Street Tree Assessment: Energy and Water Savings, Reduced Pollution

Research Year: 
2008
Issue: 

Although trees offer more than aesthetics in a landscape, the true value of their contribution is usually unknown. A street tree inventory conducted on the University of Arizona campus assisted a larger effort undertaken by the City of Tucson’s Department of Urban Planning and Design to assess the species distribution, annual costs/benefits and maintenance priorities for municipal trees.

Description of Action: 

The UA Campus Arboretum conducted a study from November 2007-November 2008 documenting the distribution, yearly costs and benefits of more than 2,000 individual trees flanking campus roads. Information for each tree, including species, size, condition and location, was logged into a PDA and loaded into a software program called STRATUM, part of the i-Tree Suite of software developed by the Center for Urban Forest Research at UC Davis. The model in the software was adapted for Phoenix and desert Southwest tree species. An updated analysis on carbon sequestration alone was conducted in 2009.

Impact: 

According to the 2007-2008 inventory, the 2,130 street trees in the study (about 26 percent of all trees on the UA campus) annually sequester 246,620 tons of carbon dioxide (CO2); reduce the energy costs for UA facilities by $18,230; reduce emission, pollutants and particulates by 9,994 pounds; and intercept more than a million gallons of rainfall or stormwater (reducing flooding).

Accounting for reductions in tree mass due to aging and maintenance losses, the net CO2 sequestered in the 2,130 UA street trees amounted to 95,290 pounds of carbon held in those trees from 2007 to 2008. An extrapolation of that data for all 7,925 trees existing on the UA campus in 2008-2009 showed that they would have held 366,500 pounds of carbon—166 metric tons—that year. Although small compared to the amount of carbon emitted from the UA, the number does represent the annual reduction of greenhouse gas emissions that is directly due to the trees on campus.

Within species, each Chinese pistache on campus contributes about $74 every year, including energy and water saved, carbon dioxide sequestered, and aesthetic value. Mesquites contribute $112; Aleppo pine, $156; California palm, $33 and blue paloverde, $93. With some campus trees living 40, 60 or even 100 years, their contributions can be considerable over their life spans. The trees contribute to quality of life and reduce the university’s “carbon footprint.”

Conact Name: 
Elizabeth Davison
Contact E-mail: