During his 1980 presidential campaign,
Ronald Reagan famously blamed trees for emitting 93 percent of the
nation’s nitrogen oxide pollution. Trees were worse for the
environment than automobiles, he said, a statement that fueled
decades of “killer tree” jokes.
Twenty-six years later,
cities in Reagan’s home state of California are trying to
live down his dendrophobic reputation. In October, Los Angeles
kicked off an effort to plant 1 million trees, part of Mayor
Antonio Villaraigosa’s election campaign promise to become
“the biggest, greenest city” in America. Civic leaders in the
Sacramento area are considering an even more ambitious effort:
planting 4 million trees over the next 40 years.
While
tree-planting in cities is nothing new, the scale and intent of the
efforts in L.A., Sacramento and a handful of other Western cities
mark a significant shift in the way urban forests are perceived.
Once seen merely as a way to beautify the concrete jungle, mass
tree-plantings have become major components of efforts to combat
global warming by sucking up carbon dioxide from the air. And where
roots and canopies were once viewed as hindrances to sewer lines,
sidewalks and power lines, trees are now being treated as part of
the civic infrastructure, on par with other public utilities.
“Trees in cities have long been undervalued,” says Greg
McPherson, a research forester at the Center for Urban Forest
Research in Davis, Calif. “Cities have done easy things to be green
and conserve energy. And it’s not working. So almost out of
desperation they are looking at trees as green or bio technology.”
In Denver, Colo., the mayor wants to plant 1 million
trees over the next 20 years. Seattle, Wash., plans to add 695,000
trees over the next 30 years. And Albuquerque, N.M., is adding
10,000 over the next five years.
Benefits of
bark
This trend began in the ’90s, when the Forest
Service came out of the rural woods to study the value that cities
can get from their trees. The agency’s Urban and Community
Forestry Program puts its research into terms politicians can
understand — money. Trees aren’t cheap: They need care
to get established, they use water, and they can crumple sidewalks
and knock out power lines. Cities budget for tree-related expenses
such as picking up leaf litter, but rarely look at what the trees
provide in return, McPherson says. According to the Center, every
dollar spent in Los Angeles on a tree yields $2.80 worth of
benefits.
“A tree in an urban setting is more valuable
than one in a rural forest,” says Hashem Akbari, staff scientist at
the Department of Energy’s Lawrence Berkeley National
Laboratory. “Both can help with carbon sequestration. But an urban
tree can do much more. It helps save energy because it shades
buildings and decreases air temperatures, thus reducing the amount
of air conditioning needed and the amount of fuel that is burned.”
Properly positioned around a house in a city like Los
Angeles, trees can cut air conditioning costs by 30 percent.
Sacramento neighborhoods with high canopy cover are typically 5 to
8 degrees cooler than neighborhoods with low cover, according to
the Sacramento Tree Foundation. And the Department of Energy says
that just three trees planted around a house can save between $100
and $250 annually in cooling and heating costs. “Our utility gives
away 30,000 trees a year,” says Rob Kerth, executive project leader
for the Sacramento Tree Foundation. “They say it is the cheapest
power plant they’ll ever build.”
Trees also help
reduce stormwater runoff by slowing down rainfall and absorbing
water that would otherwise flow quickly over impervious pavement.
Los Angeles officials predict that 1 million trees will save $5
million each year in stormwater runoff costs. “It costs so much
money to build the infrastructure for a city to deal with storm
water. It’s so much cheaper to just use the tree canopy,”
says Deborah Gangloff, executive director of American Forests.
Money talks
All this, however, takes
time — most trees don’t provide full benefits until
they are 25 to 30 years old — and it takes upfront capital,
which many cities lack. “It is damned expensive,” says Ray
Tretheway, executive director of the Sacramento Tree Foundation,
noting that the Sacramento Municipal Utility District pays $2
million a year for its tree program.
Los Angeles plans to
spend $70 million on its tree program. The city has partnered with
five nonprofits that pledged to plant 875,000 trees, with the city
planting the remainder. About half the trees will be planted on
private land. The mayor promised to focus on low-income
communities, which tend to have fewer trees; one neighborhood, for
example, has only a 5 percent canopy cover, compared to the
national average of 27 percent.
The Forest
Service’s Urban and Community Forestry Program is picking up
some of the expenses through grants to cities. But even as more
cities embrace trees, the federal program’s budget is
shrinking, dropping by 25 percent in just the past four years.
McPherson hopes his research inspires more communities to
jump on the bandwagon. In fact, his group is part of a
Sacramento-area study examining how an urban forest affects the
amount of local smog; the results may put to rest any lingering
belief in Reagan’s “killer trees.” Future research will focus
on psychological benefits, including stress reduction and workplace
productivity. “By trying to monetize everything and put it in
dollars and cents for policy makers, one could argue we are really
minimizing trees,” McPherson says. “But money talks.”
The author is an HCN
intern.
This article appeared in the print edition of the magazine with the headline Trees — A different shade of green.
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