The Modern Science of Urban Street Trees

1. Do trees do more than sweeten the air and shelter buildings and streets from hot summers and freezing winters? Yes. What do trees do?

2. Do trees clean air? Large trees improve air quality as much as 15%. A large, long- lived tree, such as an oak, can sequester 1,000 more times carbon than a small short-lived tree can, such as a crab apple.

3. Do trees reduce the need for air conditioning? Yes. How much? A large street tree growing to the west of a brick building can reduce annual A/C energy use by 2%-7%. New York City street trees save annually $47.63 per tree—a gift that keeps on giving.

4. Do trees reduce energy consumption in general? Yes. Trees planted to the west of buildings save annually 3 times more energy than trees planted to the south.

5. Do trees help with storm water dispersal and reduce storm water run-off? Yes. The average street tree intercepts 1,432 gallons—a service worth $61.00.

6. Do trees affect commerce? Yes. Research shows that shopping destinations with trees have more customers than those without trees, shoppers spend 9%-12% more, & linger longer.

7. Do trees affect real estate values? Yes. Trees, especially large trees, can increase property values as much as 20%.

8. Do trees effect human well being? What about crime? Do trees affect crime? Yes. Leafy public housing projects experience less violence than barren ones.

9. Do trees affect health? What about human health? Trees promote healing. Research shows that hospital patients who can see a tree out the window of their room are discharged one day earlier than those without such a view.

10. Do street trees effect traffic? Yes. How? Recent research shows that street trees are a natural method to slow traffic.

11. Do trees really save revenue? Yes. Each urban street tree delivers benefits of approximately $209 per year.

12. What’s my 24” Pin Oak worth? You’ll be surprised!

A 24-inch Pin Oak Quercus palustris provides benefits of $194 each year.

Storm water:       $75.92        intercepts 7,669 gallons of rain water each year

Property Value:   $75.67        raises property values

Electricity:           $17.36        saves on average 229 kilowatts

Air Quality          $17.58        stores carbon

TOTAL SAVINGS            $194         EACH YEAR

Why haven’t we heard about the benefits of urban street trees before now?  Research to quantify the economic benefits of urban street trees began in the early 1990s in Chicago in an attempt to answer the Mayor’s question:  Do trees really clean the air?  The answer was yes.  Continued research has inspired Los Angeles and New York City to begin Million Tree planting programs to save revenue.  For example, currently, New York City, under the leadership of Mayor Bloomberg, has planted 350,000 street trees toward his goal of planting 1,000,000 street trees.  New York City is currently spending $8 million per year to plant and tend street trees and $6.8 million per year to pay personnel.  The net benefit for New York City from all of its trees is $100 million per year.  Conclusion:  It pays to plant street trees.  Street trees save revenue.

Tree Facts, The Modern Science of Urban Street Trees is condensed from an article by Jill Jonnes, “What is a Tree Worth?”, The Wilson Quarterly [Winter 2011], pp. 34-41. See also www.na.fs.fed.us/urban. Free software aimed at city foresters & urban planners is i-Tree [2003] & scheduled to be released in the winter of 2011, a software package called i-Tree Hydro, which models storm water hydrology. Also see the non-profit Casey Trees’ Tree Benefit Calculator. Today, based on the modern science of urban street trees, Arbor Day’s new slogan is “Plant the Future.” Even though the best time to plant a tree was 20 years ago, the next best time is today.
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