Behind a large, luminous lake stretches an emerald lawn fringed by
tall date palms. Nearby, other expanses of green grass and bright
tropical flowers surround stately homes, shaded by eucalyptus
trees. It’s hard to believe this is the Sonoran Desert, an area
that receives only 7 inches of rain a year. Except for the fact
that it’s 103 degrees. In May. This lush landscape is located in
Scottsdale, Ariz., a suburb of Phoenix, but you’d never guess it
was anywhere near that famously arid metropolis.
A
15-minute drive into less affluent South Phoenix, however, makes
the desert much more apparent. Lawns vanish, replaced with expanses
of rock mulch and the occasional cactus. Open spaces here aren’t
filled with lakes and lawns and trees; they’re dotted by creosote
bushes and covered with dirt.
Socioeconomics determines a
lot about our environment: what kind of housing we live in, how far
we have to commute to work, the quality of our children’s schools.
In cities like Phoenix, however, it also determines how hot you’re
going to be: Researchers at the Central Arizona-Phoenix Long Term
Ecological Research project at Arizona State University have found
that wealthier neighborhoods are cooler – literally. Affluent
neighborhoods, such as those in Scottsdale, can be as much as 13
degrees Fahrenheit cooler than poorer neighborhoods. In an area
that routinely reaches hellish triple digits in the summer, every
degree counts.
Research like this is part of the
relatively new field of urban ecology, the study of how
urbanization affects interactions between the living and non-living
components of a city. Thanks to a grant from the National Science
Foundation, Phoenix – the fifth-largest city in the nation and
still growing like mad amid a fragile desert ecosystem – is one of
urban ecology’s busiest study sites. Researchers here are
discovering insights about urban ecology that they hope will apply
to other cities in the West, and to arid urban areas around the
globe. “I think we’re providing a new range of information for
people making decisions,”says Charles Redman, co-director of the
project, “all the way from the individual house owner to
homeowners’ associations to town planners.”
Traditionally, ecologists have focused on areas
far from human influence. But by next year, for the first time in
human history, more people will live in cities than not. Ecologists
increasingly recognize that they have scant understanding of how
urban systems influence larger ecological processes, such as
climate change, or how the seemingly mundane actions of residents –
such as their choice of landscaping – affect the surrounding
environment. For instance, the Phoenix researchers found that
native birds prefer drought-tolerant trees while alien bird species
prefer water-dependent trees. So xeriscaping not only saves water
and money, it also creates habitat for native desert birds within
the city.
The researchers’ project
uses all of metropolitan Phoenix, population 1.5 million, as its
laboratory. “This world we live in is becoming increasingly
influenced, if not dominated, by the activities of people,” says
Redman. “If we are going to work to make this world sustainable
well into the future, then we have to understand how humans at all
different levels of intensity influence their surroundings and each
other.”
Conducting field research in high-density areas
presents some unique problems. Ecologists usually choose random
locations to collect information on whatever they’re studying – but
when your study site is a major city, those random plots can wind
up in some weird places. “It’s led us to some interesting, if not
perverse locations,” Redman says. The program’s researchers have
found themselves in the middle of Sky Harbor Airport and on
freeways, for example, trying to take soil samples through several
inches of asphalt.
Because of the nature of the
ecosystem it’s investigating, the project must include
another area of study that traditionally has had little to do with
ecology: sociology. “We aren’t going to change human interaction
with the environment if we don’t understand how people see the
environment and how they value aspects of it,” Redman says.
Human actions drive ecological processes, which in turn
have strong effects on human health, comfort and resource use.
Those effects often correlate to social factors, such as race or
income. For instance, lush landscaping cools the surrounding
environment – but it’s expensive. “We found this relationship
across the Valley, that every $10,000 increase in median household
income lowers the temperature by a half degree F. People
essentially buy cooler microclimates,” says Sharon Harlan, an
associate professor of sociology at Arizona State University who
conducts research for the project.
Another study examined how socioeconomic factors and environmental
pollution affected childhood asthma in Phoenix. Researchers found
that children in a low-income Latino neighborhood had asthma at
twice the national rate; asthma hospitalizations were concentrated
in areas with high minority populations. Many low-income minority
neighborhoods in Phoenix and other Western cities are located near
pollution sources, an environmental hazard that’s often a legacy of
past racism. “Sociologists have traditionally studied the social
inequalities that arise from an urban society, in education, in
jobs, but we are now starting to look at the environmental
inequalities that arise from that,” Harlan says.
Humans also cause drastic inequalities in animal
populations. The two patterns common to most of the world’s cities,
says Eyal Shochat, a research associate with the project, “are an
increase in population size and at the same time a decrease in
species richness compared with the wildlands.” For instance, even
though birds are more abundant in the city, a handful of species
are responsible for most of the urban bird population. One study
found 27 different bird species living within Phoenix, but 42 in
the surrounding desert. Similar patterns also occur in
ground-dwelling insects, Shochat says. “It’s very extreme. The
proportion of wolf spiders increases from 8 percent in the desert
to 80 percent in the city.”
The creatures that dominate
in the city often are exotic introductions, such as the European
house sparrow. These invasive city slickers are better able to take
advantage of the high food and water availability in urban areas,
and they muscle out the natives. But though the urban birds are
tough in their ‘hoods, many can’t hack it in the rougher wild
desert. Urbanization of the desert has created what researchers
refer to as a “pseudo-tropical bubble,” an island of increased
resources that buffers seasonal scarcity.
House sparrows,
for example, go from the most populous bird in residential yards to
15th in the desert. Some city birds aren’t found in the desert at
all, like the peach-faced lovebird, an African import that escaped
captivity and now has breeding populations in Phoenix.
Urbanization also reduces predation pressure,
Shochat says, even though house cats are often blamed for bird
genocide. “There are many native predators that are excluded from
the city; at the same time, there are many more domestic predators.
I believe the birds we see in the city are the ones who can cope
with cats, and those who couldn’t are extinct by now.” So
city-slicker birds aren’t just good at exploiting the extra
resources we leave around, they’re also good at dodging our
household bird killers. A few superstars, in fact, excel at both,
crowding out other species that might otherwise do well in the
city.
Phoenix may be giving us a glimpse of the
future we’ve set ourselves up for: Many of the climate
changes predicted to happen on a global scale are already occurring
in the city. The conversion of lighter desert to dark
heat-absorbing roads and buildings has raised average daily
temperatures by about 5 degrees F across the entire city, as well
as raising nighttime minimum temperatures and decreasing frost
events. All that traffic necessitated by Phoenix’s sprawling design
has resulted in an atmospheric “bubble” of carbon dioxide over the
metro area that’s twice the global atmospheric mean concentration,
as well as significantly elevated levels of atmospheric nitrogen
deposition.
Urban ecology research in Phoenix can also
give city planners across the arid West ideas for managing the
needs of humans and wildlife. It can help planners learn how to
obtain the cooling effect of landscaping (good) without excessive
water use (bad). And it can help increase bird biodiversity in
urban areas. “Many, many more species could basically live in urban
habitat, but they don’t do so because of competition,” Shochat
says. Although birds may not necessarily be on city planners’
radar, their presence in urban areas is indicative of the larger
quality-of-life issues urban ecology helps to explore.
Ten years ago, when the Phoenix urban ecology project was just
embarking on its long-term mission, someone asked Redman what he
would consider a success for such a venture. His answer: “If there
were still birds singing in our city.”
Petra
Spiess is a freelance writer with a master’s degree in ecology. She
grew up in Scottsdale, Ariz., chasing lizards, snakes and
quail.
This article appeared in the print edition of the magazine with the headline Scientists and the city.
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