Streets lined with gold? Not exactly, but a new
report from the U.S. Forest Service's Pacific Southwest Research
Station estimates trees lining Californian streets and boulevards
provide benefits to municipalities and residents worth $1 billion.
"Structure, Function and Value of Street Trees in California, USA,"
published in this month's issue of "Urban Forestry and Urban
Greening," is the most up-to-date and comprehensive inventory of
"street trees" within California. Using municipal inventories analyzed
in i-Tree, a computerized tree inventory and management suite,
researchers were able to create a composite picture of not only the
number of California's street trees, but also their species, size,
location and associated benefits.
With an estimated 9.1 million trees lining California's streets
and boulevards, it averages to about one street tree for every four
residents. But according to the recently published study, room remains
for another 16 million street trees to be planted, if resources
allowed.
"Sometimes it’s easy to think of trees along city streets as
mere aesthetics, or worse, a nuisance with falling leaves and limbs or
uprooting sidewalks," said research forester and lead author Greg
McPherson. "But what our study shows is that these trees have a real
monetary benefit to the municipalities and residents who care for
them."
From carbon storage ($10.32 million) and removal of air
pollutants ($18.15 million) to interception of rainfall ($41.5 million)
and energy savings from both heating and cooling ($101.15 million),
California's street trees are paying big dividends. They even bolster
property values and home sale prices to the tune of $838.94 million.
"We've calculated for every $1 spent on planting or maintaining a
street tree, that tree returns, on average, $5.82 in benefits,"
McPherson said. "These trees are benefiting their communities 24 hours a
day, 365 days a year."
The report also highlights trends and tree demographics
McPherson and his colleagues say they hope will guide urban foresters in
future decisions regarding what trees to plant and where.
For example, while the number of street trees have increased
from 5.9 million in 1988, tree density has actually fallen from 105 to
75 trees per mile, nearly a 30 percent drop. And while statewide species
diversification appears respectable with only one species claiming
more than 10 percent relative abundance (London planetree at 10.5
percent), individually, 39 of the 49 studied communities were
over-reliant on a single species, potentially making their urban forest
susceptible to a species-specific disturbance or pathogen.
"Municipal foresters can use data from this study to see how
their trees compare to other cities in their climate zone or in the
state," McPherson said. "It might help allocate resources, whether it
be to increase planting to address low density or species
diversification, increase pruning to manage predominately younger trees
for structure and form, control pests and disease or intensively
manage older trees so as to not lose them prematurely."
Co-authors on the study include Natalie van Doorn, research
urban ecologist with the Pacific Southwest Research Station, and John de
Goede, research assistant with the University of California Davis'
Information Center for the Environment. CAL FIRE also contributed tree
inventory data for the study.
United States Forest Service Pacific Southwest Research Station http://www.fs.fed.us/psw
Press release dated June 14, 2016
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