Role of Trees in Knoxville
Why all this planning and effort for trees? Is this the best use of our time? Consider the role trees play in Knoxville (and in every city):
Human HealthTrees have a significant impact on the human health and livability of a city. This occurs through lower heat levels, lower air and water pollution, stronger community, better mental health and reductions in noise.
Trees Alleviate Heat Stress
Heat stress has been proven to cause significant public health problems and even mortality. In fact, each year, more Americans die from extreme heat than all other natural disasters combined (i.e., hurricanes, floods, tornadoes, lightning). Urban trees are widely accepted as one of the most effective long-term solutions to reducing the effects of urban heat islands. Properly placed mature tree canopy can lower overall ambient temperatures by 20° to 45°F (EPA 2015). Trees Reduce Air Pollution
Trees reduce or can completely remove many components of street-level air pollution, including carbon dioxide, ozone, nitrogen dioxide, sulfur dioxide (a component of smog), and small particulate matter (i.e., dust, ash, dirt, pollen, and smoke). Ozone and particulates can especially aggravate existing respiratory conditions (like asthma) and create long-term chronic health problems (American Lung Association 2015). Trees reduce nearby indoor air pollution by more than 50% (Maher et al. 2013) and reduce rates of childhood asthma (Lovasi et al. 2008). More neighborhood tree canopy is associated with better overall health, including lower rates of obesity, high blood pressure and asthma (Ulmer et al. 2016). Recent studies have also shown an association in total health care costs in areas with more canopy (Becker et al. 2019), with individuals in higher canopy areas paying on average $374 less every year in healthcare costs (Van Den Eeden et al. 2022). Trees Buffer Against Noise and Pollution
Pollution and noise from busy roadways and rail lines can create unhealthy and undesirable conditions for those living nearby (ALA 2015). Buffers of trees can significantly reduce both noise and pollution. A 100-foot-wide, 45-foot-high densely-planted tree buffer can reduce highway noise by 50% (NC State 2012). |
Trees improve Mental Health and Create Stronger Communities
While less quantifiable, the tree benefits related to community building are no less important than other services. Trees have been shown to have a calming and healing effect on ADHD adults and teens (Burden 2008). Increased access to trees has also been linked to reduced rates of mental illness like anxiety and depression (Rajoo et al. 2021), increases in creativity (Yu & Hsieh 2020), better test scores amongst students (Sivarajah et al. 2018), and even higher rates of quality sleep (Astrell-Burt & Feng 2019). Trees Reduce Water Pollution
Trees intercept, absorb, and slow rainwater, all of which play a major role in reducing the amount of contaminated stormwater that enters sewer systems and reducing the threat of floods. Based on recent research, urban trees may be even more effective at managing stormwater than we originally estimated, as single trees (like those planted in an open yard) appear to transpire at nearly 3X the rate of a similar tree located in a forest setting (Ponte et al. 2021). This estimates that the removal of a single tree increases stormwater runnoff by an average of 1,585 gallons (Coville et al. 2022), and even more for trees that hold their leaves year-round (Seitz and Escobedo 2008). |
Walkable Communities
Tree canopy cover is vital to a walkable community. According to the Federal Highway Administration, urban tree canopy along streets have been shown to slow traffic, helping ensure safe, walkable streets in communities The buffers between walking areas and driving lanes created by trees also make streets feel safer for pedestrians and cyclists.(U.S. Department of Transportation 2015). Driver stress levels have also been reported to be lower on tree-lined streets, contributing to a reduction in road rage and aggressive driving (Wolf 1998a, Kuo and Sullivan 2001).
Energy Savings
Trees provide energy savings by reducing cooling and heating costs, both through their shade as well as the release of moisture through transpiration. Trees properly placed around buildings can reduce air conditioning needs by 30% and can save 20–50% in energy used for heating. Computer models devised by the U.S. Department of Energy (2018) predict that the proper placement of only three trees can save an average household between $100 and $250 in energy costs annually. Even properties not directly adjacent to greenspaces can experience energy saving benefits from trees, with buildings 500 feet away from park spaces still experiencing significant cooling effects in summer, reducing the demand for cooling energy consumption by 43% (Toparlar et al. 2020).
This is especially important in low income communities, where household have a higher energy burden (larger percentage of monthly budget is spent on energy).
This is especially important in low income communities, where household have a higher energy burden (larger percentage of monthly budget is spent on energy).
Carbon Storage
Trees are constantly removing and storing carbon dioxide from the atmosphere. Most of the carbon dioxide (CO2) in the atmosphere comes from human activities that involve the burning of fossil fuels. High levels of CO2 result in climate change, which has resulted in more frequent and severe storms, droughts, and other natural stresses across the world in recent decades. An average tree in the United States can capture about 1,200 pounds of carbon dioxide per over its lifetime; the cumulative effect of all US trees results in capturing 17% of our nation’s carbon dioxide emissions annually (Daley 2022).
Successful Business Districts
In multiple studies, consumers showed a willingness to pay 11% more for goods and shopped for a longer period of time in shaded and landscaped business districts (Wolf 1998b, 1999, and 2003). Consumers also felt that the quality of products was better in business districts surrounded by trees and were willing to pay more (Wolf 1998a).
Property Value
The U.S. Forest Service estimates that the presence of street trees increases adjacent home values by an average of $9,000 (Donovan & Butry 2010).
Wildlife Habitat / Ecosystem Health
As smaller forests are connected through planned or informal urban greenways, trees provide essential habitat to a range of birds, pollinators, and other wildlife that feed on insects (Dolan 2015). Recent studies show that bees in areas with higher tree canopy have lower levels of toxins related to pollution (Barbosa et al. 2021), and trees can be an essential source of early pollen for these important pollinators (Honchar & Gnatiuk 2020). Higher density (and diversity) of trees is also associated with higher bird density, including natives and rare birds of prey (Heggie-Gracie et al. 2020 & Mirski 2020).
Associated with Lower Crime
Trees have been shown to contribute to a decrease in crime. A study in Baltimore found that a 10% increase in tree canopy was associated with a roughly 12% decrease in crime (Troy et al. 2012). In an experimental study, newly planted street trees were strongly correlated with a reduction in violent crimes, an effect especially prominent in neighborhoods with lower median household income (Burley 2018).
References
American Lung Association (ALA). 2015. State of the Air 2015. http://www.stateoftheair.org (accessed May 30, 2015).
Astrell-Burt, T., Feng, X. 2019. Does sleep grow on trees? A longitudinal study to investigate potential prevention of insufficient sleep with different types of urban green space. SSM - Population Health https://www.sciencedirect.com/science/article/pii/S2352827319301703
Barbosa, M., Fernandes, A.C.C., Alvez, R.S.C., Alves, D.A., et al. 2021. Effects of native forest and human-modified land covers on the accumulation of toxic metals and metalloids in the tropical bee Tetragonisca angustala. Ecotoxicology and Environmental Safety 215: https://doi.org/10.1016/j.ecoenv.2021.112147
Becker, D.A., Browning, M., Kuo, M., Van Den Eeden, S.K. 2019. Is green land cover associated with less health care spending? Promising findings from county-level Medicare spending in the continental United States. Urban Forestry & Urban Greening 41: 39-47.
Burden, D. 2008. "22 Benefits of Urban Street Trees." Walkable Communities, Inc. http://www.walkable.org/assets/downloads/22BenefitsofUrbanStreetTrees.pdf. Accessed March 2015.
Burley, B.A. (2018) Green infrastructure and violence: Do new street trees mitigate violent crime? Health & Place 54, 43-49
Coville, R.C., Kruegler, J., Selbig, W.R., Hirabayashi, S., Loheide, S.P., Avery, W., Shuster, W. et al. 2022. Loss of street trees predicted to cause 6000 L/tree increase in leaf-on stormwater runoff for Great Lakes urban sewershed. Urban Forestry & Urban Greening 74: https://doi.org/10.1016/j.ufug.2022.127649
Daley, J. 2022. Trees are the secret weapon of America's historic climate bill. Time https://time.com/6208895/climate-bill-forests/ Accessed March 7, 2023.
Dolan, RW. 2015. Two Hundred Year of Forest Change: Effects of Urbanization on Tree Species Composition and Structure. ISA Aboriculture & Urban Forestry 41 (3): 136-145
Donovan, G.H., & Butry, D.T. 2010. Trees in the city: valuing street trees in Portland, Oregon. Landscape and Urban Planning 94: 77-83
EPA U.S. Environmental Protection Agency. 2015. Heat Island Effect: Trees and Vegetation. http://www.epa.gov/heatislands/mitigation/trees.htm. Accessed May 30, 2015.
Heggie-Gracie, S.D., Krull, C.R., & Stanley, M.C. 2020. Urban divide: predictors of bird communities in forest fragments and the surrounding urban matrix. Emu - Austral Ornithology: https://doi.org/10.1080/01584197.2020.1857650.
Honchar, G.Y. & Gnatiuk, A.M. 2020. Urban ornamental plants for sustenance of wild bees (Hymenoptera, Apoidea). Plant Introduction 85: https://doi.org/10.46341/PI2020014
Kuo, F., and W. Sullivan. 2001. Aggression and Violence in the Inner City: Effects of Environment via Mental Fatigue. Environment and Behavior 33(4):543–571.
Lovasi, G.S., Quinn, J.W., Neckerman, K.M., Perzanowski, M.S., & Rundle, A. 2008. Children Living in Areas with More Street Trees have Lower Prevalence of Asthma. Journal of Epidemiology & Community Health. 62:7(647-49).
Maher, B.A., Ahmed, I.A.M., Davison, B., Karloukovski, V. & Clarke, R. 2013. Impact of roadside tree lines on indoor concentrations of traffic-derived particulate matter. Environmental Science & Technology 47(23): 13737-13744. https://pubs.acs.org/doi/full/10.1021/es404363m
Mirski, P. 2020. Tree cover density attracts rare bird of preay specialist to nest in urban forest. Urban Forestry & Urban Greening 55: https://doi.org/10.1016/j.ufug.2020.126836
North Carolina State University. 2012. Americans are Planting Trees of Strength. http://www.treesofstrength.org/benefits.htm. Accessed May 15, 2015.
Ponte, S., Sonti, N.F., Phillips, T.H., & Pavao-Zuckerman, M.A. 2021. Transpiration rates of red maple (Acer rubrum L.) differ between management contexts in urban forests of Maryland, USA. Scientific Reports 11: https://www.nature.com/articles/s41598-021-01804-3
Rajoo, K.S., Karam, D.S., Abdu, A, Rosli, Z., Gerusu, G.J. 2021. Addressing psychosocial issues caused by the COVID-19 lockdown: Can urban greeneries help? Urban Forestry & Urban Greening 65: https://doi.org/10.1016/j.ufug.2021.127340
Seitz, J. and F. Escobedo. 2008. Urban Forests in Florida: Trees Control Stormwater Runoff and Improve Water Quality. School of Forest Resources and Conservation Department, UF/IFAS Extension. https://edis.ifas.ufl.edu/fr239. Accessed November 3, 2015.
Sivarajah, S., Smith, S.M. & Thomas, S.C. 2018. Tree cover and species composition effects on academic performance of primary school students. PLoS ONE 13(12): e0193254. https://doi.org/10.1371/journal.pone.0193254
Toparlar, Y., Blocken, B., Maiheu, B., & van Heijst, G. 2020. More than a green space: how much energy can an urban park save? Production of Climate Responsive Urban Built Environments, proceedings book 2: 23-32.
Troy, A., Grove, J.M., O'Neil-Dunne, J. 2012. The relationship between tree canopy and crime rates across an urban-rural gradient in the greater Baltimore region. Landscape and Urban Planning 106(3): 262-270.
Ulmer, J.M., Wolf, K.L., Backman, D.R., Tretheway, R.L., Blain, C.J., O'Neil-Dunne, J.P., & Frank, L.D. 2016. Multiple health benefits of urban tree canopy: The mounting evidence for green prescription. Health & Place 42: 54-62.
US DOE - Office of Energy Efficiency & Renewable Energy. 2018. Low-Income Household Energy Burden Varies Among States — Efficiency Can Help In All of Them. https://www.energy.gov/sites/prod/files/2019/01/f58/WIP-Energy-Burden_final.pdf
Van Den Eeden, S.K., Browning, M.H., Becker, D.A., Shan, J., Alexeeff, S.E., Ray, G. T., Quesenberry, C.P., Kuo, M. 2022. Association between residential green cover and direct healthcare costs in Northern California: An individual level analysis of 5 million persons. Environment International 164: https://doi.org/10.1016/j.envint.2022.107174 Accessed October 5, 2022.
Wolf, K.L. 1998a. Urban Nature Benefits: Psycho-Social Dimensions of People and Plants. University of Washington, College of Forest Resources Fact Sheet. 1(November).
Wolf, K.L. 1998b. Trees in Business Districts: Comparing Values of Consumers and Business. University of Washington College of Forest Resources Fact Sheet. 4(November).
Wolf, K.L. 1999. Grow for the Gold. TreeLink Washington DNR Community Forestry Program. 14(spring).
Wolf, K.L. 2003. Public Response to the Urban Forest in Inner-City Business Districts. J. Arbor 29(3):117–126.
US DOT, FHWA. 2015. Bicycle & Pedestrian Planning: Best Practices Design Guide. https://www.fhwa.dot.gov/environment/bicycle_pedestrian/publications/sidewalk2/sidewalks209.cfm. Accessed January 3, 2020.
Yu, Chia-Pin & Hsieh, Hsuan 2020. Beyond restorative benefits: evaluating the effect of forest therapy on creativity. Urban Forestry & Urban Greening 51: https://doi.org/10.1016/j.ufug.2020.126670
Astrell-Burt, T., Feng, X. 2019. Does sleep grow on trees? A longitudinal study to investigate potential prevention of insufficient sleep with different types of urban green space. SSM - Population Health https://www.sciencedirect.com/science/article/pii/S2352827319301703
Barbosa, M., Fernandes, A.C.C., Alvez, R.S.C., Alves, D.A., et al. 2021. Effects of native forest and human-modified land covers on the accumulation of toxic metals and metalloids in the tropical bee Tetragonisca angustala. Ecotoxicology and Environmental Safety 215: https://doi.org/10.1016/j.ecoenv.2021.112147
Becker, D.A., Browning, M., Kuo, M., Van Den Eeden, S.K. 2019. Is green land cover associated with less health care spending? Promising findings from county-level Medicare spending in the continental United States. Urban Forestry & Urban Greening 41: 39-47.
Burden, D. 2008. "22 Benefits of Urban Street Trees." Walkable Communities, Inc. http://www.walkable.org/assets/downloads/22BenefitsofUrbanStreetTrees.pdf. Accessed March 2015.
Burley, B.A. (2018) Green infrastructure and violence: Do new street trees mitigate violent crime? Health & Place 54, 43-49
Coville, R.C., Kruegler, J., Selbig, W.R., Hirabayashi, S., Loheide, S.P., Avery, W., Shuster, W. et al. 2022. Loss of street trees predicted to cause 6000 L/tree increase in leaf-on stormwater runoff for Great Lakes urban sewershed. Urban Forestry & Urban Greening 74: https://doi.org/10.1016/j.ufug.2022.127649
Daley, J. 2022. Trees are the secret weapon of America's historic climate bill. Time https://time.com/6208895/climate-bill-forests/ Accessed March 7, 2023.
Dolan, RW. 2015. Two Hundred Year of Forest Change: Effects of Urbanization on Tree Species Composition and Structure. ISA Aboriculture & Urban Forestry 41 (3): 136-145
Donovan, G.H., & Butry, D.T. 2010. Trees in the city: valuing street trees in Portland, Oregon. Landscape and Urban Planning 94: 77-83
EPA U.S. Environmental Protection Agency. 2015. Heat Island Effect: Trees and Vegetation. http://www.epa.gov/heatislands/mitigation/trees.htm. Accessed May 30, 2015.
Heggie-Gracie, S.D., Krull, C.R., & Stanley, M.C. 2020. Urban divide: predictors of bird communities in forest fragments and the surrounding urban matrix. Emu - Austral Ornithology: https://doi.org/10.1080/01584197.2020.1857650.
Honchar, G.Y. & Gnatiuk, A.M. 2020. Urban ornamental plants for sustenance of wild bees (Hymenoptera, Apoidea). Plant Introduction 85: https://doi.org/10.46341/PI2020014
Kuo, F., and W. Sullivan. 2001. Aggression and Violence in the Inner City: Effects of Environment via Mental Fatigue. Environment and Behavior 33(4):543–571.
Lovasi, G.S., Quinn, J.W., Neckerman, K.M., Perzanowski, M.S., & Rundle, A. 2008. Children Living in Areas with More Street Trees have Lower Prevalence of Asthma. Journal of Epidemiology & Community Health. 62:7(647-49).
Maher, B.A., Ahmed, I.A.M., Davison, B., Karloukovski, V. & Clarke, R. 2013. Impact of roadside tree lines on indoor concentrations of traffic-derived particulate matter. Environmental Science & Technology 47(23): 13737-13744. https://pubs.acs.org/doi/full/10.1021/es404363m
Mirski, P. 2020. Tree cover density attracts rare bird of preay specialist to nest in urban forest. Urban Forestry & Urban Greening 55: https://doi.org/10.1016/j.ufug.2020.126836
North Carolina State University. 2012. Americans are Planting Trees of Strength. http://www.treesofstrength.org/benefits.htm. Accessed May 15, 2015.
Ponte, S., Sonti, N.F., Phillips, T.H., & Pavao-Zuckerman, M.A. 2021. Transpiration rates of red maple (Acer rubrum L.) differ between management contexts in urban forests of Maryland, USA. Scientific Reports 11: https://www.nature.com/articles/s41598-021-01804-3
Rajoo, K.S., Karam, D.S., Abdu, A, Rosli, Z., Gerusu, G.J. 2021. Addressing psychosocial issues caused by the COVID-19 lockdown: Can urban greeneries help? Urban Forestry & Urban Greening 65: https://doi.org/10.1016/j.ufug.2021.127340
Seitz, J. and F. Escobedo. 2008. Urban Forests in Florida: Trees Control Stormwater Runoff and Improve Water Quality. School of Forest Resources and Conservation Department, UF/IFAS Extension. https://edis.ifas.ufl.edu/fr239. Accessed November 3, 2015.
Sivarajah, S., Smith, S.M. & Thomas, S.C. 2018. Tree cover and species composition effects on academic performance of primary school students. PLoS ONE 13(12): e0193254. https://doi.org/10.1371/journal.pone.0193254
Toparlar, Y., Blocken, B., Maiheu, B., & van Heijst, G. 2020. More than a green space: how much energy can an urban park save? Production of Climate Responsive Urban Built Environments, proceedings book 2: 23-32.
Troy, A., Grove, J.M., O'Neil-Dunne, J. 2012. The relationship between tree canopy and crime rates across an urban-rural gradient in the greater Baltimore region. Landscape and Urban Planning 106(3): 262-270.
Ulmer, J.M., Wolf, K.L., Backman, D.R., Tretheway, R.L., Blain, C.J., O'Neil-Dunne, J.P., & Frank, L.D. 2016. Multiple health benefits of urban tree canopy: The mounting evidence for green prescription. Health & Place 42: 54-62.
US DOE - Office of Energy Efficiency & Renewable Energy. 2018. Low-Income Household Energy Burden Varies Among States — Efficiency Can Help In All of Them. https://www.energy.gov/sites/prod/files/2019/01/f58/WIP-Energy-Burden_final.pdf
Van Den Eeden, S.K., Browning, M.H., Becker, D.A., Shan, J., Alexeeff, S.E., Ray, G. T., Quesenberry, C.P., Kuo, M. 2022. Association between residential green cover and direct healthcare costs in Northern California: An individual level analysis of 5 million persons. Environment International 164: https://doi.org/10.1016/j.envint.2022.107174 Accessed October 5, 2022.
Wolf, K.L. 1998a. Urban Nature Benefits: Psycho-Social Dimensions of People and Plants. University of Washington, College of Forest Resources Fact Sheet. 1(November).
Wolf, K.L. 1998b. Trees in Business Districts: Comparing Values of Consumers and Business. University of Washington College of Forest Resources Fact Sheet. 4(November).
Wolf, K.L. 1999. Grow for the Gold. TreeLink Washington DNR Community Forestry Program. 14(spring).
Wolf, K.L. 2003. Public Response to the Urban Forest in Inner-City Business Districts. J. Arbor 29(3):117–126.
US DOT, FHWA. 2015. Bicycle & Pedestrian Planning: Best Practices Design Guide. https://www.fhwa.dot.gov/environment/bicycle_pedestrian/publications/sidewalk2/sidewalks209.cfm. Accessed January 3, 2020.
Yu, Chia-Pin & Hsieh, Hsuan 2020. Beyond restorative benefits: evaluating the effect of forest therapy on creativity. Urban Forestry & Urban Greening 51: https://doi.org/10.1016/j.ufug.2020.126670
