Portland feels like a city of trees and we are lucky to have a tree canopy that covers more than 26 percent of neighborhoods. With more than a quarter-million trees lining our streets, Portland literally is a green city.
Portland's urban forest – our vast network of street, park and private property trees – is one of our most valuable assets. As Portland Parks and Recreation's Urban Forest Action Plan (2007) aptly sums it up,
The urban forest surrounds us and contributes to the quality of our daily lives. It provides environmental, psychological, and economic benefits ranging from improved air and water quality to savings from decreased heating and cooling costs to aesthetically pleasing neighborhoods and increased resale values. It is vital to our efforts to restore fish and wildlife habitat and it provides countless opportunities for recreation and refreshment.
- Portland Parks and Recreation's Urban Forest Action Plan (2007)
Urban trees are good for the city and work for everyone every day.Trees capture and absorb stormwater so we don't have to build expensive pipes that funnel dirty water to treatment plants. Trees clean the air we breathe and cool our homes, schools and businesses. Trees are necessities, making our neighborhoods livable, reducing our costs and keeping our rivers healthy.
Our urban forest benefits all of us – economically, environmentally, and socially – and makes cleaning up after our leaves for one or two days in the fall well worth the trouble. It's in all of our interest to maintain our trees and help our urban forest grow and flourish.
- City trees boost property values
- City trees reduce heating/cooling costs for housing and buildings
- An urban forest attracts tourists
- City trees inspire shoppers to spend more
- City trees enhance productivity
- An urban forest creates jobs in natural resource management
- An urban forest lowers greenhouse gas levels
- An urban forest improves air quality
- City trees absorb storm water, preventing sewer overflow and flooding, and reducing pollution to our waterways
- City trees decrease erosion and infrastructure damage
- City trees recharge the groundwater
- City trees create habitats for wildlife and encourage biodiversity
- City trees provide cooling shade and water vapor, privacy, windbreaks, and sound barriers
- City trees foster community
- An urban forest promotes mental and physical health
- City trees lower crime
- An urban forest offers opportunities for recreation
- An urban forest is educational
- City trees are simply nice to look at and be around
"Residential Property Values Improve by Landscaping with Trees." Anderson, L. M., and H. K. Cordell, Southern Journal of Applied Forestry 9 (August 1985): 162-166. www.safnet.org/publications/southern/index.cfm.
A review of sales prices revealed that each large front-yard tree helps boost housing sales prices 1 percent.
"Trees in the City: Valuing Street Trees in Portland, Oregon." Donovan, G. H., and D. T. Butry, Landscape and Urban Planning 94 (2010): 77-83. www.fs.fed.us/pnw/pubs/journals/pnw_2010_donovan001.pdf.
Cites an earlier study by Donovan that a tree with a 300-square-feet canopy increases the value of a house and those of its neighbors by $7,593-$9,241. The authors also estimate that Portland's tree cover brings $54 million of overall benefits to Portlanders annually and $15.3 million in property taxes to the city. Because the city spends $1.2 million annually in tree maintenance, the cost-benefit ratio is 12-1.
"Valuing the Benefits of the Urban Forest." Payton, S., et al., Journal of Environmental Planning & Management 51 (November 2008): 717-736. www.tandfonline.com/toc/cjep20/51/6.
Greener vegetation around a property significantly increases housing prices.
"City Trees and Property Values." Wolf, K. L., www.naturewithin.info/Policy/Hedonics_Citations.pdf.
Wolf argues that houses can be valued to include such indirect, intangible benefits as beauty, ecosystem services, and psychological effects. She provides estimated percentage increases in value based upon previous studies: for instance, that buyers are willing to pay 10 percent more for an inner-city home within a quarter mile of a park.
"Modeling Benefits and Costs of Community Tree Plantings." McPherson, E. G., et al. Davis, Calif.: USDA Forest Service, Pacific Southwest Research Station, 1993.
Two 25-foot tall trees planted on the west side of a house save about 36 percent on cooling bills and 7 percent on heating bills annually.
"Effects of Tree Cover on Parking Lot Microclimate and Vehicle Emissions." Scott, K. I., et al., Journal of Arboriculture 25 (May 1999): 129-142. www.joa.isa-arbor.com.
Trees shading parking lots reduce air temperature 1-3 degrees Fahrenheit.
"Tree Planting and Care: A study of Attitudes and Behavior in Sacramento, California." Simpson, J. R. Residential, Journal of Arboriculture 24 (March 1998): 89-97. www.joa.isa-arbor.com.
An urban tree canopy lowers city summer high temperatures from 5-9 degrees Fahrenheit and thereby reduces demand for air conditioning.
"Where Urban and Untamed Still Coexist." Mittelbach, M., and M. Crewdson, New York Times, August 2, 2002, p. 29.
Describes ecotourism in Bronx Parks as a growing attraction.
"More in Store: Research on City Trees and Retail." Wolf, K. L., Arborist News 18 (April 2009): 22-27. www.naturewithin.info/CityBiz/ArbNews.BizTrees.4.09.pdf.
Shoppers in large cities said that they were willing to pay 12 percent more for goods and services in business districts with trees. In small cities, the number was 9 percent.
"Nature and Commerce: Human Ecology n Business Districts." Wolf, K. L., in Building Cities of Green: Proceedings of the 1999 National Urban Forest Conference. Ed. C. Kollin. Washington, D. C.: American Forests, 1999.
Consumers prefer to shop in commercial areas with trees and are willing to spend more there.
"Urban Forestry and the Work Place." Kaplan, R., in Managing Urban and High-Use Recreation Settings. Ed. P. H. Gobster. USDA Forest Service, General Technical Report NC-163. Chicago, Ill.: North Central Forest Experiment Station, 1992.
A view of urban greenery enhances worker well-being and productivity, and relieves stress.
"Proceedings of the Best of the West Summit." McPherson, E. G., and S. Mathis, eds. Sacramento, Calif.: Western Chapter, International Society of Arboriculture, 1999.
Focuses on the jobs and educational opportunities afforded by urban forestry.
"Atmospheric Carbon Dioxide Reduction by Sacramento's Urban Forest." McPherson, E. G., Journal of Arboriculture 24 (July 1998): 215-223. www.joa.isa-arbor.com.
Sacramento, California's 6 million trees absorb enough carbon dioxide to offset 1.8 percent of human-produced greenhouse gas.
"Tree Planting Potential Study and Five Year Planting and Education Plan." Portland, Oregon: Friends of Trees, 1995.
Planting 144,250 trees over five years would absorb 74,679 tons of carbon dioxide at $34 per ton.
"Impacts of Urban Forests on Offsetting Carbon Emissions from Industrial Energy Use in Hangzhou, China." Zhao, Min, et al., Journal of Environmental Management 91 (March 2010): 807-813. www.elsevier.com/wps/find/journaldescription.cws_home/622871/description.
Urban tree cover clears from the air 18.57 percent of the carbon emitted by local industry.
Canadian Wildlife 17 (May-June 2011): 16-17. Langford, C. www.cwf-fcf.org/en/resources/magazines/canadian-wildlife.
Toronto's 10 million trees provided about 60 million dollars annually in environmental services, while nearby Oakville's urban forest absorbs more than 170 tons of air pollutants.
"Air Pollution Removal by Urban Trees and Shrubs in the United States." Nowak, D. J., et al., Urban Forestry & Urban Greening 4 (April 2006): 115-123. www.sciencedirect.com/science/article/pii/S1618866706000173.
Urban trees in the United States remove approximately 711,000 metric tons of pollutants from the air annually, saving $3.8 billion in medical and maintenance costs.
"Regional Ecosystem Analysis for the Willamette/Lower Columbia Region of Northwestern Oregon and Southwestern Washington State." Washington, D.C.: American Forests, 2001.
Tree cover in the Willamette and Lower Columbia Region removes 89,000 tons of air pollutants, such as ozone, nitrogen dioxide and particles, saving an estimated $419 million in medical and maintenance costs.
"Plants in Urban Ecosystems: Essential Role of Urban Forests in Urban Metabolism and Succession toward Sustainability." Manning, W. J., International Journal of Sustainable Development & World Ecology 15 (August 2008): 362-270. www.tandf.co.uk/journals/titles/13504509.asp.
Using computer models, this study concludes urban trees are essential to reducing run-off, sewer overloads, water pollution, and heat islands.
"Benefit-cost Analysis of Modesto's Municipal Urban Forest." McPherson, E.G. et al., Journal of Arboriculture 25 (September 1999): 235-248. www.joa.isa-arbor.com.
Every urban tree reduces runoff by 845 gallons a year, thereby reducing erosion and pollution, for a savings of $7 per tree to the city's Operations and Maintenance Department.
"Regional Ecosystem Analysis for the Willamette/Lower Columbia Region of Northwestern Oregon and Southwestern Washington State." Washington, D.C.: American Forests, 2001.
The tree canopy in the Willamette/Lower Columbia Region decreases runoff by 8.5 billion cubic feet, saving an estimated $140 million annually in construction costs to control the flow.
"Effects of Street Tree Shade on Asphalt Concrete Aspahlt Performance." McPherson, E.G., and J. Muchnick., Journal of Arboriculture 31 (November 2005): 303-310. www.joa.isa-arbor.com.
A study in Modesto, California, concluded that shade trees protect streets from Aspahlt fatigue, cracking, rutting, and other distress. The city estimated it saved $7.13 per square meter over 30 years.
"Watershed-Scale Impacts of Forest Buffers on Water Quality and Runoff in Urban Environment." Matteo, M., et al., Journal of Water Resources Planning and Management 132 (May-June 2006): 144-152. www.ascelibrary.org/wro/resource/1/jwrmd5/v132/i3.
Urban forest cover reduces sediment in streams and gutters, decreases stormwater runoff, and increases the rate at which groundwater is recharging. These factors lessen the variability of the urban watershed so it's better able to withstand adverse conditions, such as large storms.
"Landscape Effects on Birds In Urban Woodlands: An Analysis of 34 Swedish Cities." Hedblom, Marcus, and B. Söderström, Journal of Biogeography 37 (July 2010): 1306-1316. www.onlinelibrary.wiley.com/doi/10.1111/jbi.2010.37.issue-7/issuetoc.
A study of 474 urban forest areas showing that some common bird species thrive in cities more than in agricultural areas because the canopy offers great habitat variety.
Wild in the City: A Guide to Portland's Natural Areas. Houck, M. C., and M. J. Cody, eds. Portland, Oregon: Oregon Historical Society Press, 2003.
This landmark books covers the geology, animals, insects, and plants to be seen in Portland's cemeteries, trails, waterways, parks, golf courses, and natural spaces. Accompanied by over 90 site maps, the authors stress the magical variety of native and exotic species.
The Ecological City. Platt, R. H., and P. C. Muick, eds. Boston, Mass.: University of Massachusetts Press, 1994.
The varieties of wildlife in various urban greenspaces are a resource for urban planners and conservationists. The authors recommend a broad perspective that encourages variety in fauna and flora to achieve sustainability and deepen psychological impact of nature on residents.
"How Urban Residents Rate and Rank the Benefits and Problems Associated with Trees in Cities." Lohr, V. I., et al., Journal of Arboriculture 30 (January 2004): 28-35. www.joa.isa-arbor.com.
Trees rate highly for their practical benefits among urban residents, and highest of all for their cooling shade.
"Calculating Carbon Dioxide Reductions through Urban Forestry Programs: Guidelines for Professional and Volunteer Tree Planters." McPherson, E. G., and J. R. Simpson, PSW Technical Report No. 171. Albany, Calif.: USDA Forest Service, 1999.
On the benefits of shade from large-canopy, medium-canopy, and small-canopy trees through the year.
Urban Forestry: Planning and Managing Urban Greenspaces. Miller, R. W., 2nd ed. Long Grove, Ill.: Waveland Press, 2007.
Supplies evidence that trees reduce high frequency noise levels.
"Fertile Ground for Community: Inner-City Neighborhood Common Spaces." Kuo, F. E., et al., American Journal of Community Psychology 26 (December 1998): 823-851. www.springer.com/psychology/community+psychology/journal/10464.
Reviews research that correlates the presence of trees in public housing with increased neighborhood social ties.
"The Fruit of Urban Nature: Vital Neighborhood Spaces." Sullivan, W. C., et al., Environment and Behavior 36 (September 2004): 678-700. www.eab.sagepub.com/content/36/5.
Discusses how the presence of trees and grass increases the use of outdoor spaces and social activities.
"Finding Common Ground: The Importance of Place Attachment to Community Participation and Planning." Manzo, L., and D. D. Perkins, Journal of Planning Literature 20 (May 2006): 335-350. www.jag85.com/classes/lis490/Finding%20Common%20Ground.pdf.
In this review of literature on greenspaces and community, the authors make connections between local environments and community psychology, including place identity, that result in great cooperation among citizens.
"Urban Trees and the Risk of Poor Birth Outcomes." Donovan, G. H., et al., Health and Place, November 2010, www.elsevier.com/locate/healthplace.
Finds a correlation between presence of shade trees in neighborhoods and healthy pregnancies in Portland, Oregon.
The Experience of Nature: A Psychological Perspective. Kaplan, R, and S. Kaplan. Cambridge, England: Cambridge University Press, 1989; and "Urban Forestry and the Workplace." Kaplan, R., in Managing urban and High-Use Recreation Settings. Ed. by Ph. H. Gobster. USDA Forest Service General Technical Report NC-163. Chicago, Ill.: North Central Forest Experimentation Center, 1992.
Cites evidence for lower illness rates among workers and greater powers of concentration for people with views of trees.
Landscape and Human Health Laboratory, University of Illinois at Urbana-Campaign, 2011. www.lhhl.illinois.edu/index.htm.
This web site reports research on the benefits of urban natural features to improving mental health and reducing crime.
"Skin Cancer Prevention: Another Good Reason to Plant Trees." Tretheway, R., and A. Manthe, in Proceedings of the Best of the West Summit. Ed. by E. G. McPherson and S. Mathis. Davis, Calif.: University of California College of Agricultural and Environmental Sciences, 1999.
The authors argue that because trees screen people from ultraviolet light, they lower risk of cataracts and skin cancers.
"The Effect of Trees on Crime in Portland, Oregon." Donovan, G. H., and J. P. Prestemon, Environments and Behavior, October 19, 2010, www.actrees.org/site/resources/research/the_effect_of_trees_on_crime_in_portland_oreg.php.
After examining 431 crimes in 2,813 single-family dwellings, the authors found that trees in the public right of way correlate with lower crimes rates.
"Environment and Crime in the Inner City: Does Vegetation Reduce Crime?" Kuo, F. E., and W. C. Sullivan, Environment and Behavior 33 (May 2001): 342-367. www.outdoorfoundation.org/pdf/EnvironmentAndCrime.pdf.
Based on police crime reports involving 98 residential buildings, the authors conclude that the greener a building's surrounds are, the fewer crimes are reported.
"Do Trees Strengthen Urban Communities, Reduce Domestic Violence?" Sullivan, W. C., and E. E. Kuo, Arborist News 5 (April 1996): 33-34. www.isa-arbor.com/membership/magazinesAndNewsletters/arboristNews.aspx.
Argues that because public areas with trees see more use, they increase sociability and reduce crime.
"Recreation Use of Urban Forests: An Inner-area Comparison." Arnberger, Arne, Urban Forestry and Urban Greening 4 (April 2006): 135-144.
This study of urban and suburban parks in Vienna, Austria, found that the urban parks were used more intensively and for routine exercise, such as dog-walking and jogging, making them an integral part of daily life.
"Green Exercise: The Benefits of Activities in Green Places." Pretty, J., et al., The Biologist 53 (August 2006): 143-148. www.societyofbiology.org/membership/biologist.
Examines the benefits of walking, cycling, horse-riding, fishing, canal-boating, conservation activities in urban greenspaces, based upon a study of 263 participants in Great Britain: among them better physical condition, improved self-esteem, and less anxiety, depression, and anger.
"Luring Shady Characters to Your House." Turner, J. M., Christian Science Monitor 91 (April 28, 1999): 17. www.csmonitor.com/1999/0428/p17s1.html.
Explains the use of urban forestry to broaden citizens' appreciation of nature and ecology by, for instance, familiarizing them with the benefits and responsibilities of planting trees during Arbor Day, and the power of trees to cool houses. (It cites a claim by Mary Tebo, a New Hampshire tree steward that one tree cools the air as much as five air conditioners running 20 hours a day.)
Nature/Human Nature: The Meaning of Plants in Our Lives. Lewis, C. A. Green. Chicago.: University of Illinois Press, 1996.
Contends that people derive pleasure, inspiration, and spiritual value from the sight of urban trees.
"The Esthetic Contribution of Trees to Residential Streets in Ohio Towns." Schroeder, H. W., and W. N. Cannon, Journal of Arboriculture 9 (September, 1983): 237-243. www.joa.isa-arbor.com.
Discusses research showing that street trees are the greatest influence on perceptions of scenic quality.
Western Washington and Oregon Community Tree Guide: Benefits, Costs, and Strategic Planning. Center for Urban Forest Research, Silverton, Oreg.: International Society of Arboriculture, Pacific Northwest Chapter, 2002. http://www.fs.fed.us/psw/programs/uesd/uep/products/cufr_164.pdf.
A comprehensive introduction, this pamphlet discusses how trees benefit Northwest cities, where to plant them, and which trees serve best.
A Technical Guide to Urban and Community Forestry. www.na.fs.fed.us/spfo/pubs/uf/techguide/toc.htm.
A web site describing the value, principals, design, implementation, and politics of forestry programs.
Green Cities: Good Health, 2010. www.greenhealth.washington.edu.
A web site discussing the scientific evidence for the benefits derived from gardens, parks, and trees for health, safety, and community building.
Portland's Urban Forest Canopy: Assessment and Public Tree Evaluation. Portland, Oreg.: Portland Parks & Recreation, 2007. www.portlandonline.com/shared/cfm/image.cfm?id=171829.
A pamphlet surveying the composition, management, and benefits of Portland's estimated 236,000 trees, which cover 26 percent of the city: a public resource with a replacement value of $2.3 billion that provides $27 million in environmental and aesthetic benefits, $3 million in air cleaning and carbon fixing services, and $36 million in savings for stormwater processing.