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HomeMy WebLinkAboutEdina Ground Cover Survey and Sequestration Baseline Study Ground Cover Survey and Carbon Sequestration Study April 2021 Revised April 29, 2021 Prepared by: Trees are sanctuaries. Whoever knows how to speak to them, whoever knows how to listen to them, can learn the truth. Herman Hesse, Poet Edina Ground Cover And Carbon Sequestration Study 1-1 Table of Contents Section 01 Introduction and Methodology Section 02 Land Coverage Characteristics Section 03 Land Cover Impacts and Benefits Section 04 Tree Canopy Economic Value Section 05 Findings Section 06 Calculating Potential Goals Section 07 Recommendations Appendix 1 i-Tree Technical Notes Appendix 2 Climate Adaptive Tree Species Introduction The intent of this study is to support the City of Edina in understanding the extent of Citywide tree canopy, grass, and impervious surface cover- age and in establishing appropriate goals and strategies to improve the environmental impacts and opportunities of land coverage within the City. The findings of this report are to support establishment of goals, strategies, and actions for the City’s Climate Action Plan. As a visionary planning document, the goals established for the City should be a “stretch” while also being achievable. Why Study the City Wide Tree Canopy? Trees play a central role in supporting community health, improving air and water quality, helping to reduce building energy use, and supporting heat island and climate mitigation. Community Health Benefit of Trees Recent studies have shown that sometimes going to a park, or even look- ing at a single tree can significantly improve a person’s health and stress levels. Our understanding of the value of trees has been expanded to include mental and physical health benefits. Trees are critical in filtering air, removing harmful pollutants, such as Car- bon Monoxide, particulate matter, and Ground-level Ozone - pollutants that can be toxic at high levels and which can cause asthma and other respiratory impacts. Stormwater Management Every tree catches the rain as it comes down, increasing the soil’s capaci- ty to retain water longer. A mature White Oak can intercept up to 12,010 Gallons of water in a single year. This water stays in the leaves until it’s absorbed by the tree or evaporates to cool our air. Within an urban en- vironment, this prevents that water from needing to be piped or treated by other stormwater infrastructure. Edina Ground Cover And Carbon Sequestration Study 1-2 Introduction Pollution Absorption Trees remove gaseous air pollution primarily by uptake via leaf stomata, though some gases are removed by the plant surface. Once inside the leaf, gases diffuse into intercellular spaces and may be absorbed by water films to form acids or react with inner-leaf surfaces. Trees also remove pollution by intercepting airborne particles. (Source: USDA Forest Service) Heat Island Mitigation Tree transpiration and tree canopies affect air temperature, radiation absorption and heat storage, wind speed, relative humidity, turbulence, surface albedo, surface roughness and consequently the evolution of the mixing-layer height. These changes in local meteorology can alter pollu- tion concentrations in urban areas. Maximum mid-day air temperature reductions due to trees are in the range of 0.07 to 0.36 degrees F for eve- ry percent canopy cover increase. (Source: USDA Forest Service) Carbon Sequestration Through photosynthesis, trees take in carbon dioxide (CO2) and release oxygen (O2). Trees then transfer the remaining carbon to their trunks, limbs, roots, and leaves as they grow. When leaves or branches fall and decompose, or trees die, the carbon that has been stored will be re- leased by respiration and/ or combustion back to the atmosphere or transferred to the soil. Edina Ground Cover And Carbon Sequestration Study 1-3 Edina Ground Cover And Carbon Seques-1-4 Introduction Methodology To arrive at recommended goals, this study looks at the existing extent of tree canopy, grass/shrub, and impervious surface coverage. Coverage for each category are established using aerial imagery and a random point technique using the USDA Forest Service’s i-Tree Canopy Software tool. i-Tree Canopy is a quick and simple method to obtain statistically valid estimates for canopy cover and other land uses based on the point method. Further technical information on i-Tree canopy is included in Appendix 1 i-Tree Canopy was used to interpret aerial images across the community using 8,149 random points. This overall picture was built up by analyzing the 14 census tracts (see map below) that make up the City of Edina. The point samples averaged 580 plots to each neighborhood until a satisfactory standard error for each land cover category was reached. The standard error (SE) achieved is typically between .2 and 2%. Classification of coverage categories included Trees/Shrubs, Lawn, Prairie Grass/Gardens, Water, Impervious Surface Light (buildings), Impervious Sur- face Light (pavement), Impervious Surface Dark (buildings), and Impervious Surface Dark (pavement). The land classes assigned and their descriptions are provided in the table below. Once statistically valid land cover calculations in these classifications were obtained for each neighborhood, calcula- tions were created, by neighborhood, for Tree Canopy Benefits, Tree Canopy Values, and Baselines for community-wide Heat Island Contribution, Stormwater Runoff, and Carbon Sequestration. With these values established a range of potential goals and strategies to protect and improve the envi- ronmental benefits of the City’s tree canopy and green infrastructure were identified and are included in the Recommendations Section of this report. Population Density of Edina Per Acre within the 14 Census Tracts Land Coverage Categories Measured 2-1 Edina Ground Cover And Carbon Sequestration Study 02 S e c t i o n Land Coverage Characteristics Click here to return to TOC Classification of coverage categories included Tree Canopy, Grass/Shrub/Crop, Water, Im- pervious Surface Light, and Impervious Sur- face Dark. Tree Canopy Coverage City Average: 35.9% Census Tract High: 46.7% Tract: 236 Census Tract Low: 12.6% Tract: 240.05 Lawns and Grass Coverage City Average: 21.2% Census Tract High: 34.1% Tract: 239.01 Census Tract Low: 10.0% Tract: 240.05 2-2 Edina Ground Cover And Carbon Sequestration Study Land Coverage Characteristics Open Water Coverage City Average: 3.9% Census Tract High: 10.2% Tract: 240.06 Census Tract Low: 0% Tract: 240.05 Light Impervious Surface Coverage (buildings+pavement) City Average: 6.4% Census Tract High: 18.4% Tract: 240.05 Census Tract Low: 3.4% Tract: 235.01 Dark Impervious Surface Coverage (buildings+pavement) City Average: 25.5% Census Tract High: 46.6% Tract: 240.04 Census Tract Low: 18.4% Tract: 240.05 3-1 Edina Ground Cover And Carbon Sequestration Study 03 S e c t i o n Land Cover Impacts and Benefits Click here to return to TOC Pollution Absorption by Trees Air pollution is a major environmental concern in most major metropolitan areas globally. Air pollutants are known to increase incidents of heart disease, asthma, emphysema, and cancer. Meanwhile, global warming projections for Min- nesota anticipate an increase in the impacts felt by air quality issues. Healthy tree canopies offer the ability to remove significant amounts of air pollutants and consequently improve environ- mental quality and human health. Pollution Absorption by Trees - Particulates Particulate matter pollution is divided into two categories: Fine Particulate (PM2.5) and Course Particulate (PM10). Numerous studies have linked fine particulate pollution with a number of health risks including respiratory disease, asthma, bronchitis, and increased heart disease and heart attacks. Course particulate matter has been shown to aggravate heart and lung diseases and to cause lung damage. The condition and health of a community’s Tree Canopy and green infrastructure and the magni- tude and nature of impervious surfaces have meaningful consequences on the area’s environ- ment. Estimating the baseline land cover contributions to the community’s environment enables the City to project the impact of potential strategies and to track improvements over time. The following maps in this section diagram the impacts and benefits of the City’s Tree Canopy, grass, and impervious surface coverage. 3-2 Edina Ground Cover And Carbon Sequestration Study Pollution Absorbed Annually by City’s Tree Canopy The values shown in the legends below are mapped by census tract on the following page. Carbon Monoxide 3,930 lbs Nitrogen Dioxide 21,211 lbs Ozone 167,710 lbs Land Cover Impacts and Benefits Sulfur Dioxide 10,673 lbs Fine Particulate (PM2.5) 8,568 lbs Course Particulate (PM10) 47,600 lbs Electric Energy Savings 21,684,278 kWh Natural Gas Savings 4,517,952 Therms Land Cover Impacts and Benefits Energy Savings Trees are important elements in many urban areas and alter the local cli- mates by producing shade, blocking winds and reducing air temperatures through evaporation of water from leaves. To determine exact energy sav- ings values, tree locations and relationships to buildings need to be as- sessed in detail. Trees which help buildings reduce their energy consump- tion based on their location - an example is a tree planted on the South side of a building helping to shade the building from hot summer sunlight - are known as energy-affecting trees. At the community-wide scale, how ever, reasonable approximations can be calculated using average energy affecting trees per acre based on community density type established through the study “Residential building energy conservation and avoided power plant emissions by urban and community trees in the United States.” Using these averages, we can estimate the total electrical and natural gas savings contributed by Edina’s tree canopy. (Note; based on regional aver- ages, it is assumed 25% of electricity consumption is for air conditioning and 80% of natural gas use is for heating buildings.) 3-3 Edina Ground Cover And Carbon Sequestration Study Energy Savings Annually From City’s Tree Canopy 3-4 Edina Ground Cover And Carbon Sequestration Study Land Cover Impacts and Benefits Heat Island Contribution of Edina Impervious Surfaces (summer values) City Average: 4.4°F Census Tract High: 8.0°F Tract: 240.04 Census Tract Low: 3.1°F Tract: 240.05 Heat Island Contribution Heat island refers to the phenomenon of higher atmospheric and sur- face temperatures occurring in developed areas than those experi- enced in the surrounding rural areas due to human activities and in- frastructure. Increased heat indices during summer months due to heat island effects raise human discomfort and health risk levels in developed areas, especially during heat waves. According to NOAA projections, if global greenhouse gas emissions proceed under a “business as usual” scenario, Edina may have an an- nual average of 50 days above 95 degrees compared to the recent 30 year average of 2. Depending upon humidity, wind, access to air- conditioning, humans may feel very uncomfortable or experience heat stress or illness, or even death on days with such high heat indices. Consequently, planning and management efforts to address Heat Is- land effects will be increasingly important to the City of Edina. Based on a 2006 study done by Minnesota State University and the University of Minnesota*, the relationship between impervious sur- face percentage of a City and the corresponding degree of heat island temperature increase can be understood as a ratio. The ratios vary slightly for each season. We’ve selected the ratio for summer heat island contribution as the effects of heat island on heat related risks are and will become increasingly more acute during summer heat waves. The numbers shown below for each of the Census Tracts rep- resents the increase in summer temperatures a City would experience if the entire region had impervious land characteristics identical to that Census Tract. These numbers do not necessarily represent the actual summer time temperature difference from tract to tract, but instead are a representation of the comparative level of overall heat island impacts for the overall community. *Comparison of impervious surface area and normalized difference vegetation index as indicators of surface urban heat island effects in Landsat imagery. Fi Yuan and Marvin Bauer, February 2007 Land Cover Impacts and Benefits Total Stormwater Runoff Generated Edina’s Impervious Surfaces An- nually City Total: 3.3 Billion Gallons Land Cover Impacts and Benefits Stormwater Runoff and Management by Green Infrastructure Increases in impervious cover can dramatically increase the impact of so-called 100-year flood events. Typically, floods in areas of high im- pervious surfaces are short-lived, but extended flooding can stress trees, leading to leaf yellowing, defoliation, and crown dieback. If damage is severe, tree mortality can occur. In addition, flooding can lead to secondary attacks by insect pests and diseases. Some species are more tolerant of flooding than others. According to data from National Climatic Data Center and NOAA, the city receives 30.6” of precipitation annually. That total precipitation level and the impervious surface coverages can then be used to esti- mate the total stormwater runoff values by neighborhood as indicated below. 3-5 Edina Ground Cover And Carbon Sequestration Study Total Stormwater Uptake by Grasses 15.8 Million Gallons Stormwater Runoff and Management by Green Infrastructure Green Infrastructure such as native grasses, wetlands, and especially trees are a critical stormwater management tool. Healthy green infrastructure within a community can help protect, restore, and mimic the natural water cycle - which has typically been significantly impacted through community development. To estimate the total stormwater uptake, in gallons, by neighborhood, we have used calculations developed by stormwater sustainability specialist Aarin Teague and US Forestry Service forester Eric Kuehler. Detailed val- ues can only be calculated using detailed soil hydrology data and accurate Land Cover Impacts and Benefits runoff curve numbers. As that level of detail is not a part of this study, we’ve used curve numbers averaged across soil groups A-D for “fair” hy- drology and cover conditions. The result should not be considered an ac- curate indication of total uptake volumes, but rather as an “order of mag- nitude” analysis tool for comparison between neighborhoods. These maps indicate the estimated total annual water uptake of trees and of grass/open land as well as the total green infrastructure water uptake as a percentage of the total stormwater runoff of each neighborhood. Total Stormwater Uptake by Trees 79 Million Gallons 3-6 Edina Ground Cover And Carbon Sequestration Study Estimated Percentage of Stormwater Runoff Uptake by Green In- frastructure City Average: 2.9% Census Tract High: 4.4% Tract: 239.02 Census Tract Low: 0.9% Tract: 240.05 3-7 Edina Ground Cover And Carbon Sequestration Study Annual Carbon Sequestration by Grasses 13,720,886 pounds (6,224 Metric Tons — 0.9% of annual GHG emissions) Land Cover Impacts and Benefits Pollution Absorption - Carbon By volume, Carbon Dioxide pollution is the largest man-made emission contributing to Global Warming. Throughout the City of Edina, 919 million cubic feet of CO2 pollution is produced by vehicles alone annually. Carbon Sequestration occurs throughout the growing season of all plants. Long- term carbon storage occurs within the tree/plant structure in the form of the plant material as well as below-grade in the form of soil carbon. 3.663 pounds of CO2 sequestered produces 1 pound of carbon stored. The fol- lowing diagrams are the annual carbon sequestration levels by neighbor- hood provided by the City’s tree canopy and by its lawns and grasses. Annual Carbon Sequestration by Trees 34,822,060 pounds (15,795 Metric Tons — 2.2% of annual GHG emissions) 3-8 Edina Ground Cover And Carbon Sequestration Study Land Cover Impacts and Benefits Pollution Absorption - Carbon The combined carbon sequestration services of grasses and trees through- out the community can be seen as a measure of equity of green infrastruc- ture when viewed on a per-acre basis. Higher per-acre carbon sequestra- tion rates reflect combined higher rates of per-acre green infrastructure (trees and grasses). In addition, these per-acre values can help guide fu- ture tree canopy increase goals by focusing on portions of the community with lower per-acre baselines. Annual Carbon Sequestration of Green Infrastructure per Acre (in Metric Tons) City Average: 4,962 Census Tract High: 5,751 Tract: 239.02 Census Tract Low: 1,783 Tract: 240.05 4-1 Edina Ground Cover And Carbon Sequestration Study 04 S e c t i o n Tree Canopy Economic Value Click here to return to TOC In recent years, several computer models have been developed by the USDA Forest Service and collabora- tors to assist cities in assessing the value and environ- mental benefits of their tree resources. Each of the benefits outlined in Section 3 of this report have eco- nomic benefit as well as environmental benefit. Air Pollution Removal Values The air pollutants estimated are the six criteria pollu- tants included in Section 3 of this report, defined by the U.S. Environmental Protection Agency (EPA); car- bon monoxide (CO), nitrogen dioxide (NO2), ozone (O3), sulfur dioxide (SO2), and particulate matter (PM), which includes particulate matter less than 2.5 microns (PM2.5) and particulate matter greater than 2.5 and less than 10 microns (PM10). Air pollution removal value estimates are based on procedures detailed in Nowak et al. (2014). This pro- cess used local tree cover, leaf area index, percent evergreen, weather, pollution, and population data to estimate pollution removal (g/m2 tree cover) and values ($/m2 tree cover) in urban and rural areas. Current i-Tree Canopy Annual Tree Benefit Estimate values per ton of pollution removed are: CO at $1,333.50; NO2 at $477.89; O3 at $2,443.66; PM2.5 at $91,955.05; SO2 at $163.18; PM10 at $6,268.44, and CO2 sequestration at $35.38. Building Energy Savings Values As outlined in Section 3 of this report, building energy savings values can be estimated using average energy affecting tree counts per acre, by community density type, established through the study “Residential build- ing energy conservation and avoided power plant emissions by urban and community trees in the Unit- ed States.” Using these averages, we can estimate the total electrical and natural gas savings contributed by the City’s tree canopy using average local electrical and natural gas costs. Annual Pollution Absorption Value of Trees $1.64 Million Annual Energy Savings Value of Trees $4.9 Million 4-2 Edina Ground Cover And Carbon Seques- Tree Benefit per Acre City Average: $660 Census Tract High: $774 Tract: 231 Census Tract Low: $233 Tract: 240.05 Tree Benefit per Household City Average: $301 Census Tract High: $1,123 Tract: 239.02 Census Tract Low: $46 Tract: 240.04 Tree Canopy Economic Value Equity in Tree Value The economic benefits outlined on the previous page can be viewed on the basis of value-per-acre and value -per-household to establish an understanding of tree benefit equity throughout the City. 5-1 Edina Ground Cover And Carbon Sequestration Study 05 S e c t i o n Findings Click here to return to TOC The health of the City’s green infrastructure and the impacts of impervious land cover affect every- one in the community and City policies and actions should consider needs of the entire communi- ty. As with all planning efforts landcover planning benefits from analysis in order to assist in estab- lishing priorities for efforts. An effort to structure a prioritization should not be seen as an attempt to discard the need to address or improve land cover impacts for any neighborhood of the city - whether or not it is defined as one of the “priority” neighborhoods. Prioritization, however, is nec- essary to ensure the greatest impact and effectiveness of limited City resources. To assist in prioritization, in the following pages, this report reviews the community Green Infra- structure and Impervious Surface data through “filters” in order to arrive at a recommended priori- tization of neighborhoods for policy action. These “filters” are based on the land coverage infor- mation detailed in Section 2 of this report. Ground Cover Charac- teristics by Census Tract Organized by Share of Low Income Population (LMI) The bar chart below provides a side-by-side comparison of the of land cover data de- tailed in Section 2, by Census Tract. Ground Cover Breakdown by Type Mo r e L M I Le s s L M I Trend Line Trend Line 5-2 Edina Ground Cover And Carbon Sequestration Study Review Criteria - Green Infrastructure Prioritization of locations for increased green infrastructure included in this report is based on an equity approach. This approach reviews a range of land cover and demographic charac- teristics of each neighborhood in an “Environmental Equity Index”. This process is based on procedures developed by the USDA Forest Service. To determine the best locations to plant trees, tree canopy and impervious cover maps devel- oped for this report’s Section 2 were used in conjunction with U.S. Census data to produce an index of priority planting areas by neighbor- hood. Index values were produced for each neighborhood with higher index values relating to higher priority of the area for tree planting. This index is a type of “environmental equity” index with areas with higher human population density, higher economic stress, lower existing tree cover, and higher total tree canopy poten- tial receiving the higher index value. The criteria used to make the index were: • Tree Stock Potential • Economic Stress Density • Population Density • Heat Island Mitigation Potential Findings Priority Tree Canopy Increase Based on Tree Stock Potential Levels: Tree stock potential level refers to the ratio of additional tree canopy potential to the total area of potential tree canopy and existing tree canopy coverage. Higher tree stock potential levels represent higher potential and priority for tree planting. Higher numbers represent higher prioritization based on this category. Priority Tree Canopy Increase Based on Eco- nomic Stress Density: The social, economic, and environmental ben- efits of a robust tree canopy are a benefit to all community residents, however, those living under economic stress are both more likely to live in areas with lower tree canopy coverage as well as those for whom the benefits have the largest positive impacts. Higher economic stress density values represent higher poten- tial for increasing environmental equity of tree canopy cover. Higher numbers represent high- er prioritization based on this category. Edina Ground Cover And Carbon Sequestration Study 5-3 Findings Priority Tree Canopy Increase Based on Population Density: The greater the popu- lation density, the greater the opportuni- ty for tree planting to impact community members. Population densities shown are estimates based on US Census data by tract. Higher numbers repre- sent higher prioritiza- tion based on this cate- gory. Priority Tree Canopy Increase Based on Heat Island Mitigation Po- tential: As outlined in Section 3, heat island or micro- heat island impacts are not equally felt throughout the city. This prioritization re- view organizes the cen- sus tracts based on op- portunity to mitigate current and future heat island impacts through tree planting. Higher Weighted Priority Tree Canopy Increase The weighted prioritization for tree canopy increase looks to balance the potential for increased tree canopy with the opportunity to im- prove tree canopy benefit equity, potential to positively impact as many households as possible, and the need for mitigation of heat is- land impacts. Higher numbers represent higher prioritization. The priorities above are weighted as follows: Potential for new trees: 20% Population density: 20% Low Income Population (equity adjustment): 30% Heat Island mitigation need: 30% Edina Ground Cover And Carbon Sequestration Study 5-4 Findings In addition to opportunities to expand and improve the city’s tree canopy, the find- ings of the ground cover study as outlined in Section 2 may be used to identify ad- ditional opportunities for increased heat island mitigation and increased native grass installations. Turf Reduction Potential As illustrated in the chart to the right, 93% of grass lands in Edina are manicured lawns—representing a great opportunity for turf reduction. Turf reduction can increase stormwater uptake, reduce potable water use, and increase soil carbon. Impervious Surface Characteristic As outlined in Section 3, the city’s experienc- es of heat island are directly impacted by the level of impervious surface coverage— particularly dark roofs and pavement. As the diagram to the right illustrates dark pavements make up 50% of all impervious surfaces, followed by dark roof surfaces at 30%. These represent significant opportuni- ties for decreasing heat island impacts in the community. Impervious Surface Characteristics by Cen- sus Tract The bar chart to the right shows the imper- vious surface characteristics by census tract. The portions of the community with the highest shares of dark building and dark pavement surfaces may benefit the most from heat island mitigation strategies like cool pavement systems or green roofs. Mo r e L M I Le s s L M I 6-1 Edina Ground Cover And Carbon Sequestration Study 06 S e c t i o n Calculating Potential Goals Click here to return to TOC Calculating Tree Canopy Coverage Goal for 2040 Total tree canopy coverage goals are central to long-range land cover goal recommendations for the city. In support of an “Environmental Equity” approach to tree canopy goalsetting, as outlined in the Findings Section of this report, identifica- tion of long-term tree canopy coverage goals includes consideration of each neighborhood’s Tree Stock value (the amount of existing tree canopy compared to available land for tree cano- py coverage), population densities, economic stress densities, and heat island mitigation need. The recommended goals for 2040 Tree Canopy coverage are based on individual neighborhood calculations, corresponding to the neighborhood prioritizations outlined in the Findings Section of this report. 2040 Tree Canopy goals are first cal culated as Tree Stock goals, that is, goals calcu- lated against the total potential Tree Stock area (existing tree canopy area + existing lawn/grass/ shrub area), with a progressive percentage in- crease goal based on neighborhood prioritiza- tion. As the total Tree Stock area (potential tree canopy) varies by neighborhood, the resulting Tree Canopy percentage varies for each neigh- borhood. The recommended Tree Stock increase goals are: For neighborhoods in the top 1/3rd Neighbor- hood Priority Ranking: 10% For neighborhoods in middle 1/3rd Neighbor- hood Priority Ranking: 6.3% For neighborhoods in bottom 1/3rd Neighbor- hood Priority Ranking: 2.5% Tree Canopy In- crease in Absolute Land Cover % Tree Canopy In- crease Over Existing Tree Canopy Area 6-2 Edina Ground Cover And Carbon Sequestration Study Calculating Potential Goals New Tree Plantings Needed to Achieve Tree Canopy Coverage Goal for 2040 While it is easy to think of the long range Tree Canopy coverage goals for each neighborhood in terms of planting trees, it is critical that tree canopy enhancement goals include a combina- tion of tree protection, tree maintenance, and tree planting in order to be fully realized and efficiently implemented. A common calculation used to determine the new tree planting requirements in order to meet the long-range tree canopy coverage goals, while recognizing the impacts of tree can- opy growth and mortality was established by a 2002 Report to North East State Forester Asso- ciation by Luley and Bond. That report offers the following conceptual analysis for increasing UTC: CB + CG - CM + CN = CT Where: CB= the existing Tree Canopy; CG= the growth of existing Tree Canopy (protection and maintenance); CM= Tree Canopy mortality or loss due to natural and man -induced causes. CN= Tree Canopy increase from new trees (planting); and CT= total Tree Canopy Result (or goal) The maps on the following pages illustrate these calculations for the city. 6-3 Edina Ground Cover And Carbon Sequestration Study Calculating Potential Goals Translating Tree Canopy Coverage Goal To New Tree Planting - Growth Rates (CG) Consideration of tree canopy growth rate is important in anticipating long-range tree canopy goals and annual new planting needs. According to a 2014 USDA report, the average growth rate for non- managed forests is 2% while the average growth rate for managed forests is 2.5% annually. Translating Tree Canopy Coverage Goal To New Tree Planting - Mortality Rates (CM) As with growth rate, consideration of tree canopy mortality is necessary for long-range Tree Canopy planning. According to the 2014 USDA report, the average mortality rate for non-managed forests is 1.86% while the average mortality rate for managed forests is 1.5% annual. There are few studies ex- ploring mortality rates for trees in urban and suburban settings, those studies that exist indicate a range from 2.7% for general suburban trees and 3.5% to 14% for street trees*. As many trees in the city exist in forest type setting on publicly owned land and much of the balance are general suburban trees observed regularly and likely seen as having value, we recommend using a mortality rate of 1.5%. Ash Tree Mortality Ash trees are projected to be significantly impacted by the infestation of the Emerald Ash Borer insect. Long-term tree canopy planning for the city should anticipate substantial (complete for all non-treated trees) Ash tree mortality within the next 10-15 years. The exact extent of Ash trees community wide has not been surveyed, however, according to a 2012 study by Whittier College, (Potential impacts of emerald ash borer invasion on biogeochemical and water cycling in residential landscapes across a metropolitan region) for the potential long-term impact on community-wide tree canopy, we recommend an estimated extent of Ash trees throughout the city of up to 19% of the existing tree canopy. We recommend a detailed tree species study be conducted to identify the City wide canopy make-up by species. Until that detailed information is available, this report will use an assumed average community wide ash tree coverage of 10%, for an additional annualized tree canopy loss of 0.667% due to potential Emerald Ash Borer loss over 15 years. With this Ash tree mortality adjustment, the total recommended tree canopy mortality rate for long-range tree canopy planning is 2.13% *How Many Trees Are Enough? Tree Death and the Urban Canopy https://scenariojournal.com/article/how-many-trees-are-enough/ 6-4 Edina Ground Cover And Carbon Sequestration Study CB (existing) CG (growth) CM (loss) CN (new) CT (year goal) UTC (year end coverage %) 2022 3555 78 74 16 3575 36.2% 2023 3575 79 74 16 3595 36.4% 2024 3595 79 75 16 3614 36.6% 2025 3614 80 75 16 3634 36.8% 2026 3634 80 76 16 3654 37.0% 2027 3654 80 76 15 3674 37.2% 2028 3674 81 77 15 3693 37.4% 2029 3693 81 77 15 3713 37.6% 2030 3713 82 77 15 3733 37.8% 2031 3733 82 78 15 3753 38.0% 2032 3753 83 78 15 3772 38.2% 2033 3772 83 79 15 3792 38.4% 2034 3792 83 79 15 3812 38.6% 2035 3812 84 79 15 3832 38.8% 2036 3832 84 80 15 3851 39.0% 2037 3851 85 80 15 3871 39.2% 2038 3871 85 81 15 3891 39.3% 2039 3891 86 81 15 3911 39.5% 2040 3911 86 81 15 3930 39.7% Translating Tree Canopy Coverage Goal To New Tree Planting - New Tree Planting Annual Target (CN) Using the new planting requirement calculation method (CB + CG - CM + CN = CT) with the previously defined values for existing tree canopy (CB), growth rates (CG), mortality rates (CM), and the 2040 Tree Canopy (CT) goals by neighborhood the required number of new trees to be planted to meet that goal can be identified. The map below shows the annual new tree count required to meet the 2040 tree canopy goals for each neighbor- hood. Calculating Potential Goals Annual Path to 2040 Tree Canopy Cover Goal The chart below shows the community wide average values for year begin- ning canopy cover (CB), annual growth rate (CG), mortality rate (CM), the new tree planting targets (CN) and the year end tree canopy goal (CT) for each year through the 2040 goal. - - + + = - + + = - + + = - + + = - + + = - + + = - + + = - + + = - + + = - + + = - + + = - + + = - + + = - + + = - + + = - + + = - + + = - + + = - + + = New Tree Planting Annual Target to Meet 2040 Tree Canopy Goal (CN) Community-Wide Total: Note, Acreage represents the canopy coverage at year of planting, with an assumed new tree crown radius of 5’: 1,976 New Trees 16 Acres 6-5 Edina Ground Cover And Carbon Sequestration Study 07 S e c t i o n Recommendations Click here to return to TOC Conclusions Even with a strong existing green infrastructure, the City has the potential for more. Using re- search from the University of Minnesota, this study indicates that the City of Edina has a heat island impact of at least 3-4 degrees in daytime and 4-6 degrees in nighttime temperature in- crease. Meanwhile, even with the significant pollution absorption services the City’s green infrastructure provides, only a fraction of the man-made air quality impacts occurring in the City are mitigated. Consequently, increases in green infrastructure offer significant reward po- tential for the City. Primary Strategic Goal Recommendations Section 6 of this report provided a range of rec- ommended goals for the City of Edina. The over- arching goals recommended in this report are: 1) To increase the tree canopy coverage throughout the City, particularly in the Priori- ty Neighborhoods identified in Section 6, to an average of at least 39.7% City-wide by 2040. 2) Decrease the quantity of “dark” impervious surfaces throughout the City by an average of at least 5% of total citywide coverage by 2040. The percentage targets identified for both of these goals are intended to be achievable goals - in both instances, exceeding the percentage goals would be ideal. Supportive Strategic Goal Recommendations Based on the 2040 Tree Canopy Cover and 2040 Heat Island Reduction goals outlined in the previ- ous page, we offer the potential additional strat- egies for consideration: Lawns and Grasslands L1: Increase pollinator supportiveness of lawns and grasslands in City of Edina and achieve a 5% turf replacement with native grasses and wildflowers by 2030. Tree Canopy T1: Create economic development potential through identification and creation of urban wood programs. T2: Create strategic compatibility between City wide tree canopy and renewable energy goals. 6-6 Edina Ground Cover And Carbon Sequestration Study A1 S e c t i o n i-Tree Technical Notes Click here to return to TOC A2 S e c t i o n Climate Adaptive Tree Species (Northern Institute of Applied Climate Science) Click here to return to TOC Prepared by: 2515 White Bear Ave, A8 Suite 177 Maplewood, MN 55109 Contact: Ted Redmond tredmond@paleBLUEdot.llc