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Urban nature: how to promote biodiversity in cities around the world

Urban nature: how to promote biodiversity in cities around the world

By Richard Conniff

A few years ago in the independent city of Baltimore, Maryland, environmental staff considered a proposal to plant trees from a local group of citizens. They asked for five trees each of 13 different species, like an arboretum, on the grounds of a primary school in a neighborhood with a high population density.

It seemed like a commendable plan, both for the effort of the volunteers and the anticipated benefits to the environment and beautification of the site. But someone noted that there were hardly any oak on the list, even though the 22 species of oak native to the area are known for their benefits to flora and fauna. Local foresters, let alone wildlife, could not recognize almost any of the species that had been proposed in their place. And to make clear the inconsistency of this logic, the school and the neighborhood were named after oaks. Someone asked, "Why are we doing this?"

This type of epiphany is happening quite frequently lately in metropolitan areas around the world, as people have to cope with the spectacular growth of urbanized areas and the corresponding loss of wild flora and fauna. The part of the planet classified as urban is on track to triple from 2000 to 2030 — that is, we are almost halfway there. Meanwhile, 17% of the roughly 800 North American bird species are declining, and all of the 20 species on the Audubon Society's list of "Common Birds in Decline" have lost at least half their populations since. 1970.

These devastating figures, which are repeated around the world, have alarmingly demonstrated that it is not enough to plant a million trees in cities, sing about the excellence of home gardens or build green roofs and elegant streets. The trees, shrubs, and flowers in that seemingly green infrastructure should also benefit birds, butterflies, and other animals. They must provide them with a habitat to reproduce, shelter and food. Wherever possible, habitat should be arranged in corridors where wildlife can move safely.

While it may be too early to be considered an urban movement for wildlife, initiatives focused on urban biodiversity seem to be catching on. The U.S. Forest Service, which once made fun of the idea that something urban could be wild, now supports an ever-expanding urban forestry program. Programs in favor of urban ecology and urban flora and fauna are also proliferating on university campuses. There is the blog “Nature of Cities”, which was launched in 2012. Researchers at the University of Virginia (University of Virginia) have recently announced the emergence of a network of biophilic cities dedicated to integrating nature into urban life, which has Singapore, Oslo and Phoenix among its founding partners. Research has shown that oak trees are beneficial for everyone from caterpillars to songbirds.

And in the independent city of Baltimore, officials now state that canopy trees, rather than specimen or ornamental trees, must account for 80% of any planting on city land, and that half of them must be oak trees. In an area where local nurseries had hardly ever stocked oak trees before, people sometimes resist, until the city's natural resources officer, Don Outen, explains his logic: Research has shown that oak trees They are beneficial to everyone from caterpillars to songbirds. Even fish are favored, because aquatic invertebrates feed on oak leaves from the bottom of streams. At that point, Outen says, people's reaction is usually "Why haven't we done it before?"

One reason is that researchers have hardly thought about what fauna and flora still exist in the city, or how to encourage more. The importance of oaks in the North American states of the Mid-Atlantic, for example, shocked most people in 2009, when Douglas Tallamy, an entomologist at the University of Delaware (University of Delaware), published a ranking of trees and shrubs in a function of how many species of caterpillars they housed. (The Royal Horticultural Society has published a similar list for the UK.) Unlike oak, which is home to 537 species, Tallamy says, the Gingko, a typical street tree in many cities, is home to just three. "But there is the myth that a tree has to come from China to survive in cities," he adds. Tallamy likes to point out that a single pair of Carolina chickadees has to bring 6,000 to 9,000 caterpillars to the nest to raise a clutch of half a dozen chicks. Black-headed 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. "Not all plants are created to be the same," he says. "The autochthonous ones are surely more beneficial than those that are not, but even among the autochthonous there are differences." For example, although tulip trees are undoubtedly majestic, at 50 meters high they are stingy with wild flora and fauna, since they only house 21 species of caterpillars. Cities concentrate around 20% of avian biodiversity, according to a researcher.

At the National Center for Ecological Analysis and Synthesis (NCEAS), based at the University of California, Santa Barbara, researchers have begun to complete a much more detailed photograph of what wild flora and fauna mean. Since the data from the study of wild flora and fauna often end up geographically dispersed and recorded in different formats, they are creating a unified database, with lists of species, abundance, and, in some cases, types of flora habitats. and urban fauna in 156 cities around the world so far.

Early evidence may be more favorable than you might expect, says Madhusudan Kattiel, an ecologist at Fresno State University. Although pigeons, starlings, sparrows, and barn swallows tend to increase in cities around the world, these four cosmopolitan species do not necessarily indicate that wild flora and fauna have become fully homogenized. Cities also concentrate around 20% of avian biodiversity, according to Katti, but warns that this data could be distorted upward because younger cities tend to have more native birds, so it could be a transitory effect. However, understanding what is happening before species begin to disappear offers the opportunity to carry out interventions and carry out designs in cities so that this does not happen.

A new study published in the journal Landscape and Urban Planning also raises better ways to understand the mix between urban flora and fauna and habitat. The study uses birds as bioindicators for other types of fauna and flora because they are easier to count than mammals, which are more timid and often nocturnal, and because in general they are more familiar with people. "They are active during the day, brightly colored and sing," says Susannah Lerman, an ornithologist at the University of Massachusetts and lead author of the new study. "So although most people don't know anything about fauna and flora, they do know something about birds."

Scientists have evaluated not only which trees characterize the neighborhoods, but also how good they are as habitats for birds.

The study proposes a marriage between i-Tree and eBird, two current methods of keeping track of the natural environment. Designed by the U.S. Forest Service, i-Tree is software used by organizations around the world to record tree cover data, from a single tree to entire forests. Its eBird equivalent, from the Cornell Lab of Ornithology, is a checklist-based system that allows thousands of ornithologists around the world to record their observations in a central database. The combination of the two allows researchers to not only assess which trees characterize a neighborhood, but also how good they are as habitat for birds, and which birds use them.

To demonstrate the usefulness of this methodology, the study co-authors looked at 10 municipalities in the northeastern United States where tree data was available. They aimed to demonstrate that technology can work in a wide variety of communities. So they included townships from Moorestown, NJ, a Philadelphia bedroom community with a population of about 20,000, to New York City, with 8.3 million people. They aspired to provide a quick tool for city planners to assess how a development proposal would affect local fauna and flora, or which neighborhood could benefit the most from habitat improvements.

Hosting wildlife in cities doesn't necessarily require a large investment, according to Lerman. You can bring in more birds, he says, just by dividing vast stretches of lawns with the right kind of shrubs to create structure and variety. Mowing these lawns less often — every two to three weeks instead of every week — increases the population of native bees and other pollinators. And with regard to bird feeders, these do not necessarily increase the bird population as a whole, but they do present a significant danger: they can become "ecological traps", luring birds to death in a kind of buffet for cats. Just keeping cats indoors, Lerman says, could prevent the loss of billions of birds across the United States each year.

In the UK, community gardens make a big difference to pollinating insects. In the UK, adds Mark Goddard of the University of Leeds, plots, or community gardens, in urban areas make a big difference to pollinating insects, probably because they tend to choose fruit trees and shrubs And because weed-covered corners are often a bit more tolerant of insects than private gardens. Concern over the number of pollinating species has also led to the recent proliferation of 60 wildflower meadows in UK cities, inspired by the extensive meadows planted around the London 2012 Olympics area.

The new study by Lerman and his co-authors may have inadvertently hit an unlikely source of hope for urban flora and fauna: civic pride and a competitive spirit. Their study looked at the relative tolerance to wild flora and fauna in 10 sample cities and reduced the differences to a series of figures that indicated how well each city was home to nine representative species. While the study expressly avoided making a general ranking of cities, it would be very easy for local supporters to look at the numbers and make odious comparisons. For example, among large cities, Philadelphia ranked first in biodiversity, followed by Washington, DC, Boston lagged far behind, but ahead of New York, and New York outpaced its Hudson River neighbor, New Jersey.

There is no formal “green city” competition in this country, at least not yet. But the 'Britain in Bloom' contest, sponsored by the Royal Horticultural Society, is increasingly focusing on pollinators and other environmental criteria. Along with a certain municipal bombast, it makes UK cities and towns strive to plant year after year.

Maybe it's a fantasy to think something like this could happen in the United States, but imagine: right now, mayors are verbally fighting over meaningless contests between teams with names simply taken from the flora and fauna — Chicago Cubs vs. St. Louis Cardinals, Anaheim Ducks vs. San Jose Sharks, Atlanta Hawks vs. Charlotte Bobcats, etc., in what is a whole zoo of rivalries.

If these mayors had to fight for what really matters - "My city has more flora and fauna than yours", "My city has more green spaces than yours", "My city is a better place to live for birds , the butterflies and the people ”- it would be a competition worth watching.

* Richard Coniff is a National Magazine Award-winning writer whose articles have appeared in Time, Smithsonian, The Atlantic, National Geographic scientific journals, as well as other publications. He has written 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 written about the price of ecosystem services and new advances that could help produce food crops that could thrive despite climate change.

Yale Environment 360


Video: Our solutions are in #nature: Biodiversity, people and culture (July 2021).