Why Trees

Why we need trees:

Environmental Benefits

Carbon Sequestration

  • Carbon—the greenhouse gas. One hundred trees per year remove 5 tons of carbon dioxide from the air.[1]
  • One acre of trees sequesters as much carbon dioxide as a car produces in 26,000 miles.[2]
  • Conserving energy in buildings reduces carbon dioxide emissions from power plants.[3]
  • The removal and mulching of dead trees releases 80 percent of their stored carbon into the air in the year of removal. The concomitant use of vehicles, chain saws, chippers, and other gasoline- and diesel-powered machines increases the carbon in the air.[4]
  • Shaded parking lots reduce hydrocarbon emissions from parked cars by 18 to 21 percent.[5]

Air Quality Improvement

  • Air pollutants—ozone, nitrogen dioxide, sulfuric oxides, particulates. One hundred trees per year remove 1,000 pounds of such pollutants.[6]
  • Trees reduce air pollutants by 25 percent in cities.[7]
  • Parking lots—heat islands. Cars parked in lots with 50 percent canopy cover emit 8 percent less evaporative emissions than cars in lots with only 8 percent canopy cover.[8]
  • One acre of trees provides enough oxygen for 18 people.[9]
  • One tree over a 50-year lifetime generates $31,250 worth of oxygen and $62,000 worth of air pollution control.[10]

Noise Reduction

  • Thick strips of vegetation combined with berms and solid barriers can reduce highway noise by 6 to 15 decibels. Plants absorb more high frequency noise (the noise most distressing to people) than low frequency noise.[11]

Energy Savings

  • Shade for cooling: direct shade and water evaporation from leaves combine to produce cooler air. Four trees planted around a house can save as much as 30 percent on summer cooling costs.[12]
  • Tree shade that protects houses and other buildings on the east and west helps keep them cool, for an estimated 36 percent reduction in cooling costs.[13]
  • Conifer windbreaks buffer houses and other buildings and create a dead air space to reduce heat loss in winter.[14]
  • Deciduous (“solar-friendly”) trees planted on the south of houses and buildings help heat houses and reduce heating costs.[15]
  • Mature, large trees produce approximately 4 to 6 times the energy savings of small trees.[16]

Financial benefits

Water Quality Improvement/Stormwater Flow Reduction

  • The greater the tree canopy percentage, the less impervious surface there is.[17]
  • Impervious surfaces increase water temperature (thermal pollution) and pollute water with lawn fertilizers, oils, and other contaminants that flow into receiving water supplies and increase costs for building retention ponds and additional stormwater facilities and treating water.[18]
  • Tree canopies and root systems naturally filter water supplies and reduce storm water runoff, flooding, and erosion.[19]
  • In heavily forested areas of western Washington, 74 percent of rainfall is released back to the atmosphere or absorbed into the ground.[20]
  • In the Puget Sound area, the rainfall interception provided by a two-story leafy canopy is especially important during our rainy winters. A two-story canopy has a leaf area 2 to 8 times the land area it covers.[21]
  • A city’s urban forest can reduce peak storm runoff by 10 to 20 percent.[22]
  • In one Milwaukee neighborhood with 42 percent tree canopy, runoff was reduced by 20 percent.[23]
  • One tree over a 50-year lifetime recycles $37,500 worth of water and controls $31,250 worth of soil erosion.[24]

Infrastructure Savings

  • Shade on asphalt roads and parking lots extends the time between needing to resurface by 50 percent. Such savings on roads can be translated into $30,000 savings per mile for resurfacing.[25]

Property Value Increases, Increased Tax Revenues, and Increased Gains

  • Studies say that four trees on a property can speed its sale by four to six weeks.[26]
  • In Sacramento, a residential mature valley oak may be appraised at $20,000 or more.[27]
  • Trees on property or associated with property increase market value by 3.5 to 7 percent.[28]
  • Mature trees raise property values by as much as 20 percent.[29]

Business Gains

  • A shaded business district encourages shoppers to linger and to spend more and has been shown to increase prices consumers will pay by as much as 12 percent. Shoppers will also increase the number of visits they make to a business.[30]
  • Employees with nature views report 23 percent fewer health ailments, a positive influence on absenteeism.[31]
  • Quality of place—treed landscapes attracts companies and the best employees.[32]

Health Gains

  • Heat-related deaths have risen dramatically since 1994—in Chicago, for instance, from an average 3 deaths per year in the years before 1995 to a sudden 15 deaths per year in 1995.[33]
  • Views of trees and visits to hospital green spaces reduce hospital stays.[34]
  • Trees reduce exposure to cancer-causing ultraviolet radiation.[35]

Social Gains/Public Safety

  • Treed neighborhoods decrease violent episodes that are associated with mental fatigue.[36]
  • In public housing complexes, outdoor spaces with trees are used significantly more often than spaces without trees. Trees thus facilitate interactions among residents, contributing to lower domestic violence and safer, more sociable neighborhood environments.[37]
  • Traffic calming—research has indicated that the presence of trees in the roadside reduces traffic stress response (road rage).[38]
  • Along tree-lined transportation corridors, cars are driven more slowly, drivers are more aware, and human comfort and safety is improved.[39]

Aesthetic Gains

  • Incalculable

Sources:


[1] Sacramento Regional Urban Forest Framework, “GreenPrint.”

[2] “How does an urban forest contribute to sustainability?” Seattle Office of Sustainability and Environment website.

[3] E. Gregory McPherson et al., “Western Washington and Oregon Community Tree Guide: Benefits, Costs, and Strategic Planning,” Center for Urban Forest Research, USDA Forest Service, Pacific Southwest Research Station, 18.

[4] E. Gregory McPherson et al., “Western Washington and Oregon Community Tree Guide: Benefits, Costs, and Strategic Planning,” Center for Urban Forest Research, USDA Forest Service, Pacific Southwest Research Station, 19.

[5] Sacramento Regional Urban Forest Framework, “GreenPrint.”

[6] Sacramento Regional Urban Forest Framework, “GreenPrint.”

[7] Sustainable Urban Forests Coalition, “National Agenda for Well Managed Urban Forests.”

[8] David Hitchcock, AICP, “Cool Houston,” Power Point screen for talk at Houston Advanced Research Center, September 2004.

[9] “How does an urban forest contribute to sustainability?” Seattle Office of Sustainability and Environment website.

[10] Michigan State University, Update Forestry.

[11] E. Gregory McPherson et al., “Western Washington and Oregon Community Tree Guide: Benefits, Costs, and Strategic Planning,” Center for Urban Forest Research, USDA Forest Service, Pacific Southwest Research Station, 11.

[12] Alliance for Community Trees, “The Value of Trees.”

[13] E. Gregory McPherson et al., “Western Washington and Oregon Community Tree Guide: Benefits, Costs, and Strategic Planning,” Center for Urban Forest Research, USDA Forest Service, Pacific Southwest Research Station, 6.

[14] “How does an urban forest contribute to sustainability?” Seattle Office of Sustainability and Environment website.

[15] E. Gregory McPherson et al., “Western Washington and Oregon Community Tree Guide: Benefits, Costs, and Strategic Planning,” Center for Urban Forest Research, USDA Forest Service, Pacific Southwest Research Station, 6.

[16] E. Gregory McPherson et al., “Western Washington and Oregon Community Tree Guide: Benefits, Costs, and Strategic Planning,” Center for Urban Forest Research, USDA Forest Service, Pacific Southwest Research Station, 31.

[17] American Forests, Regional Ecosystem Analysis Puget Sound Metropolitan Area: Calculating the Value of Nature 7/25/98.

[18] Cheryl Kollin, “Quantifying the contributions of trees and vegetation,” StormWater.

[19] Alliance for Community Trees, “The Value of Trees.”

[20] Kathleen L. Wolf, “Tree investment brings many happy returns,” Environmental Outlook 2001.

[21] Sacramento Regional Urban Forest Framework, “GreenPrint.”

[22] How does an urban forest contribute to sustainability?” Seattle Office of Sustainability and Environment website.

[23] National Arbor Day Foundation, Arbor Day, July/August 2006, 7.

[24] Michigan State University, Update Forestry.

[25] Sacramento Regional Urban Forest Framework, “GreenPrint.”

[26] Alliance for Community Trees, “The Value of Trees.”

[27] Alliance for Community Trees, “The Value of Trees.”

[28] E. Gregory McPherson et al., “Western Washington and Oregon Community Tree Guide: Benefits, Costs, and Strategic Planning,” Center for Urban Forest Research, USDA Forest Service, Pacific Southwest Research Station, 10.

[29] “How does an urban forest contribute to sustainability?” Seattle Office of Sustainability and Environment website.

[30] Sacramento Regional Urban Forest Framework, “GreenPrint.”

[31] Kathleen L. Wolf, “Tree investment brings many happy returns,” Environmental Outlook 2001.

[32] Kathleen L. Wolf, “Tree investment brings many happy returns,” Environmental Outlook 2001.

[33] David Hitchcock, AICP, “Cool Houston,” Power Point screen for talk at Houston Advanced Research Center, September 2004.

[34] David Hitchcock, AICP, “Cool Houston,” Power Point screen for talk at Houston Advanced Research Center, September 2004.

[35] E. Gregory McPherson et al., “Western Washington and Oregon Community Tree Guide: Benefits, Costs, and Strategic Planning,” Center for Urban Forest Research, USDA Forest Service, Pacific Southwest Research Station, 11, 25.

[36] Kathleen L. Wolf, “Tree investment brings many happy returns,” Environmental Outlook 2001.

[37] E. Gregory McPherson et al., “Western Washington and Oregon Community Tree Guide: Benefits, Costs, and Strategic Planning,” Center for Urban Forest Research, USDA Forest Service, Pacific Southwest Research Station, 10.

[38] Kathleen L. Wolf, “Tree investment brings many happy returns,” Environmental Outlook 2001.

[39] Sacramento Regional Urban Forest Framework, “GreenPrint.”

Identified Benefits of Community Trees and Forests, Dr. Rim D. Coder, University of Georgia, October 1996 http://www.coloradotrees.org/benefits/Identified%20Benefits%20of%20Community%20Trees.pdf

GASB 34: Urban Natural Resources as Capital Assets, Dudley R. Hartel, American Forests Publication http://www.urbanforestrysouth.org/resources/library/Citation.2004-11-03.P194/file_name

Putting trees on the payroll: here’s a greener way to clean up air and water while putting your city’s books in the black, Editorial Deborah Gangloff http://www.americanforests.org/productsandpubs/magazine/archives/2003fall/editorial.php

Don’t Sell the Value of Your trees Short, Jim Skieka http://www.isa-arbor.com/publications/arbNews/pdfs/Jun08-perspectives.pdf

Treeconomics, Linda McIntyre, Landscape Architecture Magazine, February 2008 http://www.fs.fed.us/psw/programs/cufr/products/12/psw_cufr731_LandArchTreeconomics.pdf

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