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Urban tree benefits: your bottom line

Urban tree benefits: your bottom line
Notes by J. Zimmerman, Ph.D.

Ever wondered about the value of growing a mature tree in your yard? It can save you dollars from fuel bills, medical bills, and taxes. Here's how research at U.C. Davis shows there's more than beauty in a living, urban tree...

Urban forester, Leslie Keedy suggests:
Shading Our Cities: A Resource Guide for Urban and Community Forests, edited by Gary Moll, Sara Ebenreck. "A sound overview of urban forestry with case studies of many cities. Accessible to the lay reader."
Urban Forestry: Planning and Managing Urban Greenspaces, by Robert W. Miller. "Addresses how to carefully and successfully plan for and manage urban vegetation."

First, the bottom line.

Each large yard or street tree gives over $100 savings per year (2000 dollars).

Dr. Greg McPherson (Director of the US Forest Service's Center for Urban Forest Research in Davis, CA) gives us the scoop.

He reports data for the town of Modesto, in California's San Joaquin Valley. The field data are for a typical 40-year-old London Plane tree, Platanus acerifolia.

The most obvious portion of the savings is $29 per year due to the reduction of summertime air-conditioning. A single tree can save 250 kilowatt-hours of air-conditioning. Maximum benefit comes from trees on the west of a residence. With electricity costs rising, the U.C. Davis estimate is bound to increase.

Health benefits.

Health benefits are created because each of your trees cleans up the air around your residence, improving the health of your lungs. The U.C. Davis data do not include estimates of your resulting medical savings for respiratory care and medication. But they do show (as follows) how much the trees clean the air.

A typical tree in Modesto absorbs 10 lbs. of air pollutants annually, including 4 lbs. of ozone and 3 lbs. of particulates. The savings due to that absorption is $45, assuming "the local market price of emission reduction credits."

A tree cleans 330 lbs. of CO2 (90 lbs. carbon) from the atmosphere. The value of this benefit is $5, based on the California Energy Commission's price of $30/ton. The cleaning occurs in two ways:

  1. Directly. Carbon dioxide is absorbed in the tree's photosynthesis (the process by which green plants form carbohydrates from carbon dioxide and water, thorough sunlight acing on chlorophyll). In this way, the carbon is moved in to the tree's wood.
  2. Indirectly. Power plant emissions are reduced compared to what they would have been, because energy is saved by cooling related to the tree.

Observe, however, that it would take 33 trees to remove the entire equivalent of 12,000 pounds/year of C02 released by an "average" car mentioned in their study.

A small but interesting benefit is that a large tree intercepts 760 gallons of rainfall annually in its crown. That reduces storm-water runoff and flooding. This saves city expenses (which means a tax benefit to citizens) by $6.

(Attributes vary amongst species. An example of this is that an evergreen camphor tree in coastal Southern California intercepts five times as much, up to 4,000 gallons annually.)

Increase Your Property Values.

Finally, adding a tree to your property adds about 1% to the sales price. This comes to about $25 annually, over a 40-year period, assuming a median residential property sales price of $100,000.

The total for one tree is $110 savings per year. Modesto has 90,000 trees in its streets and parks. So the city-wide benefit is on the order of $10 million!

Everyday the city and town dwellers throughout California win such benefits from the trees of the urban forest.

For the full scoop, check out the original web data at U.C. Davis Center for Urban Forest Research - see their "Quick Reference: Tree Factoids."

Book Choice.

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