final-final-A.Strobridge-Fairfax City iTree Streets Preliminary Project
1. Fairfax City iTree Streets Preliminary
Project
By Ashley Anne Strobridge
Environmental & Sustainability Studies Major, Geography/Women’s Studies Minors
George Mason University
Advisor: Dr. Matt Rice – GMU Geography and Geoinformational Sciences
Consultants: Stefanie Kupka – City of Fairfax Office of Sustainability & CJ Crabtree – City of Fairfax
Arborist
2. Introduction
Purpose of Project:
To generate a Cost-Benefit Analysis of Fairfax City Trees using:
iTree Streets, a peer-reviewed software suite designed by the USDA
Forest Service for use in urban and community forestry analysis and
benefits assessment
2010 Fairfax City Trees Survey
Steps:
1) Formatted over 2500 entries with proper tree species names and
measurements in MS Excel for use with program
2) Formatted list for use with MS Access, which is the program that
iTree recognizes
3) Retrieved required Fairfax City data inputs to create iTree Streets
project (only partially completed)
4) Created iTree Streets project
5) Ran and Analyzed iTree Streets reports
6) Explored options for further tree survey data gathering
3. Street Tree Benefits:
Trees are a valuable asset to Fairfax City.
They naturally:
Reduce stormwater runoff
Lower summer air temperatures
Reduce air pollution
Reduce heating and cooling costs
Reduce atmospheric carbon dioxide (CO2)
Enhance property values
Provide wildlife habitat
Improve health and wellbeing
Improve learning and concentration
Provide aesthetic benefits
Picture Credit: Ashley Anne Strobridge
5. Top 5 Beneficial Tree Species in
Total $ Saved per Tree
$0.00
$100.00
$200.00
$300.00
$400.00
$500.00
$600.00
$700.00
White
Oak
Oak Silver
Maple
Black
Poplar
White
Poplar
$603.01
$504.30 $502.82
$433.60
$377.77
*
*Silver Maple is Best of all species in analysis for Energy, Air Quality, and Stormwater savings
**White Poplar has worst Air Quality rating of all species in analysis, actually subtracting
value (-$9.74 per tree), but does very well in other categories
**
6. Focus on Stormwater: Trees Improve Water
Quality and Reduce Volume and Speed of
Stormwater Run-off
Interception of Stormwater:
• Trees intercept rainfall with their
leaves and branches, creating
slow stemflow of water into the
ground
• Roots take up soil moisture,
which creates evapotranspiration
of water back into atmosphere
Other Functional Benefits:
• Roots of trees maintain soil
stability, reducing erosion
• Roots and soil together filter out
pollutants that would otherwise
end up in the watershed. This
protects the Chesapeake Bay
from further pollution and
nutrient overload
8. Could Money Grow on Trees?
Trees intercept rainfall that
would otherwise become
stormwater that is costly to
handle via man-made
structures.
In 2012, Fairfax City spent
$390,000 on stormwater
infrastructure improvements.
How much of that cost could
have been avoided by planting
more trees? Especially the right
kind of trees…
Picture Credit: Retrieved from 2012 City of
Fairfax Budget Document
9. Trees in Fairfax City intercept 1,634,982 gallons of
storm water per year for an annual savings of $16,721
Top 3 $/tree species for stormwater interception
Silver Maple = $109 per tree
White Oak = $97 per tree
Black Poplar = $71 per tree
Top 3 overall $ saving trees by volume of stormwater
intercepted and by total money saved
Littleleaf Linden = $3,388 (~$8 per tree)
Oct. Glory Red Maple = $1,935 ($4.50 per tree)
Japanese Pagoda Tree = $1,646 (~$14.50 per tree)
Snap-Shot of The City of Fairfax’s City Tree
Stormwater Interception
10. But Which Trees Does Fairfax City Have the MOST of?
• Top 3 $ saved per tree species don’t even make chart %
listing (smaller than 3.5% of population)
• Silver Maple = $109 per tree (7 trees total)
• White Oak = $97 per tree (1 tree total)
• Black Poplar = $71 per tree (21 trees total)
Only very few of the most beneficial trees!
% of Total Population by Species
1) Littleleaf Linden
1st in pop size w/
433 trees
342,225 gallons
intercepted
$3,338 saved
2) Oct. Glory Red Maple
2nd in pop size w/
430 trees
195,435 gallons
$1,935 saved
3) Jap. Pagoda
7th in pop size w/
113 trees
166,259 gallons
$1,646 saved
Top 3 by-volume savers
Total Tree Pop. = 2,686
11. Increasing the Stormwater Benefit Values by
Increasing Amount of Most Productive Trees
…But what if the City had the same number of White Oaks
that it has of Littleleaf Lindens?
If we take the total $ saved by the largest population of trees
(Littleleaf Linden), and divide it by the $ per tree saved, we get
the number of L. Linden trees (figure not shown in iTree data).
So…
$3,388/$8 = 433 Littleleaf Linden trees
Then if we multiply the number of L. Lindens by the $ saved per
tree of the White Oak, we get the amount that Fairfax City would
save if there were as many White Oaks as there are currently
Littleleaf Lindens:
433 x $97 = $42,001 potential stormwater savings!
12. White Oak: Stormwater Super-Tree
So if Fairfax City planted more White Oaks, it would save close to
$42,001 annually from W. Oak stormwater interception ALONE over
the total $16,721 from ALL SPECIES stormwater interception.
That’s 2½ X the TOTAL $ in just ONE SPEICIES!
$0
$5,000
$10,000
$15,000
$20,000
$25,000
$30,000
$35,000
$40,000
$45,000
Total Stormwater
Benefits of All Trees Current Littleleaf
Linden S.W. Benefits Potential White Oak
S.W. Benefits
$16,213
$3,388
$42,001
Imagine reducing that $390,000 2012 stormwater cost by $42,000! Not bad!
13. The White Oak is an Overall Super-Saver
Currently there is only 1 White Oak in Fairfax City,
but that lone tree already accounts for a 9,848
gallons of stormwater intercepted annually.
The White Oak is the leader in the category of
Aesthetic and Property values, topping the list at a
whopping $473 benefit per tree
The White Oak is also ranked 3rd of all 61 species
in the survey for Energy savings, at ~$23 savings
per tree annually
As the Number One Beneficial Tree at a savings of
$603 per tree, it is clear that planting more White
Oaks would be financially beneficial for the City of
Fairfax
14. Potential savings benefit if there were as many
White Oaks as there are currently L. Lindens:
$0
$50,000
$100,000
$150,000
$200,000
$250,000
$300,000
Current Overall
City Tree Benefits
Current Littleleaf
Linden Benefits
Current White Oak
Benefits
Potential White
Oak Benefits
$189,512
$41,568
$603
$261,099
The savings potential from ONE species, White Oak, outstrips
the TOTAL annual benefit of all trees by nearly 50%, and is
over 6X the current annual benefit from the most beneficial-
due-to-volume tree species, Littleleaf Linden
15. Feasibility of Planting More White Oaks
According to Merrifield Garden Center, White Oaks do well in
this region
Merrifield G.C. sells W. Oaks for $195 per 15 gallon tree
With a 25-30% discount for Cities who bulk order via contractor,
plus a 65% planting fee added to the $195 cost per tree
Making the final total cost per tree = $224
With White Oaks benefiting the City $603 per tree, the cost of
purchasing & planting the W. Oaks is offset, and there is still
$379 benefit leftover per tree after initial costs are
subtracted.
Littleleaf Lindens cost $325 per 2” trunk tree at Merrifield
G.C., and are not available at the 15 gallon price, but still
require the additional 65% planting fee.
With the 65% fee, minus 30% off, L. Lindens cost $376 per tree.
And w/ L. Lindens only benefiting the City $96 per tree, that’s
leaves no benefits leftover, and actually ends up costing the city
$280 per tree planted
16. Take Away Points
Currently, Fairfax City Trees are benefiting the City a
total of $189,512 annually by:
Increasing Property Values = $142,489
Intercepting Damaging Stormwater = $16,721
Storing & Sequestering CO2 = $18,599
Providing Energy Savings = $8,845
Improving Air Quality = $2,858
Those Total Annual Benefits could be increased by 50%,
with as much as $261,099 added, if more White Oaks
were planted
It is theoretically feasible to plant more White Oaks in
Fairfax City
These totals are subject to change due to potential
inaccuracies in input data (see next slides)
17. Automatic Inputs for iTree Analysis
Electricity ($/kwh): $0.0759
Natural Gas ($/Therm): $1.046
CO2 ($/lb): $0.0075
PM10 ($/lb): $2.49
NO2 ($/lb): $6.55
SO2 ($/lb): $1.97
VOC ($/lb): $6.26
Stormwater Interception ($/gal): $0.0099
Average Home Resale Value: $600,000*
*Average Home Resale Value was originally ~$119,000. New value was calculated
by consulting the following website:
http://www.homefinders.com/county_maps/virginia/fairfax-city.php
Took average price of single family homes in sampling of zip codes in Fairfax Co.
($698,319) and weighed it against the mid-lower range average price of a home in a
sampling of popular Fairfax City communities (between $474,990 and $525,000) to
come up with Average Home Resale Value. (Wanted to take into account that
website might not list lower-end communities under “Popular Communities,” so
chose mid-low value).
18. More to be done….
To get the most accurate cost-benefit analysis
using iTree:
Need the additional City data inputs of:
Accurate Benefit Prices (list on previous slide)
Annual Costs of City Tree Maintenance (list available)
(Current analysis of benefits is most likely skewed low due to low estimations of
energy/stormwater management benefit prices, & lack of tree management costs)
Need updated tree data gathered via in-field tree
survey:
Gather new data on tree diameter, location
Include tree condition
Enlist help from Fairfax City High School AP Enviro Sci Students
Notes on iTree Streets
iTree Streets is iPad/tablet/smartphone compatible
Capability for GIS component
Editor's Notes
Imagine reducing that $390,000 2012 stormwater costs by $42,000! Not bad!
