Environmental Benefits Analysis of Public Trees for Springfield, Ohio

Transcription

1 Environmental Benefits Analysis of Public Trees for Springfield, Ohio T. Davis Sydnor and Sakthi Subburayalu School of Environment and Natural Resources and Pamela J. Bennett Ohio State University Extension December 5, 2012

2 An Analysis of Tree Benefits for Springfield, Ohio Public Trees EXECUTIVE SUMMARY An inventory of public trees in the City of Springfield, Ohio was conducted by Ohio State University Extension and the Clark County Master Gardener Volunteers. A 20% survey yielded 3,089 trees or an estimated total of 15,445 municipal trees along the streets were inventoried in the 2011 growing season. A common bid price for this service is $4.00 per inventoried tree and thus the inventory represents a value of $12,356. Most importantly, however, is that the community now has a tree inventory in a form that can be used to better manage the tree resources of Springfield. Benefits mentioned above do not include the value of the subsequent analysis and report by The Ohio State University s School of Environment and Natural Resources which would conservatively add another $11,500. Analysis of the inventory data was done using itree, a software suite distributed by the USDA Forest Service. The specific program in the itree suite used to identify tree benefits was istreets. This program allows community leaders the ability to make informed decisions about Springfield s green infrastructure or to explore many aspects including biodiversity and values of environmental services such that environmental benefits can be managed or enhanced to reduce costs and the community s carbon footprint. A long standing rule of thumb for taxonomic biodiversity in the urban forest is the 10:20:30 guideline which suggests that no more than 10 percent of trees should be from the same species, no more than 20 percent should be from the same genera, and no more than 30 percent should be from the same family. In Springfield, maple trees exceed genus and family guidelines and pears exceed the species guideline (Table 1). We recommend against any further plantings of maples or pears to protect against future concerns such as invasive exotic pests. Ash are a separate issue due to emerald ash borer (EAB) and represent an estimated 1,245 individuals or 8.1 the public trees and 9 the canopy (Table 4). This represents a significant loss of Springfield s canopy if EAB should destroy all American ashes as predicted. Based on the inventory and estimates, ash removal costs in Springfield would likely exceed $910,000. Replacement costs add another $360,000 more for a grand total of more than $1,271,000. Ash removal and/or treatment costs will need to be addressed by informed community leaders. Ohio State University Extension can assist in developing informed plans including costs and probabilities of various treatment options vs. no treatment. There is no single answer for communities facing this problem. Larger growing deciduous trees now constitute 2.5% or less of Springfield s tree canopy and should be used to replace the ashes. Suggestions include Kentucky coffeetree; Shumard, swamp white, and chinquapin oaks; American sycamore; buckeye; basswood; catalpa; and sweetgum. Introduced species can be used as well if desired. Under ideal situations tree numbers among various size classes should be similar and then decline as trees reach their mature size and older trees die. Medium-sized trees of large growing species represent nearly 56%. (Tables 2 and 3). Allowing larger growing trees to grow will increase environmental benefits. Limited numbers of smaller trees suggest the need for an ongoing planting program to replace declining trees. Canopy cover percentages are consistent with their importance value (Table 4). Smaller growing crabapples and cherries (plums) generally produce fewer benefits per tree than their larger growing counterparts. This reinforces the need for planting larger statured trees such as preferred in a Toledo, OH resident preference survey. A major benefit of urban trees is their ability to intercept rainfall and reduce storm water runoff (Table 5). Storm water runoff is a major cost for Ohio communities. Columbus, OH is embarking on a multi-billion dollar sewer and storm water upgrade for the community. Putting that into a local context, 20 Springfield public trees intercept 2

3 more than 20 million gallons of storm water annually at a savings to the community of more than $575,000 per year. This could be could be increased with strategic planting of larger-statured trees. Carbon sequestration, as reported here, represents the carbon removed from the air and stored in the trees over time (Table 6). Nearly 1.7 million pounds or 6,500 tons of carbon have been stored by the 3,089 trees sampled over time. In aggregate, Springfield s trees are estimated to sequester and avoid more than 8 million lbs of CO 2 yearly (Table 8) and would represent carbon credits worth $60 thousand per year if a carbon trading system were in place. These are net gain figures and include deductions for tree losses and maintenance. Annual CO 2 benefits vary by species and size but average $3.99 per tree per year while larger sycamores and honeylocusts remove more than $5 per tree per year. Strategic plantings could increase this over time and become a significant tool in reducing Springfield s carbon footprint if desired. Energy savings by trees are particularly important in view of the citizenry s increasing concern over the nation s energy dependency. Energy is saved by shading structures, evaporating water (evapotranspiration) and reducing wind speed around structures (Table 7). Twenty percent of Springfield trees save the community $39,000 in electricity and $70,000 in natural gas for a total savings of $110,000. This averages more than $35 per tree per year. Retaining larger trees, where possible, will enhance energy savings at the community level in time. Annual air quality savings (reduced ozone, nitrous and sulfur oxides as well as particulate matter) for the 20 the trees sampled is nearly $20,000 (Table 9). This includes both direct savings ($4,700) and avoided pollution which is much greater at $15,000. Avoided pollution is pollution not generated at a power source because energy was not required (avoided) by the community. The total annual air quality benefits are discounted by $1,300 for the volatile emissions (BVOC) generated by the trees themselves. Aesthetic and miscellaneous benefits from 20 Springfield s trees contribute $97,600 annually in the form of increased recreational opportunities, increased property values, and enhanced community identity among other things (Table 10). Research in public housing has shown that areas with trees facilitate interaction among residents and lead to reduced domestic violence and more sociable environments. Customer surveys suggest that customers prefer to spend their money and time in commercial streetscapes with trees and are willing to spend up to 11% more in such an environment. When all annual benefits are included the 3,089 trees that were sampled contribute an average of $115 per tree annually to the community (Table 11). vary in their annual benefits but mature size, longevity, and maintenance costs are but some of the factors determining annual benefits. This would be well in excess of their maintenance and planting costs for Springfield s trees. The Springfield budget for trees maintenance was estimated to be $121,000 based on the budget of $2.00 per capita required for Tree City USA status by the National Arbor Day Foundation and Springfield s population of 60,608 people. Thus while the 20% sampled (3,089 trees) require relatively little care per year they deliver $354,800 in annual benefits from storm water abatement, carbon sequestration, energy savings, air quality enhancement, aesthetic benefits, and the like. Thus the estimated 15,500 trees in Springfield would deliver a total of nearly 1.8 million in annual benefits. This is a 1400% return on investment. Returns appear high but Ohio communities studied routinely discover returns on their tree maintenance dollars of 2-300% and Toledo had a 436% annual return with one of the larger tree maintenance budgets in Ohio. Further, unlike most community infrastructure, annual tree benefits per tree continue to increase over a tree s lifetime. 3

4 Table 1. Distribution of the Most Common Trees in Springfield, Ohio Arranged from Most to Least Commonly Seen Percent Maple Pear Ash 8.06 Flowering crabapple 7.06 Linden 6.38 Honeylocust 6.25 Zelkova 2.59 Plum 2.53 Elm 2.36 American sycamore 2.23 OTHER SPECIES

5 Table 2. Relative Age Distribution of the 10 Most Commonly Planted Trees in Springfield, Ohio as a Percentage (%) of each Tree by Common Names DBH class (in) >42 Maple Pear Ash Flowering crabapple Linden Honeylocust Zelkova Plum Elm American sycamore SPRINGFIELD TOTALS

6 Table 3. Population of Springfield Public Trees by Common Name, Tree Type and Size (DBH) Class. DBH Class (in) >42 Broadleaf Deciduous Large (BDL) Maple ,064 Linden American sycamore London planetree Sweetgum Oak Black walnut Tulip tree Northern catalpa Cottonwood American basswood American beech Hackberry Eastern cottonwood Kentucky coffeetree ,537 Broadleaf Deciduous Medium (BDM) Ash Honeylocust Zelkova Elm Buckeye Ginkgo Birch Hornbeam Boxelder Goldenraintree Chinese chestnut Quaking aspen Willow Hardy rubber tree Osage-Orange Sassafras

7 DBH Class (in) >42 Broadleaf Deciduous Small (BDS) Pear Flowering crabapple Plum Dogwood Eastern redbud Japanese tree lilac Mulberry Flowering plum Hawthorn Lilac Rose-of-sharon Pawpaw Common chokecherry Broadleaf Evergreen Small (BES) Evergreen Magnolia Conifer Evergreen Large (CEL) Pine Spruce Dawn-redwood Baldcypress Conifer Evergreen Small (CES) Eastern red cedar Zone ,089 7

8 Table 3A Estimated Expenses for Ash Removal and/or Replacement of Springfield Public Trees due to Emerald Ash Borer Based on a 20% Sample SIZE NUMBER REMOVAL COSTS PER TREE REMOVAL TOTALS REPLACEMENT COST REMOVAL W/ REPLACEMENT $100 $1,000 $200 $3, $375 $35,625 $290 $63, $375 $127,500 $290 $226, $675 $266,625 $290 $381, $675 $108,000 $290 $154, $1,290 $180,600 $290 $221, $1,625 $105,625 $290 $124, $2,150 $21,500 $290 $24,400 >42 30 $2,150 $64,500 $290 $73,200 TOTALS 1245 REMOVAL ONLY TOTALS $910,975 REMOVE + REPLACE TOTALS $1,271,125 8

9 Table 4. Springfield, Ohio Public Trees Listed by Common Name from Greatest to Least Importance Value. Number of Trees Trees Leaf Area (ft2) Leaf Area Canopy Cover (ft2) Canopy Cover Importance Value Maple Ash Pear Honeylocust Linden Flowering crabapple American sycamore Elm London planetree Zelkova Sweetgum Plum Buckeye OTHER TREES , ,747, ,333,

10 Table 5. Annual Storm Water Benefits for 20% Sample of Springfield, Ohio Trees by Ordered by Decreasing Benefits/Tree. Rainfall Interception (Gal) ($) Tree Numbers $ Avg. $/tree London planetree $3, $59.61 American sycamore $4, $58.76 Maple $58, $54.71 Elm $3, $50.17 Honeylocust $8, $46.38 Ash $11, $45.50 Linden $8, $41.07 Sweetgum $1, $28.93 Zelkova $1, $20.12 Pear $4, $9.42 Buckeye $ $8.86 Plum $ $5.76 Flowering crabapple $1, $5.22 OTHER STREET TREES $9, $34.10 SPRINGFIELD TOTAL 4,275,776 $115, $

11 Table 6. Stored CO 2 Benefits in Public Trees in Springfield, Ohio by Ordered by Decreasing Benefits per Tree stored CO2 (lbs) ($) Tree Numbers $ Avg. $/tree American sycamore $5, $77.38 London planetree $4, $74.94 Elm $3, $49.20 Linden $8, $42.16 Maple $42, $40.21 Ash $9, $39.74 Sweetgum $1, $29.60 Honeylocust $5, $28.60 Zelkova $1, $20.73 Pear $5, $11.46 Plum $ $6.40 Flowering crabapple $1, $5.65 Buckeye $ $4.94 OTHER STREET TREES $9, $36.93 SPRINGFIELD TOTAL 13,271,924 $99, $

12 Table 7. Annual Energy Benefits of Springfield Public Trees by Common Name and Decreasing Energy Benefits per Tree Electricity (MWh) Electricity ($) Natural Gas (Therms) Natural Gas ($) ($) Tree Numbers $ Avg. $/tree London planetree 13 $ $1,791 $2, $49.04 Maple 238 $18, $32,019 $50, $47.10 American sycamore 15 $1, $2,092 $3, $46.96 Honeylocust 42 $3, $5,396 $8, $44.49 Ash 51 $3, $7,041 $10, $43.70 Linden 40 $3, $5,370 $8, $42.63 Elm 13 $1, $1,919 $2, $40.23 Sweetgum 7 $ $947 $1, $32.07 Pear 39 $2, $5,940 $8, $20.04 Zelkova 6 $ $834 $1, $15.83 Buckeye 3 $ $509 $ $13.55 Plum 5 $ $695 $1, $13.36 Flowering crabapple 12 $ $1,796 $2, $12.35 OTHER STREET TREES 33 $2, $4,507 $7, $26.56 SPRINGFIELD TOTAL 517 $39, $70,857 $110, $

13 Table 8. Annual Carbon Dioxide Benefits of Springfield, Ohio Trees by Common Name and Ordered by Decreasing Benefits per Tree Sequester Sequester ($) Decomp. Release Maint. Release Release ($) Avoided Avoided ($) Net ($) Tree Numbers London planetree $ $ $ $ $7.15 American sycamore $ $ $ $ $7.09 Honeylocust $ $ $ $1, $6.34 Linden $ $ $ $1, $5.46 Maple $2, $ $2, $5, $4.79 Ash $ $ $ $1, $4.55 Sweetgum $ $ $ $ $4.04 Elm $ $ $ $ $3.39 Zelkova $ $ $ $ $2.68 Pear $ $ $ $ $2.04 Buckeye 7014 $ $ $ $ $1.65 Plum 7181 $ $ $ $ $1.39 Flowering crabapple $ $ $ $ $1.28 OTHER STREET TREES $ $ $ $ $3.35 SPRINGFIELD TOTAL 847,119 $6,353-63,793-5,429 -$ ,140 $6,504 1,645,037 $12, $3.99 $ Avg. $/tree

14 Table 9. Annual Air Quality Benefits of Springfield, Ohio Trees by Common Names and Ordered by Decreasing Air Pollution Benefits per Public Tree Deposition O3 Deposition NO2 Deposition PM10 Deposition SO2 Deposition ($) Avoided NO2 Avoided PM10 Maple $2, $7, $ $9, $8.69 Ash $ $1, $ $1, $7.53 London planetree $ $ $ $ $7.34 Elm $ $ $ $ $7.31 Honeylocust $ $1, $ $1, $7.26 American sycamore $ $ $ $ $7.16 Linden $ $1, $ $1, $6.34 Sweetgum $ $ $ $ $4.86 Pear $ $1, $ $1, $3.17 Zelkova $ $ $ $ $2.61 Plum $ $ $ $ $2.05 Buckeye $ $ $ $ $1.95 Flowering crabapple $ $ $ $ $1.88 OTHER STREET TREES $ $ $ $1, $4.24 SPRINGFIELD TOTAL $4, $15, $1, $18, $6.10 Avoided VOC Avoided SO2 Avoided ($) BVOC Emissions BVOC Emissions ($) ($) Tree Numbers Avg. $/tree 14

15 Table 10. Annual Aesthetic or Other Benefits of Public Trees by in Springfield, Ohio ($) Tree Numbers $ Avg. $/tree Honeylocust $21, $ London planetree $2, $47.76 American sycamore $3, $46.74 Maple $39, $37.37 Linden $6, $34.74 Ash $7, $29.66 Zelkova $2, $27.33 Sweetgum $1, $25.08 Elm $1, $17.82 Buckeye $ $15.52 Pear $3, $7.58 Plum $ $5.12 Flowering crabapple $1, $4.64 OTHER STREET TREES $6, $24.29 SPRINGFIELD TOTAL $97, $31.62

16 Table 11. Annual Benefits per Sector and Annual Benefits per Tree by Decreasing Benefits for Springfield Public Trees Energy CO2 Air Quality Stormwater Aesthetic/ Other Honeylocust $44.49 $6.34 $7.26 $46.38 $ $ London planetree $49.04 $7.15 $7.34 $59.61 $47.76 $ American sycamore $46.96 $7.09 $7.16 $58.76 $46.74 $ Maple $47.10 $4.79 $8.69 $54.71 $37.37 $ Ash $43.70 $4.55 $7.53 $45.50 $29.66 $ Linden $42.63 $5.46 $6.34 $41.07 $34.74 $ Elm $40.23 $3.39 $7.31 $50.17 $17.82 $ Sweetgum $32.07 $4.04 $4.86 $28.93 $25.08 $94.98 Zelkova $15.83 $2.68 $2.61 $20.12 $27.33 $68.57 Pear $20.04 $2.04 $3.17 $9.42 $7.58 $42.26 Buckeye $13.55 $1.65 $1.95 $8.86 $15.52 $41.52 Plum $13.36 $1.39 $2.05 $5.76 $5.12 $27.68 Flowering crabapple $12.35 $1.28 $1.88 $5.22 $4.64 $25.36 OTHER STREET TREES $26.56 $3.35 $4.24 $34.10 $24.29 $

17 Table 12 Environmental Benefits from Five Categories for Springfield Trees Adjusted to Estimated Benefits ($) $/tree Stormwater $579,410 $37.51 Energy $550,245 $35.64 Aesthetic/Other $488,355 $31.62 Air Quality $94,270 $6.10 CO2 $61,690 $3.99 Benefits $1,774,195 $