06 Jan 2014: Analysis

Urban Nature: How to Foster
Biodiversity in World’s Cities

As the world becomes more urbanized, researchers and city managers from Baltimore to Britain are recognizing the importance of providing urban habitat that can support biodiversity. It just may be the start of an urban wildlife movement.

by richard conniff

A few years ago in Baltimore County, Maryland, environmental staffers were reviewing a tree-planting proposal from a local citizens group. It called for five trees each of 13 different species, as if in an arboretum, on the grounds of an elementary school in a densely-populated neighborhood.

It seemed like a worthy plan, both for the volunteer effort and the intended environmental and beautification benefits. Then someone pointed out that there were hardly any oaks on the list, even though the 22 oak species native to the area are known to be wildlife-friendly. Local foresters, much less local wildlife, could barely recognize some of the species that were being proposed instead. As if to drive home the logical inconsistencies,
MTA/Patrick Cashin
A peregrine falcon soars above New York City's Verrazano-Narrows Bridge.
both the school and the neighborhood were named after oak trees.

"Why are we doing this?" someone wondered.

That sort of epiphany has been happening a lot lately in metropolitan areas around the world, as people come to terms with both the dramatic increase in urbanized areas and the corresponding loss of wildlife. The portion of the planet characterized as urban is on track to triple from 2000 to 2030—that is, we are already almost halfway there. Meanwhile, 17 percent of the 800 or so North American bird species are in decline, and all 20 species on the Audubon Society’s list of "common birds in decline" have lost at least half their population since 1970.

Those kinds of stark numbers, repeated around the world, have made it disturbingly evident that it’s not enough for cities to plant a million trees, preach the gospel of backyard gardens, or build green roofs and smart streets. The trees, shrubs, and flowers in that ostensibly green infrastructure also need to benefit birds, butterflies, and other animals. They need to provide habitat for breeding, shelter, and food. Where possible, the habitat needs to be arranged in corridors where wildlife can safely travel.

Though it may be too soon to call it an urban wildlife movement, initiatives focused on urban biodiversity seem to be catching on. The U.S. Forest Service, which once laughed off the idea that anything urban could be wild,
Research has shown that oaks benefit everything from caterpillars to songbirds.
now supports a growing urban forest program. Urban ecology and urban wildlife programs are also proliferating on university campuses. There’s a "Nature of Cities" blog, launched in 2012. University of Virginia researchers recently announced the beginning of a Biophilic Cities Network devoted to integrating the natural world into urban life, with Singapore, Oslo, and Phoenix among the founding partners.

And in Baltimore County, officials now stipulate that canopy trees, rather than specimen, or ornamental, trees, must make up 80 percent of any planting on county land, and half of them need to be oaks. In an area where local nurseries hardly ever stocked oaks before, people sometimes balk, until the county’s natural resource manager, Don Outen, explains the logic of it: Research has shown that oaks benefit everything from caterpillars to songbirds. Even fish prosper, because the aquatic invertebrates they feed on favor oak leaves on stream bottoms. At that point, says Outen, the reaction tends to shift to, "Why haven’t we been doing this before?"

One reason is that researchers have barely begun to think about what wildlife already lives in the city, or how to encourage more of it. The importance of oaks in U.S. Mid-Atlantic states, for instance, came as news to most people in 2009, when Douglas Tallamy, a University of Delaware entomologist, published a ranking of trees and shrubs according to how many caterpillar species they harbor. (The Royal Horticultural Society has published a comparable list for Britain.) In contrast to oaks, which accommodate 537 species, says Tallamy, gingkoes, a standard street tree in many cities, host just three. "But there is this myth that a tree has to come from China to survive in cities," he comments.

Tallamy likes to point out that a single pair of Carolina chickadees needs to bring 6,000-9,000 caterpillars to the nest to rear a clutch of a half-dozen nestlings. Black-capped chickadees probably need more. If you want the birds, he says, you need the caterpillars, and to get the caterpillars you need the right trees. "All plants are not created equal," he says. "Natives are more likely to be beneficial than non-natives, but even among natives, there are differences." For instance, though tulip trees are undoubtedly
Cities capture about 20 percent of the world’s avian biodiversity, according to a researcher.
majestic, at 160 feet in height, they are stingy with wildlife, hosting just 21 caterpillar species.

At the National Center for Ecological Analysis and Synthesis (NCEAS), based at the University of California at San Barbara, researchers have begun to fill in a more detailed picture of what urban wildlife means. Because wildlife survey data often ends up in scattered locations, and recorded in different formats, they are developing a unified database, with species lists, abundance, and, in some cases, habitat types for urban wildlife in 156 global cities so far.

The preliminary evidence may be more encouraging than people tend to think, says Fresno State University ecologist Madhusudan Katti. Although pigeons, starlings, house sparrows, and barn swallows tend to turn up in cities worldwide, these four cosmopolitan species don’t necessarily indicate that urban wildlife has become entirely homogenized. Cities also capture about 20 percent of the world’s avian biodiversity, says Katti. That number may be skewed higher, he cautions, because younger cities tend to have more native birds. So it may be a transient effect. But understanding what’s happening before species start to disappear opens up the opportunity for interventions and urban design to retain them.

A new study in the journal Landscape and Urban Planning also looks at better ways of understanding urban wildlife and habitat in combination. The study uses birds as bio-indicators for other wildlife types because they are easier to count than shy, often nocturnal, mammals, and because they are more broadly familiar to the public. "They’re active during the day, they’re colorful, they sing," says Susannah Lerman, a University of Massachusetts ornithologist and lead author of the new study. "So even if
Scientists have assessed not just which trees characterize a neighborhood, but how good they are as bird habitat.
most people know nothing about wildlife, they know something about birds."

The study proposes a marriage of i-Tree and eBird, two current methods for keeping track of the natural world. Designed by the U.S. Forest Service, i-Tree is software used by organizations around the world to record data on urban tree cover, from single trees to entire forests. Its counterpart, eBird, from Cornell Lab of Ornithology, is a checklist system enabling thousands of birders around the world to log their observations into a central database. The combination of the two enables researchers to assess not just which trees characterize a neighborhood, but how good they are as bird habitat, and which birds are using them.

To demonstrate the usefulness of this methodology, the study’s co-authors looked at 10 municipalities in the U.S. Northeast for which tree data happened to be available. They were aiming to show that the technology can work in the broadest possible range of communities. So they included municipalities from Moorestown, N.J., a Philadelphia bedroom community with a population of about 20,000, on up to New York City with 8.3 million. The ambition was to provide a quick tool for urban planners to assess how a proposed development would affect local wildlife, or which neighborhoods could benefit most from habitat improvements.

Accommodating wildlife in cities doesn’t necessarily require massive investment, says Lerman. You can bring in more birds, she says, just by breaking up endless lawns with the right kinds of shrubs, to create structure and variety. Mowing those lawns a little less often — not weekly but every two or three weeks — will increase the population of native bees and other pollinators. As for bird feeders, they don’t necessarily increase overall bird populations, but they do present one significant hazard: They can become "ecological traps," luring birds to their deaths in a sort of cat smorgasbord. Just keeping cats indoors, says Lerman, could prevent the
In Britain, community gardens make a major difference in pollinating insects.
loss of billions of birds in the United States every year.

In Britain, adds Mark Goddard, of the University of Leeds, allotments, or community gardens, in urban areas make a major difference for pollinating insects, probably because they tend to feature fruit trees and bushes and because the weedy corners tend to be a little more insect-friendly than private gardens. Concern about dwindling pollinator species has also led to the recent proliferation of 60 wildflower meadows in British cities, modeled after the extensive meadows planted around the site of the 2012 London Olympics.

The new study by Lerman and her co-authors may also inadvertently have hit on one unlikely source of hope for urban wildlife: Civic pride and competitiveness. Their study looked at the relative wildlife-friendliness of 10 sample cities and boiled the differences down to a series of numbers indicating how well each city accommodated nine representative species. While the study scrupulously avoids an overall ranking of cities, it would be easy enough for local partisans to look at the numbers and make invidious comparisons. For instance, among the big cities, Philadelphia ranked first


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for biodiversity, followed by Washington, D.C. Boston lagged well behind. But it beat New York, and New York topped its Hudson River neighbor, Jersey City.

No formal "green city" competition exists in this country, at least not yet. But the "Britain in Bloom" contest, sponsored by the Royal Horticultural Society, increasingly focuses on pollinators and other environmental criteria. Along with a certain amount of municipal bombast, it manages to elicit a vast planting effort in British cities and towns year after year.

Maybe it’s a fantasy to think anything like that could happen in the United States. But just imagine: Right now, mayors do verbal jousting over meaningless contests between teams that are merely named for wildlife — Chicago Cubs versus St. Louis Cardinals, Anaheim Ducks versus San Jose Sharks, Atlanta Hawks versus Charlotte Bobcats, and so on, through an entire zoo’s worth of rivalries.

If those mayors had to go toe-to-toe over the real thing —"My city has more wildlife than yours," "My city has more green space than yours," "My city is a better place for bird, butterflies, and people to live"— that would be a competition worth watching.

POSTED ON 06 Jan 2014 IN Biodiversity Climate Energy Policy & Politics Pollution & Health Science & Technology Urbanization North America 


I want to do this. Dan will too.
Posted by Charles Pattison on 06 Jan 2014

I've advocated for large swaths of urban greenbelts for decades. Setting 10 percent of the urban environment aside for greenbelts seems a modest proposal, and the greenbelts should be linked, to allow for easier migration of animals. Just dotting a city here and there with parks with trees is not enough.

However, we also need to realize that every balanced ecosystem has its food chain, including predators. And in urban areas, that predator is the cat. (Mainly the cat. There are also packs of feral dogs and coyotes, but those present a danger to humans and should not be tolerated.)

The attempt to keep all cats indoors seems to me to be extremely misguided. First, because I regard the practice of keeping cats indoors all the time as a form of cruelty to animals. Cats are part domesticated and part wild, and they belong in nature just as surely as most other animals do. They need the freedom to explore, to climb trees and roll in the grass, and, yes, do some hunting. Cats can be good in an urban environment in that they keep down the "pest" populations of rats, mice, and gophers, and most of the birds they catch are common house sparrows, pigeons and doves.

Even if everyone who "owns" a cat (or vice versa) were to keep their animal friend imprisoned inside, away from nature, there would still be legions of feral cats on the prowl. The feral cat "problem" has proven to be intractable by way of trying to round them all up and euthanize them. That is why the Humane Society and many cities are now advocating the TNR — Trap, Neuter, and Release — approach instead. That way, the neutered cats won't contribute to a population explosion of kitties, but they will still be present as part of the urban wildlife ecology.

So there is little ecological benefit from keeping pet cats indoors in any case. And it seems to me to be utterly cruel abuse to take any animal and permanently separate them from nature — never to feel the cool breeze or the warm sun on their fur, never to lay in the soft grass watching the trees sway, never to prowl through the bushes or chase butterflies and grasshoppers.

Animals need to be outside in nature, just as much as humans do. Even more so. It is a profound psychological need, and any animal will suffer if removed from nature permanently.

(Except perhaps rats, who have made themselves very much at home in urban environments. Tame rats make wonderful pets for apartment dwellers — they're very smart, sweet, playful and sociable.)

Some people try to claim that it's better for cats to be kept indoors, that they live longer that way. While I think cats should be allowed indoors when they want to be inside, I don't think they should be trapped there. And I suspect those numbers are skewed by comparing cats trapped indoors with cats who are always kept outdoors. Cats need cat doors. I've had cats who lived nearly twenty years, with free use of a cat door, and who are still going strong.

If anyone offered me the choice of living another ten years, with freedom to explore nature or to be comfy inside, as I choose, versus living another twenty years trapped inside a house and never allowed out in nature again, then I know with certainty I would rather take the ten years of freedom than the twenty years of imprisonment.

Cats play the natural predatory role in the ecology of the urban environment. If they were removed from that role, then either another predator would need to step in, or else the urban ecosystem would become unbalanced. Predators are always necessary, and I fail to see why it is so terrible that cats are filling this role in our cities and suburbs.

Posted by Dee on 06 Jan 2014

This Mayor is delighted to promote the coolest little capital city's biodiversity. We have marine reserves, the world's first predator-proof urban sanctuary (like a mainland island) and thousands of volunteers.

Certainly aiming to be one on the greenest cities in the world — energy-wise as well as in biodiversity. We're enjoying being part of the international network of Biophilic Cities.

See http://wellington.govt.nz/your-council/projects/our-living-city
Posted by Mayor Celia Wade-Brown on 07 Jan 2014

Nice summary reporting, thanks for that.
Posted by Christine Thuring on 09 Jan 2014

Congratulations to Mayor Wade-Brown and may the competition begin. But, Dee, twisting this story into an argument for free-roaming cats is just perverse. Here's the best available U.S. study: "We estimate that free-ranging domestic cats kill 1.3–4.0 billion birds and 6.3–22.3 billion mammals annually." http://www.nature.com/ncomms/journal/v4/n1/full/ncomms2380.html

Posted by Richard Conniff on 09 Jan 2014

In response to Dee's plea for the Trap, Neuter and Release of feral cats, it needs to be recognized that domestic cats are an introduced invasive species. In rural areas they are an additional predator whose main prey are small birds. They are not substituting for a natural predator. Urban and suburban areas have been created by humans and have developed their own, unique ecosystems that include native birds as well as many introduced invasive species.

Even a neutered cat will continue to prey on birds. Trap, Neuter and Release programs apply primarily to feral cat colonies where the cats can be easily captured. These colonies are created by humans who deliberately feed the animals. But there are plenty of cats outside these colonies that can't be treated and continue to breed.

It's worth noting that coyotes, which are not a danger to adult humans, have invaded cities and are the principal predator on cats. Thus rebalancing the urban ecosystem.
Posted by Herb Curl on 09 Jan 2014

Some good coverage in this article, and I am glad my friend Madhu Katti was quoted. But what is missing here is the appreciation that, from Griffith Park in LA to Pelham Bay Park in New York City, existing green space is under attack in urban areas and has been since the era when interstate highways were rammed through most big parks.
Posted by David Burg on 11 Jan 2014

Finally we are seeing the effects of almost 20 years of promoting urban ecological development and education of the public. When I started my company "Down East Birdwatching and Nature Tours" in 1993, there was little discussion at all about biodiversity, especially in cities. What a difference time makes as we enter a new era in American history. If we can put an economic value on our ecology, perhaps we can really turn things around for birds and people.
There are still many issues in our cities which kill millions of birds each year. Glass windows and tall buildings kill millions of birds each year. Planting trees is a good first step, so kudos to everyone making a difference through environmental change.

The next greatly important issue is reconnecting our rivers and streams to the oceans and the revitalization of our sea-run fish!

A strong ecology = a strong economy!
Posted by MIchael J. Good, MS on 16 Jan 2014

This is fascinating, but I flinch when I read the size of some cities, e.g. New York's 8.3 million. I live in Edmonton, Alberta, a city that has signed on to the international ICLEI agreement to protect its biodiversity. Its metropolitan area is just over 1 million, and is expected to reach 3 million by 2050. It has expanded enormously over the last 20 years, with suburbia and with industry on its northern edge to serve growth in the oilsands, and I have witnessed the devastation this has caused with the loss of natural areas. It has no greenbelt (nor, incidentally, any scientific way to measure its biodiversity) and rapid growth is considered both inevitable and desirable. Conserving natural land is still the best way to preserve biodiversity and I believe there should be a way, especially in an electronic age, to keep cities (communities) small and far-flung. Instead of a competition for maintaining urban biodiversity, here in Alberta we have a competition for urban growth and becoming "world-class" (as judged by human parameters, of course).
Posted by Patsy Cotterill on 19 Jan 2014

I agree keeping urban landscapes in diverse native vegetation is important to wildlife but it does come with some tradeoffs. The closer wildlife comes to human habitation, the higher the probability of zoonotic diseases spreading. I am not saying we should not provide wildlife habitat in urban interface areas, but increased prevalence of ticks carrying tick-borne diseases such as Lyme, Babesiosis, Anaplasmosis, Powassan encephalitis, etc., can be an undesirable trade off. Research is indicating some bird species are playing a significant role in spreading ticks as well as becoming reservoir hosts of certain tick-borne diseases. Even the common gray squirrel has been found to be a reservoir host for the Lyme bacterium. Robins who were thought to be a dead-end host have shown Lyme bacteria levels remain high after being bitten by an infected tick for up to two weeks. This means any tick biting the robin after the initial bite will become infected with the bacteria. Yes, our continued urban sprawl has adversely affected wildlife, but nature may get even in the end. Maybe outside cats aren't so bad in urban areas after all?
Posted by Scott on 24 Jan 2014

This article is about planting different species of trees in an urban area to allow wild animals, especially birds, to survive in big cities. The author mentions that the trees are necessary to be the same as the birds can find in their wild environment, so they could become well-adapted to live in the middle of a big city. To me it sounds very interesting because people who live in big cities could have the fortune to share their environment with new neighbors. In this particular case could be wild birds. The birds could find a natural environment inside the cities, which is a great idea.
Posted by Roberto Garcia Roman on 26 Jan 2014

Plenty to do in France. I am setting off a club, or what we call association, to plant shaped fruit trees in town, trimming and grafting.

We are so lucky to have a ministry of social and round economy in this country doing a lot in this field. We have one conservatory in Paris, Ecole d'horticulture du Senat, with 1,000 beautiful fruit trees on 2,000 square meters, and free courses along the year to keep the tradition alive. There is a law now in France banning chemical treatment in public space.

Happy planting.

Posted by Helene Tauzin on 14 Feb 2014


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richard conniffABOUT THE AUTHOR
Richard Conniff is a National Magazine Award-winning writer whose articles have appeared in Time, Smithsonian, The Atlantic, National Geographic, and other publications. He is the author of several books, including The Species Seekers: Heroes, Fools, and the Mad Pursuit of Life on Earth. In previous articles for Yale Environment 360, he has examined how root microbiomes affect forest ecology and how community-managed areas can help preserve biodiversity.



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