Trees make a huge contribution to the green infrastructure of our towns and cities, both in carbon sequestration and aesthetics, yet the economical value of them is often forgotten leading them to be undervalued or seen as a nuisance. The i-Tree tool aims to change the way people see trees – it is a freely available software suite from the US Forest Service which provides analysis, benefit-calculations and assessment tools to quantify the contribution made by trees in the urban environment to allow communities to understand the economic benefit of protecting our urban forests.

“The benefits of trees must be made tangible. Because if we [as an industry] do not value trees, then they will be valued at nothing,” said Tim Rollinson, Director General of the Forestry Commission.

In the latest suite i-Tree v3.0 there are five applications; two analysis tools, and three assessment programs:

  • i-Tree Eco uses field data from various trees along with meteorological data and air pollution to quantify the urban forest structure, environmental effects and the value to the local community
  • i-Tree Streets quantifies the economic value of a municipality's street trees by calculating the environmental and aesthetic benefits
  • i-Tree Species advises urban foresters on the most suitable tree species to plant based on the geographic area and the function it is intended for
  • i-Tree Storm provides an assessment tool for potential storm damage in the area, whilst also providing information on time and money needed to mitigate the damage
  • i-Tree Vue (Beta) uses land cover data maps to assess local land cover, tree canopy and the subsequent services provided to the ecosystem and potential planting scenarios can also be modeled
  • The Forest Service is also working on i-Tree Hydro which is designed to simulate the effects of changes in tree and canopy cover on watershed, stream flow and water quality
  • The tool can be used to understand the contribution made by a single tree, or by a forest – it simply provides the basic data on which value can be calculated. Most services provided by trees are not captured economically: for instance clean air, which everyone wants but would never consider the price of, so the management of trees has remained intangible to community benefit. It is hoped that by using this value communities can strengthen advocacy efforts to protect their local ecosystem, and assist planners in making better management decisions for the benefit of the community, now and in the future.

    In the past four years numerous communities, non-profit organizations, consultants, students and volunteers have used the i-Tree suite in a variety of ways to understand individual trees, forests, neighborhoods, cities and even states.

    Developers at the Pacific Southwest Research Station and the University of California at Davis created STRATUM, a benefit-calculation model which was used by the New York City Parks Department to determine that the nearly 600,000 street trees in its five boroughs provide an annual benefit of US$122 million, more than five times the cost of maintaining them. STRATUM also calculated that in Chicago in 2007 the city's 3,585,000 trees removed 888 tons of pollutants each year valued at US$6.4 million a year, stored 716,000 tons of carbon with a value of $14.8 million, sequestered 25,200 tons of carbon per year with a value of US$521,000 a year, and saved US$360,000 a year in building energy reduction.

    Using i-Tree with additional information from a study conducted by Geoffrey Donovan and David Butry from the Pacific Northwest Research Station the effect of trees on the housing market has also been calculated. For example, the presence of street trees increased sale prices in east Portland by a average of US$8870, and shade trees growing beside the south and west walls of houses in Sacramento reduced the need for air conditioning to the tune of US$25.16 each electricity bill.

    The Suite has also been used for several years by the National Football League which uses it to help reduce the environmental impact of the Super Bowl by planting trees in host cities. Internationally, it is being trialled in Torbay UK.

    i-Tree was developed by the US Forest Service and the Davey Tree Expert Company and has been freely accessible in the public domain since its inception in 2006. Partners helping further develop the site and provide technical support include the National Arbor Day Foundation, the Society of Municipal Arborists, the International Society of Arborculture and Casey Trees.