How many trees are there on New York City streets?
That question will be answered this summer by some thousand volunteers in
a project called "Trees
Count." Aside from counting every tree, the volunteers will collect basic
data on each tree's location and species; they will also use handheld computers
donated by Hewlett Packard to
measure the diameter of the trunk and the crown.
All this data will be entered into a common database, then run through an economic model to determine not just how much it would cost to replace each tree, but also to assess how much each individual tree is worth.
"No one has really placed a value yet on the urban forest," said Parks
Commissioner Adrian Benepe. "This will help us do that."
In a city that just earned yet
another set of failing
marks for air quality from
the American Lung Association, parks managers are eager to quantify
to the penny how New York City street trees improve the air and
diminish energy consumption.
The first tree census in the city, conducted in 1995, came up with a total just under 500,000
Officials estimate that the number this time around will be about the same. This is true even
in the face of a short-term reduction in the local tree population. Noting
discovery of an Asian longhorn
beetle eggs, Parks Commissioner Benepe promised an
"aggressive" response. "Any trees found to have insects will be chopped
down, chipped, and the chips will be sent to the incinerator," he said.
Such promises reflect the management philosophy that, in an era of
diminishing budget resources, it's better to amputate and be safe than
waste precious time and resources developing a more nuanced approach.
One reason for the tree census, notes Jennifer Greenfeld, director of
the New York Tree Trust, is to give future resource managers a clearer
picture of what corners of the city are doing well and what corners
"[A census] helps us figure out how to balance our resources, how to
adjust our palette in terms of how we respond to different problems ,"
says Greenfeld. "This is the one thing that helps give us a snapshot so
we can plan what to do."
Although the 1995 tree census took note of tree
condition, this year's count will take more notes on the types of
things that lead to the biggest maintenance headaches -- things like
powerline and sidewalk interference and the tree guards which protect
trees over the short term but can restrict growth over the long term.
Losing larger, more established trees to such problems is especially
painful from a management perspective, Greenfeld says, because larger
trees provide exponentially more shade, oxygen and pollution-filtering
power than their sapling replacements.
"A tree is probably the only investment that a city makes that
increases over time," Greenfeld says. "Unlike a sewer line, which gets
less useful the older it gets, you want to keep [a tree] in the ground
as long as possible."
To help prove that point, New York Tree Trust will be relying on an
economic model developed by the Center for Urban Forest Research, a
laboratory at the University of California at Davis that is funded by the U.S. Forest Service. Dubbed STRATUM, the model estimates growth rates by species and
location and then multiplies the resulting size estimates with
biological data and economic estimates on the social cost of airborne
pollution and energy production. The end result, says center director
Greg McPherson, is a bottom line summary of each tree's
ability to reduce carbon, pollution, and energy bills over time.
"It provides the other side of the equation which is that trees are an
investment," says McPherson. "If you increase your investment, you can
provide yourself more of a return over time."
McPherson's lab has analyzed census data from cities such as Berkeley,
Calif., Minneapolis, and Bismarck, N.D. Estimates on the "return on
investment" for each tree planting vary by city. In Berkeley, the return on every dollar spent was
$1.37. In Bismarck, the
return was $3.09 for every dollar spent.
New York has tried to assess its trees before, in a 2001 study that concluded that urban trees statewide had a compensatory value of $84 billion and a
carbon storage value of $500 million. David Nowak, lead author of the 2001 study,
says pricing models are popping up in court cases to
assess the value of damaged trees or stolen timber and could lead to
even more creative uses. Last year, for example, the Office of the New York Attorney General mandated $47,000 worth of tree planting
in a January, 2004, settlement with four school bus companies accused
of excessive idling, one of the first attempts by a government agency
to include trees in the
bargaining process on air pollution.
Nowak expects this trend to continue, noting that trees are a classic example of a benefit enjoyed by society as a whole coming at a cost only to the individual or agency that planted the tree. This is the exact opposite of air pollution, which comes at no cost to the factories or automobiles, etc. that produce it, but produce damage felt by society as a whole. Economists call the first example, the tree, a "positive externality," and the second, the pollution, a "negative externality." Both are "external"
to the ordinary marketplace's ability to set a price. Assessing the
damage or benefits often falls on state agencies.
"A lot of things we can't quantify yet, but some of the things we can,"
The Trees Count project was launched with an Arbor Day tree planting ceremony outside the Little Sister of the Assumption Family Health Service in Spanish Harlem, a neighborhood currently experiencing the
highest childhood asthma rates in the country. According to a 2003
study involving researchers from Columbia University and Harlem
Hospital, a quarter of all children in east Harlem suffer from asthma,
more than four times the national rate. Looking past the current tree
census, both Benepe and Greenfeld point to Trees for Public Health,
managed by the Hunts Point environmental group Greening for Breathing.
Trees for Public Health seeks to reduce local air pollution levels in a corner of
the city plagued by automobile exhaust and has, to date, relied on a
patchwork funding from city, state, and federal agencies. One way to
guarantee a steady stream of funding, Benepe says, would be to confirm
a direct causal link between money spent on trees and money saved at
local asthma treatment centers thanks to declining admissions.
"We've gotten to the point where people understand anecdotally why
urban trees are valuable," says Benepe. "Our next step is to quantify
that value. For that we need the help of the scientific community."
The 2005 Trees Count project starts on June 1, 2005. Volunteers who would like
to help out can register by calling 311 or visiting the city's "Trees Count" web page. The Parks Dept. is asking
volunteers to donate at least 40 hours of their time, plus a three hour
training session. The training sessions begin in the second weekend of
May. Event sponsor Bank of America, meanwhile, is offering $1,000 to
the adult New York City resident who comes closest to guessing the
final street tree tally. The free entry form, which requires physical
address and birthdate, is
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