When everyone lives in a city

Here’s a fun thought experiment. Plot the population of the world since 500 BCE. Now plot the population of the 50 largest cities over that same time. If you distill equations to describe the two trends, you’ll notice the lines cross. At some point in the future, your models predict that the population of the 50 largest cities will overtake the world’s population. Clearly that’s impossible.

What those trends are telling you is that cities are growing faster than rural areas, something we already know. But if you take that thought experiment to its mathematical extremes, you’ll see it’s possible that there comes a point when—boom—everyone lives in a city. Rural dwellers—poof—cease to exist. Suddenly, we’re all children of the concrete jungle.

That’s what Michael Batty, a well-known urban planner and geographer, noticed when he ran through those same hypotheticals. Specifically, he calculated that by 2092 all the world will be urbanized according to those trend lines. Of course that won’t happen, and he acknowledges that. The world’s population will, at minimum, be equal to the sum of its cities, and I’m 100 percent certain that at least a handful of people will still live in the country, either by choice or chance. But Batty’s idea bears consideration. What would the world look like when, as he puts it, “all the world’s a city”?

The United Nations currently estimates the world’s population will reach 10 billion by 2100, just a few years after mathematics suggests we could all be living in cities. Now, that’s not to say the Earth would be covered by one massive city. Cities may be expanding outward faster than their population growth would warrant, but 10 billion people spread across all continents but Antarctica would live at a density of about 190 people per square mile (74 per square kilometer). Hardly a city.

But what if our notion of a city changed? A single definition is already maddeningly difficult to nail down. Take New York City, for example. It has about 8.2 million people within the polity, but the greater region has over 22 million. Where does New York really end? Houston and Tokyo, on the other hand, encompass too much. Each political entity contains vast tracts of undeveloped land. It’s clear that political boundaries aren’t adequate. So instead, what if we think of a “city” as a collection of conurbations not connected by geography but by social and economic ties, as Batty suggests? In an age of plane travel and high-speed rail, physical continuity isn’t necessarily a requirement.

With this new definition, it is possible for all the world to be one city. The Earth doesn’t have to be covered in conurbation; rather, everyone simply has to live in urban areas, and those urban areas must be sufficiently connected so as to behave like a single city.

Already metros and their regional governments cross existing political boundaries. New York City is a perfect example. And at the other extreme, there are cases like Tokyo where city governments have essentially absorbed their hinterland equivalents. (We see this all the time in the United States with combined city and county governments—New York City, San Francisco, and Lexington, Kentucky, to name a few.) These mergers grew out of necessity, and it’s easy to see the same happening in a hyper-connected world. As more and more cities join the global cluster, as Batty calls it, the pressure to coordinate will rise.

It’s possible, then, that the first true world government could emerge from this collection of cities. It would be fitting. Already mayors from around the world meet to discuss common problems, and on issues like climate change where national governments have fallen flat, they have taken the lead. But it would still be a shift of epic proportions. It wouldn’t happen overnight, but at a certain point it would be inevitable. Cities could choose to sit on the sidelines, but the benefits of joining the global cluster would be too great to ignore. Eventually, nearly everyone on Earth would count themselves a resident of the One City.

The world as one city would surely be a different place. The relationship between a city and its hinterland would be tested. Indeed, what would become of the hinterland? It would certainly be smaller—although the One City wouldn’t smother the planet, it would still have an enormous footprint. The hinterland would remain inhabited by scattered few who choose to live there, perhaps living their quiet lives amongst robotized farms. A great schism between the city and the hinterland could develop. But there could also be a reconciliation. Governments could reconfigure to cope with the changing landscape, both literal and figurative. Instead tension between the city and its hinterland, there could be cooperation fostered by a sense of shared fate. So goes the city goes the hinterland, and vice versa.

Regardless of how it all plays out, a highly urbanized global population will add nearly 6 billion people to cities that only hold about 3.6 billion today. That’s growth of almost 280 percent in less than a century. Such a percentage isn’t unprecedented—between 1900 and today, the world’s urban population grew by more than 1600 percent—but the raw numbers will be. To accommodate those people, cities will have to remake themselves like never before. It’s a daunting challenge, and as I stated in my last article, we’ll need a science of the city that’s equally formidable.

Sources:

Batty, M. (2011). When all the world’s a city, Environment and Planning A, 43 (4) 772. DOI: 10.1068/a43403

United Nations. 2011. “World Urbanization Prospects, the 2011 Revision.” Accessed October 8, 2012.

Photo by kevin dooley.

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Planet of the Cities

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Planet of the cities

Science fiction is littered with planet-wide cities. Star Wars had Coruscant, Isaac Asimov’s Foundation Series had Trantor, and even Star Trek, in an alternate timeline in First Contact, saw Earth paved over by the cybernetic Borg. City-planets are both a wonder and a terror—we stand in awe of our power to change the world, but also regard that ability with fear. What if we actually did it? Hundreds of years ago, it didn’t even seem possible. But the quickening pace of population growth in the 1800s changed that, and the vast environmental changes sweeping the planet today are a stern reminder of just how powerful we are.

Of course, Earth is not in any immediate danger of becoming one conurbation, but the trend isn’t promising. Urban areas around the world are expanding at double the rate of their populations. That means every person who moves to or is born in a city will, on average, take up more space than the person before them.

And soon there will be a lot more people wanting that extra space. Urban populations are expected to swell to 5 billion in the next two decades, and according to a recent study published in the Proceedings of the National Academy of Science, cities are expected to gobble up another 460,000-plus square miles (1.2 million square kilometers). Put simply, it means that cities will occupy three times more land in 2030 than they did in 2000.

That’s a staggering amount. The results are equally astounding. The east coast of China is likely to merge into one massive city. Cities in the region spanning Lake Victoria’s north shore—an arc from Burundi to Kenya—will swell 1,900 percent in area. Urban areas along the coastal strip from Côte d’Ivoire to Nigeria will grow 920 percent. Other countries like India, Mexico, and Turkey will also experience outsize urban growth. Even developed regions like North America and Japan will have to endure massive urban expansion.

There’s a lot to be concerned about with these statistics. Urban areas that grow several-fold in a few decades won’t be happy places to live—they’ll likely be dominated by slums, or at the very least snarled with traffic and choked with pollution. The situation is even more dire for the ecosystems they’ll be displacing, which are some of the most diverse in the world. That’s because we humans prefer to live in dangerous places, places dominated by disturbances like earthquakes, volcanoes, tsunamis, and floods, processes that produce rich and diverse ecosystems. As a result, the next two decades of urban expansion will imperil nearly 140 amphibian species, more than 40 mammal species, and 25 bird species.

That doesn’t mean we should halt progress and send everyone back to the farm. Cities are still more environmentally friendly on a global scale than the alternative. No, what it means is that we need to think hard—and fast—about how we’re going to cope with the booming urban areas of the next two decades. Much of that growth is going to happen in places like Africa that haven’t had large cities historically. Nigeria, for example, is projected to have more than 400 million people in 2050. That’s more that double its present population.

Success will depend on thinking big. It’ll require “more holistic policies that integrate traditional urban sectors—transport, energy, sanitation, buildings—with land use and conservation,” the study’s authors write. A “science of the city” that others have been arguing for. Developing that science is, in my mind, the only hope we have of taming these urban beasts. The cities of the future may not be the planet-consuming behemoths of our techno-futuristic tall tales, but they’ll be beyond anything we’ve ever seen before. We’ll need a science that’s equally formidable.

Source:

Seto, K.C., Guneralp, B. & Hutyra, L.R. (2012). Global forecasts of urban expansion to 2030 and direct impacts on biodiversity and carbon pools, Proceedings of the National Academy of Sciences, 109 (40) 16088. DOI: 10.1073/pnas.1211658109

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America’s suburban future

Why neighborhood quality matters

In the summer of 2008, I found myself lost in Chicago. I was new to the sprawling city, living there for two months while working as an intern science reporter at the Chicago Tribune. To counter weekend boredom, I would explore the city by bike. I’d often find myself mildly disoriented, but this time I had really done it. I knew I was north of the Loop, but that was about it.

Finally, I happened across Halsted Street, a major north-south thoroughfare that ran a few blocks from where I was living. Relieved, I started south, coasting past nice brick apartment buildings and row houses, big box stores and tony shops. But after a few miles, the timbre of Halsted changed. Quickly. Well-kept storefronts gave way to crumbling industrial buildings and weedy sidewalks. Then came the most depressing hulk of a building you could imagine. It was a drab beige tower surrounded by acres of asphalt and dotted with boarded up windows fringed with smoke stains. I knew exactly where I was.

Cabrini-Green’s bad reputation was well-known, especially in the Midwest where I grew up. It was among the first projects built by the Chicago Housing Authority in the mid-20th century. By the 1970s, Cabrini-Green was notorious for destitution and violence. Gangs had taken over various buildings, and internecine warfare kept even the hard-nosed Chicago police at bay. Tales of horrific murders spread around the country. My aunt, who tutored elementary school students there, would recount stories she heard from residents. Cabrini-Green was at best a place to be avoided.

And here I was, blithely riding by. Though I didn’t know it at the time, Cabrini-Green’s most notorious days were past it. The tower was largely vacant, save for a few holdouts. When I moved back to Chicago a year later, the last of the high-rises were being torn down.

Housing projects are widely viewed as a failure. Their concentrated poverty seemed to descend into a negative feedback loop, where depravity fed on itself. Over the years, Chicago tried to assert control, to no avail. They muscled up the police presence; that was met with sniper fire. In 1981, then-mayor Jane Byrne moved into a ground floor apartment guarded round the clock by uniformed officers. She moved out three weeks later.

Oddly enough, Byrne’s publicity stunt was on the right track, if completely backwards. Housing projects’ needed a shock to break the cycle. But they didn’t need a mayor moving in. They needed to move people out.

That’s exactly what the United States Department of Housing and Urban Development did in the mid-1990s, when it took over the dysfunctional Chicago Housing Authority. As a part of the Moving to Opportunity program, households could enroll in a lottery which would give winners assistance in finding and vouchers to pay for housing in low poverty neighborhoods. Chicago wasn’t the only city in the trial—New York, Boston, Los Angeles, and Baltimore were also involved. The idea was that after moving to low poverty neighborhoods, families would find more and better jobs and be healthier and happier. Nearly 5,000 families were included in the experiment.

It worked, to some extent. A study published today in the journal Science details how people involved in Moving to Opportunity have fared in the 15 years since the program started. Though those who moved to low poverty neighborhoods were still as poor as those who didn’t, there were some changes. Notably, they were happier and somewhat healthier.

The study, led by Jens Ludwig of the University of Chicago, looked at a variety of factors, ranging from poverty rate to racial segregation to mental and physical health. Though poverty rates didn’t change significantly, and racial segregation nudged only slightly lower, people’s health improved. Physical health, as measured by obesity and diabetes, were slightly better in this study. (A prior study published by Ludwig and colleagues in the New England Journal of Medicine last year reported more significant improvements.) But mental health, as measured by self-reported subjective well-being, or how people felt about their lives, was significantly improved among people who lived in low poverty neighborhoods. So while people were still poor, they were happier. That says a lot about the importance of your surroundings.

Ludwig and his colleagues point out that if the objective of Moving to Opportunity was to reduce poverty, then at this point it would be considered a failure. But if the goal was to improve people’s lives in other ways, well, it’s not doing too bad.

The study only focused on adults, in part because measuring subjective well-being of youngsters is an inexact science. Because of that, they’re missing an important component. It’s difficult to break free of poverty, especially when you’ve inherited it. But children, through better education and improved health, have more potential than their parents (even if that’s only because they have more of life left to live). It’s possible that, because of a more positive home life, kids in families living in low poverty will have better opportunities than their parents, helping them break the cycle.

Source:

Ludwig, Jens, Greg J. Duncan, Lisa A. Gennetian, Lawrence F. Katz, Ronald C. Kessler, Jeffrey R. Kling Lisa Sanbonmatsu. 2012. “Neighborhood Effects on the Long-Term Well-Being of Low-Income Adults”. Science 337(21): 15051510. DOI: 10.1126/science.1224648

Photo by puroticorico.

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Marchetti’s constant, or why the 30 minute commute is here to stay

“How far should you live from work?”

I pondered that question a few weeks ago after perusing American Community Survey data compiled by Charlie Gardner. It showed that most people in most metro areas in the United States tended to commute about 30 minutes each way to work, give or take a few. That adds up to about an hour of commute time per day. As I looked into it further, I found a lot of research that corroborated the surprising similarity of people’s commute times.

But in all ten research papers I used to footnote that article, I was missing one. Eric Fischer pointed me toward a 1994 treatise—for lack of a better term—by Cesare Marchetti. He posited that one hour per day is as long as people have been willing to travel. Ever. Since the dawn of human society.

At least, that’s what Marchetti hypothesized. He did have some data to back it up, though it wasn’t his own. It was Yacov Zahavi’s. Zahavi was a transportation engineer who consulted for the U.S. Department of Transportation and World Bank in the 1970s and early 1980s. As part of his work for the DOT, he came up with what he called the Unified Mechanism of Travel Model, or UMOT. Zahavi produced a string of reports and papers on UMOT, which he hoped would shake up how transportation planning was done in cities.

In the process of developing UMOT, Zahavi collected many juicy tidbits of data. One observation was that as people earn more money, they spend an increasing percentage of their income on everyday travel, up to about 13 percent. That number seemed to be both a hard ceiling and firm floor once households earned above a certain amount (about \$50,000 in 1976). The richer you got, the more you spent in real terms. But the percentage remained the same.

Another bit—the one that inspired Marchetti—was that people in the United States and the United Kingdom traveled about 1 hour per day. (Astute readers will notice that a 30 minute commute to work—the number most studies have settled on as the “average” commute—adds up to precisely that amount at the end of the day.) Zahavi also noticed that even though some people could travel faster—by car rather than bus, for example, they still spent the same amount of time traveling. They just traveled farther to work—a trend which more recent studies have also uncovered.

Zahavi’s data is compelling, but in Marchetti’s hands it quickly became a universal constant. If so many people in Zahavi’s study (mostly in the developed world of the 1950s and 1960s) traveled the same amount per day, Marchetti reasoned that humans must have an innate desire to travel at most and at least 1 hour per day. Boom. Marchetti’s constant.

Zahavi’s data wasn’t the only leg he had to stand on, though it certainly was his sturdiest. Cave men and Greek villages were another. Marchetti pointed out, “Walking about 5 km/hr, and coming back to the cave for the night, gives a territory radius of about 2.5 km and an area of about 20 km2. This is the definition of the territory of a village, and … this is precisely the mean area associated with Greek villages today, sedimented through centuries of history.”

Marchetti—not one to think small, apparently—then used his new universal constant as a jumping off point to explore the future of tomorrow. How fast would a transportation system need to be to serve a city of 100 billion people? An average speed of 150 km/h sounds about right. Can you turn Switzerland into one giant city? Sure, so long as you run maglev trains in sealed tunnels sucked free of atmosphere. What about if you linked Paris and Casablanca with a maglev, too? “[A] woman in Casablanca could go to work in Paris, and cook dinner for her children in the evening.”

Not a man to leave a logical extreme unreached, Marchetti realized that at some point in the future everywhere on Earth will be 30 minutes from your front door. “With mach-7 airplanes and matching Maglevs, a world city is also possible. The assimilation of the technologies in political terms, however, will take some time.”

Details. In the meantime, enjoy your 30 minute commute.

Sources:

Marchetti, C. (1994). Anthropological invariants in travel behavior, Technological Forecasting and Social Change, 47 (1) 88. DOI: 10.1016/0040-1625(94)90041-8

Zahavi, Yacov. 1976. “The Unified Mechanism of Travel (UMOT) Model.”

Photo by Lars Plougmann.

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Responsive urban design

We’ve been planning cities for almost as long as they have existed. Archaeological evidence suggests the ancient Egyptians did so 5,000 years ago. Hippodamos, considered by many to be the father of urban planning, imposed street grids on every ancient Greek city that would let him. Since then, we’ve been busily drawing, revising, and otherwise fussing about how best to design our cities.

It turns out we may have it all wrong. Or at least wrong for today’s cities. Urban areas have always been in constant flux, but we’re now demanding far more of them than before. They’ve never housed, transported, or employed so many people. To cope, cities have been changing at an astonishingly rapid pace. The results can be inspiring—as they are in Seoul, Singapore, and Tokyo—or depressing—just look at anywhere with extensive slums. In some cases, it seems urban planning is up to the task. In others, it’s not.

Where it falls flat, urban planning’s failings aren’t necessarily the fault of the designers. Too often planning is focused on minutiae—ordinances, regulations, zoning, setbacks, and so on. Even when it tackles bigger problems like economic growth, it doesn’t necessarily consider the city as a whole.¹

The solution, according to Michael Batty, an urban planner and professor at University College London, is infusing planning with science. Systems science, specifically, where bright minds and complex mathematical models try to digest the entirety of a system, like a city. It’s no simple task. IBM is just one company throwing billions of dollars and tons of silicon at the problem. What they’ll get out of it is anybody’s guess, but they seem certain they’ll get something. Cities are overflowing with collectable data. It’s making sense of it that’s difficult. The possibilities it presents is what I think is going drive us to rethink city planning.

Urban planning has its origins in the design world, which is both a bonus and a handicap. Architects make natural planners—they design the buildings, why not have them design the streets, too? When those planners are enlightened designers, the results are attractive and livable cities. If they’re not? Well, we’ve all seen what happens when they’re not. But as much as good design has created great cities, I and others suspect it can’t deal with the coming challenges. Not on its own, at least. Good design can solve many problems, but it can’t solve them all. At some point, you need science.

The rate at which cities are growing and changing presents a problem for the traditional design-centric approach. Good design requires a thorough understanding of your problem. But these days, problems are appearing and evolving so quickly that we don’t have enough time to properly observe them.

Urban planning is at a crossroads, much like ecology was 50 years ago.² Planning is still largely descriptive and not very scientific, again, much like ecology was 50 years ago. Sure, cities gather hard data like traffic and sewage flows. Yes, they model projected growth and consider the social factors behind neighborhood demands. But urban planning lacks a unified, data-driven theoretical foundation.

That’s beginning to change. Michael Batty, Geoffrey West, Luis Bettencourt, and others are proposing data-driven theories and testing them, just like Robert MacArthur and Edward O. Wilson did in ecology back in the 1960s and 70s. Though these new urban theorists are trying to shake things up, they’re not trying to eliminate planning as we know it. Their science of cities won’t be a replacement for current planning, but a superset. Think of it as a grand theory to tie it all together, to make sense of why cities have evolved the way they did and how we can coax them to cope with 5 billion people.

The science of cities may be in its infancy, but we can see where it will lead. The first stage, the one we’re in right now, is descriptive. It involves gathering data, assembling huge models, and tuning them until we’re satisfied. Then we’ll apply those models, and see how the real world reacts. There will be some stumbles, but that’ll only give us more data to work with. Eventually, we’ll arrive at a theory of cities that’s universal and flexible enough that it can be applied anywhere. It will be a foundation that will underpin models that grind through piles of data and make sound, timely recommendations which designers can implement.

Getting to that last stage is important, I think. In many cities, it’s clear that we don’t know what to do with all these new urbanites. Even in cities where things appear hunky dory, cracks are beginning to show. Subways are crowded, freeways are jammed, and sewers are overflowing. Throwing money at temporary fixes will only get us so far. We need to dig deeper and develop a responsive urbanism,³ one that’s grand in scale and scientifically focused. We need to listen to what cities are telling us, decide what we want them to do, and plan accordingly.

1. Enlightened planners out there—and there are quite a few—can take umbrage with my characterization here. But they’ll admit that there are quite a few in their profession that dabble too much in the details.
2. Though urban planning is behind the curve relative to ecology when it comes to mathematical and theoretical rigor, data gathering is one place where it’s ahead. We already have many data sets in hand along with the infrastructure to gather more.
3. I’m thinking bigger than pop-up parks, an oft cited example of “responsive urbanism”.

Sources:

Batty, M. (2008). The Size, Scale, and Shape of Cities, Science, 319 (5864) 771. DOI: 10.1126/science.1151419

Batty, M. (2012). Building a science of cities, Cities, 29 S16. DOI: 10.1016/j.cities.2011.11.008

Bettencourt, L.M.A., Lobo, J., Helbing, D., Kuhnert, C. & West, G.B. (2007). Growth, innovation, scaling, and the pace of life in cities, Proceedings of the National Academy of Sciences, 104 (17) 7306. DOI: 10.1073/pnas.0610172104

Photo by MagnusL3D

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How far should you live from work?

Thirty minutes at most, according to the wisdom of the crowds.

That comes from reams of data and piles of research that suggests commute times tend to cluster around this point. People tend to be good at weighing their options, economists think. If you live farther from work, you can usually afford a bigger house or apartment. But there’s a point where that journey becomes too onerous, and you are willing to sacrifice some of those desires to live closer to your job. That point on average seems to be between 20 and 30 minutes.

I was inspired to look into this further after seeing an article by Charlie Gardner over at his blog, The Old Urbanist. Gardner had mined the American Community Survey for average commute times in major metropolitan areas. Though there was a tight correlation between population and commute time (metros with larger populations have longer average commutes), the differences weren’t pronounced. They ranged from a low of 22.5 minutes in Kansas City to a high of 34.6 in New York City. That’s not a lot.

But before we ask why commute times hover in a tight band, perhaps we need to ask why people commute so far in the first place. Why not work next door? The answers may seem obvious, but what’s readily apparent to one person may not be to another. That’s why we examine these things scientifically. Well, in this case your hunch is probably correct. An older study by Martin Wachs and his colleagues at UCLA found, unsurprisingly, that people choose where to live not just based on commute times but also neighborhood characteristics, schools, and safety.

Now we can move on to the more curious question, why commutes tend to average 20-30 minutes. It’s not just limited to the United States, either. In the Netherlands, the average commute time in the early 2000s was about 28 minutes. Many European nations average about 35 minutes. What makes a half-hour so universal in terms of commuting?

It didn’t used to be that way. Average commute times in 1980 were around 22 minutes. Today, they’re around 25 minutes. Three minutes may not seem like much, but remember it’s an average. To increase an average by that amount, some commutes had to grow significantly to counter those that shrunk or remained the same. Now, keep in mind there is a lot of variation about those averages. Some people travel 2 minutes to work, others well over an hour. But on average, they have increased.

What’s causing that lengthening is higher job densities in major metros. Job growth is requisite to economic growth, and vice versa. As metro areas add more jobs, those jobs tend to be concentrated in business districts (after all, not everyone can work out of their homes). And as business districts fill up, commute times lengthen because the roads leading there become more congested. So when the economy booms, traffic slows to a crawl. I heard anecdotal evidence of this when I lived in San Francisco. People told me, if you think traffic is bad now, it was much worse during the tech boom of the late 1990s. When all those tech workers lost their jobs, gridlock practically evaporated, they said.

Subtle changes in urban form may also cause longer commutes. One study in the Netherlands and another in Quebec, found that polycentric metro areas—those with two or more cities, like Minneapolis-St. Paul—tend to have longer auto commute times. As cities grow and begin bumping into one another, such agglomerations are likely to become more common. It’s possible commute times may increase as well. While there may not be consensus on this point, I haven’t found any studies that claim changes in urban form will shorten commute times. That makes sense if you look at somewhere like New York City, which is both monocentric and dense. People may work a short distance from their homes, but traffic is so congested and public transit makes so many stops that commute times are still relatively long. Simply increasing density in some cities may shorten commutes for a brief period, but the honeymoon won’t last forever.

Which is a bummer, because for the most part people think their commutes are too long. A survey of 2,000 commuters in the San Francisco Bay Area reported that 52 percent of respondents said they commuted at least 5 minutes longer than they would like. Among that group, median commute times were 40 minutes, which is certainly longer than the region’s average. On the other hand, 42 percent said their commutes were just right (their median time was 15 minutes). Surprisingly, 7 percent felt their commute was too short (median of 10 minutes). But despite the fact that a majority think their commute is too long, most people said they didn’t mind it, so long as their trips were less than 100 miles.

That people don’t mind their commute may be why commute times refuse to shrink. People in the Bay Area survey who didn’t mind their commute said they agreed with statements like, “I use my commute time productively” and “My commute trip is a useful transition between home and work”, which supports anecdotal evidence I’ve heard that people enjoy the separation between work and home. Twenty to thirty minutes may be just enough time to unwind.

It’s not entirely universal, though. Tolerable commute times seem to lengthen when people switch from cars to mass transit. People may find that time more productive, or maybe the time seems shorter because driving can be stressful, while just sitting usually isn’t. Personally, I know I’m willing to commute longer by train than car. Another reason is because mass transit commutes tend to be more reliable in terms of duration (at least for trains). Not having to worry about traffic jams doubling your commute is a big advantage.

Regardless of mode, people seem to settle on an ideal commute time. And once they have settled, they don’t seem to stray from it. A study of two metro areas in Washington State discovered that commute times don’t change much when people move or switch jobs. The thinking is that if a person gets a new job that’s farther away, they are more likely to move. Plus, as people have moved to suburbia, some jobs have followed. It’s a two-way street. But that doesn’t mean employers can move to the burbs without consequences. If an employer moves and an employee doesn’t move as well, the employee is more likely to find another job. Companies looking to relocate simply to cut costs may find the high turnover that results more costly in the long run.

Commuting is a big part of our lives, so it makes perfect sense that it would affect so much of the world around us, especially the cities we live in. Take a dense city like New York that has oodles of jobs, and lots of dense housing close in. That density helps keep commute times reasonable. But somewhere like Tulsa that doesn’t have as many jobs doesn’t have as much need for density. Form follows function, and currently the freeways in Tulsa are functioning pretty well compared with New York.

That presents a real dilemma for urban planners, who have been striving to increase densities in cities across the board. One approach has been mixed-use development that blends retail, housing, and office space. That may help reduce trip times for errands and such, but it doesn’t preclude people from living in one mixed-use neighborhood and working in another. The reality is, we’re probably not going to change commute times. If we offer faster and better transportation, people will use it until it becomes overburdened. At which point they’ll just move closer to work. Attempts to influence urban form through design may not have much of an impact if jobs don’t follow.

Sources:

Cervero, R. (1996). Jobs-Housing Balance Revisited: Trends and Impacts in the San Francisco Bay Area, Journal of the American Planning Association, 62 (4) 511. DOI: 10.1080/01944369608975714

Cervero, R. & Duncan, M. (2006). ‘Which Reduces Vehicle Travel More: Jobs-Housing Balance or Retail-Housing Mixing?, Journal of the American Planning Association, 72 (4) 490. DOI: 10.1080/01944360608976767

Clark, W.A.V. & Davies Withers, S. (1999). Changing Jobs and Changing Houses: Mobility Outcomes of Employment Transitions, Journal of Regional Science, 39 (4) 673. DOI: 10.1111/0022-4146.00154

Clark, W.A.V., Huang, Y. & Withers, S. (2003). Does commuting distance matter?, Regional Science and Urban Economics, 33 (2) 221. DOI: 10.1016/S0166-0462(02)00012-1

Giuliano, G. & Small, K. (1993). Is the Journey to Work Explained by Urban Structure?, Urban Studies, 30 (9) 1500. DOI: 10.1080/00420989320081461

Levinson, D.M. (1997). Job and housing tenure and the journey to work, The Annals of Regional Science, 31 (4) 471. DOI: 10.1007/s001680050058

Schwanen, T., Dieleman, F.M. & Dijst, M. (2004). The Impact of Metropolitan Structure on Commute Behavior in the Netherlands: A Multilevel Approach, Growth and Change, 35 (3) 333. DOI: 10.1111/j.1468-2257.2004.00251.x

Schwanen, T. & Dijst, M. (2002). Travel-time ratios for visits to the workplace: the relationship between commuting time and work duration, Transportation Research Part A: Policy and Practice, 36 (7) 592. DOI: 10.1016/S0965-8564(01)00023-4

Vandersmissen, M.H., Villeneuve, P. & Thériault, M. (2003). Analyzing Changes in Urban Form and Commuting Time∗, The Professional Geographer, 55 (4) 463. DOI: 10.1111/0033-0124.5504004

Wachs, M., Taylor, B., Levine, N. & Ong, P. (1993). The Changing Commute: A Case-study of the Jobs–Housing Relationship over Time, Urban Studies, 30 (10) 1729. DOI: 10.1080/00420989320081681

Photo by Jekkone.

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If the world’s population lived like…

Shortly after I started Per Square Mile, I produced an infographic that showed how big a city would have to be to house the world’s 7 billion people. There was a wrinkle, though—the city’s limits changed drastically depending on which real city it was modeled after. If we all lived like New Yorkers, for example, 7 billion people could fit into Texas. If we lived like Houstonians, though, we’d occupy much of the conterminous United States.

Here’s that infographic one more time, in case you haven’t seen it:

What’s missing from it is the land that it takes to support such a city. In articles and comments about my infographic, some people overlooked that aspect—either mistakenly or intentionally. They shouldn’t have. Cities’ land requirements far outstrip their immediate physical footprints. They include everything from farmland to transportation networks to forests and open space that recharge fresh water sources like rivers and aquifers. And more. Just looking at a city’s geographic extents ignores its more important ecological footprint. How much land would we really need if everyone lived like New Yorkers versus Houstonians?

It turns out that question is maddeningly difficult to answer. While some cities track resource use, most don’t. Of those that do, methodologies vary city to city, making comparisons nearly impossible. Plus, cities in most developed nations still use a shocking amount of resources, regardless of whether they are as dense as New York or as sprawling as Houston. Any comparison of the cities in my original infographic would be an exercise in futility at this point.

But what we can do is compare different countries and how many resources their people—and their lifestyles—use. For countries, the differences are far, far greater than for cities. Plus, there’s a data set that allows for reliable comparisons—the National Footprint Account from the Global Footprint Network. Their methodology is based on peer-reviewed research by Mathias Wackernagel, the organization’s founder. It’s consistent and comprehensive. Each country’s footprint is assembled from sub-footprints, ranging from cropland to carbon to urbanization to fishing grounds. For my purposes, I used only terrestrial sub-footprints. I’ll let the results speak for themselves.

Sources:

Global Footprint Network. 2011. National Footprint Accounts, 2011 Edition.

Wackernagel, M., Kitzes, J., Moran, D., Goldfinger, S. & Thomas, M. (2006). The Ecological Footprint of cities and regions: comparing resource availability with resource demand, Environment and Urbanization, 18 (1) 112. DOI: 10.1177/0956247806063978

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Concrete jungles replacing urban forests

David Nowak is at it again. The tireless ecologist and his frequent collaborator Eric Greenfield have given us another comprehensive snapshot of urban forests in the United States. Nowak has published numerous studies on urban trees, one of which I’ve covered previously. But that study—which discovered that some cities are leafier than their pre-urban states—takes a longer view and paints a different picture. In this new study, Nowak and Greenfield focus on the more recent past, the 2000s, and find that 17 of the 20 cities they surveyed had significantly fewer trees than just five years earlier. Sixteen became more developed, too, with an increase in impervious surfaces like roadways, parking lots, rooftops, and sidewalks. Taken together, these findings suggest that cities across the U.S. are steadily defoliating.

In this most recent study, Nowak and Greenfield turned to a favorite tool of mine for evaluating forest cover—aerial photographs. For each city, Nowak and Greenfield found a pair of images taken three to six years apart. They scattered a minimum of 1,000 points across each city’s photo pair and manually classified them into eight categories: trees and shrubs, grass and herbaceous cover, bare soil, water, and three classes of impervious surfaces (buildings, roads, and other). They were accurate to within a few percent in every class.¹ Nowak and Greenfield also compared their subset of 20 cities to other large cities in the U.S. by sampling an additional 1,000 points in metro areas across the country. The results were largely similar, meaning what they found in the 20 cities would be indicative of nationwide trends.

With the exception of Syracuse, all cities in the study had fewer trees in the later image. Overall, existing tree cover decreased 0.9 percent per year in 18 of the 20 cities (New Orleans and Detroit were excluded from most statistics—more on why later). That may not sound like much, but like any annualized percentage, it compounds. When a small amount of trees are lost from one year to the next, the change may not be that noticeable. But over 10 years, the results can be drastic. And when you remember that trees account for just 28 percent of land area in these cities, at these rates it won’t be long before trees cover the barest sliver of our urban areas.

Nowak and Greenfield excluded two of their surveyed cities, New Orleans and Detroit, from most statistics based on their extraordinary circumstances. In New Orleans, they were interested in seeing how Hurricane Katrina changed the urban forest, and in Detroit, they were looking for signs of the emerald ash borer infestation, an invasive insect that has decimated ash trees throughout New England and the Midwest. Detroit was lucky—it emerged relatively unscathed, losing only 0.7 percent of its total tree cover, in part because vacant lots make a great home for young trees. New Orleans, on the other hand, fared poorly, losing more trees than any other city in the study, nearly 10 percent.

Those cities aside, the trends don’t bode well for urban forests. Most concerning is the conversion from trees to impervious surfaces. Losing trees to grass and bare soil may be concerning, but it’s not catastrophic. Those cover types are easy to reforest. But when land becomes covered by roads, parking lots, or buildings, it very rarely reverts to vegetation of any type. At least 71 percent of the time, the move to impervious surface was because of development, not, say, a tree dying and revealing a parking lot beneath. The majority of the time, it was the more permanent type of conversion.

Which leaves us with a question—how are we going to maintain, let alone increase, tree cover in cities where buildings, streets, and parking lots are taking over the landscape, often in irreversible ways? One is for cities to take direct action, by planting trees in existing public spaces. Lots of cities have planting programs, but in many cases they’re barely able to keep pace with deaths from disease, urban stress, and old age.

Another option is to open gaps in the concrete along streets to provide new opportunities for planting. Not only does this give the city more places to plant, it sends a good message to the neighborhood, showing that the city cares. Planting trees may also be a way of leading by example, an exercise that could be followed by the offer of free trees for neighborhood residents. It’s subtle, but potentially more effective because there’s often more land behind people’s homes than in front. Cities could also add more parkland. Trees in parks aren’t exposed to the same stresses as street trees, but parkland can be expensive to procure.

That Nowak and Greenfield’s results span the last decade makes them that much more alarming. We’ve lost 1 percent of our existing tree cover per year in that time. Where will that leave us ten years from now? We don’t know, exactly. Until we have more data from earlier years, we just won’t know for certain—these sorts of changes could be cyclical. But given trends in development and population density and the rate at which trees have been converted to impervious surfaces, I’m guessing we’re headed toward fewer trees.²

1. Just as it’s easy for even the untrained eye to see differences in income based on relative differences in tree cover, it’s a simple task for a trained photointerpreter to tell trees from grass. It’s difficult for computer algorithms to match human photointerpreters’ accuracies, but sometimes the data set is too large for manual classification. It’s always a tradeoff. In this case, the areas covered were of manageable size, so a human touch made sense.
2. I should point out that I’m not condemning population density. Rather, we need to think long and hard about the way we accommodate high population density. Cost can’t be the only consideration.

Source:

Nowak, D.J. & Greenfield, E.J. (2012). Tree and impervious cover change in U.S. cities, Urban Forestry & Urban Greening, 11 (1) 30. DOI: 10.1016/j.ufug.2011.11.005

Photo by Franco Folini.

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Your images of income inequality, seen from space

A month ago, I covered a study showing how tree cover was related to income level. A couple of weeks later, I posted images gleaned from Google Earth showing how easy it is to spot income inequality from space. I also asked you, my readers, to send me more examples of the same.

The response has been overwhelming. In fact, I’m still receiving emails and comments. I haven’t been able to go through them all, so if yours isn’t below, hang tight. I’ll get to it eventually. Consider this a post that’ll be updated continuously. As they say, check back early and often.

So without further ado, here they are. This is where you see income inequality. You may see it every day, right in your own backyard. You may have stumbled across it years ago. You may have noticed on a vacation. But collectively, you see it everywhere. Keep ‘em coming.

Mexico City

From Todd Gastelum, who writes:

Although it appears that these satellite images are presented at different scales, I assure you that they were not. The houses in Lomas truly are enormous whereas San Miguel Teotongo is typical of the dense, irregular urbanization characteristic of the city’s more peripheral zones.

Lomas de Chapultepec, Miguel Hidalgo

San Miguel Teotongo, Iztapalapa

Dar es Salaam, Tanzania

From Aaron Krolikowski, who writes:

I’m a PhD student (in Geography) from the University of Oxford. My work takes place in Dar es Salaam, Tanzania and I spend quite a bit of time looking at maps of the city. One of the first things I noticed was exactly what you mention in terms of the ability to see income inequality from a birds-eye view. I’ve shared some photos with you to give you an idea of what I look at (and live!) every day here.

The first – To the left you have unplanned settlements of “Mikoroshini” and “Makangira”…to the right, the highly affluent and very European “Oyster Bay”

The second – To the left is the informal settlement of Hanna Nassif and across the river is middle-class Upanga

Mikoroshini, Makangira, and Oyster Bay

Hanna Nassif and Upanga

Vancouver

Downtown East Side

British Properties

Lisbon, Portugal

From João Jordão.

Cascais

Income inequality, as seen from space

Last week, 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.

Below 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.

Rocinha

Zona Sul

West Oakland

Piedmont

Fourth Ward

River Oaks

Woodlawn

Hyde Park

Fengtai

Chaoyang

Boston metro area, Massachusetts

Ball Square, Somerville

West Cambridge

Do you have other cities or neighborhoods in mind? I’d love to hear from you. Send me an email with photos or link to your blog post. In the next couple of weeks, I’ll put together a follow up article that features your examples.

Be sure to include the names of the cities and neighborhoods you’re highlighting and if you’d like me to mention your name.

UPDATE

Your examples are now posted! The response to my call for examples has been unbelievable. I’ve received hundreds of messages. I have the first batch up, and as I have time, I’ll be adding many more. Keep ‘em coming.

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Urban trees reveal income inequality

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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More than just flora and fauna

Peter Sigrist, writing at Polis about what he sees as ecology’s shortcomings:

Ecology “proper” is currently limited in addressing human habitation. It doesn’t usually incorporate the theory or methods of fields like economics, anthropology, political science, sociology and history. Many subfields have emerged in answer to the need for more detailed study of human-environment interaction, including human ecology, cultural ecology, political ecology, environmental sociology, historical ecology, ecological anthropology, ecological economics and ecological urbanism. But most are not closely integrated with mainstream ecology and its methods, which are primarily focused on nonhuman nature. Many ecologists portray human environmental impact as a kind of alien intervention into the natural world, and don’t attempt to understand the political, social, economic and cultural processes through which it takes place.

Sigrist isn’t entirely wrong—our understanding of the natural world must consider human impacts. The thing is, many ecologist already do that. If Sigrist had written this decades ago, I would concede his point. But times have changed. No serious ecologist draws a firm boundary between natural and anthropogenic spheres. For years, ecologists have widely acknowledged that no part of the Earth is untouched by human influences. Some may still cling to the old distinction between human and wild, but they are increasingly few and far between. Climate change has thoroughly disabused most of that notion.

Sigrist further laid out his argument in a second post, stating:

Incorporating useful elements of cultural landscape, urban political ecology and ecological urbanism can make ecology more attuned to the ways humans experience and influence cities. This is more than a shared analytical framework or conceptual lexicon (Gandy 2008: 567); it means actual integration so that ecologists are equipped to address the full complexity of human environmental relations and help make cities more just, healthy and beneficial to the planet as a whole.

To say too few ecologists study human-environment interactions isn’t just unfair, it’s incorrect. Sigrist seems to misunderstand ecology and its relation to the myriad subfields he listed above. The ecologists he describes—the ones that focus on strictly “natural” ecosystems—aren’t members of an umbrella field but a subfield. They’re just one type of ecologist. The people who study other subfields of ecology? They’re ecologists, too.

What Sigrist is proposing for ecology already exists. Perhaps he wants ecologists to avoid over-specialization.¹ Perhaps what he means to say is that there needs to be more collaboration and cross-pollination between ecologists of different subfields. He’s not wrong—there could always be more. But he’s ignoring what’s already out there. I know ecologists of all stripes—field, physiological, sociological, and so on—who collaborate with environmental historians, economists, even electrical engineers. I know ecologists who write papers about the value of ecosystem services, how to use Wall Street’s data processing techniques to understand the water cycle, or how spirituality can affect the conservation of biodiversity. Hell, I’ve been to conferences where ecologists have wrung their hands about how ecology needs more collaboration. If anyone is conscious of the need for interdisciplinary collaboration, it’s ecologists. After all, ecology is the original interdisciplinary science.

Again, that’s not to say we shouldn’t work harder to identify how humans are affecting the natural world. I’m the last to argue against that. But we need to identify our shortcomings where they actually exist, not where we imagine them to be.

1. Not a bad idea, but good luck getting it to happen. Despite calls for interdisciplinary research, the trend for individuals is toward increasing specialization. Nipples on the surface of human knowledge and all that.

Landscape near Paris, Paul Cézanne, National Gallery of Art.

Africa’s urban quandary

I’ve heard the statistics so often they’re almost cliché: Fifty percent of the world’s population now lives in cities, and by 2050 it will be 70 percent. Yet those numbers fail to capture the enormity of the change, especially so for those of us in the developed world where for decades the majority of the population has lived in cities.

Urban growth is going to be especially taxing in Africa, where the population is expected to more than double by 2050 and urban populations are expected to triple. Furthermore, 70 percent of the urban population growth is predicted to occur in cities with less than 500,000 people today.

Such a demographic shift is occurring today in China, but the situation there is different than in Africa. China’s semi-command economy and authoritarian government make managing mass migrations easier. Furthermore, the Asian nation is two times bigger than Africa’s two largest nations—Algeria and the Democratic Republic of the Congo—combined. Planning on that scale has its advantages.

China’s and Africa’s circumstances aren’t entirely dissimilar, though. China’s expanding cities have displaced farmers on the periphery, leading to protests. Social strife in African nations is similarly problematic. Take the example of Bahir Dar, Ethiopia. Researchers from Tattori University in Japan and Mekelle University in Ethiopia mapped the city’s expansion from 1957 to 2009 and found that Bahir Dar’s area expanded 31 percent annually, or 88 hectares (217 acres) per year. That’s a shockingly rapid pace, even outpacing some of China’s cities.

It also portends social strife. The researchers interviewed 271 of the nearly 2,900 households whose farms had been seized between 2004 and 2009 to make way urban development. What they heard paints a gloomy picture. First the good news: Nearly all were offered and received monetary compensation. Now the bad: Nearly all of those who had received compensation said it wasn’t nearly enough to replace what they had lost. One farmer’s response explained the shortfall in a nutshell: “I had 300 eucalyptus trees, 45 coffee trees, ten mangos and avocados, and ten papayas on my land, but finally I received compensation only for the farmland.”

Even if monetary compensation were sufficient, it wouldn’t be what expropriated farmers need to transition to urban life. Nearly 60 percent of the surveyed households let their money sit in the bank—they hadn’t a clue what to do with it. “It would have been better to change the money into other assets. But to do this, I do not have experience and knowledge since I am illiterate,” one respondent said. A few were given other opportunities—40 percent were offered a line of credit and 24 percent were offered some sort of training. But those promises were often reneged.

The loss of farms isn’t just a tragedy for the affected families—residents of Bahir Dar will feel the effects, too. Though African cities are entering global food markets, many people still rely on outlying farms. And as cities expand, many of those farms disappear. That means crops have to be trucked greater distances, increasing food prices and further sensitizing them to rising oil prices. People in developing nations already pay a greater proportion of their income on food than those of us in developed nations. Any increases in food prices can be calamitous, as we saw in 2007 and 2008.

It doesn’t look like there is relief in sight, either. In Bahir Dar’s case, the researchers predict the city will double in extent by 2024. Similar patterns are likely to be seen across Africa as many cities will double in population by that date. As in developed countries, part of the solution will be better education and training for the displaced and newly immigrated. But given the projected magnitude of urban growth in Africa, even that may not be enough.

Source:

Haregeweyn, N., Fikadu, G., Tsunekawa, A., Tsubo, M., & Meshesha, D. (2012). The dynamics of urban expansion and its impacts on land use/land cover change and small-scale farmers living near the urban fringe: A case study of Bahir Dar, Ethiopia Landscape and Urban Planning DOI: 10.1016/j.landurbplan.2012.02.016

Photo by Marc Veraart.

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The last settler’s syndrome

In my mind, my hometown will always be a city of 24,000 people. It’ll also be supported by three major manufacturing companies. And it’ll always have a certain, intangible something. Of course, today West Bend has 5,000 more residents despite the demise of all three manufacturers. And every time I return, that certain something isn’t quite the same either. It’s like waking from a dream I can’t entirely reconstruct.

Geographer Gilbert F. White would say I’ve got “last settler’s syndrome”. To me, the ideal West Bend is the city I remember from my childhood—really, from my middle school days when my friends and I explored every street in the city by bike. White would also say I’m not alone: “Each wants his particular town and country landscape to remain just as it was when he or she arrived. The most recent settler wants to be the last settler.”

One could argue that the settlement of the United States was driven in part by last settler’s syndrome, that the pioneer spirit is just a euphemism for the malady. Pioneers who saw their wilderness fill up with other settlers may have become disillusioned. The Ohio River Valley, for example, wasn’t the same after the first trees were felled. So people picked up and moved on. It instilled a distinctly American habit—moving west for new opportunities.¹ My own ancestors followed that well-worn path, moving from Ohio to Wisconsin in the late 1800s.

Seemingly everything in our lives is touched by the last settler’s syndrome, from our childhood homes to our neighborhoods to our favorite haunts. It can be a powerful, positive force—if John Muir hadn’t been afflicted by last settler’s syndrome, there probably wouldn’t be a Yosemite National Park. But last settler’s syndrome also can be problematic. Neighborhood quarrels can result when new transplants push for change. And while obstinacy can be good in some cases—Muir and Yosemite—it also can be a barrier.

Understanding the last settler’s syndrome—how it affects people, and more importantly, how it affects ourselves—can help us better understand where we live, whether that be cities, farms, or forests. It also can help explain why change is so accelerated these days: We’re a population that moves a lot. As of 2010, less than 60 percent of Americans lived in the state in which they were born, almost 30 percent were born in another state, and almost 13 percent were born in another country. How people defined “the way things were” used to evolve over generations. Today it’s on the order of years.

In an era of constant upheaval—where cities look nothing like they did a few years ago, let alone a few decades ago—we need to consciously disassemble our relationship with places and analyze them in parts. What should we keep? What should we change? What needs to change? It’s difficult to abandon the past, but the future will be nothing like we imagine. Things are going to change whether we like it or not.

1. Why else is California so populous? I kid, I kid. Or do I?

Sources:

Nielsen, J. M., Shelby, B., & Haas, J. E. (1977). Sociological carrying capacity and the last settler syndrome Pacific Sociological Review, 20 (4), 568-581

U.S. Census. 2011. Lifetime Mobility in the United States: 2010.

White, Gilbert F. 1986. The Last Settler’s Syndrome. in Geography, Resources, and Environment: Volume 1. Robert W. Kates and Ian Burton, eds. The University of Chicago Press, Chicago.

Photo by anoldent.

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The woods that were

In Star Wars, cities are evil

George Lucas hates cities. At least that’s what I gather from decades of watching and rewatching the original Star Wars movies.

The Star Wars movies are famous for hewing to archetypal stories—hero sets out to save galaxy from evil warlords, hero confronts his (familial) past, hero grapples with his role as a savior. And the movies’ portrayal of urban agglomerations is similarly archetypal, drawing on a long tradition of damning the city while praising the countryside.

Let’s start from the beginning. When we meet our hero, Luke Skywalker, he’s lamenting how isolated life is on his aunt and uncle’s moisture farm on Tatooine. But it’s that same upbringing—away from the corrupting influence of a big city—that frames his character. Luke may be brooding and somewhat annoying on the surface, but deep down we understand him as innocent and inherently good.

A few scenes later, that isolation is shattered. His aunt and uncle are ruthlessly slaughtered by Imperial storm troopers—interlopers from the city—searching for R2-D2 and C-3PO. With few other options available, he joins Obi-Wan Kenobi, a philosophical hermit living out his days in the wilderness, on a journey to find Princess Leia. That journey starts in Mos Eisley, what Obi-Wan calls a “wretched hive of scum and villainy.” The characters in Mos Eisley live up to that description, providing a stark contrast to Luke and Obi-Wan. The cantina patrons are rude, incendiary, and violent. It’s quickly apparent that Mos Eisley has no redeeming qualities. The best thing to do in Mos Eisley is to leave—which with the help of Han Solo, they do.

The problem is, the next place they end up is even more treacherous. They drop out of hyperspace where they had expected to find Leia’s home planet of Alderaan, but instead are captured by the Death Star. The moon-sized space station is the city at its most extreme. The Death Star is not just a moon-sized spaceship with a city covering its surface—the whole thing is a city, straight through to the power station at its core. And until it’s destroyed at the end of A New Hope, it is the embodiment of the evil Empire.

But Lucas’s critique of the city doesn’t stop there. Darth Vader’s flagship, the Super Star Destroyer Executor, paints a silhouette that resembles a city skyline. Cloud City on Bespin—where our protagonists hope to find refuge—is anything but safe. Mayor Lando Calrissian betrays Han and his companions, turning them over to Vader. Granted, Lando later struggles to undo his betrayal by helping Luke, Leia, and Chewbacca escape, but it’s too little, too late. In the bowels of Cloud City, Han is frozen in carbonite and handed over to Boba Fett while Luke battles Vader, losing a hand in the process and discovering the grim truth about his father. Cloud City is like Mos Eisley—you can’t leave soon enough.

Contrast Mos Eisley, the Death Star, and Cloud City with the Rebel strongholds. The Rebel base on Yavin Four is an ancient temple nearly overrun by a jungle teeming and screeching with life. And the Rebel Alliance’s headquarters in The Empire Strikes Back are dug into the snowy surface of Hoth, a wasteland even more desolate than Tatooine.

Luke and Obi-Wan aren’t the only protagonists closely associated with the wilderness, either. We meet Yoda in the swamps of Dagoba. The little green fellow is seemingly the only sentient being on the entire planet. It’s also there on Dagoba that Luke trains to become a Jedi and where Obi-Wan shares with Luke his last bits of wisdom.

The entire trilogy comes to a climactic finish on and above the forest moon of Endor. The moon itself isn’t necessarily representative of anything, but its inhabitants are. Ewoks are introduced as primitive and superstitious, but they quickly become our heroes’ key allies. It seems improbable that their help was what sealed the deal, but really the Imperials were doomed from the start. Their base and shield generator stood out like sore thumbs in the forest. The Ewoks and their villages, on the other hand, blended right in. The Ewoks also used their superior knowledge of the forest to turn the tide of battle in their favor. Finally, Return of the Jedi ends with our heroes celebrating their victory in a tiny Ewok village, not on a massive battleship or in a city.

▪ ▪ ■ ▪ ▪

But what about Coruscant¹? you might be thinking. Its residents cheered when the Empire was defeated in Return of the Jedi. That would seem to imply that Coruscant had some redeeming quality, that not all cities in Star Wars are evil. Technically, Coruscant wasn’t in the original trilogy prior to Lucas’s tinkering, and my analysis here has been limited to the original, unadulterated trilogy. But Coruscant is hard to ignore for two reasons: One, it’s a world that’s almost entirely urbanized, and two, even if it wasn’t portrayed in the original trilogy, it plays an undeniably central role in Star Wars mythology.

Coruscant’s portrayal is more complicated than other cities in the Star Wars universe. That’s in part because it wasn’t included in the original trilogy. Lucas’s vision for the first three movies was unsubtle—there’s good and there’s evil and there’s very little overlap between the two. Even the central characters that are the most conflicted—Han and Lando—end up so unambiguously good that they spearhead the two-pronged attack on the second Death Star. Coruscant doesn’t carry the same dichotomous baggage. Its later introduction means it’s wreathed in subtleties that are missing in the original movies. But ultimately, it’s still depicted as a bad place.

Long before we meet Luke, Coruscant was the seat of the Old Republic. For thousands of years, it was a force for good in the universe. It hosted the Imperial Senate. The Jedi Order was headquartered there, too. But over time, the Old Republic rotted like a tree—from the inside out—implying that the capital was at the center of that decay. Indeed, Palpatine plotted his takeover from a penthouse office on Coruscant and later made the planet-city capital of his Empire. On balance, Coruscant is more evil than good.

▪ ▪ ■ ▪ ▪

George Lucas isn’t the only one who has juxtaposed virtuous rural folk with vile city dwellers. People have been doing that for centuries. In the late 1700s and early 1800s, the Romantic and Transcendentalist movements were intellectual reactions to the ascendancy of cities. For example, Ralph Waldo Emerson saw cities impersonal and anonymizing, their inhabitants despondent and listless. Romantics like Percy Bysshe Shelly often brooded over ancient ruins, remarking on how such constructs of society were often overwhelmed by nature, implying a sort of justice for the wrongs cities exact on humanity. Both groups built their reputations by extolling the virtues of the countryside while decrying the debasing influence of cities.

Star Wars is just another footnote in a bulging tome of intellectual criticism on cities. It may seem surprising that such commentary would come in the form of a sci-fi film littered with energy weapons and faster-than-light travel. But if you pause to consider George Lucas himself, it shouldn’t be. Just look at where he lives—on 4,700 acres of rolling oak woodlands, secluded from the chaos of the San Francisco Bay Area.

1. For the unfamiliar, Coruscant is a world almost entirely covered by a city, reminiscent of Trantor in Isaac Asimov’s Foundation series. Though artist Ralph McQuarrie sketched concepts of a capital city for the original trilogy, Coruscant was never officially named or seen before Lucas tinkered with the films.

Thanks to Maura Chhun for her invaluable feedback.

Interview: Jon Christensen on California's cities

The U.S. Census released a report on urban population on Monday, and in it was a perhaps-unexpected fact: Of the ten most densely populated cities, seven of them are in California. Indeed, California’s showing was so strong that the great bastion of urbanism in the United States — the New York-Newark metro area — just barely made the top five.

John King, the San Francisco Chronicle’s urban design critic, interviewed a number of experts about California’s unique status. Among them was Jon Christensen, executive director of the Bill Lane Center for the American West at Stanford University. One of Christensen’s quotes caught my attention, so I followed up with him via email to explore why California is such a hotbed of urbanism. Our correspondence follows:

Tim De Chant: What’s special about California that it has so many dense urban areas?

Jon Christensen: The American West, in general, and California, in particular, is really a metropolitan region and has been for a long time. California, Nevada, Utah, and Arizona are among the 10 most urbanized states. The settlement pattern in the West is one of concentrated cities surrounded by wide open spaces — often substantially made up of public lands. This is true of California as well.

So it’s really the interplay of the history of cities and their hinterlands in the American West that explains why California has such dense urban areas. The fact that they are among the most dense urban areas in the country is also a result of population growth in California. The state has been and still is a great place for many people to live.

De Chant: In your chat with John King, you said, “It’s a legacy of how in our minds’ eye we have always separated California into ‘urban’ land and ‘productive’ land and then wilderness, the cathedrals of nature.” Do you think that mental dichotomy has played a role in how California urbanized?

Christensen: I actually think that the way we have urbanized and the creation of that mental division, which is really a legacy of John Muir’s vision of California, have both played crucial roles in how we think about cities in California. This, in turn, shapes the way that density is measured, of course. Take the San Francisco-Oakland urban area, which as it is measured by the Census includes the populated areas of Marin but not the open lands of the Golden Gate National Recreation Area just to the west.

If those lands were included in the San Francisco-Oakland area, the denominator for the equation of people per square mile would be bigger, and the measure of density would be lower. That wouldn’t change the fact that the city is still one of the most densely populated in the country. But it does miss the fact that we live in a very densely populated metropolitan region that also has ready access to conserved public lands practically at our doorsteps, or a short drive or bus or bike ride away.

De Chant: In other parts of the country, that distinction isn’t so clear. Has that played a role in sprawl?

Christensen: I’m not sure that the mental distinction has played as important a role as the existence of public lands. Of course, public lands are, in some ways and particularly in some cases, the products of intentional human agency, political organizing, and conservation movements. This is true of the Golden Gate National Recreation Area and much of the rest of the lands protected around the Bay Area, for example.

A strong conservation vision runs deeply through the history of the Bay Area as Richard Walker shows in his great book The Country in the City. That explains a lot, here. But it doesn’t necessarily explain Los Angeles, Phoenix, or Las Vegas. For that, we have to look at public lands that were never homesteaded and thus have, to varying degrees, constrained cities. We also have to look at geography and topography. The San Gabriel Mountains constrain Los Angeles even more than the coastal mountains constrain the Bay Area.

De Chant: In a tweet you said you think of California as “quite a mixed up rather than clearly divided landscape.” Why the divide between the California of our imaginations and the California of reality?

Christensen: I think we still live in John Muir’s California in our minds, a state divided between the cities, the productive landscapes of farming, ranching, and mining, and the wilderness cathedrals of the Sierra Nevada. I think that’s changing as we recognize that people have played a role in constructing, shaping, and changing nature from the city out through the countryside and even to the wilderness, and that nature runs through it all as well.

The focus on hybrid human and natural landscapes, novel ecosystems, and ecosystem services all point to the ways that our thinking about nature is changing. But it’s changing slowly. John Muir’s California is still a powerful vision. It’s just too simple to be very useful in thinking about the present, let alone the future.

De Chant: In much of California, nature never feels far away. Why is that?

Christensen: Because it never is far away. Because of geography, topography, the history of settlement, and a long history of conservation efforts, wild nature is close in to the city in much of California, sometimes right in the middle of the city. We’re also bringing nature back to the city, daylighting creeks, restoring the L.A. River, planting urban gardens. And we’re increasingly realizing that nature is in the city already. It never went away. And we need to be more cognizant of the processes of nature that flow through the city and of which the city is made if we are going to fashion more sustainable urban living here in California and around the world.

De Chant: There’s on old saying, “As goes California, so goes the nation.” Do you think that’s the case with urban development?

Christensen: I do think that we have many useful things to share with the nation and the world from our history and experience. And from our current efforts to understand and shape nature in our metropolitan regions—in San Francisco, but even more so in Los Angeles, which is truly a global city in so many ways and the most densely populated city in the United States, as it happens.

But I don’t think it’s a simple matter of “as goes California, so goes the nation” or the world. Differences are important, whether they are historical, geographic, political, economic, cultural, or other differences. I think there are many similarities between cities in the United States and around the world, which makes me think that vocabularies, rules of thumb, lessons even, could be transferable. But they will have to be adapted to different cities, by the people making those cities.

De Chant: How do we transfer those lessons learned in California to other places?

Christensen: Your saying that “as goes California, so goes the nation” does get at a historical reality that California has been a site of innovations in ideas, technologies, policies that have influenced the nation and the world. And our dense cities in the San Francisco Bay Area and Los Angeles have also been key nodes in global networks of ideas, commerce, technology, and even species. The eucalyptus and palm are iconic examples. So I think the lessons will spread. But I also think it’s imperative that we speed up the process.

Over roughly the next two generations the urban population on the planet will double, and the urban built environment will have to double. How that happens will dramatically shape the future of how human beings live together and live with nature on Earth.

I don’t have answers, and I’m eager to learn, but I think we can start by mining our rich, diverse history and experience of thinking about and doing conservation and development together, in relationship to each other, over time in our cities, to come up with some common vocabularies, ways of speaking about this relationship, and rules of thumb, basic guides to planning and constructing hybrid human and natural cities, that can be adapted to different circumstances in different places. Then we need to figure out how to share these conceptual tools with the people who are actually going to build the cities of the future soon.

Photo by Neil Kremer.

Seeing historical processes in road networks' patterns

Once a road, always a road. That’s the gist of a recent paper that studied 14 different municipalities in the Groane region of Italy near Milan. In cataloging 174 years of road construction, the study’s authors discovered that nearly 90 percent of the regions 100 most vital routes today were already present in 1833.

The researchers also uncovered evidence that the layout and characteristics of road networks are indicative of the age in which they were built. This is nothing new. Take a look at any metro region surrounded by a postwar subdivision—stick straight roads of the late 19th and early 20th centuries give way to ever more writhing tangles of spaghetti. What’s new is that this study claims that top-down planning didn’t drive the changes. Rather, the researchers say Groane’s roads reflect broader societal changes, that the unique circumstances of each era—agricultural through modern—shape road networks more than central planning—or lack thereof.

To arrive at that conclusion, physicist Marc Barthélemy and his colleagues digitized roads using maps and aerial photographs from seven different dates between 1833 to 2007. They threw the resultant vectors into a geographic information system, or GIS, and then distilled primal graphs—simplified maps that show only roads (called “links” in graph theory) and intersections (“nodes”).

Between 1833 and 2007, the number of intersections grew proportionately with population. The number of intersections skyrocketed—there were only 255 in 1833 but over 5,000 in 2007—but the number of connections remained relatively constant at 2.7 on average. The number of roads also increased linearly with the number of intersections. It’s almost as if the expansion of Groane’s social network was mirrored in its transportation corridors.

How those roads interacted with each other changed through time. In the early days, many roads either intersected another mid-link—forming a T-junction—while the others simply petered out in a dead end. Main drags radiated out from town centers like spokes on a wheel. Congruent 4-cornered intersections were rare. Yet as time progressed and cities spread into the countryside, the previous radial expansion gave way to the grid. In other studies, the advent of the grid was attributed to the arrival of master planning, but here in Groane, Barthélemy and his colleagues note that urban planning was never the region’s strong suit. Groane, they write, “never witnessed any large scale planning whatsoever.”

It is because of Groane’s lack of central planning that Barthélemy and his colleagues are able to draw their conclusion, that road networks morphed not because of changes in our approach to planning but because of changes in society as a whole. In essence, they assert that changes to the network were not consciously done.

It’s not surprising, really. Roads are built to handle the traffic of their time. When navigating Cambridge’s labyrinthine streets, I’m constantly reminded that they were built for horse and carriage, not a horseless carriage. The demands of the automobile are sufficiently different from horse or foot traffic. Their greater speeds require straighter rights-of-way. Intersections need to be clear and predictable. Navigation also needs to be simplified—drivers moving at 10 miles per hour have more time to look for their next turn than those moving three times faster. The grid tackles these problems with aplomb.

Road networks are a product of the processes that created them, whether that be wagon traffic from farm fields plodding to town or taxi cabs streaming out from downtown. Discerning process from pattern is also the domain of another field—landscape ecology. Landscape ecologists sweat the details of spatial configuration to learn what ecological processes are at work. The laws of landscape ecology apply just as well in the city as they do in the natural world. The city is nothing but an anthropogenic ecosystem.

Ever since Geoffrey West and his colleagues uncovered the mathematics behind why big cities are economically successfully—but also crime ridden—it has been popular to search for formulae that describe urban processes and city development. This paper by Barthélemy and his colleagues is but the latest addition to a growing literature. By themselves, these discoveries are clever and insightful. But the interesting stuff will happen when urban planning completes the transition from an observation-based science to a mathematical one, much as ecology did in the recent past. Then we’ll have a real sense of how these models will change our understanding of cities.

Map scanned by University of Texas PCL Map Collection.

Source:

Strano, E., Nicosia, V., Latora, V., Porta, S., & Barthélemy, M. (2012). Elementary processes governing the evolution of road networks Scientific Reports, 2 DOI: 10.1038/srep00296

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Can crowdsourcing save the city?

TED is currently in full swing, and the program this year has an entire section devoted to the city. Fitting, given that this year’s TED Prize went to a city-centric project, one that hopes to crowdsource ideas to solve urban problems and reinvent cities. It’s predictably named The City 2.0. The site has a flashy splash page, but the innards still need some work—tapping in my current city of Cambridge, Massachusetts, sent me to a generic index page that encouraged me to “get connected” with other aspiring urban planners in my area, but responded to my clicks with little more than a broken Google Maps interface and some “COMING SOON” dialog boxes. For now, it’s long on pizzazz and short on details.

The TED Prize website fortunately has more on what The City 2.0 hopes to accomplish:

For phase I, the website (www.thecity2.org) will focus on helping individuals in forming cross-disciplinary groups to:

1. determine the issue they want to tackle (i.e. traffic, lack of trees);
2. determine a solution;
3. develop an action plan;
4. work to implement the solution;
5. share the story of their success or failure with others.

Companies and organizations will be able to offer their tools to site users for use in executing their action plans. Ten micro grants of \$10,000, coming out of the \$100,000 TED Prize money, will be awarded in July 2012 to ten local projects that have the best hope of spurring the creation of their City 2.0.

To be clear, that’s \$100,000 to be equally split among ten groups. Not a lot of money to tackle problems that probably need millions, even billions, of dollars thrown at them. Thankfully, there’s more:

As the site continues to grow and the overall platform grows we expect to:

1. expand the functionality for individuals to connect and act;
2. develop and design templates for knowledge sharing between new ideas formulated on the site and preexisting projects;
3. build out our resource section with new local and global partners;
4. introduce technology solutions for non-web based communities;
5. expand our financial incentive program with larger grant offerings for active projects
6. establish local and/or global gatherings on the City 2.0.

That’s a little better. This part of the project should have a longer-lasting impact than the small pot of grant money. Local civic groups often don’t have the skills or wherewithal to build a connected platform to publish their ideas and solicit feedback. The City 2.0 could provide that. But soliciting ideas is just the beginning. Many other hurdles stand in the way, and from what I can see The City 2.0 doesn’t propose how to address them.

The most obvious barrier is money. The City 2.0 acknowledges that to be successful it needs “companies and organizations willing to offer empowering resources” and “financial support”. It seems to me they are simply hoping companies and philanthropists will step forward and reward the best projects. That’s papering over a big problem.

The next issue is how to choose the best project. The City 2.0 says in its intro video that it will “combine the reach of the crowd with the power of the cloud”. Both crowdsourcing and the cloud are hot topics these days. Crowdsourcing in particular can give people a voice who otherwise may not have spoken up, and it leverages the law of big numbers to extract a handful of singular, stand-out ideas. But the real problem with crowdsourcing solutions for cities is more fundamental than that: Who decides which ideas to implement?

Lior Zoref, a crowdsourcing advocate, gave a TED talk this year about the wisdom of crowds in which he was joined on stage by an ox. After the gasps died down, he asked everyone to guess the weight of the animal and submit it to a website. At the end of his talk, he announced the average of the audience’s guesses: 1,792 pounds. The real weight of the cow? 1,795 pounds.

It is an impressive demonstration, but one that doesn’t sell me on the crowd’s ability to reinvent the city. That’s because crowd wisdom cannot apply to projects like The City 2.0. With the ox’s weight, there is one right answer. The crowd’s wisdom can be unambiguously verified. But with ideas and concepts like those solicited by The City 2.0, there is no right answer. And you certainly can’t distill an “average” idea from them all. Ultimately, a panel will have to pick the winners and losers. Those panelists will have enormous sway over the outcome of The City 2.0. If they are experts in their field, what’s to say the winners will be revolutionary, or even substantially different from their own work?

If winners are picked by popular vote—which I highly doubt—that, too, is no guarantee that the most promising proposals will be selected. People don’t always know what they want. “It’s really hard to design products by focus groups,” Steve Jobs once said. “A lot of times, people don’t know what they want until you show it to them.” There may be wisdom in crowds, but genius is usually confined to individuals.

I suspect it’ll take true genius to remake the city. We’ve been spinning our wheels in recent years, rehashing concepts of the city that have been around for decades, even centuries. Those ideas may have worked well in the past, but they didn’t have to contend with airports, globalization, or climate change. Today’s best solution may be unlike anything we have come to expect from cities.

I’m sure The City 2.0 will fund some great projects, but we won’t really know how they work until we really try them. Not small bits here and there, but big implementations. Trying on that scale takes money, and the only organizations with the money to do it are governments.

Does that mean it’s back to the old way, sitting through planning meetings and zoning boards? Maybe. Crowdsourcing is a great way to gather ideas, but implementing them takes community and persistence and enthusiasm. It’s possible that a website could create that community, but I’m skeptical—most social media tools piggyback on existing, real-world social bonds. I know I sound pessimistic about The City 2.0. I’m not entirely. I hope that the project will uncover a work of genius that would have otherwise been ignored, but I’m not holding my breath.

Photo from The City 2.0.

Flyways and greenways

Earlier this week I pointed out that urban areas can actually increase tree cover over time, albeit with a caveat. The two studies I cited measured tree cover and only tree cover—they made no claims about ecological function. Luckily, other studies have done just that, including one that looked at migratory bird use of greenways in urban areas.

Migratory routes are important, though most research into migratory bird decline has focused on habitat loss in their breeding and wintering grounds. That has left a large piece of the puzzle unsolved—the habitat between point A and point B. Think of it this way: If snowbirds—you know, northern (human) retirees who flock to warmer climes in the winter—started disappearing and our best solution was to look for them at their apartment in New York or their rental in Boca Raton—ignoring rest stops and motels along I-95—we’d be doing a great disservice to our older generations. Ignoring flyways is similarly foolish.

There have been studies in more recent years that aim to fill this gap, and one published in 2009 by Salina Kohut, George Hess, and Christopher Moorman picks up the trail along, well, trails. They surveyed bird species abundance and richness—how many and how varied the itinerants were—in 47 greenways in and around Raleigh, North Carolina.

Greenways are a common and convenient way for cities to conserve natural habitat. Their linear form is well suited to urban areas, and they easily double as parks or recreational trails. They also can serve as stop-over habitat for migratory birds. Kohut, Hess, and Moorman were hoping to find the right type of corridor for migrating birds, where our feathered friends can take a load off and fatten up.

It turns out that most birds were not picky and would stop at just about any greenway, regardless of vegetation, adjacent land use, or corridor width. That’s not to say all greenways were entirely equal. Overall, birds favored corridors with taller trees and lots of native shrubs teeming with fruit. And among birds that live in forest interiors far away from human development and even open fields, greenways wider than 150 meters (about 500 feet) surrounded by low-intensity development were the most popular.

None of the greenways Kohut and her colleagues studied were as good as a regular forest, though. Still, with some tweaks—including widening corridors, siting them near low-intensity development, and planting with natives—greenways can make decent stand-ins for the real thing, at least as far as migratory birds are concerned. Residential neighborhoods can even make themselves into agreeable stopover habitat by mimicking vegetation found at popular stops along the flyway.

So greenways make for good bird habitat, but let’s not forget that they’re good neighbors, too. In addition to helping migrating fauna, they boost property values, add recreational opportunities, and work well as commuting corridors for cyclists. Five benefits from one land use. Not too shabby.

Photo by qmnonic.

Source:

Kohut, S., Hess, G., & Moorman, C. (2009). Avian use of suburban greenways as stopover habitat Urban Ecosystems, 12 (4), 487-502 DOI: 10.1007/s11252-009-0099-6

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Tree City

Cities aren’t called “concrete jungles” for their leafy greenness. But perhaps it’s an inappropriate nickname. Several cities actually have more—not less—tree cover than what came before them. By way of example, take this from historian William Cronon: “There are more trees in southern Wisconsin now than at any point in the last 7,000 years.” That’s in part due to more than a century of fire suppression, but also the intense pace of urban development.

There’s ample scientific evidence to back up Cronon’s assertion. In the early 1990s, David Nowak, an urban forester with the U.S. Forest Service, found that tree cover in Oakland, California, between 1850 and 1989 rose sharply from 2 percent to 19 percent. Now, a new study by Adam Berland, a PhD student at the University of Minnesota, found a similar pattern in and around Minneapolis, Minnesota.

Oakland and Minneapolis—and many other metro areas, I suspect—were sparsely forested before urban development. As far back as 1500 BCE, what would become Oakland was regularly burned by the Coastanoan Indians to clear out the underbrush to simplify acorn gathering. What trees remained in the 1700s were logged for lumber and firewood by the missions. Then in 1848, what was left nearly vanished when gold was discovered in California. By the time Oakland incorporated in 1852, its namesake was nearly gone.

Fire likewise held forests in southern Minnesota at bay for thousands of years. Yet unlike in central California, a part of central Minnesota quickly afforested during a brief climate cooling 400 years ago. It wasn’t long lived, though—shortly after their arrival, European settlers swiftly knocked down most of the Big Woods for farming. The remaining flecks large enough to be called forests cover only 2 percent of the original area. In other words, forests near Oakland and Minneapolis had nowhere to go but up.

The arrival of dense settlement was something of a godsend for trees. Young neighborhoods and cities are often depauperate—it’s easier to build without big trees in your way—but they tend to accumulate tree cover as they age. And relative to the denuded landscape that came before Oakland and Minneapolis, those urban forests are more akin to a real jungle than a concrete one.

Urban forests are certainly an improvement from a tree’s perspective, but they’re not a panacea for habitat loss. Neither of these studies examined how those forests function ecologically. Just like 11 random people do not make a soccer team, a bunch of trees is not the ecological equivalent of a real forest. Not only is the understory substantially different in cities—houses are terrible forage for most insects and animals—but the types of trees are often radically different.

Still, these two studies should make abundantly clear that cities do function as ecosystems, albeit limited ones. And in some cases, they are more diverse and productive than what came before. This is especially true for metropolitan Minneapolis, where monocultures of wheat and corn were less diverse than the Big Woods they replaced and maybe less ecologically complex than the cities that replaced them. These two cases also underline the need for an urban ecology that doesn’t just study what systems cities create, but strives to shape those systems for greater ecological complexity and diversity.

Sources:

Berland, A. (2012). Long-term urbanization effects on tree canopy cover along an urban–rural gradient Urban Ecosystems DOI: 10.1007/s11252-012-0224-9

Nowak, David J. (1993). Historical vegetation change in Oakland and its implications for urban forest management Journal of Arboriculture, 19 (5), 313-319

Photo by frozenchipmunk.

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