, they found that increased crown area of both street trees and trees on a house’s lot was associated with decreased crime. Conversely, the more trees on a lot, the higher the association with increased crime. That last finding makes intuitive sense: Multiple small trees around a house could obscure its visibility from the street or from neighbor’s homes. But how would larger, more mature trees deter crime? The “broken windows” theory, proposed in 1982 by political scientist James Q. Wilson, might provide an explanation. “If there are signs of neighborhood disorder, people will think the neighborhood is not well cared for and not subject to effective authority,” Donovan told us. “Criminals are less likely to be caught. If signs of disorder and care increase crime, perhaps trees do the opposite. I’m not suggesting this is a conscious calculation by criminals. The trees might show a history of care and social stability. Nicer neighborhoods have nice trees.” He believes the association is real: “We controlled for neighborhood characteristics, the value of homes, and other factors. We believe it suggests causation, and it’s consistent with other research.” Donovan, whose background is in the economic consequences of wildfire, plans additional urban-forest studies. “We’re a largely urban society,” he said. “Our biggest interaction with the natural environment is in the city. If you’re interested in the effects of the natural environment on people, that’s where you look.”

Source: Geoffrey Donovan’s website:

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