An Analysis of Street Tree Benefits for. Bellbrook

Transcription

1 An Analysis of Street Tree Benefits for Bellbrook By T. Davis Sydnor and Sakthi Subburayalu School of Environment and Natural Resources The Ohio State University Columbus, OH In cooperation with OSU Green County Extension

2 An Analysis of Street Tree Benefits for Bellbrook, OH EXECUTIVE SUMMARY An inventory of street trees was conducted by Greene County Master Gardener Volunteers, Ohio Certified Volunteer Naturalists, from the OSU Greene County Extension Office as well as, Bellbrook Garden Club members and interested Bellbrook citizen volunteers to allow an analysis of environmental benefits to be run. A total of 540 street trees were inventoried but did not include park trees for this report. A common bid price for this service is $3.00 per tree and thus the inventory represents a savings of $1,640 for Bellbrook taxpayers had the inventory been bid. More importantly however, is that the City of Bellbrook now has a tree inventory that can be used to better manage the street tree resource. Benefits mentioned above do not include the subsequent analysis which was performed by The School of Environment and Natural Resources at The Ohio State University. 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 benefits was Street Tree Resource Analysis Tool for Urban forest Managers (STRATUM). This program allows individuals to make informed decisions about the community tree resource and to evaluate costs and benefits of some management decisions such as whether to increase biodiversity in the community. A long-standing rule of thumb for biodiversity is the guideline which suggests that no more than 10 percent of city s trees should be from the same species, no more than twenty percent should be from the same genera, and no more than thirty percent should be from the same family. In Bellbrook, maples at 44% exceed the genera limit of 20% and the family limit of 30%. Many communities in Ohio have maples in the 30-40% range. This suggests that Bellbrook is likely to have a more difficult time dealing with Asian longhorned beetle (ALB) should it reach central Ohio than it has at present with the emerald ash borer (EAB) as ash constitutes only 4% of the street trees. The problem with emerald ash borer, now established in central Ohio, is well known. We recommend planting no additional maples in Bellbrook until the percentage of maples in the community drops below 20% in order to maintain a diverse tree canopy and limit potential problems with exotic pests. The potential for losses from EAB to street trees is likely to be modest as Bellbrook has only 24 ashes but 239 maples which are sensitive to ALB but may be a concern in parks which have more ashes. Under ideal conditions, tree numbers among size classes of larger growing trees such as oaks and maples should remain somewhat constant to inch diameter then decline as tree size increases and trees die from old age (Table 2). Younger plantings (3-15 inch) have been heavily skewed toward maples (Table 3). Consider other large trees for the future to minimize the risk of an exotic pest and to increase environmental benefits for the community as larger trees yield greater environmental benefits. Many of Bellbrook s trees are now beginning to reach sizes where environmental benefits per tree will increase. Larger growing broadleaved deciduous trees such as oaks, hackberry, tulip-poplar and elms will consistently deliver greater environmental benefits than trees below 18-inch DBH. Bellbrook s black walnut and black locust have average DBHs about 21 and 23inch respectively. In comparison, maples average ~ 16-inch DBH and deliver reduced benefits per tree. This further demonstrates Bellbrook s need for larger statured trees whenever possible while avoiding conflicts such as utility lines. 2

3 A major benefit of urban trees is their ability to intercept rainfall and reduce storm water runoff (Table 4). Storm water runoff is a major cost for many communities. Columbus is about to embark on a multibillion dollar sewer and storm water upgrade for the community. Bellbrook s street trees intercept 766 CCF (573,008 gallons) of storm water annually at a savings of $15,535 per year to the community. Carbon sequestration, as reported here, represents the carbon removed from the air and stored in Bellbrook s street trees over time (Table 5). Nearly 1.4 million pounds or 697 tons of carbon have been stored by the community s 540 street trees over time. Additionally, Bellbrook s trees annually sequester and avoid more than 233,253 lbs of CO 2 (Table 7) and could represent carbon credits worth $1,749 per year if a carbon trading system were in place and if a system for accounting for them were available for community trees. These are net gain figures and include deductions for tree losses and maintenance. Annual CO 2 benefits vary by species but are confounded by size as larger trees would produce more benefits. Larger, longer lived species and species requiring less maintenance would also produce greater benefits (Table 7). Energy savings by trees are exceptionally important in view of the citizenry s increasing concern over the nation s energy dependency. Planting trees in our communities is likely more cost effective than building power plants as an alternative to meeting some of our energy needs. Energy is saved by shading structures, evaporating water (evapotranspiration) and reducing wind speed around structures (Table 6). Community-wide, Bellbrook saves $5,600 in electricity and $10,000 in natural gas for a total savings of $15,600 or nearly $29 per tree with larger trees resulting in greater savings. Annual air quality savings (reduced ozone, nitrous and sulfur oxides as well as particulate matter) for Bellbrook s trees are $2,540 (Table 8). This includes both direct savings ($575) from the trees and avoided pollution which is even greater ($2,193). Avoided pollution is pollution not generated at power source because energy was not required by the community. The total annual air quality benefits are discounted by $228 for the volatile emissions given off by the trees themselves. Aesthetic and miscellaneous benefits from trees contribute $15,457 annually to the community in the form of increased property values and enhanced community identity among other things (Table 9). Research in public housing has shown that areas with trees 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 settings. When all benefits are included the average street tree in Bellbrook contributes $94.22 per tree annually to the community (Tables 10 & 11). Species vary in their annual benefits. Mature size, longevity, and maintenance costs are but some of the factors determining annual benefits. In total Bellbrook s 540 trees contribute $50,881. This would be well in excess of their maintenance and planting costs. The City of Bellbrook does not have a specific budget for tree care but we can use the Tree City guideline suggesting a minimum expenditure of $2 per capita to yield a $14,000 budget estimate. Dividing benefits by costs yields a 363% return on the community s investment. Trees are truly a contributing part of Bellbrook. Unlike most community infrastructure, tree benefits per tree continue to increase over a tree s lifetime and peak between 24 and 36 inches in diameter depending on mature size. 3

4 Table 1 Distribution of Bellbrook s Ten Most Commonly Planted Street Trees (%) Species Percent Maples Callery pear 7.59 Spruces 5.56 Pines 5.37 Flowering crabapple 5.00 Ashes 4.44 Eastern red cedar 3.15 Sweetgum 3.15 Elms 3.15 Eastern redbud 1.85 Other species

5 Table 2. Relative Age Distribution (%) of the Top 10 Most Commonly Planted Street Trees in Bellbrook Species Name >42 Maples Callery pear Spruces Pines Flowering crabapple Ashes Eastern red cedar Sweetgum Elms Eastern redbud Bellbrook Street Tree

6 Table 3. Inventory of Bellbrook Trees by Scientific Name and Size Species >42 Broadleaf Deciduous Large (BDL) Acer species Liquidambar styraciflua Juglans nigra Celtis occidentalis Populus species Quercus species Catalpa species Platanus occidentalis Tilia species Liriodendron tulipifera Ailanthus altissima Broadleaf Deciduous Medium (BDM) Pyrus calleryana Fraxinus species Ulmus species Zelkova serrata Acer negundo Robinia pseudoacacia Carpinus betulus Aesculus glabra Ginkgo biloba Salix species Betula nigra Gleditsia triacanthos Broadleaf Deciduous Small (BDS) Malus hybrid Cercis canadensis Prunus cerasifera Prunus species Syringa reticulata Amelanchier species Morus species Lonicera maackii Conifer Evergreen Large (CEL) Picea species Thuja occidentalis

7 Species >42 Conifer Evergreen Medium (CEM) Pinus Species Conifer Evergreen Small (CES) Juniperus virginiana Bellbrook

8 Table 4. Annual Storm water Benefits of Bellbrook s Street Trees by Common Name and Ordered by Average Benefit per Tree Species Rainfall Interception (CCF) ($) % of Tree Numbers % of $ Avg. $/tree Black walnut 18.7 $ $63.24 Black locust 17.6 $ $59.61 Elms 31.8 $ $37.90 Spruces 54.7 $1, $36.95 aples $8, $34.14 Boxelder 8.2 $ $27.67 Ashes 31.2 $ $26.35 Other street trees 54.9 $1, $24.75 Sweetgum 20.7 $ $24.68 Callery pear 49.6 $1, $24.51 Eastern red cedar 19.4 $ $23.19 Pines 32.6 $ $22.76 Plums 3.9 $ $13.14 Flowering crabapple 15.5 $ $11.61 Eastern redbud 3.5 $ $7.06 Zelkova 0.9 $ $2.54 Cherry plum 0.4 $ $1.15 Japanese tree lilac 0.3 $ $1.03 Bellbrook total $15, $

9 Table 5. Stored CO2 Benefits of Bellbrook s Street Trees by Common Name and Ordered by Average Benefits per Tree Species stored CO2 (lbs) ($) % Tree Numbers % of $ Avg. $/tree Black walnut $ $66.15 Black locust $ $53.55 Elm $ $31.44 Maple $5, $23.03 Ash $ $20.34 Boxelder $ $18.86 Plum $ $17.60 Callery pear $ $17.12 Sweetgum $ $14.74 Flowering crabapple $ $13.32 Spruce $ $9.92 Eastern redbud $ $7.69 Eastern red cedar 8806 $ $3.89 Pine $ $3.02 Zelkova 1306 $ $1.40 Cherry plum 753 $ $0.81 Japanese tree lilac 575 $ $0.72 Other street trees $1, $25.36 Bellbrook total 1,395,189 $10, $

10 Table 6. Annual Energy Benefits of Bellbrook s Street Trees by Common Name and Ordered by Numbers of Trees Species Electricity (MWh) Electricity ($) Natural Gas (MBtu) Natural Gas ($) ($) % of Tree Numbers % of $ Avg. $/tree Black locust 1.4 $ $208 $ $53.02 Black walnut 1.4 $ $181 $ $48.57 Elm 3.1 $ $428 $ $39.09 Maple 39.4 $2, $5,275 $8, $34.59 Callery pear 5.8 $ $815 $1, $30.61 Ash 3.3 $ $471 $ $29.92 Sweetgum 2.4 $ $307 $ $28.96 Boxelder 0.8 $ $103 $ $27.00 Flowering crabapple 3.2 $ $467 $ $26.32 Plum 0.7 $ $99 $ $25.23 Spruce 2.8 $ $368 $ $19.36 Eastern redbud 0.7 $ $110 $ $16.61 Pine 2.1 $ $299 $ $15.66 Eastern red cedar 1.0 $ $151 $ $13.47 Zelkova 0.2 $ $27 $ $5.81 Cherry plum 0.1 $7 1.7 $17 $ $3.46 Japanese tree lilac 0.1 $6 1.3 $13 $ $3.13 Other street trees 5.0 $ $675 $1, $23.43 Citywide total 73.6 $5, $10,014 $15, $

11 Table 7. Annual Carbon Dioxide Benefits of Bellbrook s Street Trees by Species and Ordered by Average Benefits per Tree Species Sequestered Sequestered ($) Decomp Release Maint Release Release ($) Avoided Avoided ($) Net ($) % Tree Numbers Black walnut 3227 $ $ $ $6.75 Black locust 2020 $ $ $ $5.30 Elm 4808 $ $ $ $4.27 Sweetgum 4969 $ $ $ $3.93 Maple $ $ $ $3.92 Boxelder 1712 $ $ $ $3.67 Callery pear $ $ $ $3.65 Ash 5829 $ $ $ $3.43 Flowering crabapple 4766 $ $ $ $2.75 Plum 725 $ $ $ $2.26 Spruce 2881 $ $ $ $1.85 Eastern redbud 1113 $ $ $ $1.72 Pine 1301 $ $ $ $1.21 Eastern red cedar 500 $ $ $ $0.96 Zelkova 417 $ $ $ $0.76 Cherry plum 178 $ $ $ $0.36 Japanese tree lilac 140 $ $ $ $0.33 Other street trees 8951 $ $ $ $2.77 Bellbrook total 116,614 $ , ,441 $ ,253 $1, $3.24 % of $ Avg. $/tree

12 Table 8. Annual Air Quality Benefits of Bellbrook s Street Trees by Species and Ordered by Average Dollars per Tree Species Deposit O3 Deposit NO2 Deposit PM10 Deposit SO2 Deposit ($) Avoided NO2 Avoided PM10 Avoided VOC Avoided SO2 Avoided ($) Black locust $ $ $ $ $9.24 Black walnut $ $ $ $ $8.55 Elm $ $ $ $ $6.62 Maple $ $1, $ $1, $6.01 Callery pear $ $ $ $ $4.85 Ash $ $ $ $ $4.82 Sweetgum $ $ $ $ $4.56 Plum $ $ $ $ $4.24 Flowering crabapple $ $ $ $ $4.18 Boxelder $ $ $ $ $4.18 Other street trees $ $ $ $ $3.92 Eastern redbud $ $ $ $ $2.55 Pine $ $ $ $ $1.69 Spruce $ $ $ $ $1.60 Eastern red cedar $ $ $ $ $1.08 Zelkova $ $ $ $ $0.80 Cherry plum $ $ $ $ $0.45 Japanese tree lilac $ $ $ $ $0.41 Citywide total $ $2, $ $2, $4.70 BVOC Emitted BVOC Emitted ($) Net ($) % Tree Numbers Avg. $/tree 12

13 Table 9. Annual Aesthetic or Other Benefits of Bellbrook s Street Trees by Common Name and Ordered by Average Benefit per Tree Species ($) % Tree Numbers % of $ Avg. $/tree Black walnut $ $47.42 Maple $8, $36.89 Sweetgum $ $34.66 Black locust $ $32.42 Boxelder $ $31.90 Elm $ $29.18 Callery pear $1, $28.36 Ash $ $26.31 Spruce $ $23.80 Pine $ $20.89 Eastern red cedar $ $14.37 Zelkova $ $10.52 Flowering crabapple $ $10.10 Plum $ $6.91 Eastern redbud $ $6.28 Cherry plum $ $1.19 Japanese tree lilac $ $1.05 Other street trees $1, $23.57 Bellbrook total $15, $28.62

14 Table 10. Average Annual Benefits of Bellbrook s Street Trees ordered by dollars/tree Species Energy CO2 Air Quality Storm water Aesthetic /Other Black walnut $48.57 $6.75 $8.55 $63.24 $47.42 $ Black locust $53.02 $5.30 $9.24 $59.61 $32.42 $ Elms $39.09 $4.27 $6.62 $37.90 $29.18 $ Maples $34.59 $3.92 $6.01 $34.14 $36.89 $ Sweetgum $28.96 $3.93 $4.56 $24.68 $34.66 $96.79 Boxelder $27.00 $3.67 $4.18 $27.67 $31.90 $94.41 Callery pear $30.61 $3.65 $4.85 $24.51 $28.36 $91.99 Ashes $29.92 $3.43 $4.82 $26.35 $26.31 $90.84 Spruces $19.36 $1.85 $1.60 $36.95 $23.80 $83.56 Pines $15.66 $1.21 $1.69 $22.76 $20.89 $62.21 Flowering crabapple $26.32 $2.75 $4.18 $11.61 $10.10 $54.96 Eastern red cedar $13.47 $0.96 $1.08 $23.19 $14.37 $53.07 Plums $25.23 $2.26 $4.24 $13.14 $6.91 $51.78 Eastern redbud $16.61 $1.72 $2.55 $7.06 $6.28 $34.22 Zelkova $5.81 $0.76 $0.80 $2.54 $10.52 $20.44 Cherry plum $3.46 $0.36 $0.45 $1.15 $1.19 $6.61 Japanese tree lilac $3.13 $0.33 $0.41 $1.03 $1.05 $5.95 Other street trees $23.43 $2.77 $3.92 $24.75 $23.57 $

15 Table 11. s for Five Benefit Categories and Grand for Bellbrook Street Tree Benefits Benefits ($) $/tree $/capita CO2 $1,749 $3.24 $0.25 Air Quality $2,540 $4.70 $0.36 Aesthetic/Other $15,457 $28.62 $2.21 Storm water $15,535 $28.77 $2.22 Energy $15,600 $28.89 $2.23 Benefits $50,881 $94.22 $7.26 This is a savings in benefits of $7.26 per person in Bellbrook for street trees alone 15