Urban Forest Resource Analysis

Transcription

1 City of Elko, Nevada Urban Forest Resource Analysis

2 City of Elko, Nevada Urban Forest Resource Analysis Prepared for: City of Elko 1751 College Avenue Elko, NV (775) Prepared by: Davey Resource Group A Division of The Davey Tree Expert Company 7627 Morro Road Atascadero, California Phone: (805) Toll Free: (800) Fax: (805) Acknowledgements Funding for this project was provided by the Nevada Division of Forestry, Urban and Community Forestry Program and The USDA Forest Service, with support from the City of Elko. The United States Department of Agriculture (USDA) prohibits discrimination in all of its programs and activities on the basis of race, color, national origin, gender, religion, age, disability, political beliefs, sexual orientation, and marital or familial status religion. Not all prohibited based apply to all programs. Persons with disabilities who require alternative means for communication of program information such as Braille, Large print, or audio tape should contact USDA s TARGET center at (202) for voice and TDD. To file a complaint of discrimination, either write to the USDA, Director of Office of Civil Rights, Room 326-W, Whitten Building, 14 th and Independence Avenue SW, Washington DC or call (202) for voice and TDD. USDA is an equal opportunity provider and employer. While the specific reports and recommendations can be attributed to this study, the basis for its structure and written content comes from the entire series of Municipal Forest Resource Analysis reports prepared and published by the USDA Forest Service, Pacific Southwest Research Station, Center for Urban Forest Research, and credit should be given to those authors. The Municipal Forest Resource Analysis Reports are companions to the regional Tree Guides and i-tree s STRATUM application developed by the USDA Forest Service, Pacific Southwest Research Station, Center for Urban Forest Research.

3 Table of Contents Table of Contents... i Executive Summary... 1 Introduction... 2 Chapter 1: Urban Forest Resource Summary... 4 Summary of Urban Forest Resource Structure... 4 Summary of Urban Forest Benefits... 4 Urban Forest Resource Management... 5 Chapter 2: Elko s Urban Forest Resource... 7 Population Composition... 7 Species Richness and Composition... 8 Species Importance Relative Age Distribution Urban Forest Condition and Relative Performance Replacement Value Chapter 3: Urban Forest Resource Benefits Energy Savings Electricity and Natural Gas Reduction Atmospheric Carbon Dioxide Reduction Sequestered Carbon Dioxide Air Quality Improvement Deposition and Interception Avoided Pollutants BVOC Emissions Net Air Quality Improvement Stormwater Runoff Reductions Aesthetic, Property Value and Socioeconomic Benefits Combined Public Tree Benefits Net Benefits and Benefit-Investment Ratio (BIR) Conclusion Appendix A: Methods and Procedures Appendix B: References Appendix C: Reports City of Elko, Urban Forest Resource Analysis i

4 Figures Figure 1. Composition of Elko s Public Tree Population... 7 Figure 2. Species Frequency in Elko s Public Tree Population... 8 Figure 3. Overall Relative Age Distribution of Elko s Public Tree Inventory Figure 4. Relative Age Distribution of Elko s Top Ten Public Tree Species Figure 5. Overall Condition of Elko s Public Trees Figure 6. Annual Electricity and Natural Gas Benefits - Top 5 Species Figure 7. Annual Reduction of CO2 - Top 5 species Figure 8. Annual Improvement to Air Quality - Top 5 Species Figure 9. Annual Reduction in Stormwater Runoff - Top 5 Species Figure 10. Annual Increase in Property and Socioeconomic Values - Top 5 Species Figure 11. Summary of Annual per Tree Benefits from Elko s Most Prevalent Public Tree Species Tables Table 1. Population Summary of Elko s Public Tree Inventory... 9 Table 2. Importance Value (IV) of Elko s Most Abundant Public Tree Species Table 3. Relative Performance Index (RPI) for Elko s Most Abundant Public Tree Species Table 4. Tree species which may be underutilized, based on RPI and relative age distribution. 16 Table 5. Replacement Value of Elko s Most Common Public Tree Species Table 6. Annual Electric and Natural Gas Benefits from Elko s Public Tree Resource Table 7. Annual CO2 Reduction Benefits Provided by Elko s Public Tree Resource Table 8. Annual Air Quality Improvements Provided by Elko s Public Tree Resource Table 9. Annual Stormwater Runoff Reduction Benefits Provided by Elko s Public Tree Resource Table 10. Annual Property Value, Aesthetic, and Socioeconomic Benefits of Elko s Public Tree Resource Table 11. Summary of Average Current Annual per Tree Benefits from Elko s Public Tree Resource Table 12. Average Annual Benefits by Species from Elko s Public Tree Resource Table 13. Benefit Versus Investment Summary for Elko s Public Tree Resource Table 14. Elko Benefit Prices Used In This Analysis City of Elko, Urban Forest Resource Analysis ii

5 Executive Summary Trees play a vital role in the community of Elko, Nevada, providing cooling shade, energy savings, and aesthetic benefits, to residents and visitors. In an effort to quantify these benefits, managers recently requested an inventory and resource analysis to determine the health, condition and location of public trees, and quantify their benefits. The inventory, conducted in early 2012 by the Davey Resource Group (DRG), identified trees in cemeteries, in parks, and at some city facilities. Trees on private property and streets were not included, so it is important to note this analysis represents just a portion of Elko s community forest. The inventory included a brief inspection by a Certified Arborist who recorded information including species, size, condition, and current maintenance needs, as well as the geographic location of 2,195 trees. Upon completion of the inventory, DRG developed this analysis of the current structure, function, and value of this tree resource using the inventory data in conjunction with i-tree benefit-cost modeling software. This resource analysis found several positive attributes of Elko s public tree resource. It is a relatively young to middle aged population, so many of the problems associated with age and decline are yet to be experienced citywide. With adequate maintenance, as young, largestature trees mature, they will provide increasing benefits with every growing season. Furthermore, species diversity is high, with more than 56 different species, and distribution is nearly ideal, with only one greatly over represented species (Siberian elm). The analysis determined that Elko s public tree population is a cost-effective resource that provides annual benefits of $285,273 ($14.85 per capita). These benefits include energy savings, air quality improvements, stormwater interception, atmospheric CO 2 reduction, and aesthetic contributions to the social and economic health of the community. Considering the annual investment of $16,350 ($0.85 per capita) to provide care for this resource, the community realizes an overall net benefit of $268,923. The bottom line is that for every $1 spent on public trees, the community of Elko receives $17.45 in benefits. Elko s public urban forest is reducing annual electric energy consumption by 265 megawatt hours (MWh) and annual natural gas consumption by 21,372 therms, for a combined value of $44, annually. In addition, these trees are removing 0.8 of a ton of pollutants from the air, including ozone (O 3 ), nitrogen dioxide (NO 2 ), and particulates (PM 10 ) for an overall annual air quality benefit of $5,078. Canopy from this population is reducing annual stormwater runoff volume by 7.9 million gallons, protecting local water resources by reducing sediment and pollution loading. City of Elko, Urban Forest Resource Analysis 1

6 Introduction Elko s urban forest plays an important role in the community s quality of life. Research has demonstrated that healthy urban trees can improve the local environment and lessen the impact resulting from urbanization and industry (CUFR). Trees improve air quality by manufacturing oxygen and absorbing carbon dioxide (CO 2 ), as well as filtering and reducing airborne particulate matter such as smoke and dust. Urban trees reduce energy consumption by shading structures from solar energy and reducing the overall rise in temperature created through urban heat island effects (EPA). Trees slow and reduce stormwater runoff, helping to protect critical waterways from excess pollutants and particulates, and damaging heavy flows. In addition, urban trees provide critical habitat for wildlife and promote a connection to the natural world. In addition to these direct improvements, healthy urban trees increase the overall attractiveness of a community and have been proven to increase the value of local real estate by 7 to 10%, as well as promoting shopping, retail sales, and tourism (Wolf, 2007). Trees support a more livable community, fostering psychological health and providing residents with a greater sense of place (Ulrich, 1986; Kaplan, 1989). Community trees, both public and private, soften the urban hardscape by providing a green sanctuary and making Elko a more enjoyable place to live, work, and play. The City s 2,195 public trees play a prominent role in the urban forest benefits afforded to the community and the citizens rely on the City of Elko to protect and maintain this vital resource. In 2012, an ISA Certified Arborist mapped the location of a portion of the publicly owned trees on City owned properties using global positioning system (GPS) technology. The resulting inventory data will be maintained by the City's tree maintenance staff using TreeKeeper 7.7, a software management system developed by Davey to provide accurate and dependable inventory data specific to tree characteristics, health, and maintenance performed. In addition to location, DRG arborists collected information about the species, size, condition, and current maintenance needs of each tree. The collected data was used in conjunction with i-tree Streets, a Street Tree Resource Assessment Tool for Urban forest Managers (STRATUM) Analysis Tool (Streets v5.0.0; i-tree v5.0.5), to develop a resource analysis and report of the current condition of the urban forest. This report, unique to Elko, effectively quantifies the value of the community s public trees in regards to actual benefits derived from the tree resource. In addition, the report provides baseline values that can be used when developing and updating an urban forest management plan. This helps in determining where to focus available resources and setting benchmarks for measuring progress. With this data, managers can strategically allocate scarce resources and staff time. This resource analysis provides additional information beyond the inventory to quantify the benefits trees provide. This may help to support an understanding of the need for additional funding to maintain the city s valuable tree resource. Information about the composition, health, and age of the urban forest can inform ordinance and policy development by identifying opportunities for growth, possible regulation and needs for more regular scheduling of tree maintenance. The purpose of the urban forest resource analysis and report is to provide information on the structure, function, and value of a specific tree resource at one point in time. From this City of Elko, Urban Forest Resource Analysis 2

7 information, managers and citizens alike can make informed decisions about budgetary support and management priorities. This report provides the following information: A description of the current structure of Elko s public tree resource and an established benchmark for future management decisions. Current, detailed management expenditures for a portion of Elko s publicly managed trees and critical baseline information for evaluating program efficiency. A quantified value of the environmental benefits provided by Elko s public trees illustrating the relevance and relationship of the resource to local quality of life issues such as air quality, environmental health, economic development, and psychological health. Data that may be used by resource managers in the pursuit of additional funding sources and collaborative relationships with utility purveyors, non-governmental organizations, air quality districts, federal and state agencies, legislative initiatives, or local assessment fees. Benchmark data that can be used in the development of a long-term urban forest management plan. City of Elko, Urban Forest Resource Analysis 3

8 Chapter 1: Urban Forest Resource Summary Summary of Urban Forest Resource Structure The City of Elko s urban forest resource currently includes 2,195 publicly managed trees. A structural analysis is the first step towards understanding the benefits provided by these trees as well as their management needs. Upon examination of species composition, diversity, age distribution, condition, canopy coverage, and replacement value, DRG determined that the following information characterizes Elko s public tree resource: More than 56 distinct tree species were identified in the inventory. The most predominant tree species is Siberian elm (Ulmus pumila, 28%) The age structure of Elko s public tree population is generally young, with 50% of trees measuring between 0 to 12 inches DBH (diameter at breast height, measured at 4 6 above the ground) and 57% under 18 DBH. A few species population distributions are weighted toward larger, older trees. For example, 86.5% of Siberian elms are over 18 DBH, and three other top species are greater than 50% over 18 DBH. Elko s trees were determined to be equally in good or fair condition (about 42% in each category). Maintaining the condition of existing trees for as long as possible will increase their useful lifespan and promote a steady flow of benefits to the community. Replacement of Elko s 2,195 public trees with trees of similar size, species, and condition would cost more than $13.7 million. Elko s public tree population has sequestered 9,464 tons of carbon (CO 2 ), valued at approximately $141,957. Replacement of Elko s 2,195 public trees with trees of similar size, species, and condition would cost more than $13.7 million. Summary of Urban Forest Benefits Annually, Elko s inventoried trees provide cumulative benefits to the community at an average value of $ per tree, for a total gross value of $285,273 per year. The City s trees are providing the following substantial annual benefits: Public trees reduce electricity and natural gas use in Elko through shading and climate effects; a benefit totaling $44,800, an average of $20.41 per tree. The inventoried trees in Elko currently sequester 220 tons of atmospheric CO 2 per year. An additional 293 tons is avoided through decreased energy use, resulting in a net value of $6,790 and an average of $3.09 per tree. Net air quality improvements provided by the inventoried tree population through the removal and avoidance of air pollutants are valued at $5,078, an average per tree benefit of $2.31. Elko s inventoried trees intercept an estimated 7.9 million gallons of stormwater annually for a total value of $85,640 per year, an average of $39.02 per tree. City of Elko, Urban Forest Resource Analysis 4

9 The total annual benefits contributed by Elko s public trees to property value increases, aesthetics, and socioeconomic value are more than $142,965, an average of $63.13 per tree. When the City s annual investment of $16,350 for maintenance of this urban forest resource is considered, the annual net benefit (benefits minus investment) to the City is $268,923. The average net benefit for an individual public tree in Elko is $ per year. In other words, Elko receives $17.45 in benefits for every $1 spent on the public tree population. Urban Forest Resource Management Elko s public tree population is a dynamic resource that is worth increased investment to maintain and extend its full benefit potential. The community forest is one of the few assets that has the potential to increase in value with time and proper management. Appropriate and timely tree care can substantially increase lifespan, preserving the higher benefit stream that results from a mature community forest. As individual trees continue to mature, and aging trees are replaced, stocking levels can increase. This can increase the overall value of the community forest and the amount of benefits provided. This vital, living resource is, however, vulnerable to a host of stressors and requires ecologically sound and sustainable best management practices to ensure a continued flow of benefits for future generations. With the benefit of a relatively young urban forest in fair to good condition, Elko can focus resources on maximizing the flow of benefits from the current healthy tree population, and work towards reducing the proportion of fair, poor, critical, and dead trees through a more proactive maintenance program. Based on the resource analysis, Davey Resource Group recommends the following: When trees are removed, or new tree sites are identified, focus on planting largestature trees where conditions are sustainable to maximize benefits. Maintain an appropriate age distribution by planting new trees to improve long-term resource sustainability and greater canopy coverage. Maximize the benefits of the existing tree resource through comprehensive tree maintenance and a cyclical pruning schedule. Implement a structural pruning program for young and establishing trees to promote healthy structure, extend life expectancy, and reduce future costs and liability. The value of Elko s public tree resource may increase as existing trees mature and new trees are planted. As the resource grows, continued investment in management is critical in ensuring that residents will continue receiving a high return on investment in the future. It is not as simple as planting more trees to increase canopy cover and benefits. Planning and funding for tree care and tree management must complement planting efforts in order to ensure the long-term success and health of Elko s urban forest. Existing mature trees should be maintained and protected whenever possible, since the greatest benefits accrue from the continued growth and longevity of the existing canopy. Elko can take pride in knowing that street trees improve the quality of life in the city and that trees are well worth the investment. This urban forest resource analysis and report, based on the current inventory status, defines the population and structure of Elko s public urban forest and quantifies the benefits of that City of Elko, Urban Forest Resource Analysis 5

10 resource. The analysis focuses solely on publicly owned, City-managed trees in parks, and City facilities, using i-tree Streets to establish baseline information on the value to the community. This report and the included analysis, which is unique to Elko, effectively estimates and quantifies the value of these public tree assets in regards to actual benefits derived from this resource. In addition, the report provides a baseline analysis that can be used when creating, implementing, and updating an urban forest management plan, determining where best to focus available resources and setting benchmarks for measuring progress. An urban forest resource analysis provides information on the structure, function, and value of the urban forest and its assets so that forest managers and citizens alike can make informed decisions about budgetary support and management priorities. This report provides the following information: A description of the current structure of Elko s public urban forest resources, establishing a benchmark for future management decisions. Current, detailed management expenditures for Elko s public trees and critical baseline information for evaluating program efficiency. A quantified value of the environmental benefits provided by Elko s public urban forest, illustrating the relevance and relationship of the resource to local quality of life issues, such as air quality and environmental health, economic development, and psychological health. Quantified data that may be used by forest resource managers in the pursuit of alternative funding sources and collaborative relationships with utility managers, non-profit organizations, air quality districts, federal and state agencies, legislative initiatives, and/or in establishing or updating local assessment fees. Benchmark data that can be used in the development of a long-term urban and community forest management plan. For every $1 invested in public trees, Elko receives $17.45 in benefits City of Elko, Urban Forest Resource Analysis 6

11 Chapter 2: Elko s Urban Forest Resource Population Composition Broadleaf hardwood species dominate Elko s tree population, comprising 69% of the total inventory. Broadleaf trees typically have larger canopies than coniferous trees of the same size DBH. Since many of the measurable benefits derived from trees are directly related to leaf surface area in the canopy, broadleaf trees generally provide the highest level of benefits to a community. Larger-statured broadleaf tree species provide greater benefits than smallerstatured trees, independent of diameter (DBH). Deciduous broadleaf species make up 69% of Elko s public tree population, including 51% large-stature, 2% medium-stature, and 16% small-stature trees. Elko does not have any evergreen broadleaf trees recorded in its inventory. Large-stature conifers represent 14% of the overall population, 13% mediumstature, and 4% small-stature trees (Figure 1). Conifer Evergreen Medium 13% Conifer Evergreen Small 4% Conifer Evergreen Large 14% Broadleaf Deciduous Large 51% Broadleaf Deciduous Small 16% Broadleaf Deciduous Medium 2% Figure 1. Composition of Elko s Public Tree Population City of Elko, Urban Forest Resource Analysis 7

12 Species Richness and Composition Elko s public tree population includes a mix of more than 56 unique species, slightly more than that of the mean of 53 species reported by McPherson and Rowntree (1989) in their nationwide survey of street tree populations in 22 U.S. cities. The top ten species represent 85% of the total population (Figure 2 and Table 1). There is a widely accepted rule that no single species should represent greater than 10% of the total population, while no single genus more than 20% (Clark Et al, 1997). Siberian elm is the greatest overrepresented species (28%), while blue spruce (13%) and Austrian pine (10%) are at the threshold. A complete population summary can be found in Appendix C. Siberian elm 27.9% Blue spruce Austrian pine Green ash 10.4% 9.6% 12.8% Crabapple 7.0% Russian olive Honeylocust Common chokecherry Juniper Scotch pine 4.5% 3.7% 3.5% 3.5% 1.8% Other species 15.4% % of Population Figure 2. Species Frequency in Elko s Public Tree Population Maintaining a diverse population within an urban forest is important. Dominance of any single species or genus can have detrimental consequences in the event of storms, drought, disease, pests, or other stressors that can severely affect an urban forest and the flow of benefits and costs over time. Catastrophic pathogens, such as Dutch Elm Disease (Ophiostoma ulmi), Emerald Ash Borer (Agrilus planipennis), Asian Longhorned Beetle (Anoplophora glabripennis), and Sudden Oak Death (SOD) (Phytophthora ramorum) are some examples of unexpected, devastating, and costly pests and pathogens that highlight the importance of diversity and the balanced distribution of species and genera. City of Elko, Urban Forest Resource Analysis 8

13 Species DBH Class (in) >42 Total Broadleaf Deciduous Large (BDL) Siberian elm Green ash Honeylocust Eastern cottonwood Elm BDL OTHER Total ,122 Broadleaf Deciduous Medium (BDM) BDM OTHER Total Broadleaf Deciduous Small (BDS) Crabapple Russian olive Common chokecherry BDS OTHER Total Conifer Evergreen Large (CEL) Blue spruce CEL OTHER Total Conifer Evergreen Medium (CEM) Austrian pine Scotch pine CEM OTHER Total Conifer Evergreen Small (CES) Juniper CES OTHER Total Citywide Total ,195 Table 1. Population Summary of Elko s Public Tree Inventory City of Elko, Urban Forest Resource Analysis 9

14 Species Importance To quantify the significance of any one particular species found in Elko s public tree population, an importance value (IV) is derived for each of the most common species in the inventory. Importance values are particularly meaningful to urban forest managers because they indicate a community s reliance on the functional capacity of particular species. The importance value is calculated based on the mean of three values: percentage of total population, percentage of total leaf area, and percentage of total canopy cover. Importance value goes beyond tree numbers alone to suggest reliance on specific species based on the benefits they provide. The importance value can range from zero (which implies no reliance) to 100 (suggesting total reliance). No single species should dominate the composition in the City s urban forest population. Because importance value goes beyond population numbers alone, it can help managers to better comprehend the resulting loss of benefits from a catastrophic loss of any one species. When importance values are comparatively equal among the ten to 15 most abundant species, the risk of major reductions to benefits is significantly reduced. Of course, suitability of the dominant species is another important consideration. Planting short-lived or poorly adapted species can result in short rotations and increased long-term management costs. The twelve most abundant species, those that comprise greater than 1% of the population, represent 87% of the total population, 92% of the total leaf area, and 85% of the inventoried tree canopy cover for a combined importance value of 83.6 (Table 2). Of these species, Elko relies most on the Siberian elm (Ulmus pumila, IV=54), followed by blue spruce (Picea pungens, IV=11). Table 2. Importance Value (IV) of Elko s Most Abundant Public Tree Species Species Number of Trees % of Total Trees Leaf Area (ft2) % of Total Leaf Area Canopy Cover (ft2) % of Total Canopy Cover Importance Value Siberian elm ,751, ,388, Blue spruce ,475, , Austrian pine , , Green ash , , Crabapple , , Russian olive , , Honeylocust , , Juniper , , Common chokecherry , , Scotch pine , , Eastern cottonwood , , Elm , , Other species , , Total 2, % 11,644, ,092, % 100% City of Elko, Urban Forest Resource Analysis 10

15 Due to their relatively small leaf area and canopy coverage, immature and small-stature trees tend to have lower importance values than their population numbers might suggest. Consideration of tree type along with age distribution can provide additional significance to the importance value. One prevalent species, crabapple (Malus spp.), which represents 7% of the population, with an importance value of only 2.7, will never achieve a more significant importance value in the overall population due to its smaller stature. Relative Age Distribution The distribution of individual tree ages within a tree population influences present and future costs as well as the flow of benefits. An unevenly aged population allows managers to allocate annual maintenance costs uniformly over many years and assures continuity in overall tree canopy coverage and associated benefits. A desirable distribution has a high proportion of young trees to offset establishment and age related mortality as the percentage of older trees declines over time (Richards, 1982/83). This ideal, albeit uneven, distribution suggests a large fraction of trees (+/-40% of the total) should be young with diameters at breast height (DBH) less than eight inches, while only 10% should be in the large diameter classes (>24 inches). Generally, the age distribution of Elko s public tree population is weighted in young trees, with 50% of the population consisting of trees with a DBH (diameter at breast height) of twelve inches or smaller. However, trees greater than 36 inches DBH make up 19% of the overall population. This leaves a deficiency in the mid-range sized trees from the ideal distribution (Figure 3). With a relatively young urban forest and continued proactive management, Elko can expect greater benefits as this vital resource matures. New installations should carefully consider species selection, increasing the use of underutilized and well-performing species, and account for mortality of overmature, large diameter trees. In addition to planting, it is critical that long-term resources be dedicated to ensuring proper maintenance as trees mature. A long-term, sustainable management plan, including regular inspection and reasonable pruning cycles, can ensure Elko s urban forest remains healthy and well-structured, thereby maximizing environmental services to the community, reducing risk, and promoting a consistent flow of benefits for many generations to come. City of Elko, Urban Forest Resource Analysis 11

16 All Trees Ideal % DBH Class Figure 3. Overall Relative Age Distribution of Elko s Public Tree Inventory Of Elko s top ten public tree species (Figure 4), Austrian pine and honeylocust are young populations with 63% and 62% of their populations under 6 DBH respectively. This indicates those species may have been favored in recent plantings, or that there are environmental factors causing these species to remain small. Ninety three percent of common chokecherry and ninety one percent of crabapple are under 6 DBH, but because these are small stature trees, reaching a maximum height of 30, the DBH class is not a clear indicator of the age class of these species. Considering large and medium stature trees, Russian olive and Scotch pine are well represented in the 6-24 DBH classes, with 54% and 43% respectively falling into this medium DBH category. These species may have been prevalent in past planting palettes, but have not been as prevalent in recent plantings. In areas of the city where these species are performing well, they may be considered for future planting. Considering large and medium-statured trees, blue spruce and Siberian elm have significant representation in the DBH classes over 24, with 51% of blue spruce and 80% of Siberian elm in this older, established cohort. These two species are the top two most numerous in the City, together representing about 41% of the citywide tree population, and their age, stature, and leaf area make them important contributors to the urban forest benefit stream. These mature populations are critical contributors to the urban forest benefit stream as indicated by their high species importance values (blue spruce 11.4, Siberian elm 53.6). While 91% of blue spruce are rated as good or fair, nearly 20% of Siberian elm are poor, dead or dying. These older populations should be monitored to determine whether some individuals are coming to the end of their useful lives. It is important to keep in mind that, as populations mature and eventually begin to senesce, their maintenance needs are likely to become more substantial. Future plantings should adequately represent long-standing and high-performing species, making sure to provide sufficient replacements to ensure the functional capacity and benefit streams from these populations, even as individuals begin to decline. City of Elko, Urban Forest Resource Analysis 12

17 % Ideal Austrian pine Blue spruce Common chokecherry Crabapple Green ash DBH Class % Ideal Honeylocust Juniper Russian olive Scotch pine Siberian elm 10 0 DBH Class Figure 4. Relative Age Distribution of Elko s Top Ten Public Tree Species City of Elko, Urban Forest Resource Analysis 13

18 Urban Forest Condition and Relative Performance Tree condition is an indication of how well trees are managed and how well they are performing in a given site-specific environment (e.g., street median, parking lot, etc.). Each inventoried tree was rated for overall condition, including consideration for structure, foliage, and the root collar. When trees are performing at their peak, as are 42% of Elko s trees, the benefits they provide are maximized. The inventory found 41% of Elko s trees in fair condition, which may be an indication of age, inadequate resources or maintenance, and/or a poorly sited species, along with many other factors. Seventeen percent (17%) of the Good 42% Poor 14% Fair 41% Dead or Dying 3% Figure 5. Overall Condition of Elko s Public Trees population was found to be in poor, critical, or dead condition. Removal or mitigation of dead and failing trees is recommended as soon as possible to reduce liability exposure. The relative performance index (RPI) is one way to further analyze the condition and suitability of specific tree species. The RPI provides an urban forest manager with a detailed perspective on how one species performance compares to that of another. The index compares the condition ratings of each tree species with the condition ratings of every other tree species within a given urban forest population. An RPI value of 1.0 or better indicates that the species is performing as well or better than average when compared to other species. An RPI value below 1.0 indicates that the species is not performing as well in comparison to the rest of the population. RPI is most useful when applied to relatively large populations of species with widely distributed DBH classes. In small, very old or very young populations, species performance can be difficult to extrapolate citywide. Eleven species have populations greater than 1% of the total citywide population. Among these 11 species, eight are performing above average, and three are below average. Chinese pistache (Pistacia chinensis) and crapemyrtle (Lagerstroemia indica) have the highest RPIs (1.14 and 1.15 respectively), followed by camphor (1.09) Southern magnolia (1.09) Northern red oak (1.07), and red maple (1.04). Elko s third most prevalent tree species, Austrian pine (Pinus nigra) has an RPI value of 1.2, also the third highest RPI of the population. The species age classes are generally young, with 73% of the population under 12 DBH. This species is a great asset to the urban forest with 79% of the population rated as good; however it is on the verge of over-representation in the population, so despite its high performance, future planting strategies should include less reliance on this species. City of Elko, Urban Forest Resource Analysis 14

19 Siberian elm (Ulmus pumila) represent 28% of the population and 80% of those trees are mature with DBHs over 24. Their RPI is the second lowest of the top 11 species (0.85), followed by the closely related, Russian olive (Elaengus angustifolia, RPI 0.72, 4.46% of the citywide tree population). These populations will require increased maintenance and removal as they decline. Species Good Fair Poor Dead or Dying City of Elko, Urban Forest Resource Analysis 15 RPI % of All Trees Juniper Eastern cottonwood Austrian pine Scotch pine Green ash Blue spruce Crabapple Honeylocust Common chokecherry Siberian elm Russian olive All trees % Table 3. Relative Performance Index (RPI) for Elko s Most Abundant Public Tree Species The RPI can be a useful tool for urban forestry managers. For example, if a city has been planting new species in their urban forest, the RPI can be utilized to compare their relative performance. If the RPI indicates that one is performing relatively poorly, a municipality may decide to reduce or even stop planting that species and subsequently save money on both planting stock and replacement costs. The RPI enables managers to look at the performance of long-standing species as well. Species planted for many years that have an RPI of 1.00 or greater have performed well when compared to the population as a whole. These top performers should be retained as a significant portion of the urban forest population. It is important to keep in mind that because RPI is based on condition, it may not reflect cosmetic or nuisance issues, especially seasonal issues that are not threatening the health or structure of the trees. An RPI value less than 1.00 may be indicative of a species that is not well adapted to local conditions. Poorly adapted species are more likely to present increased safety and maintenance issues. Species with an RPI less than 1.00 should receive careful consideration before being selected for future planting choices. Prior to selecting or deselecting trees on the basis of RPI alone, managers are encouraged to take into account the age distribution of the species, among other factors. A species that has a RPI of less than 1.00, but has a significant number of trees in larger DBH classes, may just be exhibiting signs of population senescence. The individuals of this species may have produced substantial benefits over the years and should continue to be considered when making species selection determinations for future planting. The RPI value can also be used to identify underutilized species that are demonstrating good performance. Trees with an RPI value greater than 1.00 and a reasonably wide DBH distribution may be very suitable in the local environment and should receive consideration for additional planting (Table 4). To establish additional possibly underutilized species, managers should find populations that have at least 20 individuals with representation in young and medium age

20 classes, and check for an RPI over If such a population is found, it may indicate that the species performs well. It is not as useful to look at the RPI of even-aged, or very small populations, because good or bad performance may be more related to the environmental factors or age, and not truly reflect the fitness of the species itself. Based on RPI, relative age distribution, and percentage in the population, the following species may be underused in Elko s urban forest: Table 4. Tree species which may be underutilized, based on RPI and relative age distribution Species RPI # of Trees % of All Trees Conifer Evergreen Large Scotch pine % Broadleaf Deciduous Large Eastern cottonwood % Replacement Value The current value of Elko s public tree resource is approximately $13.7 million. The community forest is a public asset which, when properly cared for, has the potential to appreciate in value as the trees mature over time. Replacement value accounts for the historical investment in trees over their lifetime and is a way of describing the value of a tree population (and/or average value per tree) at a given time. Replacement value is a reflection of current population numbers, stature, placement, and condition. There are several methods available for obtaining a fair and reasonable perception of a tree s value (CTLA, 1992; Watson, 2002). The cost approach, trunk formula method used in this analysis assumes the value of a tree is equal to the cost of replacing the tree in its current state (Cullen, 2002). To replace Elko s current public tree population of 2,195 trees with trees of similar size, species, and condition would cost more than $13.7 million (Table 5 and Appendix C). The average replacement value per tree is $6,257. The population of Siberian elm (Ulmus pumila) accounts for 28% ($7.2 million) of the tree resource s replacement value, followed by blue spruce (Picea pungens, 13%, $2.9 million. The high value of each of these species reinforces their importance to the City. Many of the highest valued species are large and medium-stature trees with large canopies and are therefore likely to have high Importance Values (IV) as well. Species with lower replacement values are generally smaller-stature trees with a lower IV, as evidenced by crabapple (Malus spp.) with a replacement value of $70,272 (0.5%), despite its relative prevalence in the population (7%). Elko s urban forest is a vital component of the City s infrastructure and a public asset valued at approximately $13.7 million an asset that, with proper care and maintenance, will increase in value over time. Distinguishing replacement value from the value of annual benefits produced by Elko s public trees is very important. Annual benefits are discussed in Chapter 3. City of Elko, Urban Forest Resource Analysis 16

21 Table 5. Replacement Value of Elko s Most Common Public Tree Species DBH Class (in) Species % of % of >42 Total Pop. Total Siberian elm 1, , , , , , ,157, ,458, ,732, ,222, Blue spruce 7, , , , , , ,018, , , ,888, Austrian pine 12, , , , , , , , , , Green ash 40, , , , , , , Crabapple 21, , , , , , Russian olive 1, , , , , , , , , , Honeylocust 5, , , , , , , Juniper 5, , , , , , , , Common chokecherry 6, , , , Scotch pine , , , , , , , , , Eastern cottonwood , , , , , , , , , Elm 2, , , , , , Other species 22, , , , , , , , , , All trees $128, $125, $212, $486, $746, $1,747, $2,781, $2,694, $4,810, $13,733, % 100% City of Elko, Urban Forest Resource Analysis 17

22 Chapter 3: Urban Forest Resource Benefits Trees are important to Elko. Environmentally, they help conserve and reduce energy use, reduce local and global carbon dioxide (CO 2 ) levels, improve air quality, and mitigate stormwater runoff. Additionally, trees provide a wealth of well-documented psychological, social, and economic benefits related primarily to their aesthetic effects. Environmentally, trees make good sense, working ceaselessly to provide benefits back to the community. However, the question remains: are the collective benefits worth the costs of management? In other words, are trees a good investment for the City of Elko? To answer this question, the benefits must be quantified in financial terms. This analysis provides a snapshot of the annual benefits (along with the value of those benefits) produced by Elko s public urban forest. While the annual benefits produced by the urban forest can be substantial, it's important to recognize that the greatest benefits from the urban forest are derived from the benefit stream that results over a greater period of time from a mature forest where trees are well managed, healthy, and long-lived. This analysis utilized Elko s current public tree inventory and i-tree s Streets model to assess and quantify the beneficial functions of this public tree resource and to place a dollar value on the annual environmental benefits these trees provide. These estimates provide first-order approximations of tree value. While i-tree Streets only generally accounts for the benefits produced by Elko s public tree population, it is an accounting based on the best available and current scientific research with an accepted degree of uncertainty. The data returned from i-tree Streets provides a platform from which management decisions can be made (Maco and McPherson, 2003). A discussion on the methods used to quantify and put a monetary value on these benefits can be found in Appendix A. Energy Savings Trees modify climate and conserve energy in three principal ways: Shading reduces the amount of radiant energy absorbed and stored by hardscape surfaces, thereby reducing the heat island effect. Transpiration converts moisture to water vapor, thereby cooling the air by using solar energy that would otherwise result in heating of the air. Reduction of wind speed and the movement of outside air into interior spaces and conductive heat loss where thermal conductivity is relatively high (e.g., glass windows) (Simpson, 1998). Heat island effect describes the increase in urban temperatures in relation to surrounding locations and is associated with an increase in hardscape and impervious surfaces. Trees and other vegetation within an urbanized environment help reduce the heat island effect by lowering air temperatures 5 F (3 C) compared with outside the green space (Chandler, 1965). On a larger citywide scale, temperature differences of more than 9 F (5 C) have been observed between city centers without adequate canopy coverage and more vegetated suburban areas (Akbari and others, 1992). The relative importance of these effects depends upon the size and configuration of trees and other landscape elements (McPherson, 1993). Tree spacing, crown spread, and vertical distribution of leaf area each influence the transport of warm air and pollutants along streets and out of urban canyons. City of Clovis, Urban Forest Resource Analysis 18 April 2011

23 By reducing air movement into buildings and against conductive surfaces (e.g., glass, metal siding), trees reduce conductive heat loss from buildings. Trees can reduce wind speed and the resulting air infiltration by up to 50%, translating into potential annual heating savings of 25% (Heisler, 1986). Electricity and Natural Gas Reduction Electricity and natural gas saved annually in Elko from both the shading and climate effects of public trees is equal to 265 MWh ($26,776) and 21,372 therms ($18,023), for a total retail savings of approximately $44,800 and an average of $20.41 per tree (Table 6). Siberian elm (Ulmus pumila) provides 60% of the energy savings overall, due in part to its medium to large stature and large percent of the population (28%). Siberian elm also has the highest pertree average annual contribution of $43.57 (Figure 6). In contrast, crabapple (Malus spp.), the fifth most abundant public tree in Elko (7% of the total population), accounts for less than two percent of the total energy savings due to its small stature (Table 6). Siberian elm $43.57 Elm Eastern cottonwood Blue spruce $24.73 $29.94 $27.40 Russian olive $15.06 $0 $10 $20 $30 $40 $50 Figure 6. Annual Electricity and Natural Gas Benefits - Top 5 Species City of Clovis, Urban Forest Resource Analysis 19 April 2011

24 Species Total Electricity (MWh) Electricity ($) Total Natural Gas (Therms) Natural Gas ($) Total ($) % of Total Tree Numbers % of Total $ Avg. $/tree Siberian elm , , , , Blue spruce , , , , Austrian pine , Green ash , Crabapple Russian olive , Honeylocust Juniper Common chokecherry Scotch pine Eastern cottonwood Elm Other species , , , , All trees $26, , $18, $44, % 100% $20.41 Table 6. Annual Electric and Natural Gas Benefits from Elko s Public Tree Resource Atmospheric Carbon Dioxide Reduction As environmental awareness continues to increase, governments are paying particular attention to global warming and the effects of greenhouse gas emissions. Two national policy options are currently under debate, the establishment of a carbon tax and a greenhouse gas cap-and-trade system, aimed at the reduction of atmospheric carbon dioxide (CO 2 ) and other greenhouse gases. A carbon tax would place a tax burden on each unit of greenhouse gas emission and would require regulated entities to pay for their level of emissions. Alternatively, in a cap-and-trade system, an upper limit (or cap) is placed on global (federal, regional, or other jurisdiction) levels of greenhouse gas emissions and the regulated entities would be required to either reduce emissions to required limits or purchase emissions allowances in order to meet the cap (Williams and others, 2007). The concept of purchasing emission allowances (offsets) has led to the acceptance of carbon credits as a commodity that can be exchanged for financial gain. The Center for Urban Forest Research (CUFR, Pacific Southwest Research Station, and USDA Forest Service) recently led the development of Urban Forest Project Reporting Protocol. The protocol, which incorporates methods of the Kyoto Protocol and Voluntary Carbon Standard (VCS), establishes methods for calculating reductions, provides guidance for accounting and reporting, and guides urban forest managers in developing tree planting and stewardship projects that could be registered for greenhouse gas (GHG) reduction credits (offsets). The protocol can be applied to urban tree planting projects within municipalities, campuses, and utility service areas anywhere in the United States. City of Elko, Urban Forest Resource Analysis 20

25 While Elko s urban forest resource may or may not qualify for carbon offset credits or be traded in the open market, the City s public trees are nonetheless providing a significant reduction in atmospheric carbon dioxide (CO 2 ) for a positive environmental and financial benefit to the community. Urban trees reduce atmospheric carbon dioxide (CO 2 ) in two ways: Directly, through growth and the sequestration of CO 2 as wood and foliar biomass. Indirectly, by lowering the demand for heating and air conditioning, thereby reducing the emissions associated with electric power generation and natural gas consumption. Conversely, CO 2 is released by vehicles and other combustible engines used to plant and care for trees. Additionally, when a tree dies, most of the CO 2 that accumulated as woody biomass is released back into the atmosphere during decomposition, except in cases where the wood is recycled. Each of these factors must be considered when calculating the CO 2 reduction benefits of trees. Sequestered Carbon Dioxide To date, Elko s public urban forest has sequestered a total of 9,464 tons of carbon dioxide (CO 2 ) valued at $141, This calculation is based on the current living tree population, calculating the woody biomass and leaf volume of the tree resource. Annually, this tree resource directly sequesters 220 tons of CO 2, valued at $3,293, into woody and foliar biomass. Accounting for estimated CO 2 emissions from tree decomposition (45 tons), tree related maintenance activity (15 tons), and avoided CO 2 (293 tons), Elko s trees provide an annual net reduction in atmospheric CO 2 of 453 tons, valued at $6,790 with an average of $3.09 per tree (Table 7). Siberian elm (Ulmus pumila, $7.48), elm species (Ulmus spp., $3.61) and eastern cottonwood (Populus deltoides, $3.34) have the highest average value of carbon impact per tree (Figure 7). The population of Siberian elm (Ulmus pumila) is by far providing the largest proportion of total carbon sequestration value at 68% (Table 7). 1 Based on i-tree Streets default value of $15 per ton. Market value may vary. City of Elko, Urban Forest Resource Analysis 21

26 Siberian elm $7.48 Elm Eastern cottonwood Blue spruce Russian olive $3.61 $3.34 $2.80 $1.78 $0.00 $2.00 $4.00 $6.00 $8.00 Figure 7. Annual Reduction of CO2 - Top 5 species City of Elko, Urban Forest Resource Analysis 22

27 Species Sequestered (lb) Table 7. Annual CO2 Reduction Benefits Provided by Elko s Public Tree Resource Sequestered ($) Decomposition Release (lb) Maintenance Release (lb) Total Release ($) Avoided (lb) Avoided ($) Net Total (lb) Total ($) % of Total Tree Numbers % of Total $ Avg. $/tree Siberian elm 322, , , , , , , , Blue spruce 40, , , , , Austrian pine 7, , , , , Green ash 11, , , Crabapple 3, , , Russian olive 8, , , , , Honeylocust 7, , , Juniper , , Common chokecherry 2, , , Scotch pine 2, , , Eastern cottonwood 4, , , , Elm 4, , , , Other species 22, , , , , All trees 439, $3, , , $ , $4, , $6, % 100% $3.09 City of Elko, Urban Forest Resource Analysis 23

28 Air Quality Improvement Urban trees improve air quality in five fundamental ways: Absorption of gaseous pollutants such as ozone (O 3 ) and nitrogen dioxide (NO 2 ) through leaf surfaces, Interception of particulate matter (PM 10 ), such as dust, ash, dirt, pollen, and smoke, Reduction of emissions from power generation by reducing energy consumption, Increase of oxygen levels through photosynthesis, and Transpiration of water and shade provision, resulting in lower local air temperatures, thereby reducing ozone (O 3 ) levels. In the absence of cooling effects provided by trees, higher temperatures contribute to ozone (O 3 ) formation. Additionally, short-term increases in ozone concentrations have been statistically associated with increased tree mortality for 95 large US cities (Bell, 2004). However, it should be noted that while trees do a great deal to absorb air pollutants (especially ozone and particulate matter), they also negatively contribute to air pollution. Trees emit various biogenic volatile organic compounds (BVOCs), such as isoprenes and monoterpenes, which can also contribute to ozone formation. These BVOC emissions are accounted for by i-tree Streets in the air quality net benefit and summarized below and in Table 8. Deposition and Interception Each year, approximately 0.8 of a ton of nitrogen dioxide (NO 2 ), small particulate matter (PM 10 ), and ozone (O 3 ) are intercepted or absorbed by the public trees in Elko, for a value of $4,149 (Table 8). As a population, Siberian elm (Ulmus pumila, 1,160 lbs.) is the greatest contributor to air quality improvements, accounting for approximately 69% of total air quality benefits. Avoided Pollutants By reducing energy needs, the energy savings provided by trees have the additional indirect benefit of reducing air pollutant emissions (NO 2, PM 10, SO 2, and VOCs) that result from energy production. Altogether, 0.84 ton of pollutants, valued at $2,913, are avoided annually through the shading effects of Elko s public trees. The populations of Siberian elm (Ulmus pumila, 1,052 lbs.) and blue spruce (Picea pungens, 236 lbs.) provide a combined 77% of the total benefits and have the greatest impact on reducing energy needs and therefore avoiding the additional generation of pollutants. BVOC Emissions Biogenic volatile organic compound (BVOC) emissions from trees, which negatively affect air quality, must also be considered. Approximately 0.38 ton of BVOCs are emitted annually from Elko s public trees, offsetting the total air quality benefit by -$1,985. Blue spruce (Picea pungens) is dramatically the heaviest per tree emitter of BVOCs (555 lbs.), accounting for 73% of the total BVOC emissions, while representing only 13% of the total population. Blue spruce has a negative BVOC impact valued at -$5.17 per tree, and even City of Elko, Urban Forest Resource Analysis 24

29 when the positive air quality benefits are accounted for, the net air quality impact is still negative (-$2.13). Net Air Quality Improvement Net air pollutants removed, avoided, and released by Elko s public tree population are valued at $5,078 annually. The average net benefit per tree is $2.31. Trees vary dramatically in their ability to produce net air quality benefits. Typically, large-canopied trees with large leaf surface areas that are not high emitters of BVOCs produce the greatest benefits. On a per tree basis, Siberian elm (Ulmus pumila) and elm species (Ulmus spp.) currently produce the greatest per tree net air quality benefits ($7.52 and $5.39, respectively) followed by eastern cottonwood (Populus deltoides, $4.31) and Russian olive (Elaegus angustifolia, $3.02) (Figure 8). Siberian elm $7.62 Elm $5.39 Eastern cottonwood $4.31 Russian olive $3.02 Other species $1.22 $0.00 $2.00 $4.00 $6.00 $8.00 Figure 8. Annual Improvement to Air Quality - Top 5 Species City of Elko, Urban Forest Resource Analysis 25

30 Table 8. Annual Air Quality Improvements Provided by Elko s Public Tree Resource Species Deposition O3 (lb) Deposition NO2 (lb) Deposition PM10 (lb) Total Deposition ($) Avoided NO2 (lb) Avoided PM10 (lb) Avoided VOC (lb) Avoided SO2 (lb) Total Avoided ($) BVOC Emissions (lb) BVOC Emissions ($) Total (lb) Total ($) % of Total Tree Numbers Avg. $/tree Siberian elm , , , , Blue spruce , Austrian pine Green ash Crabapple Russian olive Honeylocust Juniper Common chokecherry Scotch pine Eastern cottonwood Elm Other species All trees 1, $4, $2, $1, , $5, % $2.31 City of Elko, Urban Forest Resource Analysis 26

31 Stormwater Runoff Reductions According to Federal Clean Water Act regulations, municipalities must obtain a permit for managing their stormwater discharges into water bodies. Each city s program must identify the best management practices (BMPs) it will implement to reduce its pollutant discharge. Rainfall interception by trees can reduce the amount of stormwater that enters collection and treatment facilities during large storm events. Trees intercept rainfall in their canopy, acting as mini-reservoirs, controlling runoff at the source. This is especially important in an urban setting with a significant quantity of impervious surfaces near a major waterway. Healthy urban trees can reduce the amount of runoff and pollutant loading in receiving waters in three primary ways: Leaves and branch surfaces intercept and store rainfall, thereby reducing runoff volumes and delaying the onset of peak flows. Root growth and decomposition increase the capacity and rate of soil infiltration by rainfall and reduce overland flow. Tree canopies reduce soil erosion and surface flows by diminishing the impact of raindrops on barren surfaces. Elko s public trees intercept 7.9 million gallons of stormwater annually for an average of 3,612 gallons per tree (Table 9). That amount of water would fill twelve Olympic-sized swimming pools. The total value of this benefit to the City is $85,640, an average of $39.02 per tree. Siberian elm (Ulmus pumila, 69%, $96.06/tree) provides the greatest per-tree benefits, while the population of blue spruce (Picea pungens, $49.28/tree) provides the second greatest portion of the total benefit, 16% (Table 9). Crabapple (Malus spp.) and common chokecherry (Prunus virginiana) provide the smallest stormwater benefits among the most prevalent 12 species, primarily due to their small stature (Table 9). Siberian elm $96.06 Blue spruce Scotch pine Elm Eastern cottonwood $49.28 $33.92 $32.02 $28.09 $0 $20 $40 $60 $80 $100 Figure 9. Annual Reduction in Stormwater Runoff - Top 5 Species City of Elko, Urban Forest Resource Analysis 27

32 Table 9. Annual Stormwater Runoff Reduction Benefits Provided by Elko s Public Tree Resource Species Total Rainfall Interception (Gal) Total ($) % of Total Tree Numbers % of Total $ Avg. $/tree Siberian elm 5,451, , Blue spruce 1,277, , Austrian pine 297, , Green ash 65, Crabapple 8, Russian olive 66, Honeylocust 63, Juniper 26, Common chokecherry 4, Scotch pine 125, , Eastern cottonwood 80, Elm 80, Other species 381, , All trees 7,929, $85, % 100% $39.02 Aesthetic, Property Value and Socioeconomic Benefits Trees provide beauty in the urban landscape, privacy to homeowners, improved human health, a sense of comfort and place, and habitat for urban wildlife. There is documented evidence that trees promote better business by stimulating more frequent and extended shopping and a willingness to pay more for goods and parking (Wolf, 1999). Some of these benefits may be captured as a percentage of the value of the property on which a tree stands. To determine the value of these less tangible benefits, i-tree Streets uses research that compares differences in sales prices of homes to estimate the contribution associated with trees. Differences in housing prices in relation to the presence (or lack) of a street tree help define the aesthetic value of street trees in the urban environment. Consideration is given to the location of the street tree in relation to the land use. Street trees located in front of multifamily homes will not increase the property value at the same rate as single-family homes. Furthermore, street trees located adjacent to commercial and nonresidential properties do not have the same resale potential as residential areas. These factors are taken into consideration and the value of those trees is adjusted accordingly. The calculation of annual aesthetic and other benefits corresponds with a tree s annual increase in leaf area. When a tree is actively growing, leaf area may increase dramatically. Once a tree is mature, there may be little or no net increase in leaf area from one year to the next; thus, there is little or no incremental annual aesthetic benefit for that year, although the cumulative benefit over the course of the entire life of the tree may be large. Since this report represents a one-year sample snapshot of the public tree population, aesthetic benefits reflect the increase in leaf area for each species population over the course of a single year. As a result, young populations which are actively growing will impact aesthetic values more than established or slow-growing species. The total annual benefit associated with property value increases and other less tangible benefits is $142,965, an average of $65.13 per tree (Table 10). Tree species that produced the highest average per tree aesthetic benefits include Siberian elm (Ulmus pumila, $114.61), City of Elko, Urban Forest Resource Analysis 28

33 honeylocust (Gleditsia triacanthos, $92.33) and eastern cottonwood (Populus deltoides, $78.79). Although blue spruce (Picea pungens, $55.16) provides a slightly below-average aesthetic benefit, the population as a whole provides the second largest proportion of benefits to the total with 11% (after Siberian elm, 49%). Siberian elm $ Honeylocust Eastern cottonwood $78.79 $92.33 Blue spruce Other species $55.16 $53.32 $0 $40 $80 $120 Figure 10. Annual Increase in Property and Socioeconomic Values - Top 5 Species Species Total ($) % of Total Tree Numbers % of Total $ Avg. $/tree Siberian elm 70, Blue spruce 15, Austrian pine 7, Green ash 10, Crabapple 4, Russian olive 4, Honeylocust 7, Juniper 1, Common chokecherry 2, Scotch pine 1, Eastern cottonwood 2, Elm 1, Other species 14, All trees $142, % 100% $65.13 Table 10. Annual Property Value, Aesthetic, and Socioeconomic Benefits of Elko s Public Tree Resource City of Elko, Urban Forest Resource Analysis 29

34 Combined Public Tree Benefits Siberian elm Eastern cottonwood Blue spruce Honeylocust Elm Scotch pine Russian olive Green ash Austrian pine Crabapple Juniper Aesthetic/ Other $ Energy $ Air Quality $ Stormwater $ CO2 $ Common chokecherry Other species -$50 $50 $150 $250 Figure 11. Summary of Annual per Tree Benefits from Elko s Most Prevalent Public Tree Species City of Elko, Urban Forest Resource Analysis 30

35 Species Aesthetic/ Other $ Energy $ Air Quality $ Stormwater $ CO2 $ Total per Tree $ % of Pop. Siberian elm Blue spruce Austrian pine Green ash Crabapple Russian olive Honeylocust Common chokecherry Juniper Scotch pine Eastern cottonwood Elm Other species All trees $51.51 $15.03 $1.58 $23.12 $2.01 $ % Table 11. Summary of Average Current Annual per Tree Benefits from Elko s Public Tree Resource Species % of Pop. Aesthetic/Other Energy Air Quality Stormwater CO2 Total ($) % of Total $ Total per Tree $ Siberian elm , , , , , , Blue spruce , , , , Austrian pine , , , , Green ash , , , Crabapple , , Russian olive , , , Honeylocust , , Juniper , , Common chokecherry , , Scotch pine , , , Eastern cottonwood , , Elm , , Other species , , , , All trees 100% ######### 44, , , , , % $77.82 Table 12. Average Annual Benefits by Species from Elko s Public Tree Resource City of Elko, Urban Forest Resource Analysis 31

36 Net Benefits and Benefit-Investment Ratio (BIR) Elko receives substantial benefits from public trees; however, the City must also consider the costs of maintaining this resource. Applying a benefit-investment ratio (BIR) is a useful way to evaluate the public investment in the community tree population. A BIR is an indicator used to summarize the overall value compared to the costs of a given project. Specifically, in this analysis, BIR is the ratio of the total benefits provided by the City s public trees expressed in monetary terms compared to the costs (investment) associated with their management, also expressed in monetary terms. Elko s public trees have beneficial effects on the environment. Approximately 54% ($237,683) of the total annual benefits quantified in this study are environmental services (Table 13). Energy savings ($109,719) account for 46% of the annual environmental benefits and 25% of all annual benefits. Air quality benefits ($83,490) account for 35% of annual environmental benefits and 19% of all annual benefits. Stormwater benefits ($35,565) account for 15% of the annual environmental benefits and 8% of all benefits. Carbon reduction benefits, valued at $8,909, account for 4% of environmental benefits and 2% of all benefits. Annual increases in property value, socioeconomic, and other aesthetic values are substantial benefits ($206,147), accounting for 46% of the total benefits. The estimated sum of benefits provided by Elko s public tree resource is $443,830, a value of $56.02 per tree and $16.14 per capita. These benefits are realized on an annual basis. It is important to acknowledge that this is not a full accounting of the benefits provided by this public tree resource as some benefits are intangible and/or difficult to quantify, such as impacts on psychological health, crime, and violence. Empirical evidence of these benefits does exist (Wolf, 2007; Kaplan, 1989; Ulrich, 1986), but there is limited knowledge about the physical processes at work and their interactions make quantification imprecise. Tree growth and mortality rates are highly variable. A true and full accounting of benefits and costs must consider variability among sites (e.g., tree species, growing conditions, maintenance practices) throughout the City, as well as variability in tree growth. The total annual quantifiable benefit that public trees provide to the City of Elko is $443,830. When the City s annual tree related expenditures (or investment) of $72,379 are considered, the net annual benefit (benefits minus investment) to the City is $371,451. The average net benefit for an individual public tree in Elko is $46.89 and the per capita net benefit is $ Based on the inventory of 7,922 public trees, Elko is receiving $6.13 in benefits for every $1 that is spent on its urban forest resource (Table 13). Considering the relatively young age of this tree population, with 65% of the population consisting of trees with a DBH (diameter at breast height) of twelve inches or smaller, Elko can expect greater benefits as these tress continue to mature. Increasing the stocking level (currently 70.5%) will further maximize canopy cover and increase the value and benefits of this resource over time. City of Elko, Urban Forest Resource Analysis 32

37 $300,000 $250,000 $200,000 $150,000 $100,000 $6,790 - CO2 $85,640 - Stormwater $5,078 - Air Quality $44,800 - Energy $142,965 - Aesthetic/Other $50,000 $0 Total Annual Benefits from Elko s Public Tree Resource: $285,273 Average Annual per Tree Benefits: $ Annual Value of Benefits Per Capita: $14.85 Pest Management $20,000 $15,000 $10,000 $5,000 $0 Removal Irrigation Contract Pruning Purchasing Trees and Planting Administration Litter Clean-up Infrastructure Repairs Total Annual Investment to Maintain Elko s Public Tree Resource: $16,350 Average Annual per Tree Investment: $7.45 Annual Investment Per Capita: $0.85 City of Elko, Urban Forest Resource Analysis 33

38 300, , , ,000 Annual Benefits, $285,273 Net Benefits, $268, ,000 50,000 0 Annual Investment, $16,350 Annual Net Benefits of Elko s Public Tree Resource: $268,923 For EVERY $1 Invested in public trees, Elko receives $17.45 in Benefits. City of Elko, Urban Forest Resource Analysis 34