Trees and Income Inequality

Many of us intuitively associate trees and “nice” areas. Realtors know this; if a house for sale is on a tree-lined street, the ad always says so.

In 2008,  researchers looking into the question found that the demand for trees rises with income level. From the abstract:

This study investigates the impact of selected potential factors on the demand for urban forests at the city level…The empirical findings suggest that the demand for urban forests is elastic with respect to price and highly responsive to changes in income. Urban forest area increases as total population grows but at a lower rate than population growth. (Demand for urban forests in United States cities: Pengyu Zhu, University of Southern California and Yaoqi Zhang, Auburn University)


Then in May 2012, blogger Tim de Chant wrote about the study: “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.” He went on to analyze the paper – “…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.

It’s a pattern, the paper’s authors say, that’s typical of luxury goods. Which would be fine if all that trees did was look pretty.  As Mr de Chant points out, trees benefit cities: temperature control, reducing particulate pollution, reducing stress, and even fighting crime. [For this last, he cites a recent article in the SF Chron: “Geoffrey Donovan Researches Trees and Crime.”]

“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 while large and wealthy cities have recognized this, he points out, poorer cities are much less likely to be planting trees, mainly because of funding issues.


Mr de Chant’s blog-post was picked up by Boing Boing, a popular site that links to quirky and interesting items on the Internet. Its article was headed: Income inequality can be seen from space. “How? It’s surprisingly simple. Turns out, demand for trees in neighborhoods behaves a lot like a luxury item, as opposed to a basic necessity.” It introduced the blog-post, then said, “Then, he went out and found examples, using images from Google Earth.

That was in another blog-post on the subject: Income Inequality As Seen From Space. He shows pairs of Google Earth maps of neighborhoods in cities across the world; the poor neighborhoods are relatively tree-less, the wealthier ones are green.

This is one pair of many pictures on his blog-post. It clearly indicates the difference between West Oakland (above) and Piedmont (below).

In case any of our readers are interested in studying this further: On his blog, he requests readers to send him more such picture-pairs.


The story in San Francisco seems to be more mixed. Fortunately, trees aren’t confined only to up-market neighborhoods like Forest Hills and Cole Valley and Sea Cliff. People are increasingly aware of the benefits of the urban forest: (This article lists nine of them.)

Still, it’s difficult. The two organizations planting trees, the City and the non-profit Friends of the Urban Forest, are playing catch-up. Pitch pine canker has affected many of the city’s Monterey Pines, which together with eucalyptus, provide a significant proportion of the urban forest canopy. More trees are destroyed each year, and of course the trees removed are the mature older trees – which provide the most benefits to health, value, and ecology – while the trees planted are saplings.

It’s not helped by plans to gut two of the most important urban forests in the city, both over 100 years old:

A 2007 USDA report, San Francisco’s Urban Forest,  estimated the tree population then at 669,000 trees, with a canopy coverage of under 12% of the city’s area.  Cutting down thousands of trees will have a significant impact on a city-wide scale.

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