NORTH LITTLE ROCK, ARKANSAS
URBAN TREE CANOPY ASSESSMENT PROJECT 2013
Pl an - I t G eo LLC | 569 0 W ebst er Str eet , A r vad a, Col o r ad o, 80 0 0 2 | ww w .p l an i t geo . c o m
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North Little Rock, Arkansas Urban Tree Canopy Assessment Completed August 2013 Prepared By:
Acknowledgements Funding for this project was provided by the USDA Forest Service (USFS).
Core partners included U.S. Forest Service, City of North Little Rock, and the Arkansas Forestry Commission. In addition, thanks go specifically to Patti Erwin, Robert Voyles Don Daily, and Wade Dunlap for their assistance at many stages of this project. The U.S. Department of Agriculture (USDA) prohibits discrimination in all its programs and activities on the basis of race, color, national origin, sex, religion, age, disability, sexual orientation, marital status, family status, status as a parent (in education and training programs and activities), because all or part of an individual’s income is derived from any public assistance program, or retaliation.
Prepared For: Arkansas Forestry Commission City of North Little Rock
An Urban Tree Canopy Study is one of many elements needed to inform management and planning initiatives for urban forests. Complete and sustainable urban forestry programs involve a shared vision for the desired quality of life and level of service that urban tree canopy can provide.
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CONTENTS EXECUTIVE SUMMARY .............................. 1 URBAN FOREST ASSESSMENT APPROACH ............1 URBAN TREE CANOPY IN NORTH LITTLE ROCK....1 ECOSYSTEM SERVICES ANALYSIS............................1 UTC GOALS ..............................................................2 RECOMMENDATIONS AND SUMMARY ..................2 PROJECT BACKGROUND ............................ 3 MAJOR FINDINGS ..................................... 5 PROJECT FUNDAMENTALS ........................ 6 MAPPING LAND COVER AND URBAN TREE CANOPY.....................................................................6 TERMINOLOGY .........................................................6 UTC ASSESSMENT BOUNDARIES............................8 ASSESSMENT RESULTS AND PRODUCTS..... 9 LAND COVER IN NORTH LITTLE ROCK .................11 TREE CANOPY IN NORTH LITTLE ROCK ................12 TREE CANOPY BY ZONING.....................................13 APPLIED GOAL SETTING BY ZONING TYPE ..........14 TREE CANOPY METRICS BY WARDS ....................16 TREE CANOPY METRICS BY STREET RIGHTS-OFWAY ........................................................................18 ECOSYSTEM SERVICES ...........................................19 RECOMMENDATIONS ..............................21 LAND COVER ANALYSIS .........................................21 UTC ASSESSMENT .................................................21 TOOLS FOR STRATEGIC CANOPY DEVELOPMENT SCENARIOS ...................... ERROR! BOOKMARK NOT DEFINED. TRAINING AND CORE TEAM PARTNERS ..............22 SUMMARY ...............................................23 APPENDIX .......................................................... 24
NORTH LITTLE ROCK, ARKANSAS URBAN TREE CANOPY ASSESSMENT 2013
EXECUTIVE SUMMARY The City of North Little Rock’s urban forest is comprised of trees, gardens, green spaces and other natural areas. This urban forest provides numerous benefits by making environments cleaner, safer, and more livable, therefore contributing directly to public health and reducing the costs associated with many required services. To manage, monitor and enhance the quality and stream of benefits received from its urban forests, the City of North Little Rock has initiated this study assessing the extent of Urban Tree Canopy (UTC) across the City. This report presents results for current land cover and UTC distribution and offers data analysis, custom maps and tools, and recommendations for setting and achieving UTC goals.
URBAN FOREST ASSESSMENT APPROACH Natural resource managers use top-down (remote sensing) and bottom-up (field-based) assessment approaches to measure land cover, trees and other green infrastructure, and associated ecosystem services. Terms and methods for UTC assessment and Ecosystem Services Analysis are presented in this report. Additionally, steps used to identify potential planting areas and UTC goals are described and explained. See Project Fundamentals section on pages 7-8.
URBAN TREE CANOPY IN NORTH LITTLE ROCK Unsuitable UTC Area 29% UTC 36% Plantable Area (Impervious) 7% Plantable Area (Vegetation) 34%
Figure 1: Distribution of UTC in North Little Rock
This study encompasses 35,252 acres defined by the City limits of the North Little Rock. Based on a land area (after excluding water) of 33,440 acres, the City has 11,913 acres (36%) of existing Urban Tree Canopy, 13,696 acres (41%) of total Possible Planting Area, or PPA, which is defined as non-road, non-building land area where it is biophysically possible to plant trees, and 9,643 acres (29%) that are likely unsuitable for tree planting. The land cover data was used to assess similar metrics for the City’s wards, street rights-of-way (ROW), and zoning categories. See Results section on pages 10-19.
ECOSYSTEM SERVICES ANALYSIS
Trees and forests in communities provide many “ecosystem services”, or direct and indirect economic and environmental benefits such as removing air pollutants, storing and sequestering carbon, mitigating
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stormwater runoff, conserving energy through shade and wind block, improving public health, and providing wildlife habitat. North Little Rock’s tree canopy currently provides an estimated $3.9M in air quality services each year, $1.1M in carbon storage and sequestration benefits, and $78M in total stormwater management savings ($6.8M annually). See Ecosystem Services section on pages 20-21.
UTC GOALS To support and facilitate future tree planting and canopy preservation policies, attainable UTC goals must be developed. Due to the unique nature of zoning classes, individual goals were developed for each type as follows; maintain 30% UTC within Commercial and Industrial zoning classes, 50% UTC within Conservation lands (requiring 124 acres of additional planting), 60% UTC within Public Lands (requiring 201 acres of additional planting), and 50% UTC within residential lands (requiring 1,000 acres of additional planting). These goals would result in an overall UTC of 42% citywide. See Applied Goal Setting section on pages 15-16 for details and supporting maps.
RECOMMENDATIONS AND SUMMARY Understanding how and where trees are concentrated and distributed in North Little Rock is essential for maintaining a healthy and sustainable urban forest. This study provides the most up-to-date analysis to foster this overarching goal. North Little Rock’s urban forest is vibrant and already provides substantial benefits that can be quantified, monetized, and forecasted. Strategic canopy increases, ongoing care and maintenance, and education on the benefits of urban tree canopy are essential to expand and enhance this critical green infrastructure resource. Doing so will ensure North Little Rock’s tree canopy appreciates in value over time and provides the maximum contribution toward addresses issues and improving community health. See Recommendations and Summary sections on pages 22-24.
Acres of Tree Canopy Citywide
11,913
Percent of Possible Planting Area Citywide
41%
Percent Tree Canopy Cover in Public Lands Percent of Total UTC found in Residential Zoning
53% 47%
36% UTC North Little Rock, Arkansas
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PROJECT BACKGROUND The City of North Little Rock (CONLR) is located in Central Arkansas, covers approximately 55 square miles, and has a population of about 62,000 (2010 census). The City’s existing trees and forests provide numerous social, environmental, and economic benefits, but to date, urban tree canopy and associated benefits have not been mapped or estimated. For this project, Plan-It Geo was contracted by the Arkansas Forestry Commission (AFC) to create an accurate baseline of land cover and provided GIS assessment data, maps, ecosystem services analysis, and reporting. Working with AFC, CONLR, and the U.S. Forest Service Urban Forestry South (UFS), Plan-It Geo used high-resolution multispectral imagery and GIS and remote sensing technologies to map land cover data, characterize existing UTC and planting areas, and assess the ecosystem benefits of the current and potential future tree canopy. The processes can be repeated in other communities and in future studies in CONLR. The tools and information resulting from this analysis can be used by community members, planners and managers to understand and improve urban forest management across the City.
CONLR Facts:
- City Limits: 55 sq. miles - Population (2010): 62,000 - No. of Households: 25,542 - Burns Park: 1,700 acres
Figure 2: City of North Little Rock project boundary Urban Tree Canopy Assessment – North Little Rock, AR
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Land cover classes mapped based off of 1-meter pixel resolution aerial imagery for CONLR are listed and defined as follows:
Urban Tree Canopy: Tree cover, when viewed and mapped from above Vegetation: Irrigated and non-irrigated vegetation Impervious: Surfaces: roads, buildings, airport runways and other impervious surfaces Soil: Dry vegetation/ bare soil Water: All water bodies, including lakes, rivers, and streams The land cover data are used to examine the area and percent cover for existing tree canopy, possible planting area (in vegetated grass areas and paved impervious areas), and areas unsuitable for planting (buildings, roads, water, agricultural fields, and sports fields). Within CONLR, these metrics were calculated for four (4) assessment boundaries: (1) City Limits, (2) Wards, (3) Street Rights-of-Way, (4) and Zoning by Parcels (see Table 1 on page 9).
Specific objectives of this assessment were to: Map five (5) land cover classes across the City of North Little Rock. Assess existing urban tree canopy and possible planting areas for the City and three other finer-scale assessment boundaries. Evaluate ecosystem benefits provided by CONLR’s urban trees and forests including air quality improvement, carbon storage and sequestration, and stormwater mitigation. Provide reporting and training resources that allow City, state, and county officials to understand current conditions and areas where the City’s urban forest can be improved.
North Little Rock’s Urban Tree Canopy Assessment represents an opportunity to better understand baseline conditions of tree canopy, where public and private trees can be planted, and the value of this resource in economic and environmental terms. With support and leadership from AFC and Plan-It Geo during and after this assessment, the City can use the data to develop street tree planting plans, revise policies associated with tree canopy, develop management plans, and foster greater understanding of tree benefits such as mitigation of air quality and other urban challenges.
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MAJOR FINDINGS NORTH LITTLE ROCK’S URBAN TREE CANOPY: North Little Rock is comprised of 36% (~12,000 acres) urban tree canopy, and 41% (~14,000 acres) total possible planting area. Possible planting area includes 34% (~11,000 acres) vegetation and 7% (~2,000 acres) paved surfaces (i.e. sidewalks or parking lots) where tree planting is feasible.
CANOPY BY RIGHTS OF WAY (ROW): Canopy cover in the ROW averages 17% (557 acres), or roughly 5% of all tree canopy. Total possible planting area (PPA) comprises 35% (1,182 acres) of City Rights-of-way.
CANOPY BY WARDS: Ward 4 has the highest canopy cover at 55% (3,226 acres). Ward 2 has the lowest canopy cover at 19% (2,664 acres) and the highest percent of total PPA at 54% (7,613 acres).
LAND USE / ZONING: Residential lots make up 36% (12,700 acres) of North Little Rock with an average tree cover of 42% (5,351 acres) citywide. This represents 47% of the City’s total tree canopy and 41% (5,198 acres) of possible planting area.
ECOSYSTEM SERVICES: The current urban forest removes nearly 907,000 pounds of air pollutants from the air annually, valued at $3.9 million per year. The tree canopy provides an estimated value of $78 million in avoided stormwater facility construction costs, valued at $6.8 million annually. North Little Rock’s canopy provides $1.1M in carbon storage and sequestration benefits annually.
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PROJECT FUNDAMENTALS The “top-down” urban tree canopy assessment conducted for North Little Rock provides an accurate evaluation of the myriad ways urban forests contribute to the health and vitality of a community at many management scales. The Project Fundamentals section describes the data and methods used for land cover classification, the terminology for defining and assessing Urban Tree Canopy (UTC) and Possible Planting Areas (PPA), and the boundaries (geographic units of scale) that were assessed.
MAPPING LAND COVER AND URBAN TREE CANOPY Geographic information systems (GIS), Land Use / Land Cover data, and high-resolution aerial imagery provided the basis for urban tree canopy assessments. Multispectral (4-band) aerial imagery from the 2010 National Agriculture Imagery Program and LiDAR 2012 were used to map five land cover classes in North Little Rock: (1) tree canopy, (2) other low-lying vegetation, (3) impervious surfaces, (4) bare soil/dry vegetation, and (5) water.
Land Cover: Trees Vegetation Impervious Surfaces Soil Water
Object-based image classification results were combined with existing GIS data provided by the City to produce a seven (7) class land cover layer that breaks impervious surfaces into three classes; (1) buildings, (2) roads, and (3) other impervious areas (see Appendix for more details). The land cover data was then summarized across assessment boundaries to provide UTC estimates at multiple scales.
Why a UTC Assessment Matters to you:
Figure 3: Land cover becomes the foundation of a UTC assessment and a vital aspect in the accuracy of data.
"North Little Rock focuses on initiatives which recognize the relationship between the built environment and green space. The City of North Little Rock has been a Tree City USA for 18 years. This distinction tells our visitors that our community cares about our environment and pursues ways to make the City more livable and sustainable." North Little Rock SMART: Urban Design & Nature Read more at: http://nlrsmart.org/urban-designnature/
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TERMINOLOGY Urban Tree Canopy Urban Tree Canopy (UTC) types describe how each category of land cover is related to the City’s urban forest. The final seven land cover classes were grouped into four UTC Types described at left and below that describe metrics for measuring current and possible urban forest conditions in various locations across the City.
Planting Areas: Grass/Open Space
UTC Types assessed in this Report: Existing UTC comprises forests and individual trees viewed and mapped from above.
Possible Planting Areas - Vegetation is
Planting Areas: Impervious Surfaces
the total area of grass and open space where tree canopy does not exist and it is biophysically possible to plant trees. For the CONLR UTC assessment, sports fields and other grass areas unsuitable for tree planting were removed from PPA – Vegetation.
Possible Planting Areas - Impervious is non-road, non-building hardscape surfaces that contribute to stormwater runoff where establishing tree canopy is biophysically feasible.
Unsuitable Planting Areas
Unsuitable UTC - the combination of buildings, roads, water and other areas where it is not feasible to plant trees (sports fields, golf course fairways & greens, airport grounds etc.).
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UTC ASSESSMENT BOUNDARIES Assessment boundaries provide geographic units linked to where we live, work and play. Metrics for UTC Types were assessed for the GIS boundaries in Table 1. These summaries provide data for resource managers and planners at different spatial scales. This resulted in summaries, maps, tools, and other products that will be used for targeted outreach campaigns. Table 1: Four UTC assessment boundaries examined in North Little Rock
Assessment Boundary
# of Types or Features
Description
North Little Rock City Limits
1
North Little Rock City Limits
4
Divisions of North Little Rock for representative, electoral, or administrative purposes
Zoning
7
Zoning Categories include: Residential, Commercial, Industrial, Conservation, Public Land, Street Rightsof-Way
Street Rights-of-Way
N/A
The public rights-of-way (ROW) along streets.
Wards
Urban Tree Canopy Assessment – North Little Rock, AR
Map
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ASSESSMENT RESULTS AND PRODUCTS The citywide UTC data, maps, summary tables, report, and other tools are being used to develop management recommendations, policies, partnerships, and education, outreach, and funding strategies to reach and maintain canopy cover goals. In order for UTC data and analyses are to be useful to planners, scientists and citizens on the ground, results need to be made available for multiple scales and purposes. Different assessment boundaries are governed, owned, managed, and used in different ways by different groups. The following sections present canopy cover and planting potential at various scales to assist the City in utilizing the assessment results for developing an urban forest management plan and other actions.
How Are UTC Results Used? To set and implement canopy cover goals To assess ecosystem services benefits of urban trees To prioritize areas for tree planting and preservation To analyze and visualize opportunities to enhance the urban forest to meet multiple environmental, social, and economic goals To determine if land use policies and ordinances are meeting goals based on desired tree conditions To provide a framework for multiple, diverse partners to achieve and maintain urban forest goals
We all Impact UTC: Within the City of North Little Rock, the fate of urban forests relies upon City planners, council members, business owners, and residents alike. Sustainable community efforts must be met by all parties of North Little Rock in order for the City’s urban forest to thrive. Local involvement includes:
Establishing and enforcing tree planting ordinances across all zoning types.
Community outreach to educate residents of the economic and health benefits of trees on private properties.
Preserving or offsetting existing high-quality tree canopy in areas at risk to forest loss from development pressures.
Involvement from the Green Committee and City council in development of an urban forest management plan.
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Figure 4: Various scales assessed in the North Little Rock UTC study.
The Applications of Scale: Larger assessment boundaries (Cities) are important for understanding regional trends and for cooperative goal setting. Medium-sized assessment boundaries (Wards) are useful for viewing general distribution of UTC and PPA in a region and identifying target areas for urban forest management activities. Small assessment boundaries (Zoning) are useful for engaging and initiating on-theground forest management action-items like planting projects and preservation ordinances with individual landowners, or planting initiatives on public lands.
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LAND COVER IN NORTH LITTLE ROCK This study encompasses 35,252 acres defined by the 2010 North Little Rock City limits. Land cover results demonstrate a snapshot of conditions based on the 2010 imagery. As shown in Figure 6, tree canopy covers 34% (approximately 12,000 acres) of North Little Rock. The two predominate land cover types for the study area are vegetation (grass and open space) at 11,526 acres (33%) and impervious surfaces, consisting of parking lots, driveways, patios, and other paved surfaces, comprising of 22% of North Little Rock, or 7,769 acres. Water covers 5% of the City’s area and bare soil/dry vegetation covers 2,231 acres, or 6% of North Little Rock’s city boundary.
Figure 5: North Little Rock 5-class Land Cover.
Figure 6: Distribution of land cover in North Little Rock.
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TREE CANOPY IN NORTH LITTLE ROCK Across North Little Rock, trees and forests comprise 11,913 acres, or 36% of the City’s total land area (Table 2 and Figure 7). Of the remaining land area, 13,696 acres (4 1%) are potentially available for tree planting and 9,643 acres (29%) are considered unsuitable to plant additional trees.
Total Acres 35,252
Total Acres UTC Acres (Excluding Water) 33,440
11,913
UTC % 36%
Table 2: North Little Rock land cover metrics by Zoning.
(Non-tree vegetation)
Figure 7: Distribution of UTC metrics in North Little Rock
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TREE CANOPY BY ZONING Many of the policies, regulations, ordinances, and actions influencing tree canopy in North Little Rock are dependent on zoning. To provide data that advances urban forest management, six broad zoning categories based on the County tax assessor’s database were assessed for tree canopy and possible planting areas (Figure 8). This was the finest scale assessment boundary and included 3,009 records. Results can be queried and symbolized using GIS to drill down and identify specific planting opportunities in wards or zoning types. Table 3 provides complete results for UTC and PPA metrics by zoning. Figure 8: Map of Zoning classes in North Little Rock.
Figure 9: Pie Chart: Distribution of total UTC by zoning in North Little Rock Table 3: UTC across Zoning classes
Zoning
Total Acres
Total Acres (Excluding Water)
UTC Acres
UTC %
Commercial Conservation Industrial Public Lands Residential Street ROW TOTALS
3,962 2,101 9,007 3,069 12,908 4,202 35,249
3,951 1,727 8,801 2,902 12,700 3,355 33,436
1,093 739 2,633 1,540 5,351 557 11,912
28% 43% 30% 53% 42% 17% 36%
Total Possible Total Possible Planting Acres Planting %
Urban Tree Canopy Assessment – North Little Rock, AR
1,504 888 4,006 917 5,198 1,181 12,513
38% 51% 46% 32% 41% 35% 37%
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APPLIED GOAL SETTING BY ZONING TYPE In order for City planners to effectively utilize the results from this assessment, goal setting should be incorporated into landscape ordinances, tree preservation policies and planning documents such as the comprehensive plan. Tree canopy goals should be assigned appropriately for zoning categories. Suggested practical and attainable UTC goals for North Little Rock over the next 20 years are presented here.
Commercial/Industrial: Maintain the current 30% UTC.
Local Involvement in Urban Forestry:
Conservation Lands: Increase UTC to 50% (add 124 UTC acres)
Public Lands: Increase UTC to 60% (add 201 UTC acres), and
Residential Lands: Increase UTC to 50% (add 1,000 UTC acres). Successful implementation of these goals would result in an overall citywide UTC of 42%. Zoning Type
# of Trees to Plant
Commercial
4,321
Conservation
5,791
Industrial
350
Public Lands
9,369
Residential
46,566
Street ROW
13,152
TOTAL
79,549
North Little Rock has already developed progressive ordinances towards a thriving urban forest. Administering and implementing these regulations will help increase canopy cover and meet these goals. ‘Screening Ordinance’: Requires one tree per six parking spaces and street trees with all new developments. ‘Street Trees’: Street trees to be planted every 20 to 40 feet. ‘T.R.E.E. Fund’: Fund proposed by the City of North Little Rock used for the replenishment of trees in the City. “Tree Replacement’: Trees that die shall be replaced one for one by the responsible party per CONLR’s landscape ordinance requirement. North Little Rock Electric Department’s involvement: Support ‘Utility Friendly’ Trees
Aspects of Increasing UTC: While tree planting is one technique to increase urban tree canopy, recent research by the USFS (Nowak 2012) suggests that a large percentage of gains can occur through natural regeneration. In order to effectively increase UTC in North Little Rock, the City must incorporate 1) greater tree planting, 2) preservation of existing trees, and 3) establishing areas suitable for forest regeneration. Areas suitable for regeneration include:
Areas adjacent to large patches of tree canopy Areas within a riparian buffer (i.e. public conservation lands along the Arkansas River) Where soils will experience conditions of flooding or high saturation Vacant or abandoned properties
Figure 10: Distribution of acres needed to reach suggested goal by zoning type.
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Areas to Focus Planting Resources by Zoning: Commercial Areas < 30% UTC: Tree planting in commercial lots below the current average of 30% UTC will help offset future losses from development. Furthermore, these areas should be a primary focus for tree planting to mitigate urban heat islands to maintain 30% tree canopy cover across commercial zoning. An emphasis on tree preservation should be executed in commercial areas.
Conservation Areas < 50% UTC: Conservation lots under the suggested goal of 50% tree cover should be a primary focus for tree planting within this zoning class. Much of the conservation areas in Ward 1 have high PPA Vegetation and should be taken into consideration when planning for increased UTC. Areas should be established on conservation lands for natural regeneration (see previous page).
Industrial Areas < 30% UTC: Many industrial lots fall below the suggested goal of 30% UTC. While some of these areas may be deemed unsuitable, such as rail yards, many tree planting opportunities are available in these areas to offset possible tree canopy losses due to future development.
Public Lands < 60% UTC: Public lands below the suggested goal of 60% are areas where local and state government can directly manage tree planting and preservation. Areas in public lands should be established for both priority tree planting and natural regeneration (see previous page).
Residential Areas < 50% UTC: Roughly 995 out of 1655 residential lots in North Little Rock fall below the tree canopy goal of 50%. UTC on residential lots accounts for the majority of UTC acres in North Little Rock, and has the most area for growth. Trees provide many economic and social benefits on residential properties, and community outreach and education of these benefits is essential to maximize residential tree planting and care.
Urban Tree Canopy Assessment â&#x20AC;&#x201C; North Little Rock, AR
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TREE CANOPY METRICS BY WARDS The City of North Little Rock has four wards each with the authority and funding for managing planting projects for public places such as in parks, along streets, and at schools. City councilman can also enact tree management policies that limit or control how private trees are managed. It is therefore important to understand how UTC varies across each Ward and at finer spatial detail within specific areas of each Ward. Tree cover across wards ranged from 19% (2,664 acres in Ward 2) to 55% (3,226 acres in Ward 4), while Ward 3 had the highest UTC by acreage (4,355 acres). Maps on the following pages illustrate how authorities may focus resources on planting within their own Ward. Figure 11: Wards color-coded by percent UTC. Darker areas indicate a higher urban tree canopy cover percent. Percent UTC ranged from a high of 55% in ward 4 to a low of 19% in Ward 2.
Figure 12: Percent Existing UTC, Total PPA, and Unsuitable UTC area across North Little Rockâ&#x20AC;&#x2122;s 4 Wards. Urban Tree Canopy Assessment â&#x20AC;&#x201C; North Little Rock, AR
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Who will use the Data and How? By inspecting the data at a finer scale, planners and resource managers can 000 determine direct areas where tree planning can and should be improved. This example focuses on Ward 1.
Businesses: CONLR’s “1-in-6” tree planting ordinance requires 1 tree to be planted for every 6 parking spaces. Enforcing this ordinance in commercial parking lots would increase canopy cover, alleviate urban heat islands (see p. 26), and promote retail in business areas.
Industrial Areas:
Citizens: Enforcing and further developing the “1 in Yard” tree planting ordinance on single family residential and apartment properties can significantly increase CONLR’s UTC. Growth of UTC in residential neighborhoods from 42% to 48% would result in a citywide UTC average of 38%. Involving and educating citizens on the economic benefits and enhanced quality of life that trees offer homes may be an incentive to plant.
State & Local Government: Large lots zoned as conservation should be a focus for costeffective tree canopy expansion. Tree preservation ordinances should also be a focus for the City Council to protect existing UTC and establish areas for natural regeneration.
While rail yards are considered unsuitable for tree planting, many industrial areas can benefit from canopy gains. Federal regulation requires CONLR’s electric company to set carbon offsets which tree planting can help contribute to.
City Planners: Enforcing the City’s street tree ordinance which requires street trees to be planted every 20-40 feet will help increase overall canopy, provide shade, help mitigate stormwater runoff, and increase the value of homes in a neighborhood.
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TREE CANOPY METRICS BY STREET RIGHTS-OF-WAY North Little Rock’s urban forestry program plants, manages, and maintains trees in the street rights-of-way (ROW) where the City has the most direct opportunity to increase tree planting. Using the UTC assessment data, the city may target strategic areas to increase tree canopy in streets and highway corridors to improve aesthetics and air quality. ROW total land area is equal to 3,358 acres (10%) of the City’s total land area. Key findings in CONLR’s ROW are: Existing UTC in the ROW is 557 acres for 17% average tree cover. This represents 5% of all UTC citywide. PPA Vegetation totals 861 acres (26%) of the ROW; PPA Impervious totals 321 acres (10%) of the ROW. ROW in Ward 3 has the highest UTC at 24%, equaling 38% of all UTC in North Little Rock’s street ROW.
Tier 1 Planting Potential (Best) UTC < 20% & PPA > 30% Tier 2 Planting Potential (Good) UTC < 30% & PPA > 20% Tier 3 Planting Potential (Some) UTC < 40% & PPA > 5% Other ROW City Limits
Figure 13: Potential planting area in the Street ROW. The GIS queries in the map legend show 3 colors based on ranges of Existing UTC and Total PPA. As an example, streets colored red have less than 20% tree canopy cover and greater than 30% total planting area, therefore were classified as “Tier 1” possible planting areas. Urban Tree Canopy Assessment – North Little Rock, AR
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ECOSYSTEM SERVICES Urban forests are an integral part of the character of the City of North Little Rock. While trees are often appreciated for their aesthetic appeal, the true benefits of trees and forests, contributing to the health and vitality of residents’ daily life, is often unknown or under-valued. This report quantifies some of the benefits of urban trees, referred to as “ecosystem services.” While the net benefits of urban trees are usually positive, costs are also part of this study’s ecosystem service evaluation and scenario tools for managers. Current and future values were estimated for the following three ecosystem service types:
Air Quality—Trees naturally remove pollutants and lower air temperature, which reduces energy cooling costs. Stormwater mitigation—Trees intercept stormwater, reducing runoff and filtering out pollutants that would otherwise enter rivers and lakes, and decrease stormwater control costs. Carbon sequestration and storage—Through photosynthesis, trees absorb atmospheric carbon and use it for new growth (stems, branches, roots and leaves), acting as a natural carbon sink. http://www.itreetools.org/resources/reports/Corvallis_Urban _Tree_Assessment.pdf
Why Evaluate Ecosystem Services? Assigning a dollar value to the benefits provided by CONLR’s trees and forests can motivate community members to preserve and enhance their urban forest. This is critical to understanding how trees impact on our homes, communities, and environment.
Other Benefits of Urban Trees and Forests: Wildlife habitat – Trees create local ecosystems that provide habitat and food for birds and animals, increasing biodiversity in urban areas. Property value – numerous studies across the country show that residential homes with healthy trees add property value (up to 15%). Energy conservation – trees lower energy demand through summer shade and winter wind block, additionally offsetting carbon emissions at the power plant. Economic Development – trees attract businesses, tourists, and increase shopping. Public health – trees help reduce asthma rates and other respiratory illnesses. Safe walking environments – trees reduce traffic speeds and soften harsh urban landscapes. Crime and domestic violence – urban forests help build stronger communities. Nature and trees provide settings in which relationships grow stronger and violence is reduced.
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CITYgreen and i-Tree Vue software were used to estimate the benefits of North Little Rock’s existing urban tree canopy and scenarios with decreased and increased canopy cover. i-Tree Vue benefits related to carbon storage and sequestration and air pollutant removal. CITYgreen was used to calculate stormwater mitigation benefits of urban forests. See complete details below and in Figure 14.
Carbon and Air Quality Findings: The study shows that existing canopy in CONLR stores approximately 1.7 million tons of carbon, valued at $33.3 million, and each year sequesters approximately 56 thousand tons of carbon dioxide, valued at $1.1 million. An increase in tree canopy to the suggested goal of 42% would result in 2.05 million tons of carbon stored, increasing the City’s annual savings to $1.3 million. i-Tree Vue findings also reveal that tree canopy in North Little Rock removes 906 thousand pounds of air pollution annually, valued at $3.9 million. An increase in tree canopy to 42% would remove 1.1 million pounds of air pollution annually; a value of $4.6 million.
Stormwater Mitigation Findings: Plan-It Geo’s environmental analysis reveals that North Little Rock’s current tree canopy intercepts 26 million cubic ft. of stormwater runoff every year, a benefit valued at $6.8 million in savings of stormwater facilities management, and a total stormwater value of $78 million. An increase in canopy to the suggested goal of 42.5% would intercept roughly 27 million cubic ft. of stormwater runoff annually; a total stormwater value of $82 million. A decrease in canopy cover to 30% would intercept 17.8 million cubic ft. of stormwater runoff annually; a total stormwater value of $53.5 million.
Figure 14: The chart above illustrates the monetary values that trees provide in relation to air pollution, carbon offsets, and stormwater mitigation, with current canopy conditions and scenarios of increasing and decreasing canopy. Urban Tree Canopy Assessment – North Little Rock, AR
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RECOMMENDATIONS Management of North Little Rock’s urban forest requires planners to balance allocation of limited resources (time and money) and make choices that provide the best outcomes based on the environmental, social, and economic needs of all community members. To help support these decisions, below are recommendations that follow the organization of this report, describing ways to use the resources provided through this assessment and techniques to use over time that will lead to the enhancement of CONLR’s urban forest.
LAND COVER ANALYSIS Disseminate the GIS land cover data layers broadly to diverse partners for use in other applications while the data is current. Utilize web-mapping opportunities that increase accessibility and simplify the user experience when analyzing GIS data. Integrate the land cover data and ecosystem services benefit values into decision-making and implementation planning. Re-assess canopy cover in 5-10 year intervals, and use LiDAR data again if available, aiming for 95% overall accuracy, in order to assess gains and losses in canopy cover as progress towards goals.
URBAN TREE CANOPY ASSESSMENT Use the assessment data to: o
Protect canopy at risk to development within industrial and commercial zones, and offset tree canopy losses with new planting areas, preserving the 30% tree canopy in these areas.
o
Promote private tree planting within residential lots; strive to reach 50% UTC (or 1,000 additional acres of UTC) across residential zoning.
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Establish canopy goals by City and land uses through development of implementation plans in a collaborative, multidisciplinary process. Reassess canopy periodically to measure progress toward goals and effectiveness of education/outreach and tree-related management and policies.
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Foster public and private tree planting in priority areas within each neighborhood.
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o
Determine if tree planting in new development is achieving desired outcomes.
Host the UTC data layers in an online application focused on urban forest planning. Work with communities, school boards, developers, environmental non-profits, and public health professionals to enable volunteerism and citizen science to advance urban tree canopy benefits. Using project data, tools, and results, develop targeted presentations for City leaders, planners, engineers, air and water quality managers, and others on the functional benefits of urban tree canopy in addressing critical regional issues.
UTC GOALS Reassess or draft tree related ordinances and update the City’s comprehensive plan to incorporate a citywide urban tree canopy cover goal of 42% suggested in this report, specifically by: o
Preserving and maintaining 30% average tree canopy cover across Commercial and Industrial zones.
o
Expanding canopy in conservation and public lands to 50% and 60%, respectively.
o
Expanding canopy in residential areas to an average 50% tree cover.
MAXIMIZING ECOSYSTEM SERVICES Use the data and maps, specifically planting potential along street ROW by census blocks in each ward, to target tree plantings for improved air quality.
Use the land cover data, specifically Existing UTC and PPA Impervious maps, to assess the effectiveness of landscaping ordinances and to target new plantings. Benefits near these large impervious areas will include mitigation of the urban heat island effect and stormwater runoff, while revitalizing business retail and local economic conditions.
Maximizing the Urban Forest: Community Objectives In order for North Little Rock to successfully reach and maintain a higher tree canopy goal, collective commitments must be met by City officials, business owners, and residents (Clark 1997). With the attainment of this UTC assessment, continuing objectives include: Involvement of large private and institutional land holders Citizen-municipality-business interaction and involvement in urban forest management Intense management and maintenance of publicly owned trees Municipality-wide funding for a comprehensive urban forest management plan
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SUMMARY Urban forests are dynamic resources that are constantly changing through natural and human processes. Managing urban forests effectively over time requires an understanding of where trees are presently, where they can be planted equitably to maximize benefits, and how to overcome regulatory and physical restrictions that impede goals. This 2013 UTC assessment provides the City of North Little Rock with an accurate and dependable tree cover benchmark for the City to aide in future management planning, monitoring, and outreach. Highlights from this study: Data from this study indicates that 36% of North Little Rock’s City limits are covered by tree canopy, with nearly 41% of land area available for additional tree planting (Total PPA). North Little Rock’s 4 Wards ranged from 19% UTC (2,664 acres in Ward 2) to 55% UTC (3,226 acres in Ward 4). Residential Zoning accounts for 36% of North Little Rock’s land area (12,700 acres), accounts for nearly 47% (5,351 acres) of all UTC in North Little Rock, and still has 42% (5,198 acres) of Total PPA to grow. Industrial zoning accounts for 25% of total land area, has nearly 30% UTC (2,633 acres), yet has over 4,000 acres, or 32% of total possible planting area in North Little Rock. Projected goals for 2033 are to achieve 50% UTC in Residential parcels, 50% and 60% in Conservation and Public Lands parcels (respectively), and preserve the roughly 30% UTC in both Commercial and Industrial parcels. This will result in an overall citywide target of 42%. The City of North Little Rock’s tree canopy currently provides an estimated $3.86M in air quality services each year, $1.1M in carbon storage and sequestration benefits, and $6.8M in savings for annual stormwater management.
An increase in canopy to the suggested goal of 42% would intercept roughly 27 million cubic ft. of stormwater runoff annually; a total stormwater value of $82 million, remove 1.1 million pounds of air pollution annually; a value of $4.6 million, and would result in 2.05 million tons of carbon stored, increasing the City’s annual savings to $1.3 million. These combined benefits total $13M in savings if UTC was increased to 42%. The Future of Canopy in North Little Rock A detailed and accurate baseline of land cover has been thoroughly analyzed and presented in this report. An ongoing challenge will be to balance new development with the protection and conservation of environmental values related to tree and forest cover such as energy conservation, air quality, and climate adaptation related to carbon storage and stormwater mitigation. The social, environmental, and economic benefits provided by urban trees and forests are an incentive to continue in this direction. Using the UTC data when writing an urban forest management plan in North Little Rock will help protect and enhance the urban forest in many ways: Preserve existing canopy in sensitive habitat and zoning districts such as commercial and industrial Expansion of urban tree canopy along roads, highways, and other visual corridors Proliferation of trees in residential neighborhoods for health, beautification, and quality of life Targeted canopy increases in office and retail areas to stimulate local economic development
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APPENDIX Additional details on the City of North Little Rockâ&#x20AC;&#x2122;s 2013 urban tree canopy assessment are provided including supporting information on:
A1: Glossary of Terms A2: Canopy Calculator A3: Land Cover Classification Accuracy Assessment A4: Complete UTC Assessment Tables A5: Additional UTC Assessment Maps A6: Additional Related Resources A7: References
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A1: GLOSSARY OF TERMS Air Quality – trees absorb, trap, offset and hold air pollutants such as particulate matter, ozone, sulfur dioxide, carbon monoxide, and CO2. Carbon Sequestration – The rate that carbon is captured. Carbon Storage – Cumulative amount of carbon stored in trees over time. CITYgreen – A GIS software developed by American Forests which uses research from the U.S. Forest Service and Natural Resource Conservation Service (NRCS), which calculates benefits of existing tree canopy. Ecosystem Services – Direct and indirect benefits that trees provide that we tend to take for granted because they are not assigned a dollar value. Energy conservation – trees lower energy demand through summer shade and winter wind block, additionally offsetting carbon emissions at the power plant. Geographic Information Systems - a system for storing and manipulating geographical information on computer. Impervious Land Cover – Hardscape surfaces that do not allow rainfall to infiltrate the soil (Buildings, roads, parking lots). i-Tree Vue – As part of the i-Tree suite developed by the USDA Forest Service, this tool uses National Land Cover Data (NLCD) to assess land cover, and ecosystem services. PPA Vegetation – The percent of the polygon’s land area that is covered by grass/low-lying vegetation. PPA Impervious – The percent of the polygon’s land area that is covered by non-building, non-road impervious surface (primarily parking lots, patios, etc.) where tree planting is biophysically possible.
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Street Right-of-Way – Land commonly owned by a public entity where facilities such as roads, rail ways, and power lines are built and maintained. Urban heat island effect – refers to developed areas that are hotter than surrounding rural areas due to the abundance of man-made materials there which absorb the sun’s energy much more than trees or other plants, and in turn warm the air around them (Center for Environmental Studies, Brown University, “Trees and the Urban Heat Island Effect”, 2010). UTC – (Urban Tree Canopy) is defined as the layer of leaves and stems of trees that cover the ground when viewed from above. Water Quality and Stormwater Runoff Mitigation – trees infiltrate, evapotranspire, and intercept stormwater while also increasing soil permeability and ground water recharge.
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A2: CANOPY CALCULATOR To assist in advanced UTC goal setting, Plan-It Geo’s Canopy Calculator (MS Excel) tool is provided as a deliverable to the City of North Little Rock. The City may quickly and easily enter various goals and determine future tree canopy cover and tree planting scenarios.
Figure 15: Screenshots of CONLR’s UTC Calculator
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A3: LAND COVER CLASSIFICATION ACCURACY ASSESSMENT City of North Little Rock Land Cover Classifications This report describes the methods used and generated results in mapping land cover types across the City of North Little Rock, Arkansas (CONLR). National Agricultural Inventory Program (NAIP) aerial photography from 2010 and GIS data were combined to map five land cover classes: (1) Tree Canopy, (2) Impervious Surface, (3) Green Vegetation, (4). Soil and Dry Vegetation, and (5) Water. Object-based image analysis (OBIA) software (Feature Analyst v.5.0) was used to map trees, other vegetation, impervious surfaces and soil/dry vegetation areas. Impervious surfaces were augmented with existing buildings (supplied by CONLR GIS) and by buffering existing road centerlines. Water was mapped using features provided by CONLR GIS in addition to manual digitizing at 1:1,000 scale.
Figure 16: Aerial imagery for land cover classification.
Figure 17: This graphic depicts various imagery used inland cover classification .
Figure 18: The breakdown of a 5-class land cover to a 7-class land cover and the conversion into UTC Metrics.
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Accuracy Assessment Classification accuracy serves two main purposes: First, accuracy assessments provide information to technicians producing the classification about where processes need to be improved and where they are effective. Secondly, measures of accuracy provide information about how to use the classification and how well land cover classes are expected to estimate actual land cover on the ground. Even with high resolution imagery, very small differences in classification methodology and quality can have a large impact on overall map area estimations. The classification accuracy error matrix illustrated in Table 1 contains confidence intervals that report the high and low values that could be expected for any comparison between the classification data and what actual, on the ground land cover was in 2010. One thousand (1,000) sample points were randomly distributed across the study area and assigned a random numeric value. Sorting from lowest random value to highest, each sample point was referenced using the NAIP imagery and assigned one of the five land cover classes (Reference ID) mentioned above. Random values ensure sample points are geographically distributed across the entire study area. An automated script is then used to assign values from the classification (Evaluation ID). Misclassified points (where reference ID does not equal evaluation ID) and corresponding land cover are inspected for necessary corrections. The procedure was repeated until an acceptable accuracy percent and classification quality are achieved.
Figure 19: Error Matrix interpretation
Statistical relationships between the reference pixels (representing the true conditions on the ground) and the intersecting classified pixels are used to understand how closely the entire classified map represents the CONLR landscape. The sample error matrix represents the intersection of reference pixels manually identified by a human observer (columns) and classification category of pixels in the classified image (rows).
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The white boxes along the diagonals of the matrix represent agreement between the two pixel maps. Off-diagonal values represent the number pixels manually referenced to the column class that were classified as another category in the classification image. Overall accuracy is computed by dividing the total number of correct pixels by the total number of pixels reported in the matrix (331+211+292+46+52 = 932 / 996 = 94%), and the matrix can be used to calculate per class accuracy percentages. For example, 340 pixels were manually digitized in the reference map as Tree Canopy, but only 331 of those pixels were classified as Tree Canopy in the classification map, with 2 pixels misclassified as Vegetation and 7 as Impervious. This relationship is called the “Producer’s Accuracy” and is calculated by dividing the agreement pixel total (diagonal) by the reference pixel total (column total). Therefore, the Producer’s Accuracy for Tree Canopy is calculated as: (331 / 340 = 0.97), meaning that we can expect that 97% of all tree canopy in CONLR was classified as Tree Canopy in the classification map. Conversely, the “User’s Accuracy” is calculated by dividing the number agreement pixel total by the total number of classified pixels in the row category. For example, 349 classification pixels intersecting reference pixels were classified as Tree Canopy, but 6 pixels were identified as Vegetation and 12 as Impervious in the reference map. Therefore, the User’s Accuracy for Tree Canopy is calculated as: (331 /349 = 0.95), meaning that pixels classified as Tree Canopy the classification were actual tree canopy in the CONLR. It is important to recognize the Producer’s and User’s accuracy percent values are based on a sample of the true ground cover, represented by the reference pixels at each sample point.
Figure 20: An example of North Little Rock’s 5 class land cover raster GIS data layer.
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A4: COMPLETE UTC ASSESSMENT TABLES The following tables and charts provide more comprehensive UTC results for each boundary assessed in this study. Urban Tree Canopy by Ward
Urban Tree Canopy by Zoning Class
Tree Canopy in Street ROW by Ward:
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Urban Tree Canopy in Street Rights-of-Way by Ward
Figure 21 (Left): Total tree canopy distribution in street Rights-of-Way by Ward. Figure 22 (Right) Total possible planting area distribution in street Rights-of-Way by Ward.
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A5: ADDITIONAL UTC MAPS The following maps on pages 35 â&#x20AC;&#x201C; 39 provide more comprehensive results from this UTC assessment.
Figure 23: Percent UTC by zoning districts. The insets illustrate physical tree canopy polygons (top right) and on the ground vegetated possible planting areas (bottom left).
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WARD 1:
Figure 24 (Top): Percent UTC in street Rights-of-Ways by census blocks in Ward 1. Figure 25 (Bottom): Percent Total PPA in street Rights-of-Way by census blocks in Ward 1.
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WARD 2:
Figure 26 (Top): Percent UTC in street Rights-of-Ways by census blocks in Ward 2. Figure 27 (Bottom): Percent Total PPA in street Rights-of-Way by census blocks in Ward 2.
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WARD 3:
Figure 28 (Top): Percent UTC in street Rights-ofWays by census blocks in Ward 3. Figure 29 (Bottom): Percent Total PPA in street Rights-of-Way by census blocks in Ward 3.
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WARD 4:
Figure 30 (Top): Percent UTC in street Rights-ofWays by census blocks in Ward 4. Figure 31 (Bottom): Percent Total PPA in street Rights-of-Way by census blocks in Ward 4.
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A6: ADDITIONAL RELATED RESOURCES Community Efforts: Vibrant Communities (http://vibrantcities.org/) The Vibrant Communities, “Trees are the Key” online toolkit provides several free web-based tools that can be used to increase awareness and participation in enhancing North Little Rock’s urban forest. Ecosystem Services: For a more complete list of the scientifically proven benefits of urban forests, see the “Benefits of Trees and Urban Forests: A Research List”, by the Alliance for Community Trees; http://www.actrees.org/files/Research/benefits_of_trees.pdf. Urban Forest Assessments Resource Guide: American Forests (America’s oldest nonprofit conservation organization) recently published the “Resource Guide to Urban Forest Assessments” which highlights a number of the most state of the art tools and techniques available for maximizing the usefulness of available urban forest management resources. http://www.americanforests.org/ourprograms/urbanforests/urban-forests-tools-resources/urban-forest-assessments-resource-guide/
Ordinance Examples at Work across the US: Tree Planting Incentives: ‘The District of Columbia Department of the Environment’s River Smart Homes initiative’: gives rebates to homeowners who install stormwater mitigating features on their property. The District will cover up to $1,200 in landscaping costs for installing trees, pervious surfaces, rain barrels, and other features. ddoe.dc.gov/riversmarthomes City Ordinance: The City of Denton, TX passed an ordinance requiring developers of non-residential sites to preserve at least 25% of existing trees, while residential sites must preserve at least 20% of existing trees. http://www.Cityofdenton.com/departments-services/sustainable-denton/land/tree-preservation
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REFERENCES Clark, N. Matheny, G. Cross, V. Wake. "A Model of Urban Forest Sustainability ." Journal of Arboriculture, 1997: 23: 1730. Downing, Adam, 2011. Ecology, Air: What’s a Tree Got to Do with It? Accessed November 2, 2012.
http://www.ecology.com/2011/09/13/air-tree/.
Nowak, David. 2012. Contrasting natural regeneration and tree planting in fourteen North American cities. Urban Forestry & Urban Greening. 11(4): 374-382. <http://www.nrs.fs.fed.us/pubs/jrnl/2012/nrs_2012_Nowak_003.pdf>
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Pl an - I t G eo LLC | 569 0 W ebst er Str eet , A r vad a, Col o r ad o, 80 0 0 2 | ww w .p l an it geo . c o m
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