Urban Forest
Research
October 2001
Center for Urban Forest Research • Pacific Southwest Research Station • USDA Forest Service
New Research Findings
Climate Zones and County Boundaries
Green Plants or Power Plants?
A case for planting more trees
A new study at the Center for
Urban Forest Research examined
the shading effect California’s
community forests have on the
state’s energy consumption. The
results show that energy savings
would be substantial and fewer
power plants would have to be built
if citizens planted 50 million shade
trees in strategic energy-saving
locations (see map).
If you live in another state, your
savings will depend on the number
of planting sites available and your
climate. Despite these differences
between states, the findings have
implications for all of us as we
struggle to cope with increasing
demand and higher energy prices.
Are trees really the
answer?
The response to the recent
energy crisis in California by most
utilities and the state has been to
focus on immediate solutions to
peak load demand, such as power
plants, and discontinue investments
in shade tree programs, a somewhat
surprising move.
Dr. Greg McPherson and Dr. Jim
Simpson, Center for Urban Forest
Research, conducted the new energy
research. They understand the
dilemma facing utilities and the
state, and agree that more new trees
will not affect the peak load demand
in the near future.
“It will take about 5–15 years for
trees to fully contribute to the energy conservation process. However, if
we don’t continue investing in
energy conserving trees, they will
not be available in 15 years when
the demand for energy will be even
greater,” says Dr. McPherson.
Can shade trees replace
power plants?
“If we look at the solutions to the
energy crisis, power plants are not
the total answer,” says Dr.
McPherson. “Somewhere in between
Energy savings could be substantial if
citizens planted 50 million shade trees in
strategic energy-saving locations.
is a blend of conservation measures
and more power plants, especially as
California’s population continues to
grow.”
(continued on next page)
Center for Urban Forest Research
Pacific Southwest Research Station, USDA Forest Service
c/o Department of Environmental Horticulture
University of California
1 Shields Avenue, Suite 1103
Davis, CA 95616-8587
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US Postage
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Hayward, CA
Permit #3335
2
The research findings show
Cost Effectiveness of Tree Planting by Region
that existing trees in California
already play a significant role
in conserving energy. There
are approximately 177 million
trees in energy conserving
locations. Most of them are
around homes where
substantial energy savings are
the greatest. As a result:
California utilities already
save $500 million annually in
wholesale electricity purchases
or generation costs.
Maximum amount that can be spent per tree planted for
Customers already save
programs to be cost effective.
about $1 billion in retail
plants that are not needed—
expenses for air conditioning.
equivalent to power for 1.4 million
Peak load demand is reduced by
homes and 3.5 million people.
about 10%.
California utilities will save an
The energy savings from these
additional $462 million annually in
177 million trees are equivalent to
wholesale electricity purchases or
7.3 100 MW power plants.
Plus, these trees provide a host of generation costs.
Residents will save an additional
other benefits that make them an
$1 billion annually in retail energy
invaluable component of every
costs for air conditioning over what
communities’ green infrastructure.
Dr. McPherson points out that “since they currently save from existing
trees.
up-front costs to establish these
trees have already been made, keep- Peak load demand will be reduced
ing these trees healthy and function- by another 9% over the reductions
already provided by existing trees,
al is one of the best investments
for a total of 19%.
communities can make.”
What more trees can do
There are approximately 242
million empty planting sites in
California. All of these sites have
energy saving potential. If
Californians establish 50 million
more trees in strategic locations on
the east and west side of residential
buildings, in 15 years the annual
energy savings will be 6,100 GW.
What does this mean to us:
At least 7.0 100 MW power plants
will not have to be built, almost
doubling (14.3) the number of power
A complete copy of this report can
be downloaded from our website
at http://cufr.ucdavis.edu.
Urban Forest Research
It’s not as simple as just
planting trees
Since the 50 million trees represent only 21% of the potential planting sites, it is critical for Californians
to select sites with the greatest
potential of conserving energy.
Energy saving potential from tree
planting is greatest in climate
regions with the hottest summers
and the greatest need to use air
conditioners: deserts, inland empire,
central valley, and south valleys.
Climate regions with the greatest
number of empty planting sites are
the south valleys, mid-central valley,
central coast, and inland empire.
Together, these four regions account
for two-thirds of all empty sites.
Plus, saturation of sites is lowest in
the mid-central valley and
inland empire regions,
indicating that these regions
have the greatest opportunity
for new trees.
The present value of benefits
per new tree ranges from $5 in
the mountains to $146 in the
south-central valley (see figure
to left). Therefore, to be costeffective, shade tree program
costs must be less than these
amounts. Assuming program
costs of $50/tree planted,
potentially cost-effective
programs are in the inland
empire, central valley, and desert
zones.
It’s a long term solution
“We’ll still need power plants, but
we won’t need as many” says Dr.
McPherson. “Shade tree programs
can be a very cost-effective measure
for conserving energy, especially
peak load demand. Strategically
locating trees to shade west walls
and windows in climate regions
where the benefits are highest will
save energy dollars and postpone, if
not eliminate, the need for some
power plants. Although shade trees
do not curtail peak loads immediately, they do promise reductions
that will increase as trees grow
larger. Planting trees now for future
peak load reduction and improved
air quality and climate is a sensible
way to lessen the impact of a
growing population on limited
energy resources and quality of life.”
Urban Forest Research
is a publication of the Center
for Urban Forest Research,
Pacific Southwest Research
Station, USDA Forest Service. For more
information, contact the Center at the
Department of Environmental
Horticulture, University of California,
1 Shields Ave, Suite 1103, Davis, CA
95616-8587. (530) 752-7636
Editor: Laurie Litman, InfoWright
October 2001
Fact Sheet #2: Save Dollars With Shade
Just Plant Trees
Imagine a solution to rising energy bills as simple as planting a tree. We’ve all
grown up with trees, climbed in them, and probably even planted a few. But
how many of us know that they significantly contribute to cooling our homes,
businesses, and communities?
General Tree Planting Recommendations:
Plant shade trees on the west and northwest sides of homes (west and southwest sides in northern climates) to provide the greatest energy benefit. Plant
deciduous trees on the east side of homes to provide the next greatest energy
benefit.
Avoid planting trees in front of south windows.
Locate trees so, when mature, they will not shade solar collectors.
Plant evergreen trees as windbreaks. Check with your state urban forester or
local tree professional for site-specific information.
Use shade trees to make paved driveways and patios cooler and more
comfortable.
Shade your air conditioner to reduce its energy use, but do not plant vegetation
so close that it will obstruct air flow around the unit.
Locate trees to shade west and east
windows and walls.
More than half of a
building’s heat gain
in summer/winter
comes from sunlight
shining through
windows.
Plant appropriate trees near overhead power lines, and do not plant directly
above underground water and sewer lines.
Be sure to pick the right tree and right location. Check with your local tree
professional for advice on selecting appropriate species and properly locating,
planting, and maintaining them.
Trees Conserve
Energy By:
Shading, which reduces the
amount of radiant energy
absorbed and stored by built
surfaces.
Evapotranspiration, which
converts liquid water in leaves to
vapor, thereby cooling the air.
Reducing the velocity of wind,
which slows the infiltration of
outside air into inside spaces.
Different trees have different planting locations.
October 2001
Urban Forest Research
References: Save Dollars With Shade
For more information on the benefit/cost of the urban forest, refer to the following
publications, written by Center researchers and associates:
McPherson, E. Gregory; Simpson,
James R. 1995. Shade trees as a
demand side resource. Home
Energy 12: 11–17.
McPherson, E. Gregory. 1996.
Urban forest landscapes, how
greenery saves greenbacks. In:
Wagner, C., ed. Annual Meeting
Proceedings, American Society of
Landscape Architects. Washington,
DC.: 27–29.
McPherson, E. Gregory; Simpson,
James R.; Peper, P.J.; Xiao, Q.;
Pettinger, D.R.; Hodel, D.R. 2001.
Tree guidelines for Inland Empire
communities. Local Government
Commission: Sacramento, CA.;
92 p.
McPherson, E. Gregory; Simpson,
James R.; Peper, P.J.; Xiao, Q. 1999.
Benefit-cost analysis of Modesto’s
municipal urban forest. Journal of
Arboriculture 25(5): 235–248.
McPherson, E. Gregory. 1993.
Evaluating the cost effectiveness
of shade trees for demand side
management. The Electricity
Journal 6(9): 57–65.
Scott, Klaus; Simpson, James R.;
McPherson, E. Gregory. 1999.
Effects of tree cover on parking
lot microclimate and vehicle
emissions. Journal Arboriculture
25: 129–141.
Simpson, James R. 1998. Urban
forest impacts on regional
cooling and heating energy use:
Sacramento County case study.
Journal Arboriculture 24: 201–214.
Checklist for designing a tree planting program
Your whole community needs energy-conserving trees. If you would like
to organize a community-wide tree planting program, use this checklist.
Envision your communities future with trees
Create a tree advocacy group
Develop a tree planting plan
Set goals and priorities
Recruit, mobilize and recognize volunteers
Provide timely, hands-on training and technical assistance
Develop list of recommended trees
Obtain high quality nursery stock
Commit to long term care and maintenance
Educate the public
Continually evaluate your progress
Urban Forest Research
Simpson, James R.; McPherson, E.
Gregory 1998. Simulation of tree
shade impacts on residential
energy use for space conditioning
in Sacramento. Atmospheric
Environment: Urban Atmospheres
32: 69–74.
Simpson, James R.; McPherson, E.
Gregory. 1996. Potential of tree
shade for reducing residential
energy use in California. Journal
Arboriculture 22: 10–18.
McPherson, E. Gregory; Simpson,
James R. 1995. Technical
potential for shade tree planting
in Sacramento County. Davis, CA:
Western Center for Urban Forest
Research; 79 p.
McPherson, E. Gregory; Simpson,
James R. 1999. Carbon dioxide
reduction through urban forestry:
Guidelines for professional and
volunteer tree planters. Gen.
Tech. Rep. PSW-GTR-171. Albany,
CA: Pacific Southwest Research
Station, Forest Service, U.S.
Department of Agriculture; 237 p.
Visit our
website at
http://cufr.ucdavis.edu
October 2001
3
Trees for a Green LA
Program Provides Energy Savings Plus…
Shade trees lower energy costs by
up to 20%—great news to everyone
in these times of energy crisis and
especially good news to utility
companies. Now the LA Department
of Water and Power (DWP) is taking
the tree/savings connection to the
streets with its new program, Trees
for a Green LA.
Over the next 30 months, Trees
for a Green LA plans to plant
200,000 new trees throughout the
city of Los Angeles. The program will
provide 198,000+ trees for residential and new construction, 2,000+
trees for public spaces and special
projects, and up to 1,500 trees to
replace high-risk trees under power
lines. And this will all be accomplished at a surprisingly low cost of
$37.50 per tree (excluding removal/
replacement of trees under power
lines).
The Trees for a Green LA plan
involves partnerships with other
local organizations. The Los Angeles
Conservation Corps will be the contractor for the program. Corps members will work with local nurseries to
grow quality trees and will manage
three staging areas to distribute trees
to community members. Most of the
trees to be planted are five-gallon
trees, which are less expensive and
easier to transport, handle, and plant
than larger trees.
Local community-based organizations and schools will subcontract
to deliver workshops to educate
community members about proper
tree placement and energy savings
potential. These organizations will
earn money for their participation.
Program developers did quite a
bit of homework before designing
this program. They studied other
successful tree planting programs,
such as Sacramento Municipal
October 2001
Utility District’s Shade Tree Program
and Anaheim’s TreePower Program,
aspects of which were modified and
integrated into the final Green LA
plan.
Organizers also went to the
Center for Urban Forest Research to
get some hard numbers on the
benefits of their proposed program.
The benefit-cost analysis, based on
DWP’s operations, found a benefitcost ratio of 1.40 (which means a
$1.40 return on every $1.00
invested) for energy conservation
benefits alone. The trees planted
under Trees for a Green LA are
expected to reduce energy use by
485 GWh over 30 years. The average
annual savings is 16,172 MWh/year
or 81 KWh/tree.
While it is obvious that energy
benefits alone would completely
justify this program, when other
environmental and social benefits
are taken into account, the benefitcost ratio goes way up, increasing to
17.5 ($17.50 per $1.00 spent)!
These additional benefits include:
Air Quality—Trees for a Green LA
is estimated to reduce nitrogen
dioxide (NO2) by 5,204 tons, ozone
by 1,906 tons, particulate matter
(PM10) by 1,869 tons, sulfur dioxide
(SO2) by 460 tons, and carbon
monoxide (CO) by 101 tons.
Carbon dioxide sequestration—
By sequestering carbon dioxide,
trees help lower the rate of global
warming. Atmospheric carbon
dioxide reduction is expected to
total 870,282 tons.
Stormwater management—By
trapping and holding up to 50
gallons of water each, trees reduce
the stormwater runoff that causes
flooding and pollution during the
rainy season.
Aesthetic beauty
Increased property values
In addition, there are other less
tangible benefits of this program,
including employment and job
training for approximately 100
young people from the Los Angeles
Conservation Corps, cost savings to
DWP related to tree replacement,
improved reliability of electric
service, reduced power outages, and
goodwill.
For more information about
Trees for a Green LA, call the DWP
Customer Call Center at 1-800GreenLA. For more on benefit-cost
analysis, contact the Center for
Urban Forest Research.
Urban Forest Research
4
New Research Project
We are pleased to
announce a new research
project: For the first time we
will be conducting our
research in the wildland/
urban interface.
We’ve known for years
that the landscapes people
create and manage around
their homes influence the
susceptibility of their
residences to wildfire.
However, little research on
“firewise” landscapes has
taken into consideration the
vegetation characteristics that
homeowners may consider most
important—such as beauty, shade,
privacy, and wildlife habitat.
Dr. Lisa Mabli of our Center is
developing a set of alternative
landscape designs that will enable
homeowners to meet their personal
needs at the same time that they
increase fire safety. The focus of this
research is the identification of
optimum forest structure for
wildland/urban interface areas. One
of the end products of this study will
be a web-based computerized
decision tool that can evaluate costs
and risks associated with alternative
landscape prescriptions.
NOTE: We’ve changed our name!
We are no longer the Western
Center…we are now the
Center for Urban Forest Research.
Schedule of Upcoming
Presentations
OCTOBER 21-24
The tool will:
Help to objectively evaluate the
fire risk associated with landscapes
of single-family homes.
Enable a quick assessment of the
positive and negative impacts of
landscape maintenance practices.
Allow homeowners to customize
alternative landscape prescriptions
to reflect preferences for vegetation
species and placement.
Research partners include: the
Natural Resource Conservation
Service, National Institute for
Standards and Technology,
Earthview Computing, and
University of California at Berkeley
Forest Products Laboratory.
Welcome aboard
“Strategies to Reduce
Infrastructure Damage by Tree
Roots” by Greg McPherson. Urban
Forestry on the Prairie—A Part of
the City’s Infrastructure
Conference in Fargo, ND.
NOVEMBER 15
“Urban Forest Research and
Development: A West-wide
Perspective” by Greg McPherson.
Oregon Urban and Community
Forestry Research and Development
Forum in Corvallis, OR.
“Urban Forestry—Forestry's Final
Frontier” by Greg McPherson.
Starker Lecture Series, College of
Forestry, Oregon State University in
Corvallis, OR.
DECEMBER 5
“The Role of Research in Urban and
Community Forestry” by Greg
McPherson. UC Davis, Geography
200, Research Trends.
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Send to Center for Urban Forest Research, Pacific Southwest Research Station, USDA
Forest Service, c/o Department of Environmental Horticulture, University of California,
1 Shields Avenue, Suite 1103, Davis, CA 95616-8587.
Urban Forest Research
Urban forestry
resources,
information and
articles can be found
at our website
http://cufr.ucdavis.edu/
October 2001