Russell Square, London (photo by F. Kaid Benfield)
We humans have an intrinsic emotional need to connect with nature. The eminent biologist E. O. Wilson first called our affinity for the natural world “biophilia,” and the term has stuck. Yet cities also, and fundamentally, need the structure of hardscape urbanism—streets, buildings, and infrastructure—in sufficient density to achieve environmental and economic efficiency and nurture social bonds. It is critical that we incorporate nature into cities, but we must do so in a way that supports urbanity rather than replaces it.
I remember a happy day in our neighborhood a few years back. When I came home from work, three new trees had been planted on our block. That’s a small thing, of course, just three street trees. But their predecessors had been sorely missed for a few years. When we moved into the neighborhood a little over 20 years ago, one of its major assets was large, stately street trees, most of them oaks, on nearly every block. The neighborhood was built in the 1920s, so our oldest trees would have been around 70 years old when we moved in.
Visitors are always struck by them, especially if they have come from a newer suburb. Many of those older trees remain, but over the time that we have lived in the neighborhood we have lost quite a few to disease and, mostly, storms. I’m sure I was not the only one whose spirits were lifted by the discovery that new ones had been planted: researchers have shown that even just a view of greenery from a window can give us a psychological and physical boost.
Indeed, for our ancestors a keen awareness of the natural environment was essential to survival. When we are deprived of nature, we lose a basic aspect of humanity. Who among us has not enjoyed a stroll, ridden a bike, read a book or magazine, learned a sport, fallen in love, taken a nap, or otherwise enjoyed the respite and communion with nature provided by a natural area or lovely city park? In cities, the presence of nature—whether interspersed among our streets, buildings, and yards or more organized into parks—connects us with growth and with the seasons, providing a softness to complement the concrete of our streets and sidewalks and the brick and wood of our houses.
Among parks, I love those that are neighborhood-scaled the most. While large green spaces such as New York’s Central Park, San Francisco’s Golden Gate Park, or Washington, DC’s Rock Creek Park are wonderful, there is a more personal dimension to those that are a bit smaller, more a part of their neighborhoods. Indeed, one of my favorites is only about an acre and a half in size. It’s tucked into a neighborhood of single-family homes on small lots in Chevy Chase, Maryland, right on the boundary separating Chevy Chase from Bethesda and only a block from Bethesda’s very busy and urban main street.
Elm Street Park is so well scaled to its neighborhood and has such beautiful large, mature trees that I go out of my way to stop there if I’m riding my bike nearby, which I do often. There are small gazebos, a playground, and scattered picnic tables but otherwise it has no special facilities. It’s just there, and I love it.
The Science of Urban Nature and People Habitat
Research suggests that I should. At the University of Michigan, a test group of students walking through an urban arboretum scored better on memory and mood indicia than a control group walking on city streets. When the roles of the two groups were reversed a week later, the students who walked through the arboretum again scored higher. The researchers suggested that the additional mental demands of with city streets—particularly attention to cars—caused stress, while in nature we can let our minds wander, enabling us to “rest our attention.”
More broadly, an academically rigorous review of 86 peer-reviewed studies published since 2000, conducted by Danish researchers for the International Federation of Parks and Recreation Administration, was published in January 2013. It found an immense range of correlations between nature and public health, from reduced headaches to longevity:
“Nature and green spaces contribute directly to public health by reducing stress and mental disorders, increasing the effect of physical activity, reducing health inequalities, and increasing perception of life quality and self-reported general health. Indirect health effects are conveyed by providing arenas and opportunities for physical activity, increasing satisfaction of living environment and social interactions, and by different modes of recreation…
“The direct health benefits for which we found evidence on positive effects included psychological well-being, reduced obesity, reduced stress, self-perceived health, reduced headache, better mental health, stroke mortality, concentration capacity, quality of life, reduced Attention Disorder Hyperactivity Disorder (ADHD) symptoms, reduced cardiovascular symptoms and reduced mortality for respiratory disorders, reduced health complaints, overall mortality, longevity, birth weight and gestational age in low socioeconomic population, post-disaster recovery, and reduced cortisol.” [Citations omitted.]
The evidence for positive impacts of urban parks on physical activity was highlighted as “strong,” with the academically established evidence in support of other effects found to be at least “moderate.” (Conversely, when a correlation between parks and health was insufficiently established in the literature, as with the effects on lung cancer or diabetes, the authors said so.)
Elm Street Park, Chevy Chase, Maryland (photo by F. Kaid Benfield)
Another large study, reported in a monograph published by the National Recreation and Park Association in 2010, found a direct correlation between health effects and proximity of parks:
“Scientists in the Netherlands examined the prevalence of anxiety disorders in more than 345,000 residents and found that people who lived in residential areas with the least green spaces had a 44 percent higher rate of physician-diagnosed anxiety disorders than people who lived in the greenest residential areas. The effect was strongest among those most likely to spend their time near home, including children and those with low levels of education and income.
“Time spent in the lushness of green environments also reduces sadness and depression. In the Dutch study, the prevalence of physician-diagnosed depression was 33 percent higher in the residential areas with the fewest green spaces, compared to the neighborhoods with the most.”
The NRPA report even cites studies finding lower levels of aggression, violence, and crime in Chicago housing projects with views of vegetation than in those without.
People intuitively appreciate these benefits and, as a result, are willing to pay a significant premium for living near nature. According to a 2006 report published by the Trust for Public Land, a review of 25 studies investigating whether parks and open space contributed to values of neighboring properties found increased value in 20 of the studies. Those benefits accrue to the municipalities as well:
“The higher value of these homes means that their owners pay higher property taxes. In some instances, the additional property taxes are sufficient to pay the annual debt charges on the bonds used to finance the park’s acquisition and development. ‘In these cases, the park is obtained at no long-term cost to the jurisdiction,’ [Texas A&M professor John] Crompton writes.”
The TPL report cites corroborating evidence from the University of Southern California, finding that investment in a pocket park in a dense urban neighborhood would pay for itself in 15 years as a result of increased tax revenues.
Environmental Services Provided by Urban Nature
Back to the trees in my neighborhood, I would love them without knowing why but, in my day job as an advocate, it’s very useful to know that science can reveal some of the reasons. Apart from what they may do for me, trees also provide measurable environmental services to their communities. If you’re interested in learning more about the benefits of trees, visit the websites of the National Arbor Day Foundation and the US Forest Service. Among the tidbits I have discovered on one or the other of those two sites are these:
- The net cooling effect of a young, healthy tree is equivalent to ten room-size air conditioners operating 20 hours a day.
- If you plant a tree today on the west side of your home, in 5 years your energy bills should be 3 percent less. In 15 years the savings will be nearly 12 percent.
- One acre of forest absorbs six tons of carbon dioxide and puts out four tons of oxygen.
- A number of studies have shown that real estate agents and home buyers assign between 10 and 23 percent of the value of a residence to the trees on the property.
- Surgery patients who could see a grove of deciduous trees recuperated faster and required less pain-killing medicine than similar patients who viewed only brick walls.
- In one study, stands of trees reduced particulates by 9 to 13 percent, and reduced the amount reaching the ground below by 27 to 42 percent compared to an open area.
Several years ago walkability guru Dan Burden, who founded the Pedestrian and Bicycle Information Center, wrote a detailed monograph titled 22 Benefits of Urban Street Trees. Among other things, Burden calculated that “for a planting cost of $250-600 (includes first 3 years of maintenance) a single street tree returns over $90,000 of direct benefits (not including aesthetic, social and natural) in the lifetime of the tree.” He cites data finding that street trees create slower and more appropriate urban traffic speeds, increase customer attraction to businesses, and obviate increments of costly drainage infrastructure. In at least two recent studies (reported after Burden’s analysis), trees were even found to be associated with reduced crime.
4-way duty as tree cover, street median, stormwater catchment, and pocket park (photo by F. Kaid Benfield)
Burden summarizes trees’ biological and emotional functions:
“Urban street trees provide a canopy, root structure and setting for important insect and bacterial life below the surface; at grade for pets and romantic people to pause for what pets and romantic people pause for; they act as essential lofty environments for song birds, seeds, nuts, squirrels and other urban life. Indeed, street trees so well establish natural and comfortable urban life it is unlikely we will ever see any advertisement for any marketed urban product, including cars, to be featured without street trees making the ultimate dominant, bold visual statement about place.”
Intuitively if not explicitly, street trees remind us that, even in the city, we are a part of living nature. They connect us to something larger and wondrous, yet protective and comforting. They remind us that we are creatures in a habitat, and that is a very good thing.
The Emerging Field of Green Infrastructure
Urban greenery can also help control water pollution. An increasingly popular set of techniques is called “green infrastructure,” in the form of strategically designed vegetation and landscaping to filter stormwater (while also lowering summer temperatures and releasing oxygen).
The stormwater control provided by green infrastructure is significant. One of the most pressing environmental challenges facing cities and suburbs in the US is the impact of rainfall that becomes polluted runoff when it flows over impervious surfaces—such as highways, parking lots, rooftops and driveways—on its way into our rivers, lakes, and coastal waters. The federal EPA estimates that more than 10 trillion gallons of untreated urban and suburban stormwater runoff enters our surface waters each year, degrading recreation, destroying fish habitat, and altering stream ecology and hydrology.
Capitol Avenue, Hartford, before (courtesy of US Environmental Protection Agency)
Capitol Avenue, Hartford, as imagined (courtesy of US Environmental Protection Agency)
The problem becomes particularly acute in cities that drain both stormwater and sewage into a common, and typically aging, set of pipes and conveyances. When major storm events prove to be more than these systems can handle, the result is “combined sewer overflows,” a noxious mess.
Green infrastructure (also known as the key component of “low impact development”) captures and filters stormwater before it runs off into sewers or urban waterways. It replicates the way nature deals with precipitation—using vegetation and soils as natural sponges for runoff—rather than relying exclusively on the “gray infrastructure” of old technology, such as concrete pipes and holding tanks. Types of green infrastructure include green roofs, roadside plantings, rain gardens, permeable paving, and rainwater harvesting, among others.
The American Society of Landscape Architects maintains a massive database containing hundreds of case studies of successful examples, half of which are placed within existing development. Another sizable batch involves urban redevelopment projects. The organization has found that the use of green infrastructure reduces development costs more frequently than it adds them, probably because successful green infrastructure can obviate some of the concrete “gray infrastructure” otherwise required to drain runoff.
Bioswales were the most common type employed, with rain gardens and porous pavers close behind. Of all of the profiled projects, 40 percent reflected the management of an acre or less of land; 75 percent were employed on five acres or less. Sixty-eight percent of the projects were assisted with public funds.
Philadelphia is perhaps the country’s leading example of a city committed to large-scale green infrastructure implementation. Under a formal plan to meet Clean Water Act requirements, approved by environmental regulators, the city has now agreed to transform at least one-third of the impervious areas served by its sewer system into “greened acres”—spaces that use green infrastructure to infiltrate, or otherwise collect, the first inch of runoff from any storm. My colleagues at the Natural Resources Defense Council say the program will keep 80-90% of annual rainfall from these areas out of Philadelphia’s over-burdened sewer system.
In a different undertaking, the federal Environmental Protection Agency has launched an innovative planning program designed to help bring more green infrastructure (and green building practices) to our country’s state capitals, making them simultaneously more environmentally resilient and more beautiful. The idea behind Greening America’s Capitals is that these particularly prominent cities are inevitably ambassadors of a sort for their respective states and for other cities.
Indeed, elected representatives and their staffs typically come from all around their respective states but work at least part-time every year in the capital cities. What they experience there, good or bad, imparts lessons that can be taken back to the representatives’ home districts or even incorporated into statewide policy. Many visitors frequent state capitals for business or pleasure, each forming and taking away impressions. I took a close look at the EPA-assisted plan for greening Hartford, Connecticut and was seriously impressed.
As I have written often, smart growth—growing our metropolitan regions in more compact patterns—does its own part in reducing the volume of runoff across watersheds, because it reduces the spread of new pavement into previously undeveloped or minimally developed areas. But it is not enough, because we need waterways near our existing developed areas to become cleaner and safer. Many cities and suburbs are now undergoing more intensive development, as they must to address other environmental concerns such as transportation efficiency and land conservation. We clearly need urban density in order to even approach solving problems related to land conservation and transportation patterns and emissions. But, if the development is not sensitive to the potential for runoff, some waterways could become even more polluted.
I have become a big fan of green infrastructure because these techniques—in most cases literally as well as figuratively green—have the effect of softening urban density, making it more appealing as well as better functioning. In fact, I would argue that, in places where there is significant rainfall, smart growth simply isn’t smart without it.
More about City Greenery
Perhaps My Favorite City Park
Whenever I am lucky enough to be in Paris, I always make a point to stay within easy walking distance of that city’s wonderful Jardin du Luxembourg (Luxembourg Garden). When my wife and I are there together, we spend a little time there almost every day. It’s one of my favorite public spaces in the world.
What makes it work so well? I can think of a few things right away: First, it’s a great size for a large city park, at 60 acres. That means one still feels “in the city” when there, but in an especially tranquil part. Second, like great cities themselves, it embodies a variety of vistas and experiences, from the majestic old Luxembourg Palace (now the seat of the French Senate), to the central pond where kids play with toy boats, to a bandstand, a marionette theater, a carrousel, tennis courts, the Medici fountain, terrific nooks and crannies in which to eat and drink, and so on.
Third, it strikes a great balance by nearly always hosting a good crowd while avoiding the feeling that it is jammed with people, in the sense that, say, Bryant Park or parts of Central Park in New York City do. There’s almost always a place to sit. Fourth, the buildings and landscape architecture are humane rather than heroic or pastoral, and to my eyes, beautiful. In addition, as with many great places in Europe, the park conveys a sense of history (it’s been there since 1625) that few places close to home can match.
Jardin du Luxembourg, Paris (photo by F. Kaid Benfield)
But don’t take my word for it. Here’s what the Project for Public Spaces has to say:
“The Luxembourg Garden may well be one of the most successful parks in the world, partly because it is so well integrated into the fabric of the city around it, which makes it easily accessible. There are also many things to do there, evidenced by the wide range of people who use it: children, older people, Sorbonne students, people cutting through on a lunch break, etc. People come to stroll, play chess, to sit and read, people watch, to sit at one of the cafes or to bring their children or grandchildren to one of the many attractions for kids. Organized activities at the park include tennis, pony rides, puppet theaters, and toy sailboat rental (children float them in the large central fountain). Visitors can also stop inside the Palais and attend a hearing of the French Senate, which is open to the public…
“Some of the Garden’s more notable features include the Medici Fountain, erected in 1861, and a bronze replica of the Statue of Liberty. The park, which closes at sunset, also has a multitude of strolling paths, and is filled with hundreds of movable chairs, which can be rented. Outdoor concerts also occur in the Luxembourg Garden.
“The design is basically formal: a central parterre dominated by terraces. Alleés of trees surround the central terraces and continue in every direction except north, where the Palais du Luxembourg dominates. A free, more English-style garden is situated along Rue Guynemer and Rue Auguste-Comte; it was built during the first Empire and contains winding paths, grassy open areas, and a wide array of sculpture.”
There’s more about the Jardin’s history, and a great slide show, on PPS’s website.
There’s also an eloquent passage by David Whitley quoted in Terry Sisk’s Travel With Terry website. Here’s part of it:
“That it is called a garden rather than a park is a deliberate statement, the emphasis being on magnificent floral displays rather than vast expanses of lawn. The octagonal pool is surrounded by pots filled with vivid blooms which could pierce through the grayest of days. It’s a scene to make you fall in love with the city instantly, particularly when you start looking at the detail…
“Just to wander from sector to sector, swigging from a bottle of water, is a delightfully affirmative experience. It’s like a scene from 50 years ago, done up with modern costumes, and for the people-watcher, there’s just so much to see. So many people, so many activities, so many expressions…It’s magical in the most simplistic way, and if you can’t fall under the charm of Paris here, watching happy children rubbing the manes of their donkeys as they ride around the premises, then heaven help.”
I can’t say it better than that.