Category Archives: Landscapes

How cities change the weather


Late in the day on June 13, 2005, a thunderstorm was bearing down on the city of Indianapolis. As the main cell approached from the southwest, it reared up, convection currents pushing it higher and higher until it towered over the city. Luckily for Indianapolis, the cloud threatened more than it menaced, eventually dumping just an inch of rain on suburbs and farm fields to the northeast. On the surface, it may not have seemed particularly special. But for meteorologists studying the storm, it was perfect.

What set that storm apart from others, they suspected, was the fact that it passed over Indianapolis. The fact that the city was there—the subtle but significant change it made to the texture and composition of the Earth’s surface—was enough to alter the structure of the storm. Using a model they built to test the city’s impact, meteorologists couldn’t accurately simulate the June 13 storm without Indianapolis.

Humans altering the weather is the stuff of science fiction. (Not climate, mind you. That’s unfortunately all too real.) Not that we haven’t tried—cloud seeding, while not as promising as once thought, is still used on occasion to coax more precipitation from the sky or to wring clouds dry, as was the case during the Beijing Olympics. Cloud seeding is small scale stuff, though, and the amount of effort required makes it unsustainable over the long term. But while tactical, widespread weather control remains beyond our grasp, we routinely change the weather around the world simply by living in cities. And most of us don’t even know it.

The most common—and well known—way that we change the weather is through the urban heat island effect. In an urban heat island, a city’s mass of asphalt and concrete and lack of tree cover traps and holds heat. That effect may drive other shifts in the weather, including the change in structure of the June 13th storm over Indianapolis. Heat rising off a city, meteorologists think, increases convection within storms, pushing the storm cloud higher faster and raising its reflectivity core, or the size and distribution of rain droplets within the cloud. In some cases, cities can even split the reflectivity core—the buildings exert drag on the atmosphere, which disrupts the storm’s airflow.

Von Karman vortexes near Guadalupe Island

That a city’s physical structure can affect a massive system like a thunderstorm may seem unlikely, but it’s not improbable. Scores of satellite images have captured islands cleaving clouds, creating successive swirls downwind, a phenomenon known as the Von Karman effect. No one has seen cities create disturbances as charismatic as the Van Karman effect, but Marshall Shepherd, a professor at the University of Georgia and president of the American Meteorological Society, told me that one of his students has found traces of it in his research models. Unfortunately, the results weren’t strong enough to include in a publication.

Apart from changes in cloud structure, there’s also some evidence that cities change the amount of rainfall a storm produces. A large field experiment carried out in North America in the 1970s, known as METROMEX, concluded that cities increased cumulative precipitation by 5-25 percent, most of which fell downwind of the city. Size mattered, too. Bigger cities tended to induce more rainfall that fell over a larger area. Since then, some studies have disagreed, claiming there’s no change, but an even larger number seem to confirm the patterns found in METROMEX. Depending on the region, these new studies found that cities may increase rainfall by up to 60 percent, several-fold more than previously thought. What’s causing that? Any number of factors, including aerosols from pollution, the urban heat island, and changes in airflow over buildings, could be driving the urban rainfall effect. But to date, no one can definitively explain why it occurs.

When you add it all up—and throw in a few other variables I haven’t discussed, including lightning strikes and wind speeds—it’s clear that cities have an undeniable impact on the weather. That many of those effects extend far beyond political boundaries should only reinforce the idea that cities and their countrysides are inextricably linked.


Shepherd J.M. (2013). Impacts of Urbanization on Precipitation and Storms: Physical Insights and Vulnerabilities, Climate Vulnerability: Understanding and Addressing Threats to Essential Resources, 109-125. DOI:

Niyogi D., Pyle P., Lei M., Arya S.P., Kishtawal C.M., Shepherd M., Chen F. & Wolfe B. (2011). Urban Modification of Thunderstorms: An Observational Storm Climatology and Model Case Study for the Indianapolis Urban Region, Journal of Applied Meteorology and Climatology, 50 (5) 1129-1144. DOI:

Photos by fehlart and NASA.

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Can you tell urban from rural?

If you were given a section of a map, could you tell if was from a city or the countryside? The answer to that question may be trickier than you expect. I pondered this a year and a half ago when I wrote, “ ‘countryside’ is inherently interpretable term, one that depends more on how the land is used than it does on population density.”

It first struck me when I was traveling around Taiwan. There, the distinction between the rural and urban areas wasn’t always apparent to my Western eyes. The same can be true with maps. Distinguishing between urban and rural depends as much on geographic and cultural contexts as it does on visual cues like road networks.

Can you tell which is which?

The following maps are road networks from a variety of locations around the globe. Guess which are cities and which are rural areas. All maps are drawn to the same scale.

1. 1. Urban or rural?

2. 2. Urban or rural?

3. 3. Urban or rural?





From top to bottom: 1. city (Denver) 2. countryside (Japan) 3. city (New York City) 4. city (Houston) 5. countryside (Taiwan) 6. city (Los Angeles) 7. countryside (Wisconsin)

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Town, section, range, and the transportation psychology of a nation

Farms west of Montreal

The flight from Boston to Chicago isn’t the most scenic, but if you’re lucky enough to snag a window seat—no mean feat these days—study the patchwork landscape with a discerning eye about 40 minutes into the flight. You’ll notice something a bit peculiar, at least for North America. Instead of the usual tableau of square or rectangular farmsteads, you’ll see ribbons of agronomy. They’re a Canadian ghost of geography, a relic from when the region was known as Nouvelle-France.

Back in the early 17th century, France was trying to stabilize its colonial foothold in the New World. Cardinal Richelieu, an advisor to the king and powerhouse in French politics, hatched a plan to encourage more intensive settlement. As a part of that, he parceled the land similarly to the way it was divided in France—long, thin strips oriented perpendicular to a transportation route, which in New France was primarily the St. Lawrence River. The layout traces its roots back to medieval times, but what’s more intriguing, at least to me, is how ribbon farms—or rather the lack thereof in the much of North America—shaped attitudes toward transportation.

Part of the beauty of ribbon farms is how easy it is to transport goods from them. Moving around the farm itself is a bit more difficult—the farthest part is much farther away from the house and barn than the most distant part of a square farm. But between farms and from farms to market, ribbon farms are superior. Roads running past ribbon farms can serve more addresses over the same distance. Neighbors are a short walk away, cities and crossroads closer than you’d expect. Since the system started with the transportation network and built out from there, ribbon farms have certain efficiencies square farms never could.¹

Farms north of Detroit

Much of arable North America, though, was not allocated in ribbon farms. The Public Land Survey System carved up large portions of the United States into one square mile sections, each of which were subdivided to create farms and aggregated to form townships. Canada adopted a similar system for its prairie provinces, called the Dominion Land Survey. Under such schemes, farms are more square than linear, a quirk of geography that I believe influenced the development of the entire nation.

Here’s how: Roads snaked out to farms where they were needed, which is to say nearly everywhere. Farmsteads, and later suburban houses, were more or less evenly distributed across the landscape rather than concentrated next to existing roadsides. The fact that the farm, not the transportation, came first is important. In New France, transportation was clearly the foundation. But in much of the rest of North America, parcels were delineated first. Transportation routes followed, a geographic case of the tail wagging the dog.

Here’s why that matters: With ribbon farms, the expectation is that transportation is king. Living under such a plan, I imagine networks have a certain planning primacy which dictate certain characteristics of the parcel. But when the U.S. started with square farms, the process and the results were the exact opposite. We plotted the farms and then pondered the logistics. In that context, it’s no surprise that we feel transportation should come to us instead of the other way around. As Americans, we pick a place to live and then figure out how to get where we need to go. If no way exists, we build it. Roads, arterials, highways, Interstates, and so on. Flexible and distributed transportation networks are really the only solution compatible with that way of thinking. Trains, which rely on a strong central network, never had a chance. We were destined for the automobile all the way back in 1787, when we first decided to carve up the countryside into tidy squares.

Town, section, range. Pick your plot, worry about the details later. It’s the American way, and it’s driven the psychology of an entire nation.

  1. Did I mention you don’t have to turn your oxen or tractor as frequently, either?

Satellite images courtesy Google Maps.

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To cultivate better students, plant a few trees

Lone tree

Look at that tree up there. Do you feel smarter? You should, provided that you’re a teenager. And that tree above? Well, it’s should be right outside your high school’s cafeteria windows, or even your classrooms’. Better still if all of your school’s windows are filled with a similarly arboreal tableau.

That’s the upshot of a 2010 paper that reports on how the view out high school windows can influence students’ academic performance. That may seem limited, but this is science, where we have to take things one step at a time. This step involves high schoolers. It’s possible that such benefits extend beyond just high schoolers—after all, people who have views of nature while at work are happier at their jobs—but for now, it’s just high schoolers.

The study looked at 101 public high schools in southeastern Michigan. I presume they spanned a variety of socioeconomic conditions and geographic settings, though the author didn’t confirm that, so I can’t be certain. However, when calculating his final statistics, he did control for socioeconomic status, as measured by student participation in free and reduced lunch, ethnicity, school size, and age of the school building.

For each school, he also gathered a variety of environmental variables, including the area of the campus taken up by athletic fields, parking lots, and other landscaping, as well as the ratio of trees to shrubs to lawns in that landscaping. He measured the size of the windows in classrooms and cafeterias and noted whether students could eat lunch outside. Finally, he judged how nice those views were, how much nature they contained. It’s a somewhat subjective measure, but an important one nonetheless.

To see how those views affected students, the author considered three academic and two behavioral criteria—graduation rates, four-year college plans, percentage of students who won the Michigan merit award (based on standardized test scores), disorderly conduct, and truancy.

Lo and behold, views of nature did have an effect. Students who could see real nature outside their cafeteria windows were more likely to graduate, to plan to attend a four-year college, and to win a Michigan merit award. They were also less likely to commit a crime. The bigger the windows, the better the results in some cases, including for four-year college plans (they were higher) and criminal activity (it was lower). Classroom windows didn’t have a noticeable influence, perhaps because students spend more time staring at the teacher and the board than out the window. That’s probably a good thing.

Put simply, students performed better academically at schools with more nature around it and bigger cafeteria windows to view it. They were more likely to graduate, more likely to plan to attend college, and less likely to be miscreants. The opposite was also true. If the school was surrounded by a large parking lot or expansive athletic fields, students there were less likely to want to attend college.

Now, planting trees and installing floor-to-ceiling windows in the cafeteria isn’t suddenly going to turn a struggling school into a star performer. Socioeconomic conditions, quality of life at home, and classroom sizes all exert far more influence over student performance. But the results presented in this paper aren’t insignificant. Views of nature improved most measures by 5 to 15 percent. That’s pretty impressive.

It also suggests that we shouldn’t build schools as cheaply as possible, which often means fewer windows and more cheap cinder block.¹ Opening up the walls, and making the views worthwhile, could do wonders. A few trees here and there along with a little less mowing could boost student academic achievement, reign in delinquency, and do so inexpensively. It’s not going to solve the problems that plague many of our schools,² but planting trees is so simple that it would be foolish to ignore. What are we waiting for?

  1. I should know. My high school was one of those.
  2. See the previous paragraph for what really needs to be tackled.


Matsuoka R.H. (2010). Student performance and high school landscapes: Examining the links, Landscape and Urban Planning, 97 (4) 273-282. DOI:

Photo by Kevin.

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Designing systems, scientifically

Japanese countryside

A couple of months ago, I was talking with a friend about design. Well, really, about the scope of design. Many designers tend to think in terms of discrete objects—a chair, a phone, a building. This exasperated him, and for good reason. See, discrete objects aren’t the only things that are designed. Cities are, too, he argued. “You see that city over there,” he said, emphasizing his point. “People made that.”

If we were to pick up this conversation again—and we might—I’d add landscapes to the list. Our understanding of ecology has matured to the point that we are beginning to grasp our species impact on the planet. We are, and have been for thousands of years, changing our surroundings to suit our needs. Today, there isn’t a single ecosystem that’s untouched by humanity. That’s a definition of design if I’ve ever heard one.

But in many ways, we’ve been molding ecosystems haphazardly, at best. If design isn’t just the result of human activities, but is a considered plan put together with purpose and intent, then maybe we’re not designing landscapes after all.

Both sides of the argument are equally valid, I think. But one thing is clear—when we change our surroundings, we need to place more emphasis on design. A couple of recent papers have made that clear to me.

In one, Joan Nassauer and Paul Opdam wrote an op-ed of sorts in the influential journal Landscape Ecology back in 2008. Nassauer and Opdam suggested that the field of landscape ecology add design as a third tenet to the existing two, pattern and process. It would help address a shortcoming of the field. Landscape ecology was originally formulated based on the premise that we can learn how a landscape functions by studying how it is configured. If we get pattern, then we’ll get process. It’s been a phenomenally successful framework, but like many sciences, landscape ecology has stumbled when it comes to the implementation part.

That’s problematic because we humans are always mucking about with the landscape. Every time we repave a road, carve out a new subdivision, or erect a skyscraper, we’re altering the face of the Earth. And currently, we’re doing it in perhaps the most uncoordinated way possible. When set out to build a road, skyscraper, or city, our ambitions may be big, but our thinking is small. We tend to focus on the immediate impacts—how much steel we’ll need, how much land we’ll use up, and so on. We forget to consider how that creation will affect the surrounding landscape.

There are a few exceptions. Nassauer and Opdam cite two case studies, an ecological corridor network in Denmark and a watershed workshop in Iowa. Another paper by Simon Swaffield referred to an overhaul of the wetlands and waterways in and around Christchurch, New Zealand. There are others, too. When I was in graduate school, members of my lab were working on the Sierra Nevada Adaptive Management Project. The U.S. Forest Service was working with scientists and locals to come up with a way to minimize potentially catastrophic wildfires. The centerpiece of the Forest Service’s original plan was to clearcut a giant checkerboard of chevrons into 11 national forests. It’s design on a landscape scale if I’ve ever seen it. Their process is, too. Though the Forest Service wasn’t keen on the idea initially, they now are working closely with locals to ensure the final implementation is palatable to everyone. Researchers from the University of California are serving as arbiters, of sorts, making sure the science is sound and that everyone’s voice is heard. The back and forth, the multiple stages, the consideration of possible outcomes—that’s the design process.

If landscape ecology can successfully incorporate design as a third tenet, it will be in a league of it’s own. It’s a science that thinks on a system-wide scale; few such sciences worry about design. There are other systems that have design applied to them—cities are certainly one—but those design processes aren’t always informed by the sort of systems science that’s inherent to landscape ecology. The field could be a real pioneer, and in the process provide some order to slapdash overhaul we’re currently giving our surroundings.


Nassauer, J.I. & Opdam, P. (2008). Design in science: extending the landscape ecology paradigm, Landscape Ecology, 23 (6) 644. DOI: 10.1007/s10980-008-9226-7

Swaffield, S. Empowering landscape ecology-connecting science to governance through design values, Landscape Ecology, DOI: 10.1007/s10980-012-9765-9

Photo by Tim De Chant.

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Lone tree

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.


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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Nature’s burning library


Let’s imagine it’s 48 B.C.E., and the Library of Alexandria is burning.¹ Bits of ash are floating down from the superheated updrafts, remnants of what was the world’s greatest collection of written knowledge to date. You’re standing just outside the door, and you have five minutes to dash in and grab whatever you can carry. Do you focus on one section to save, say, Aristotle’s works on biology and anatomy? Or do you run from stack to stack, hoping to rescue a cross-section of classical scholarship?

Fun choice, huh? Yet those are the sorts of decisions that conservation biologists make all the time. They’re constantly trying to answer a question that has no good answer: “Which remaining bits of nature should we try to protect?” They know we can’t save them all. There’s only so much money and land to go around. They also know that how is an equally important question. Do you set aside a single large reserve or several small ones? Get the answer wrong, and poof, nature as we know it is gone.

With stakes like those, it’s no wonder conservation biologists have been arguing over that question for several decades. David Quammen ably covered the debate in The Song of the Dodo—a highly recommend read—but I’ll briefly summarize it here.

In the 1960s, young scientists Robert MacArthur and Edward O. Wilson were restless. MacArthur was a quantitative ecologist looking to shake up the sleepy field of biogeography—what species occur where and why—and Wilson was an entomologist cum field ecologist tired of merely cataloging new facts about ants. MacArthur was searching for a way to describe mathematically what he saw in biogeographic data. Wilson had such data from his research on Pacific islands and their ant species. Together, they hammered out the theory of island biogeography, which says that larger islands hold more species. Specifically, an island that is 10-times smaller will have two-times fewer species. When MacArthur and Wilson published their ideas, they swept through ecology like wildfire, quickly modernizing the once descriptive and theoretically-challenged science.

Fast-forward to 1975. Jared Diamond—yes, that Jared Diamond—had been conducting his own biogeographic research. Now, he was proposing that to best protect biodiversity, a single large reserve would be preferable to several small ones that totaled the same area. It was, he argued, a logical extension of MacArthur and Wilson’s theory of island biogeography. After all, protected areas are themselves islands marooned in a sea of cities and farms. Just as a larger island tends to hold more species, so too could a larger park protect more biodiversity. And, he added, larger parks are better habitat for big, charismatic megafauna like elephants, lions, and bears.

Needless to say, not everyone agreed. Dan Simberloff—who had been Wilson’s grad student in the 1960s—and Lawrence Abele published a rebuttal to Diamond’s paper the following year. They argued that, given the realities of conservation, putting all our eggs into large parks would be both untenable—purchasing large tracts of land is costly and difficult—and unwise—problems in a single park could doom an entire species. But small parks would provide some insurance and be easier to establish. Plus, there are many species for which reserve size isn’t everything, but geography is. Smaller, more targeted reserves would be a better fit for them.

Not long after Simberloff and Abele published their paper, ecologists began picking sides. It was a contentious debate then, and it still pops up at conferences and in scientific journals. If you talk to participants today, as I did in 2005, each side will say they won, that the debate has been settled. Clearly, that’s not the case.

One of the more recent flare-ups came from a quartet of Australian scientists who asked the same question for the umpteen-thousandth time—single large or several small? But this time, they added a twist. They admitted—in mathematical terms—that we don’t know the answer to a particularly germane question: Which species will go extinct and when?

Typically when conservation biologists design protected areas, they attempt to minimize extinction risk. To do that, they first need to determine what the expected extinction risks are. Those are difficult numbers to pin down accurately. So the authors of the new paper suggest a different approach. Rather than attempting to minimize risks, we should be striving for acceptably small risks. It’s a subtle distinction that could change everything.

Acceptable risk rather than absolute minimum risk is a more realistic target. Reserves designed for minimum extinction risk are setting themselves up for failure, in a way. There’s no way they can reduce extinctions to an absolute minimum. For one, it’s impossible to exclude people from an area entirely, and, as we’ve come to realize, many landscapes wouldn’t exist without human intervention. Besides, no species are really beyond human reach any more—climate change has made sure of that. Aiming for acceptably small risks acknowledges both the limits of our knowledge and the extent of human impact.

But the paper’s authors don’t stop there. They can’t help but toss their two cents into the single large or several small debate. Their answer? Seven reserves. If that number seems too precise to fit all scenarios, remember that this was a modeling experiment—hypotheticals have a way of being oddly exact. What’s more important is that “seven” represents a middle path, of sorts. Seven is neither a single reserve nor is it many. It does lean more toward the “single large” camp—the authors admit as much—but it also recognizes that one monolithic reserve is a risky bet. With seven, individual reserves can be large enough to buffer park interiors, while the overall network provides redundancy.

That’s not to say this paper settles the debate. Quite the opposite, I would bet. But I think it does make an important contribution, that some level of extinction risk is acceptable. For too long, we’ve viewed conservation in black and white, that if we don’t do everything to save a species, we might as well do nothing. In reality, there are a million shades of gray. By liberating ourselves from this binding dichotomy, we can devote more energy and resources to slowing extinction rates.

Ultimately, though, setting aside land for protection will only get us so far. It’s an approach we’ve been using for years, and it hasn’t done much to slow extinction rates. Nature’s library is still burning. If we really want to protect biodiversity, we’ll have to do more. We’ll have to put out the fire. For that, we’ll need more than a few people running in to save what they can. Like an old fashioned bucket brigade, we’ll all have to chip in. That will require real change on our part. All of us.

  1. Historians debate whether the library actually burned then, during Julius Caesar’s siege of the city. But for the sake of the analogy, let’s assume it did.


Michael A. McCarthy, Colin J. Thompson, Alana L. Moore, & Hugh P. Possingham (2011). Designing nature reserves in the face of uncertainty. Ecology Letters, 14 (5), 470-5 PMID: 21371231

Quammen, David. 1996. The Song of the Dodo: Island Biogeography in an Age of Extinctions. Scribner, New York. 702 pp.

Photo by ken2754@Yokohama.

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An office with a view

Office in the woods

There’s a scene in the movie Office Space where Peter, the protagonist, unscrews part of his cubicle and ceremoniously pushes the wall over, sending it and its shelved contents crashing to the floor. With a satisfied smile, he pats his desk a few times, kicks back, and enjoys his new view.

As I write this, the view out my window isn’t much more than Peter’s. Just a handful trees—no mountains, no idyllic nature scene, nothing that would make Ansel Adams jealous. Just one scrubby street tree and a couple of canopies poking their heads above the adjacent apartment building.

But according to Rachel Kaplan, an environmental psychologist, those few trees are far better than nothing at all. Kaplan has documented numerous cases in which workers reported feeling happier and more satisfied with their jobs because of the view they had out their window. Even views of parking lots—so long as they had trees or some other landscaping—were enough to brighten some people’s days.

Kaplan has made a career out of studying how views of nature affect various parts of people’s lives, from patient recovery times to worker productivity. Currently, I’m interested in her research on the latter topic. Staring out at a busy street is better than no view at all, but sometimes I feel antsy and distracted for no apparent reason. I’ve wondered if a more bucolic view would focus my efforts and lift my spirits. Coincidentally, Kaplan’s research suggests that’s exactly what would happen.

Kaplan says windows give people the opportunity for short restorative breaks. After hours spent staring at a computer screen or hammering through some repetitive task, a brief diversion or daydream is sometimes all that’s needed to push through the rest of the day. Allowing ourselves a short mental break boosts our happiness, which also increases our productivity.

But restorative breaks are more effective, according to Kaplan’s research, if they include gazing upon a natural scene. There’s something irreplaceable about nature. Not just greenery—office plants had a small positive effect, but one that paled in comparison to a natural view. Just adding a few natural elements to a windowful of buildings or parking lots raised employee satisfaction by a significant amount. Workers with nature views reported feeling less frustrated, more patient, and more satisfied with their jobs. Perhaps improbably, they also felt their jobs were more challenging and expressed greater enthusiasm for their work, despite the fact everyone surveyed had relatively similar jobs. Furthermore, workers with nature views also reported fewer ailments than those without.

People with outdoor jobs in natural settings—park rangers and park maintenance staff—had it best of all. They said their jobs were less demanding, lower pressure, less frustrating, and so on. It’s possible that such jobs are actually less demanding and lower pressure, but given how nature affects office workers, I wouldn’t be surprised if being immersed in nature plays an important role.

Alas, as a writer I don’t have many excuses to work outside. But I shouldn’t complain too much. My three trees are certainly better than Peter’s view before his renovations and far better than many people who work in windowless caverns.

Photo by Jeremy Levine Design.


Kaplan, R. (1993). The role of nature in the context of the workplace Landscape and Urban Planning, 26 (1-4), 193-201 DOI: 10.1016/0169-2046(93)90016-7

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What do we mean by “rural”?

Taiwanese countryside

The day after Thanksgiving I was on the tail end of a journey that spanned three flights and four airports. I was zipping through the Taiwanese countryside, though I didn’t realize where I was at the time. You could be forgiven if you thought my confusion was caused by the 28 hours of travel I had endured the day before, or maybe the intense jetlag, but you’d be wrong. I was fully alert.

This being my first time in Taiwan—my first time in Asia, in fact—I felt like a kindergartener on his first day of school. Everything felt foreign, new, and exciting. Mopeds raced ahead of automobiles at every stoplight and surged through crowds of people wandering the famous markets. Their rattling exhaust mingled with the vaguely eggy smell of effluent seeping from sewer grates. Politicians beamed down from billboards, thumbs erect in positive estimations of the country’s prospects. Lights pulsed along every roadside, manmade rainbows framing incomprehensible Chinese characters and occasionally humorous English phrases.

Amidst all the clamor, my density-obsessed mind couldn’t help but notice something else. This place was crowded. It was so packed with three-story houses, mopeds, Mazda 3s and Mitsubishi Delicas that it felt like one continuous city. In fact, I didn’t know we had left the city until my wife told me so. That was the source of my confusion.

When she mentioned that, I was taken aback. This was the Taiwanese countryside? To me it looked more like a confused mishmash of industry, farmland, and suburbia. But then realization settled in. I was in Taiwan, the second most densely populated country in the world.¹ With 23 million people living mostly on the slim plains sandwiched between the west coast and the rugged mountains that dominate two-thirds of the island, it makes similarly-sized Holland seem depopulated.

Satellite view of Taiwan

That Taiwan is a mountainous island no doubt partially accounts for its teeming population. But so too does the humid, tropical climate of the lower elevations. Tropical ecosystems are the most productive in the world, in part due to their year-round growing season and generous precipitation. It’s why the majority of Taiwan’s population lives on the flat, western sliver, and why farmers there don’t need large land holdings. It’s also why the Taiwanese countryside is as populous as some American suburbs.

As we whizzed by parked cars, rice paddies, and murky fish farms, I had an epiphany. I was in the country. Sweeping aside my preconceptions, I realized that “countryside” is inherently interpretable term, one that depends more on how the land is used than it does on population density.

¹ If you don’t count city-states or tiny oceanic flecks like the Maldives.

Photo by Tim De Chant, satellite image from NASA.

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Spare or share? Farm practices and the future of biodiversity

Ghosts of ecology

Roman mosaic

If you want a glimpse of our ecological future, take a look at present-day Europe. Continuous and intensive human habitation for millennia have crafted ecosystems that not only thrive on human disturbance, they’re dependent on it. But even in places where pastoral uses have fallen by the wayside, the ghosts of past practices linger. If you have any doubt that the changes we’re making to the earth right now will be felt thousands of years from now, these two studies should wipe those away.

This post was chosen as an Editor's Selection for ResearchBlogging.orgThe first takes place in a post-apocalyptic landscape masquerading as a charming woods, the Tronçais forest. Smack in the middle of France, Tronçais is the site of a recent discovery of 106 Roman settlements. Photographs of the settlements call to mind Mayan ruins in Yucatan jungles, with trees overtaking helpless stone walls. Tronçais was not unique in this way—following the fall of the Roman Empire, many settlements reverted to forest after the 3rd and 4th centuries CE.

Ecologists studying plant diversity in the area noticed two distinct trends. First, the soil became markedly different as they sampled further from the center of the settlements. Nearly every measure of soil nutrients declined—nitrogen, phosphorous, and charcoal were all lower at further distances. Soil acidity declined, too. Second, plant diversity dropped off as sample sites moved further into the Roman hinterland, and likely a result of changes in the soil.

The researchers suspect the direct impacts of the settlement and Roman farming practices are behind the trends. High phosphorous and nitrogen levels were probably due to manuring. The abundance of charcoal is clearly from cooking fires, while soil pH was affected by two uses of lime common in the Roman empire—mortar used in building and marling, the spreading of lime and clay as a fertilizer. The combined effects of these practices fostered plant diversity after the settlements fell into ruin, the effects of which can be seen to this day.

The second study was undertaken by another group of ecologists who canvased grasslands in northern and western Estonia. While threatened today by the usual suspects—intensive agriculture and urbanization—the calcareous grasslands of Estonia have a long history of human stewardship which helped a wide variety of grasses and herbs to flourish. They were greatly expanded by the Vikings, who settled the area between 800 and 1100 CE. Knowing this history, the researchers suspected population density may have boosted floral diversity. They sampled exhaustively, recording plant species and communities in 15 quadrats at 45 sites for a total of 675 sample plots. They also drew 20 soil samples at each site. To estimate population density during the Viking Period, they used an established model that estimated settlement size and extent based on known ruins.

Soil qualities naturally had an affect on present-day plant diversity, but human population density during and shortly after the Viking Period also emerged as a significant predictor. As with the Roman study, changes to soil nutrients because of human activities are likely behind the results. But that’s not all. The researchers point out that seed dispersal 1,000 years ago also influenced present-day diversity. When the Vikings expanded the grasslands, they connected different patches that had previously been isolated, allowing previously isolated species to germinate in new areas.

These are not the first studies to reveal a shadow of human habitation in present day ecosystems—the Amazonian rainforest is littered with evidence of agriculture before European contact, for example. But these studies show the ghosts of ecology persisting for millennia, not centuries. Not only does it bolster the notion that no landscape is pristine—an idea that has been gaining traction with the ecological community—it should underscore the persistence of any human activity.


Dambrine, E., Dupouey, J., Laüt, L., Humbert, L., Thinon, M., Beaufils, T., & Richard, H. (2007). Present forest biodiversity patterns in France related to former Roman agriculture Ecology, 88 (6), 1430-1439 DOI: 10.1890/05-1314

PÄRTEL, M., HELM, A., REITALU, T., LIIRA, J., & ZOBEL, M. (2007). Grassland diversity related to the Late Iron Age human population density Journal of Ecology, 95 (3), 574-582 DOI: 10.1111/j.1365-2745.2007.01230.x

Photo by mharrsch.

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Ghosts of geography

As I was walking home from work in San Francisco a number of years ago, a Days Inn caught my eye. The hotel itself is nothing special, but it sat at an odd angle to the street. Why would anyone build that way, I wondered. Next to it was a wide-open parking lot, something of a rarity in the city. Clearly, something had prevented the hotel owners from building on a rectangular footprint. But what could it have been?

At home, I pored over aerial photographs of the building and the parking lot. Upon zooming out, the answer was apparent. A trail of parking lots and angled buildings snaked through the neighborhood back to the freeway. Oddly shaped buildings remained, accommodating an interloper that is now gone. The disruptive structure was a double-decker spur of the Central Freeway built in the 1960s amidst the San Francisco freeway revolts. Like other double-decker freeways in the Bay Area, it was badly damaged during the 1989 Loma Prieta earthquake and had to be removed.

Click to view interactive before-and-after photographs of Octavia Blvd.

click to view interactive version

Parts of the old right-of-way have been reclaimed. The old ramps leading to and from Fell St. and Oak St. are now the Hayes Valley Farm. Octavia Boulevard has been transformed into a bike and pedestrian friendly thoroughfare. And buildings now stand in other places.

Such ghosts of geography are everywhere. Old land uses and geologic processes can leave marks on the landscape that are sometimes blurred but not always expunged. Chicago is full of geographic ghosts that resulted from the removal of old train tracks. Trees trace the path of an old section of the Green Line.

Click to view interactive before-and-after photographs of Chicago's Green Line

click to view interactive version

And buildings balloon to fill old right-of-ways formerly used by freight trains.

Building filling an old freight line right-of-way in Chicago

Even geology expresses itself in today’s land uses. Farmers planting on drumlins unwittingly map the direction of the Wisconsinan glaciers.

Aerial view of area around Beaver Dam, Wisconsin

Terrain view of area around Beaver Dam, Wisconsin

The Appalachian Mountains dictate where people farm and live.

Satellite view of Appalachian Mountains in Pennsylvania

Terrain view of Appalachian Mountains in Pennsylvania

Ghosts of geography may be obvious, like New York City’s High Line…

Click to view interactive before-and-after photographs of New York City's High Line

click to view interactive version

..or more subtle like the trees in Sue Bierman Park that used to line the on and off ramps that fed the now-dismantled Embarcadero Freeway in San Francisco.

Click to view interactive before-and-after photographs of Sue Bierman Park

click to view interactive version

The past is reflected everywhere in geography. What ghosts are in your neighborhood?

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Urban forests just aren’t the same

Farms giving way to subdivisions in Southeastern Wisconsin

If you were a squirrel living in Southeastern Wisconsin, you’d be pleasantly surprised by the state of things. In many places, there are as many—if not more—trees than there were 200 years ago. But that rosy image doesn’t tell the entire story. Comparing the forests that cover the cities and suburbs around Milwaukee—and likely in many places around the world—is like comparing Rome before and after the fall. It’s still Rome, but it’s not quite the same as it used to be.

Southern Wisconsin is a case study of the changes that were affecting much of the country in the 20th century. Most of the forests had been cleared in the 1800s by farmers, resulting in a landscape that little resembled what came before. The woodlots that remained were small and scattered. In one famous study, only 4.8 percent of the original forests remained by 1935. Milwaukee and its surrounding cities grew steadily in the run-up to World War II, but positively boomed thereafter. They needed room to grow, and since cleared land is easy to build on, farm after farm was subdivided.

The path from forest to front yard seems clear cut. A woods is cleared to make way for farmland, which is later subdivided into lots and sold off to make way for homes. But the reality is much more complex than that. Though a neighborhood may maintain its wooded appearance, it’s original character is gone.

In Wisconsin, subdivisions are invariably preceded by farms. Farming is a tough life. There’s not much money to be made with a small family farm, and an farmer’s property often doubles as his retirement fund. To maximize the investment, he’ll usually subdivide it for housing. It usually works out well for him, because land that’s good for growing crops is also good for building houses—it’s not too steep and most of it doesn’t need to be cleared.

That’s not to say farms are entirely devoid of trees. Most contain small woodlots and extensive fencerows that separated fields of corn, wheat, and soybeans. They’re relics of bygone forests, and in many places that’s all that’s left. Though the relationship is a bit one-sided, relic trees and farms have existed side-by-side for decades.

Maintaining that landscape during subdivision isn’t difficult. Building houses around trees is easy if you don’t take a cookie cutter approach, and houses with big trees in their yards tend to sell for more. But conservation rarely happens. That’s the conclusion of one study of Southeastern Wisconsin. It looked at the fate of extant vegetation as farms gave way to subdivisions between 1937 and 1975. Though the sum total of forested land didn’t drop as much as anticipated, very little of the original vegetation that made it through the transition. By 1975, the trees that dotted subdivisions and roadsides were almost entirely new.

That study reminds us that sum totals seldom tell an entire story. The relationship between forests, farms, and yards is complex and multidirectional. Forests are often cleared for farms, but abandoned farms can return to their forested state over time—much of New England underwent this process. However, urbanization can intervene along the way, removing the little remaining vegetation and replacing it with landscaped yards. But that’s not all the forest loss development is responsible for. Though many subdivisions are carved from land cleared previously for farms, they can be indirectly responsible for the loss of even more forests. Street and yard trees can’t offset this entirely. Similar patterns are well documented in developing nations. In Brazil, for example, expanding soy production has pushed cattle ranchers to clear land further into the frontier. It’s easy to forget these same processes are at work here in the United States.

Even when subdivisions spring fully formed from forested land—skipping the intermediate farm stage—their lots are often cleared of existing vegetation. Some of my research in graduate school documented the stark changes forest edges undergo when houses move in. In old black-and-white aerial photographs, the bare earth of cleared building sites stood out in stark contrast to the dark gray of the surrounding woodlands. Straight, sharp lines separated the two. In time, the edge bled back into the yards, but it wasn’t quite the same.

Suburban development isn’t going away anytime soon, but some of the structure and function of the old woodlands they replaced can be recovered. Homeowners can plant native trees. People can lobby their cities to plant native trees as well, rather than the whatever low-maintenance tree is in fashion among city foresters this year. The result won’t be the same as an intact woodland, but at least it will be similar.


Sharpe, D., Stearns, F., Leitner, L., & Dorney, J. (1986). Fate of natural vegetation during urban development of rural landscapes in Southeastern Wisconsin Urban Ecology, 9 (3-4), 267-287 DOI: 10.1016/0304-4009(86)90004-5

Photo by sierraromeo.

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Salvaging disturbed forests may not save biodiversity

Never buy a car with a salvage title. Anyone who has ever driven a car after a major accident can tell you why—it’s just not the same as before the crash. Though all the parts might be in the right place and the paint just as shiny as before, there’s invariably some new rattle, shake, or whistle that you can’t fix. The magic that is gone, and nothing will bring it back. Cars are a lot like primary tropical forests in that way.

Biodiversity thrives in undisturbed tropical forests. But once they have been selectively logged, burned, or leveled, what grows back in their place just isn’t as rich, vibrant, or diverse as the original, according to a new paper released online today in Nature. The meta-analysis—written by a number of authors including Bill Laurence and Tom Lovejoy, two deans of tropical conservation—synthesized 2,220 pairwise comparisons of primary and disturbed tropical forests from 138 different studies on four different continents to arrive at that one conclusion.

The dominant image of deforestation—at least from an American perspective—is the Amazon. Photographs and satellite images of logging and agricultural conversion show in graphic detail splintered tree stumps, smoking ashes, and herringbone tentacles of human influence. But while the authors found South American forests are greatly threatened by human disturbance, Asian forests are even more imperiled.

To compare results from numerous studies, the study’s authors the measured effect size of human disturbance on biodiversity. It’s a statistical technique which describes the magnitude of differences between populations. The effect size of land-use changes in Asia was more than twice that of second place South America and even larger still than those of Africa and Central America.

To give you an idea of the severity of Asia’s biodiversity threats, let’s review the guidelines on interpreting effect sizes. Generally, a small effect size is 0.2, medium is 0.5, and large is 0.8 and above. In the study, Central America checks in at 0.11, Africa at 0.34, and South America at 0.44. (A quick caveat before we continue: The African result may not be representative. The continent’s tropical forests are understudied because of continued conflict, and future disturbance rates could accelerate in the face of population growth.) Asia is far ahead of the rest of the pack, blowing them all away with an effect size of 0.95.

Asian tropical forests are more threatened by every type of human impact than tropical forests on other continents. Agricultural conversion is responsible for a large portion of biodiversity loss in the region, with plantations and selective logging operations following not far behind. Plantations are of particular concern because the crops they yield—primarily palm oil and exotic woods—are lucrative. Their profit potential draws interest not only from multinational corporations, but governments as well. These organizations have large amounts of capital and can convert vast tracts of primary forest into ecologically sterile plantations that practically print money.

Plantations also have the advantage—for governments and corporations, at least—of looking deceptively like natural forests to many people. Asia Pulp & Paper, a company with large plantation holdings throughout Southeast Asia, has been exploiting this confusion through a series of recent TV ads. The Indonesian government has been in on the ruse, too, suggesting that it may push for their plantations—many of which were carved from primary forests—to count as forest land under REDD schemes, or reduction of emissions through deforestation and forest degradation. That means the government would not only profit from the plantations’ crops, but also from international payments to purportedly offset or reduce carbon emissions.

If we have to use forest land at all, the best bet to preserve biodiversity seems to be selective logging. Though the practice still harms overall biodiversity, it does so less than other land uses. Still, the paper’s authors caution that selective logging’s ill effects may be masked by proximity to less disturbed primary forests, which may export species to depauperate tracts. If this is the case, then selectively logged areas may be running the ecological equivalent of a trade deficit with primary forests. Without some reciprocation, the two will eventually go bankrupt.

This new meta-analysis confirms what many ecologists have long suspected—that minimally disturbed primary forests are some of the best bastions of biodiversity. It puts another hole in the idea that agroforestry projects, plantations, and even selective logging can extract resources without adversely affecting ecosystems. Like a car that’s been in an accident, primary can never be the same as before. But unlike cars, we can’t go out and buy new ones.


Gibson, L., Lee, T., Koh, L., Brook, B., Gardner, T., Barlow, J., Peres, C., Bradshaw, C., Laurance, W., Lovejoy, T., & Sodhi, N. (2011). Primary forests are irreplaceable for sustaining tropical biodiversity Nature DOI: 10.1038/nature10425

Photo by WWF Deutschland.

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The importance of sentimental landscapes

Looking out from Melrose Rock

When I was packing for the move from Chicago to Cambridge, I figured the transition would be easy for two reasons, both of which are related. First, the two cities share a temperate climate. I grew up in Wisconsin and love—absolutely love—the changing seasons. For example, I’m not merely unfazed by below zero weather, I revel in it. The second reason is partially a consequence of the first—the Midwest and New England share a similar flora. Deciduous forests were the playground of my youth, where I went to escape the heat of the summer or romp through the snowy winter.

Having been a Cantabrigian for just just over two months, I can’t speak to the winters yet. But I can say something about the plants. A jaunt to Middlesex Fells over the Labor Day weekend affirmed my fondness for temperate deciduous forests. Still, I wasn’t quite at home. The Fells has a marvelous mix of deciduous oaks and evergreen pines perched on rolling hills and rocky outcrops. The whole landscape is reminiscent of the Calvin and Hobbes cartoons I devoured as a kid, but there was something missing. That something is my history with the place, or lack thereof. Research confirms it.

I wasn’t a part of the study in question—it took place almost a decade ago—but its findings confirm why I am both predisposed to liking New England’s woods and why they aren’t quite home yet. The study’s authors surveyed 328 park users in Ann Arbor, Michigan, to see whether they were attached to a particular park or just a particular setting. The study’s authors classified participants as park neighbors, visitors, volunteers, or staff, reasoning that these backgrounds would tint the lenses through which people viewed the parks.

The researchers found that neighbors who frequented a particular park were smitten by that place in particular. Perhaps the bond was formed during solitary reflective walks, or maybe weekend picnics with the family. Regardless, they liked those place in particular and didn’t find substitutes as appealing. Park volunteers and staff, however, were more inclined to treasure a park’s ecological contributions rather than sentimental ones. When shown photographs of a particular ecosystem, say a prairie, volunteers and staff were more likely to rate those shots highly regardless of their location. Volunteers and staff, who the researchers reasoned to be more ecologically knowledgeable, were also more open to restoration projects that supplanted invasive species with natives. Park neighbors and visitors tended to be happy with the landscape the way it was and generally opposed changes.

The differing perspectives of sentimental park users and ecologically principled individuals may help explain my hesitant fondness for the Massachusetts wilderness. The study seems to confirm that I straddle the line between two types of people. I have a feeling that many people are like me, especially those who recently moved. Our sentimental side aches for a favorite tree or preferred vista, but the rational ecologist in us appreciates native plant assemblages and landscapes.

People develop not just an affinity for nature, but the nature outside their window. That suggests not only that we should get outside, but also bring the outdoors closer to home, whether that be in the form of a city park or wild backyard. First-hand experiences with nature can be powerful ways to inspire people to adopt their own environmental ethic. I’m not the first to posit this theory—David Gessner does just that in his book My Green Manifesto, which I’m currently reading, as have others before him. Indeed, I can trace part of my own environmental ethic to a childhood spent in the park down the street or at the seven acres of scrubby, overgrazed woods just outside of town that my dad was rehabilitating. They are the type of landscapes I love and am fighting to preserve. Indeed, part of the reason I’m fascinated with higher density living is the potential it has to keep the wild places wild, the semi-wild places semi-wild. Calvin and Hobbes’s zany woodland adventures captured my childhood imagination because I saw in them a bit of my own al fresco self. I want future generations to have that chance, too.


Ryan, R. (2005). Exploring the Effects of Environmental Experience on Attachment to Urban Natural Areas Environment and Behavior, 37 (1), 3-42 DOI: 10.1177/0013916504264147

Photo by Paul-W.

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Spare or share? Farm practices and the future of biodiversity

Forest-farm edge in the Bolivian Amazon

Farming giveth and farming taketh away. Let’s parse that statement: Farming provides food—that much is obvious. But farming also gobbles up land that would otherwise accommodate endless biodiversity and beneficial ecosystem services. To counter the ecological harm done by farms, we have two options. One is to make farming more ecosystem friendly. Known as land sharing, this choice differs from garden variety organic farming by enmeshing cultivation with conservation rather than just minimizing detrimental impacts. The other option, land sparing, intensifies current cultivation while leaving other land as wild as possible. If you’re looking to feed people and maximize biodiversity conservation, you have to pick one.

The correct answer, at least according to a study published today in Science, is land sparing. The study’s authors examined farms and forests in southwest Ghana and northern India. They found more overall diversity of bird and tree species per square kilometer in land sparing setups—where farming is intense and reserves off limits—than in land sharing schemes—where farming and conservation occur on the same plot of land.

The ecologists involved in the study mapped out 25 one square kilometer plots in Ghana and 20 in India. The Ghanaian plots were divided almost equally among forest (8), large-scale oil palm plantations (8), and forest-farm mosaic (9). In India, they were split among five forest and 15 farm plots, five of which were low yield and ten of which were high yield. In each plot, the researchers measured average population densities of bird and tree species and binned each species into two broad categories—those that would thrive under a particular farming regime and those that would suffer. They then compared biodiversity statistics for land sparing regions (which contained both farmed and forested plots) with land sharing ones.

Unsurprisingly, all species fared worse when land was farmed. But the disheartening part—at least for those of us who dream of harmonious, ecotopian farms—was that more species were worse off on a region-wide basis under land sharing than land sparing. So although land shared between farm and forest is better for biodiversity on a single plot scale, the overall region is better off when some plots are intensively farmed and others are left alone.

In other words, sparing appears to be the least worst option. While some generalists thrive under land sharing, less mobile species with higher habitat constraints need special protection. Habitat reserves provide that, and land sparing schemes can support larger reserves. The only way land sharing excels at protecting biodiversity is when farm yields are impossibly low.

Land sharing, then, is the futon of biodiversity conservation. Just as a futon is both a middling bed and mediocre couch, land sharing is merely passable at producing food and so-so at protecting biodiversity. Neither futons nor land sharing systems excel at their dual tasks. As The Dude in The Big Lebowski would say, “This is a bummer, man.”

One drawback of land sparing is that it requires an immense amount of self-control on the part of individuals and society as a whole. Time and again we’ve challenged the inviolability of protected areas when we are—or think we are—short on resources. Conservation is hard, and plowing more land will always be the easier option. To prevent ourselves from doing that, we need to raise yields, which takes resources, training, and discipline. None of this will be easy.

Furthermore, raising yields sustainably, which the authors endorse, is going to be difficult. There are certainly some easy places to start—yields in much of Africa are dishearteningly low. But the world has embraced fossil fuel-driven, industrial agriculture for a reason—it’s the easiest way to squeeze more food from the land. If non-fossil fuel farming were the easiest option, we would have done that by now. Land sharing, on the other hand, trades low yields for closeness to nature. Locally this may be more sustainable, but is there enough land to feed 10 billion people that way? Probably not.

The choice between land sparing and land sharing is just one of many we will face as the planet’s resources stretch thin. While I’m quietly rooting for integrated, ecologically friendly approaches, there seems to be growing evidence that intensively exploiting a limited footprint may be the better option. If that’s true, the Romantic in me hopes we don’t lose our connection with nature in the process.

Ben Phalan, Malvika Onial, Andrew Balmford, & Rhys E. Green (2011). Reconciling Food Production and Biodiversity Conservation: Land Sharing and Land Sparing Compared Science, 333 (6047), 1289-1291 : 10.1126/science.1208742

Photo by Sam Beebe / Ecotrust.

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Front yards, minus the grass

Berkeley front yard

If you were on a quest to rid the world of excess turf grass, the front lawn would be a good place to start. No one does anything with their grassy front lawn except mow it. Back yards are far more amenable to relaxation and play—they’re sheltered from the noise of the street, protected by a large, immobile structure, the house. Front lawns dominated by grass are, for the most part, wasted space. This also makes them the perfect place to start developing ecologically sound landscapes in cities. But a quick trip through nearly any city, small or large, in the United States and Canada reveals the size of the fight ahead. In the front yard, lawns still rule.

It doesn’t have to be that way. Though most tend to toe the line when it comes to front yard lawns, people are surprisingly open to alternative landscaping, with one proviso—that it’s not a messy mass of weeds. Joan Nassauer showed this in her pioneering work in the early 1990s. In it, she presented seven types of simulated front yards to over 200 people from the Minneapolis-St. Paul suburbs and asked their opinions. About a third of those people had some knowledge of native plants while the others did not. Treatments ranged from conventional turf grass to messy weeds to native prairie and more. While the less knowledgeable people tended to prefer conventional lawns, they were amenable to yards with 50 percent native prairie grasses. The key to buy-in amongst non-floraphiles was a yard’s overall orderliness. Native grasses were deemed attractive provided that they were bounded by neatly trimmed turf grass.

This post was chosen as an Editor's Selection for ResearchBlogging.orgClearly, people are not as wedded to turf grass front lawns as we might suspect. But translating that open-mindedness into action is another task entirely. One Canadian study suggests that people are hesitant to break free of the lawn for a number of reasons. Peer pressures is high on the list. If your neighbor has a mowed lawn, you’re more likely to have the same. But beyond social compulsion, physical structure of the neighborhood plays a role. Older neighborhoods with small front yards and tall trees tend to have more “alternative” front yards, because smaller yards lend themselves to more creative landscaping and homeowners may not want to own a lawnmower to tend a tiny strip of grass. Finally, tall trees in older neighborhoods make growing grass notoriously difficult. There were a few problems, however. Alternative front yards were not common, and where they were, grass was most often replaced with non-native ornamentals.

Don’t take those results as gospel, though. You may have noticed that I used a lot of qualifiers in the previous paragraph. That’s because the study it summarizes is rife with shortcomings. Many of those are probably to be due to the date of publication, 1998. While sophisticated geographic information systems (GIS) and statistical packages were available then, their use wasn’t widespread. The study’s authors had the right ideas, and if the study were redone today with updated methods, the results would be far more convincing.

Here’s why. The researchers mapped front yards and classified them by type of planting—20 percent or less turf grass, 40 percent or less turf grass, and everything else—but then failed to apply any spatial statistics to quantify the city-wide distribution of alternative yards. They also estimated road widths and lawn sizes, but only in relative terms. Such data would be relatively easy to come by these days, either with GIS layers or the use of laser range finders. Nor did the authors associate their data with census tracts or tax records, which would have added meaningful socioeconomic dimensions to their analysis. In short, the paper feels like an old ecology paper—lots of qualitative observations with little hard data to support their conclusions.

That’s not to say the authors don’t propose some insightful reasons why alternative lawns appeared where they did: Tall trees give a sense of enclosed space, which may encourage people to make an “outdoor room” of their front yard. Small parkways between the sidewalk and road are easier to landscape than large ones, thus fostering grassless experimentation. And tiny yards make homeowners ask, “Why bother mowing?”

It may seem like I’m at war with the lawn and turf grass in general. I’m not—in fact, I’m a bit of a fan. Rather, I’m arguing against useless lawns. I firmly believe that lawns play an important aesthetic and recreational role in cities. It’s just that front yards don’t play that role very well. They don’t support recreation in the same way back yards do—for example, it’s easier to play catch when you don’t have to worry about a ball rolling into the street. And regarding aesthetics, it’s clear that lawns do not have to be entirely turf grass to be socially acceptable. The key is care, as Nassauer would say. People welcome nature in the city so long as its curated. Think of turf grass front yards as blank canvases—I use that cliché because I mean it somewhat literally. So long as front yards are matted and framed by kempt grass, we are free to plant whatever we like. I say it’s time to start painting with something other than a turf grass brush.


Henderson, S. (1998). Residential lawn alternatives: a study of their distribution, form and structure Landscape and Urban Planning, 42 (2-4), 135-145 DOI: 10.1016/S0169-2046(98)00084-X

Nassauer, Joan Iverson (1993). Ecological function and the perception of suburban residential landscapes Managing Urban and High Use Recreation Settings, General Technical Report, USDA Forest Service North Central Forest Exp. Sta., St. Paul, MN., 55-60

Photo by hortulus.

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In race against fire, only the fleetest trees survive

Acacia tortolis trees on the African savanna

Density matters. That’s the premise of this blog, after all. The number of people per square mile influences the character of a place—a topic I’ve covered repeatedly—but human population density isn’t everything. Take savannas. They are ecosystems defined by density.

Savannas are grasslands dotted with trees—not too many and not too few. They can have no less than 20 percent tree cover and no more than 80 percent. They exist thanks to fire, a devastatingly destructive natural process that keeps the trees in check. If fires occur too often, they will strip a savanna of its trees and revert it to prairie. If they become to infrequent, trees will takeover and the savanna will become a forest. Yet for all its power in shaping ecosystems, fire matters inasmuch as it can keep trees from breaking through to the canopy. Growth is a tree’s countermeasure. If a sapling can stretch skywards with enough haste, its tender apical buds can escape a fire’s most intense heat and survive. Savannas are shaped by more than just frequency of fire, then. They are held in balance between destruction and development.

That balance is confirmed by a study of three Acacia species—A. karroo, A. gerrardii, and A. tortolis—in South African savannas. The paper’s authors wanted to see what it takes for a tree to reach the canopy before fire returned. In South African savannas, that’s quite a lot. Fires typically burn every 2.9 years in drier areas and every 3.8 years in wetter areas. Occasionally, the interval slips to 10 years. Between 2000 and 2007 when the scientists were measuring the trees, three fires swept through—one each in 2000, 2002, and 2004.

Most trees couldn’t grow fast enough. On average, A. tortolis and A. gerrardii saplings grew about 11 to 14 cm per year, respectively, A. karroo saplings at 25 cm per year. None of these are quick enough for the trees to make it to the canopy height of 3 meters (about 10 feet) in 10 years, let alone a more typical 3 to 4 year interval.

The saplings most likely to make it to the canopy, the ecologists found, were the swiftest growers. In the savanna, “Only the exceptional become trees,” the authors wrote. They speculate that savanna canopy trees are not only bequeathed with superior genes, they also have the good fortune of growing in rich, wet soil without suffering ravenous herbivores or stiff competition from grass. But even with all these advantages, the fleetest 5 percent still need longer than 3 to 4 years to graduate to the canopy. Longer fire-free periods appear to be necessary to maintain a savanna.

Density in the savanna is the result of a complex set of processes that settle into a delicate balance. There’s so much going on it’s like a symphony of ecological interactions: Staccato fires interrupted by brief yet unpredictable intermissions, an orchestra of trees performing a slow march, and a handful of virtuoso trees playing at a furious pace.

Savannas occupy a sweet spot of tree densities, one that is both visually appealing and ecologically important. One of the largest savannas, the Serengeti, is home to some of the world’s most charismatic fauna. Others probably fostered the rise of our own species. Even more prosaic ones host thousands of wonderful and endangered species. But savannas are imperiled, with fire suppression turning them into forests and climate change messing the life cycles of their constituent species. Anything that upsets one part of a savanna or another threatens to undo the whole system. That’s precisely why they are among the world’s most endangered ecosystems, and why they need to be protected.


Wakeling, J., Staver, A., & Bond, W. (2011). Simply the best: the transition of savanna saplings to trees Oikos DOI: 10.1111/j.1600-0706.2011.19957.x

Photo by Kalense Kid.

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The curious relationship between place names and population density

Political map with toponyms

Giving a name to a place is an important act. It says a place has meaning, that it should be remembered. For thousands of years, the way we kept track of place names—or toponyms—was by using our memory. Today, we’re not nearly so limited, and the number of toponyms seems to have exploded. Yet oddly enough, the number of places we name in a given area follows a trend uncannily similar to one seen in hunter-gatherer societies.

Eugene Hunn, now a professor emeritus of anthropology at the University of Washington, stumbled upon what appears to be a fundamental relationship between toponyms and population density when he published a paper on the subject in 1994. His discovery stemmed from a literature survey of twelve hunter-gatherer societies from around the globe. Hunn tabulated each society’s toponym repertoire and the size of their home territory to calculate the number of toponyms per square mile, or toponymic density. From this data, he distilled two trends.

First, the average number of toponyms converged on what he called the “magic number 500”. Hunn found that trend in a few other papers on topics like folk taxonomies of plants and animals, and he posited that the number was an inherent limitation of the human mind—that when relying on memory alone, individuals tend to retain names to 500 items per category. A hunter-gatherer, for example, may be able to name 500 different types of plants. Unfortunately, Hunn’s “magic number 500” wasn’t all that magical given the variability about it—individuals in the hunter-gatherer groups he studied actually recalled between 200 to 1000 toponyms. The concept doesn’t appear to have caught on in the academic world.

Hunn’s second finding, though, is more compelling. When he arranged the toponymic and population densities of the twelve hunter-gatherer groups on a graph, a clear relationship stood out. Where people lived closer together, the number of place names per square mile skyrocketed. Where they lived farther apart, they named fewer places per square mile. The figure, which I’ve reproduced below, appears to have a linear relationship. That’s an artifact of the logarithmic scale of the axes, which compresses the data as you move away from the origin. The scale is hiding a subtle curve, one that bends down as though the x-axis has roped the line and is pulling it closer.

Toponymic and Population Density of Twelve Hunter Gatherer Groups

The general trend in Hunn’s figure—that we name more places when living at higher densities—makes such good sense that I knew there had to be a modern corollary. Despite all our sophisticated maps and petabytes of computer storage, I suspected that we still hew to the same basic pattern as our hunter-gatherer forebears. So I dove into a simple yet relatively modern set of toponyms—the U.S. Postal Service’s ZIP code system.

First proposed in the 1940s, ZIP codes were meant to speed the processing of mail at sorting facilities. Most major cities at the time were already divided into postal zones, like “Milwaukee 4”, but small towns and rural areas had no such system. Mail volume swelled after World War II, so the postal service introduced the Zone Improvement Plan in 1963. From what I can tell, there don’t appear to be any hard and fast rules about the size of ZIP codes. Exactly how they are delineated seems to be a postal service secret and one that likely depends on their logistical needs. They can even overlap. But none of that really matters, because ZIP codes give names to places. They’re toponyms. I suspected that the more densely populated states had a higher density of ZIP codes, just like in hunter-gatherer societies. And sure enough, they do.

ZIP code and population density by state

The wrinkle lies in the trend line’s curve, which is masked by logarithmic axes the same way the curve in Hunn’s figure is hidden. The best way to read both graphs is backwards, from right to left, from high population density to low population density, paying special attention to the scale of the axes. Before we start, we should assume one thing, that people name places at the same rate per square mile regardless of population density. In other words, people will name seven things per square mile regardless of whether they live at ten or 100 people per square mile. Returning to the graphs, if we start at high population densities on the right and move left to lower population densities, the curve drops below our straight line assumption. Not only do people name fewer things at lower population densities, they name fewer things per square mile than our fixed rate assumption would have predicted. In other words, a hypothetical group living at ten people per square mile will name only four things per square mile, compared with the seven named if the population density were 100 people per square mile.

That’s key. There are plenty of gullies and hillocks of grass in the Great Plains, for example, but few people. As such, we name fewer things per square mile. It makes navigation easier—fewer waypoints to remember when traveling—and keeps us focused on the resources that matter. After all, population density is often driven by resource availability, whether that be food, water, shelter, or some other necessity. It’s as though our minds can’t cope with vastness, and so we name fewer things to compress the interstitial space.

The intriguing part is that ZIP codes and Hunn’s hunter-gatherer toponyms are described by one particular mathematical relationship (a power law, for the interested math-types). Not only that, they’re following the trend in a strikingly similar way.¹ As humans, we seem to have settled on a comfortable way of describing the world regardless of whether we remember it with neurons or silicon.

  1. Toponymic density = 0.3675(population density)0.8388

    ZIP code density = 0.0005(population density)0.6944


Hunn, E. (1994). Place-Names, Population Density, and the Magic Number 500 Current Anthropology, 35 (1) DOI: 10.1086/204245

Photo by Tim De Chant.

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Thinking about how we think about landscapes

Thomas Cole - View from Mount Holyoke, Northampton, Massachusetts, after a Thunderstorm (The Oxbow)

Take a look at the painting above. It’s one of Thomas Cole’s most famous works, commonly known as The Oxbow.¹ It’s got a little something for everyone. A twisted old tree. A menacing thunderstorm. Soaring cumulonimbus clouds. A spot of sunlight. A meandering river. Well manicured farm fields. I could go on and on.

Part of the genius behind Cole’s Oxbow is that it appeals to various cognitive processes that draw us into a landscape. There have been a few frameworks proposed to study how we perceive landscapes, one of which was devised by Rachel and Stephen Kaplan, a husband and wife team in Michigan. The Kaplans’ theory is based on experiments with numerous collaborators where they surveyed the reactions of participants to various landscapes.

After poring over the data, the Kaplans noticed two cognitive processes—understanding and exploration—stood out. Within those processes, they further classified the way we react to different landscapes. Coherence and complexity are different ways we understand a scene, how we make sense of it based information that is physically present. Legibility and mystery are two ways we explore a landscape, how we extrapolate information where detail is lacking. Cole’s painting elicits in us a reaction to each of these, but one more so than the others. And that is precisely why it lures us in.

The Kaplans’ theoretical framework for landscape perception is a four-square of variables, with coherence occupying the upper left corner. Cole checks this first box with ease. As with all great art, The Oxbow displays a subtle orderliness that, while not necessarily obvious, balances the painting—the turbulent air and tortured trees give way to the glassy, defined river and neatly delineated farm fields—while imbuing it with suspense—our eyes sweep downwards from the dark clouds in upper left, following the trunk of the tree and canopies behind it down to the banks of the river, which disappears out the lower right.

From there our eyes are free to roam the details, picking out the umbrella jutting out from a promontory. Or following the slope back to find Cole himself tucked next to a rock, painting that very scene. Or the clearcuts on the hillside in the background. These details enliven the painting with complexity, which happens to be the Kaplans’ second variable, nestled in the upper right of their square. Our brain delights in such complexity, which is complexity with order. The bright river curling through the center of the painting, anchors the scene, giving order to the surrounding commotion. If we are ever overwhelmed with detail, we can always find our way back to the great silver arc. The availability of such landmarks also happens to be another of the Kaplans’ pillars, the somewhat oddly named legibility. Legibility is our ability to navigate a landscape within our brain. We rarely get lost in “legible” landscapes, but can be hopelessly disoriented in busy, messy ones.

That leaves us with one square still undefined. It is what the Kaplans consider to be the most important part of landscape perception, and the reason why I think so many people find The Oxbow so captivating. Mystery. The Kaplans define it as the “promise of new but related information”, and Cole’s painting has it in spades. The gusty thunderstorm provides motion to the scene, promising to upend the tranquility of the valley, or perhaps topple another tree. The dim, hazy horizon hints doesn’t reveal the remainder of the scene, instead leaving the viewer to discover it in his or her imagination. The river, too, hints that more lies beyond the frame.²

The Oxbow is a case of art imitating life more than a century before life caught up with a theoretical cognitive framework for studying landscape perception. Thomas Cole enshrined in oil and canvas a perfect landscape to delight our brains. In a way, it was an easy task to accomplish—after all, it’s an idealized scene. Replicating such complexity, motion, comfort, and mystery in real landscapes is much more difficult. Yet as we continue to modify the natural world apace, that is exactly what we will have to do if we want more than willy-nilly weeds. Just the other day, the National Park Service announced that it would be removing some Ponderosa pines from the floor of Yosemite Valley to restore the grand vistas of El Capitan. Such management also has an ecological benefit, restoring prairies that disappeared when fire was eliminated a century ago. But it is also a harbinger of what seems to be inevitable—the complete human management of the world’s ecosystems.

As we turn the world into our canvas, important choices will have to be made. Which ecosystems do we value at the expense of others? Who decides which ones have value? What tools will we use, and what is our vision? From my brief scan of the mighty stack of research on landscape perception, it’s clear that not everyone will have the same opinions. But there do seem to be hints of universality here and there. It will be a long time before we discover which landscapes, if any, bind us together. But in the meantime, I’ll be sifting through the papers, sharing my thoughts along the way. Stay tuned.

  1. The actual title is far longer, more Romantic with a capital R, and less catchy: View from Mount Holyoke, Northampton, Massachusetts, after a Thunderstorm.
  2. It seems to be flowing to the lower right corner, though I have no way of knowing this for certain except that it just feels right. I suspect Cole knew this.


Kaplan, R., Kaplan, S., & Brown, T. (1989). Environmental Preference: A Comparison of Four Domains of Predictors Environment and Behavior, 21 (5), 509-530 DOI: 10.1177/0013916589215001

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An ecology of gardens and yards

City wildflowers

Tucked amidst acres of asphalt jungle are cities’ unsung environmental heroes. Yards, lawns, gardens—call them whatever you please—these bits of unpaved earth play a real role in supporting thriving urban ecosystems. And they could play the part even more eloquently if we thought of them as parts of a larger whole.

Anyone who has spent more than five minutes in a city knows they are not always welcoming to people, let alone plants and animals. It’s common to see thin, scrappy weeds straining against their concrete binders, or birds clinging to wiry utility lines in lieu of more customary branches and brambles. But behind houses, or even hidden out front in plain sight, are postage stamps of possibility. With all the clipping, prodding, and spraying these diced green patches receive, it’s easy to forget that they are part of a real ecosystem.

Cities have long been overlooked by ecologists, mostly because the logistics involved in studying them can be convoluted. Getting permission from dozens, even hundreds of landowners is one of the biggest headaches, so urban ecologists typically resort to the next best thing—parks, forest preserves, greenways, and so on. Parks can be fantastic reservoirs of habitat, but their area pales in comparison to the amount of land scattered throughout the city as yards and gardens. Real urban conservation plans needs to account for everyone’s little patch of nature.

Here’s where landscape ecology can help. Landscape ecology teaches us to look beyond—or within—the various bits and pieces, components and parts that make up an ecosystem. Scale is king in landscape ecology, be it spatial or temporal. In the context of a city, this means that each individual yard and garden—which on its own can seem hopelessly small, only able to support a salamander, some insects, and a few birds at best—is just one piece of a larger patchwork, one connected by birds that fly across town, salamanders that waddle beneath fences, bees that hum between flower beds, and seeds that disperse on the wind. Protecting them all is only possible when conservation plans cover the gamut of spatial and temporal scales.

Unfortunately, much of this potential has yet to be tapped. By and large, cities remain natural wastelands. Habitat fragmentation keeps down the abundance and diversity of species. Inspired landscaping can counter the diversity problem, but it usually does so with exotic species that are poor ecological substitutes for natives. Pets—especially cats—take a toll on native animal populations, while air, light, and sound pollution add further disruptions to an already taxed ecosystem.

Still, most cities have enough material for a solid conservation foundation. Many people are earnestly invested in their yards, carefully curating selections of grasses, trees, and shrubs, attracting musical entertainment through bird feeders, and in doing so supporting a diversity of mammals, amphibians, reptiles, and invertebrates. This has all been accomplished without significant coordination. Programs like the Audubon Society’s “Audubon at Home” or the National Wildlife Federation’s backyard certification scheme have nibbled at the edges, but lots more could be done.

A recent review of the landscape ecology of gardens suggests that to encourage habitat friendly yards and gardens a bottom up approach would be best. Top down programs can help cities meet conservation targets, but they do little to change people’s attitudes. Encouraging a “conservation ethic of the city” would probably be more successful, but also more difficult to engender. Lawn culture is heavily embedded in many Western nations, especially the U.S. and Canada. Lawns will always have their place; besides recreation, they are surprisingly productive ecosystems. Yet most are far larger than they need to be. Substituting appropriate plantings for classic Kentucky bluegrass would save people time and effort, reduce emissions from mowing, and boost habitat diversity and complexity.

Lawns are just one part of the equation. Landscape ecologists can step in to identify the driving forces behind landowner decisions. Where the conservation ethic exists, ecologists can encourage neighbors to coordinate their landscaping, clumping their native plantings so that four quarters can add up to one whole, for instance. Depending on the area’s ecology, landscape ecologists can further define optimal sizes for these native plots—for example, will it take twenty percent of four yards or six to meet the needs of a native bird? Or in other cases, water features like ponds may be more important than contiguity. Each city, even neighborhood, will have its own gestalt, and landscape ecologists can help discover it.


Falk, J. (1976). Energetics of a Suburban Lawn Ecosystem Ecology, 57 (1) DOI: 10.2307/1936405

Goddard, M., Dougill, A., & Benton, T. (2010). Scaling up from gardens: biodiversity conservation in urban environments Trends in Ecology & Evolution, 25 (2), 90-98 DOI: 10.1016/j.tree.2009.07.016

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Photo by Per Ola Wiberg.