Trees are essential to healthy communities.

In the past decades. many in cities across the country have cited issues with the presence of urban trees - damage to sidewalks, presence of leaf litter and as a source of potential property damage from falling limbs.   However, technology and modeling tools show that trees are proven to be valuable city infrastructure and essential for vibrant communities.  We can calculate the value of the benefits  trees provide and show that they outweigh the investment needed for planting and maintenance. 
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  1. Trees provide effective and low-cost solutions to a variety of urban challenges. Urban trees have proven to be an effective tool that many city and county agencies can use to fulfill their missions, including planning, economic development, public health, public works, stormwater, and sanitation departments. Trees have been proven to reduce water and air pollution, improve public health, increase property value, and enhance the success of business districts.
  2. Trees are a smart investment. On an annual basis, cities often see a strong return on investment related to tree costs and benefits. A recent five-city study found that cities received benefits ranging from $1.50–$3.00 for every dollar invested in trees (U.S. Environmental Protection Agency 2015).  
  3. Trees increase in value over time. Unlike man-made systems, trees are the only urban infrastructure that actually increase services and value over time. As trees mature, benefits increase exponentially, unlike more traditional city infrastructure such as roads and bridges that deteriorate with age. 

What is a Tree Canopy?


​Urban Tree Canopy (UTC) refers to the layer of tree leaves, branches, and stems that provide tree coverage of the ground when viewed from above.  
"The nation behaves well if it treats the natural resources as assets which it must turn over to the next generation increased; and not impaired in value."
-Theodore Roosevelt

Services of Urban Trees

​Trees can remove up to 60% of street-level air pollution, including carbon dioxide, ozone, nitrogen dioxide, sulfuric dioxide (a component of smog), and particulate matter (i.e., dust, ash, dirt, pollen, and smoke) (Coder 1996).  This service has a very significant impact on public health.
Studies have shown that tree-covered commercial shopping districts are more successful than those without canopy. 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). 
​Urban trees are widely accepted as one of the most effective long-term solutions to reducing the effects of urban heat islands, and can lower ambient temperatures by 20–45°F (EPA 2015).
Why is this even important?  ​Heat stress has been proven to cause significant public health problems and even mortality. Each year, more Americans die from extreme heat than all other natural disasters combined (i.e., hurricanes, floods, tornadoes, lightning). 
Trees have been shown to create healthy environments for people by improving air quality and reducing heat island effects. New York City saw a significant decrease of asthma in young children (-29%) after increasing its tree canopy through the installation of over 300 trees for each square kilometer (Lovasi et al. 2008).  Studies have also shown that individuals with views or access to greenspace tend to be healthier; employees experience 23% less sick time and greater job satisfaction,
and hospital patients recover faster with fewer drugs
​ (Ulrich 1984).​​
Walkability and pedestrian-friendly areas tend to draw the most people; also, tree cover is a powerful tool in revitalizing districts and neighborhoods.  Urban trees have been shown to slow traffic and help ensure safe, walkable streets. Traffic speeds and driver stress levels have 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). According to the Federal Highway Administration, tree canopy along a street discourages speeding (U.S. Department of Transportation 2015). The buffers between walking areas and driving lanes created by trees make streets feel safer. 
Tree-lined streets can create stronger communities and attract new residents. While less quantifiable, the tree benefits related to community building are no less important than other services. One study showed that residents of apartment buildings surrounded by trees reported knowing their neighbors better, socializing with them more often, having stronger community, and feeling safer and better adjusted than did residents of more barren, but otherwise identical areas (Kuo and Sullivan 2001)
A study in Baltimore found that a 10% increase in tree canopy was associated with a roughly 12% decrease in crime. It has also been shown that outdoor areas populated with trees tend to suffer from less graffiti, vandalism, and littering than their treeless neighbors (PHS 2015).
Pollution and noise from busy roadways and rail lines can create unhealthy and undesirable conditions for those living nearby (ALA 2015). Buffers of trees 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).
It's been found that the more tree cover around a school, the better test scores will be. Why? The increased exposure to nature that trees provide helps to increase concentration and engagement, while also leading to less disruptive behavior (Kuo et. all 2020).
​Trees are an essential component to habitat and conservation in urban areas. They intercept and clean large quantities of polluted stormwater, preventing further degradation to vital aquatic and terrestrial habitats. Additionally, 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). A healthy wildlife population indicates a healthy place for people to live too.
As cities grow, the amount of land that naturally absorbs rainwater (i.e., lawns, parks, fields, woods) tends to shrink, while hard surfaces that cause rain to runoff (i.e., roads, buildings, parking lots) increase in area. After flowing over roads, parking lots, and lawns, rainwater accumulates fertilizers, oil, chemicals, grass clippings, litter, pet waste, and other contaminants, polluting water. One mature deciduous tree can intercept over 500 gallons of rainwater a year, while a tree that holds leaves all year (e.g., pine, magnolia) can intercept up to 4,000 gallons per year (Seitz 2008).
​Trees reduce cooling and heating costs, both through their shade as well as emissions of moisture. In fact, the cooling effect of one healthy tree is equivalent to 10 room-sized air conditioners operating 20 hours a day (North Carolina State University 2012). The shade of properly-placed trees can save homeowners up to 58% on daytime air conditioning costs, while mobile homeowners can save up to 65% (Smith 1999).
​Trees have been shown to increase residential property and commercial rental values by an average of 7% (Wolf 2007).

References

American Lung Association (ALA). 2015. State of the Air 2015. http://www.stateoftheair.org (accessed May 30, 2015).
Coder, R.D. 1996. “Identified Benefits of Community Trees and Forests.” University of Georgia Cooperative Extension Service, Forest Resources Publication FOR96-39.
​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
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.
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.
​Kuo, M., Klein, S., Browning, M., Zaplatosch, J. 2021. "Greening for Academic Achievement: Prioritizing What to Plant and Where." Landscape and Urban Planning 206:103962.
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).
North Carolina State University. 2012. “Americans are Planting Trees of Strength.” http://www.treesofstrength.org/benefits.htm. Accessed May 15, 2015.
Pennsylvania Horticultural Society (PHS). 2015. Greening LandCare Program: Evidence of Success. http://phsonline.org/programs/landcare-program/evidence-of-success. Accessed June 10, 2015.
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.
Smith, D. 1999. “The Case for Greener Cities.” American Forests. Autumn 1999 v. 105 (3).
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.
Wolf, K.L. 2007. “City Trees and Property Values”. Arborist News (August):34–36.
Ulrich, R. S. 1984. “View through a window may influence recovery from surgery.” Science, 224, 420–421.
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.