Urban trees reveal income inequality

Street trees

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.

But 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.¹ 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.


  1. Though like many of Chicago’s boasts that number was probably inflated by including replacement trees.

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

Photo by Alex E. Proimos.

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  1. =v= Adapting trees to urban life is a long-term project, longer even than the lifespan of a homeowner. Municipalities used to understand this and accepted the responsibility of maintaining street trees, even in working- and lower-class neighborhoods.

    Cutbacks in tree maintenance hit New York City in the 1970s (“Ford to City: Drop Dead”) and spread to the rest of the U.S. during the Reagan years. It’s one of those long-term things that it seems can be put off, until a decade later when limbs start crashing down on precious cars. Then the municipality scrambles to deal with the problem.

    One short-term approach I’ve seen is to defer annual maintenance to every 2 or 3 years, by drastically overpruning the tree. This reduces the tree’s lifespan and its canopy, and with that, its shading and traffic-calming benefits. Trees respond to overpruning by sending out quick-growing but weakly-attached branches, which are more likely to come crashing down. After which, of course, the tree is pruned back even more. Eventually it is destroyed and might be replaced with a sapling (or might not, since trees are blamed for this kind of trouble).

    Another short-term approach is to make the homeowners of abutting properties responsible for the street tree, but this encourages the same overpruning practices, particularly in lower-income communities.

    Non-profits have stepped in to fill some of the gap (I’m a volunteer with some of them, which is why I know all this stuff), but have to contend with their own funding uncertainties. What urban forests truly need is a long-term commitment.

  2. “They scrub the air of pollution…”

    I have only just come upon your blog, and started to explore your various posts. I would be very interested in talking to you about trees though – you can email me at witsendnj at yahoo dot com if you would like to.

    The statement you made, that trees absorb air pollution, is often seen. Rarely is it accompanied by the question, what happens to trees that absorb pollution?

    When people breathe in air pollution, it increases their risk of cancer, heart disease, emphysema, asthma, and various other maladies.

    When plants are exposed to air pollution, the result is even worse. It interferes with their ability to photosynthesize. Cumulative damage through stomata in leaves or needles leads to decreased allocation of carbohydrates to roots, causing vulnerability to wind and drought. It also decreases immunity to insects, disease and fungus.

    The result is that, in essence, trees have AIDS. It’s been documented that whether in urban or even remote areas, the background level of tropospheric ozone is inexorably rising as emissions of precursors travel the globe, and trees are dying off at a rapidly accelerating rate. In addition, annual crop yield and quality are significantly reduced, with serious consequences to agriculture.

    It’s really up to tree lovers – since most people pay little attention to them – to understand this and communicate with all due urgency the extent and implications of this existential threat.

    You can read more about this at the link here:

    http://www.deadtrees-dyingforests.com/pillage-plunder-pollute-llc/

    I hope to hear from you. Too many people are ignoring the ominous trend of a worldwide decline in trees.

    Gail

  3. I think it’s a little more complicated than just trees = money. I think the difference may be in the number of *planted* and maintained trees versus the number of wild trees. In my low-income neighborhood in Columbus, Ohio, we have several wooded lots–some of them encompassing several acres–where there simply hasn’t been any development and nature has been left to do her thing. Out in the suburbs, though, where farmland has fallen victim to urban sprawl, we’ve seen one subdivision after another appear, each one full of McMansions and devoid of trees any bigger than newly planted saplings.

  4. I am actually surprised that in many urban neighborhoods in Baltimore, poorer areas have better tree canopies. I think this may be due to the fact that in many affluent areas the trees have been replaced with smaller trees that have yet to mature.
    This is not true once one gets out of the urban area of the city into areas with detached homes, which are generally more affluent and have a many trees.

  5. If you’re interested in quantifying urban nature, I’ve created a website that does just that– http://streetnaturescore.org . You can search for your address, and even put a badge on your own website listing the score of a property you’re selling / renting. My goal is to promote urban nature, for the reasons you list.

    I only have data for Seattle and San Francisco currently, but with GIS analysis volunteers or enough donors can expand to other cities!

  6. correlation is not causation !!!!!!!!

    Low income families locate in cheaper housing areas DUH !!

    Cheaper housing areas have less trees, that is one of the reasons they are cheaper

    If we put a major park in a poor area, and maintain it, the areas surrounding the park will gentrify. So the income disparity will continue.

    That doesn’t even address the problem that tree canopy is not always a good idea, despite the ideological push for it. In some ecosystems canopied tries actually have a negative effect, and in almost all cities, street tree canopy increases water pollution (yes INCREASES) because the organic run off caused by leaves in the streets. I live in an urban forest. We have the right ecology for our oak/ask climax forest, and the trees in the forest produce leaf mold, retaining run off. A few blocks away, on classic city streets, everything from the street trees ends up in the streams.

    1. I guess most people living in American have relied on air condition so much and so deeply. No matter how hot outdoor, air condition can always make people feel chilly.(except small proportion workers in fields).
      Trees do save electric bills but energy cost in America is not high and the saving doesn’t make a significant difference. Then for most people, only AESTHETIC purpose was left. No wonder that tree cover is more typical of demand for luxury goods than necessities.
      But trees can still provide cool shade for jogging and bicycling in summer. Even though, trees are not welcome because people worried its root will make surface uneven.

  7. A person who is concerned about putting food on the table each day, or getting rent to keep the roof above them, they will not have very much energy or time to think about trees – for those who have the opportunity and the time, it is very easy to see the value in trees; as something beautiful, beneficial and good.

    It is not simply a desire for luxury or overflow from a surplus of wealth.

    1. They should plant fruit trees … two birds with one stone but I think the poor have a different mindset, as you suggest, and part of the reason for their being poor is poor choices.

      1. The average fruit you buy at retail has had a hideous cost in time, water and chemicals. Backyard fruit trees that are not pruned, watered in droughts and supported with some form of pest management will yield very little. And that’s all fruits across the board. Cane borers, plum curculios, apple codling moths and more, they are all there even in urban situations.The lack of urban bees and subsequent poor pollination also takes a toll.

        People fantasize a cornucopia from a backyard but it anything but. Lotsa sugar equals lotsa pests. Some fruits are so insipid, like elderberries and mulberries, they are not worth planting. The only fruit I have seen do well is jostaberries/gooseberries and they have plenty of large seeds and would be an acquired taste for US gardeners best suited for highly sugared preserves which brings up the aspect of health problems.

  8. I surprised the devastating die off from dutch elm disease hasn’t been mentioned. Our town is a good example of one that lost its cathedral like tunnels of elms, which were then never replaced or replaced with a smattering of low growing trees like honey locusts. Dutch elm disease (and now we get emerald ash borer!), cleared out whole cities in the northeast of a peculiarly elegant urban tree cover which spanned neighborhoods rich and poor – and which was never replaced.

  9. Vandalism is another driver. Tree saplings planted in very poor areas with bored teenagers tend to get vandalised and don’t get replanted to grow large. Mature trees, of the kind found in wealthier, more established neighbourhoods are harder to kill. New neighbourhoods build with richer folk in mind are more likely to plan to preserve existing mature trees. I wonder if fuel poverty might also be an issue. On an ice cold winter, a good sized tree can be a tempting target. Even in first world countries, people do freeze to death in winter (recent cases in Ireland in the cold winters of ’10 and ’11).

  10. Have you see what happens to trees in poorer cities? They are vandalized to no end, and end up looking terrible anyways. Poor cities cannot have nice things because they don’t care for them.

  11. Trees increase the value of your property. When you redo a house the thing you get the most bang for your buck is landscaping.

    I do not know what it is about the poor mindset but I have seen repeatedly that a nice, big, established tree will be cut down because the people in the neighborhood do not want to rake the leaves.

    Poor and stupid.

  12. with the dismantling of California’s CRA’s, this is all the more true. funds for “nice to have” infrastructure (like parks) are increasingly private. so, the amenities stay in the neighborhoods where people have the capacity to pay for them.

  13. I can think of some counter examples in DC, the city of my birth. Looking at Google it seems Anacostia has more trees than Dupont Circle.

  14. If nothing else, this study of the distribution of trees in affluent vs. non-affluent areas underscores the need to better plan for and support green space in all urban sectors. Yes, there are exceptions to this correlation, and yes, there can be challenges, as noted in the other comments. But none of that makes the goal of equitable green space improvements any less worthwhile.

    1. If you want trees in all urban sectors, you face two issues. One, subsidizing plantings in poor using public funds from affluent districts seems unlikely given the current attitudes. People don’t their taxes to benefit people they many not like. Two, property rights come into play. Turning street parking into an urban grove isn’t going to fly.

      Not that I disagree with this but the value of trees as part of a higher-quality living environment. But when public services like schools are under attack what chances do trees have?

  15. I note most mention street trees. What about homeowner trees and empty lots? Well the empty lots eventually disappear as housing. And poor urban areas carry 5-15% illegal apartments, which adds to parking needs off street. The trees are either gone in backyards or barely surviving at fence lines. A decision by one slum landlord to have an off the books basement apartment, affects generations afterward.

    I have personally watched in my neighborhood of maybe 60 acres, the disappearance of about 6 acres of trees total from private land, some large patches, other circumstances a tree at a time, over the course of 30 years. There is no hope.

    I myself planted a quarter acre of trees and mixed plants and now I am at the point of selling the land and I have taken down most of the plant matter. Over the course of time you also fight city code which likes things to be 2 to 3 inches high and no more.

    For those looking to buck the tide and plant some urban trees but are hesitant due to the time they will take to grow, there are fast growing short lifespan trees. I can recommend northern catalpa, chinese elm, hybrid poplar, various willows including Austrees. After ten years you will have a 20-30 foot tree.