Quantifying the Value of Trees

[Carl DuPoldt]

Quantifying the Value of Trees
By Janice Kaspersen
http://foresternetwork.com/daily/soil/erosion-control/quantifying-t...
What’s the one thing that can increase property values, improve air quality, reduce stormwater runoff, and cool down city streets? A tree—or better yet, hundreds of them, strategically placed in urban areas.
Several presentations at StormCon last week focused on the role of trees—specifically, how trees in urban settings can mitigate peak flows, slow erosion, and reduce nutrients in stormwater runoff. Did you know that a 50-foot-tall hackberry tree with a 35-foot canopy has about 7,000 square feet of leaf area and can temporarily retain about 34 gallons of water during a storm? It holds onto that water from 10 minutes to as long as three hours. The tree also transpires from 7 to 60 cubic feet of water a day.
Many cities are realizing, or rediscovering, the value of the tree. Phoenix, AZ, for example, has placed large orange plastic tags on hundreds of trees around the city, showing on one side what type of tree it is and some of the benefits it provides—such as how much carbon it removes from the atmosphere—and on the other its dollar value to the community. The idea is to convey to the public the tangible benefits of trees.
Phoenix has about 3.2 million trees (93,000 of them in public spaces). Tree canopy currently covers about 9 to 12% of the city’s 520 square miles. The city is trying to increase that to 25% over the next 15 years. Studies by the city, the University of Arizona, and Arizona State University show that achieving 25% coverage could reduce near-ground temperatures by more than 4 degrees—a definite advantage in a city where average summer high temperatures run to three digits.
According to Project Desert Canopy, a study funded by the US Forest Service to quantify the value of trees in four Southwest cities—Phoenix; Albuquerque and Las Cruces, NM; and El Paso, TX—Phoenix’s tree canopy removes 1,770 tons of air pollution annually, removes enough carbon to offset 10,412 cars, and reduces stormwater runoff by 91.7 million cubic feet. You can find more details in this blog from the Arizona Municipal Water Users Association. An article coming up in the October issue of our sister publication Stormwater will provide a wealth of information on the benefits trees can provide in specific climates and at different rainfall intensities.
-----------------------