By Lisa Ciecko, Forterra, and Kathleen Wolf, Ph.D., University of Washington and USDA Forest Service PNW Research Station

What is Seattle’s urban forest worth? Not many people give this question much thought. Yet recent research indicates that Seattle’s urban forest would cost $4.9 billion dollars to replace. Replacement cost is just one way to estimate value. Seattle’s trees are an important capital asset. They produce many ecosystem services and provide value to urban communities by sequestering and storing carbon, removing materials that cause air pollution, and contributing to energy savings.

A new report, “Seattle’s Forest Ecosystem Values: Analysis of the Structure, Function, and Economic Values,” tells more about these findings. Data collection over the last two years included extensive field work on private property and used the i-Tree Eco methods. i-Tree Eco is one of a suite of software tools, developed by the USDA Forest Service. Eco provides information on forest conditions, including the structure (age, species composition, etc.), environmental function (energy savings, carbon storage, etc.), and economic values of trees.

The project team adapted i-Tree Eco to collect data applicable to the special conditions in the Pacific Northwest. Tree canopy cover values are an important performance benchmark for urban forest managers. Project data compared field-based canopy estimates to those derived from 2009 satellite imagery. In addition, deciduous and evergreen species distribution, as well as current and expected tree sizes, were analyzed to better describe local conditions. Finally, the distribution of two invasive species, English holly and cherry laurel, was analyzed.

Project results are being incorporated into citywide urban forest planning, including revisions to the Seattle Urban Forest Management Plan.

This work is one of many studies by the Green Cities Research Alliance (GCRA). GCRA was initiated by the Pacific Northwest Research Station, USDA Forest Service, in 2009 to research urban ecosystems in the Puget Sound region. GCRA pairs scientists with practitioners and local decision makers to co-design and implement research efforts that provide relevant and practical information. The purpose of this collaboration is to increase the knowledge needed to build sustainable urban environments. In addition to US Forest Service scientists, major collaborators include the University of Washington, Forterra (formerly the Cascade Land Conservancy), and King County Parks and Recreation. Additional forest ecosystem values research is underway in King County parklands and along the Green-Duwamish River, with results expected in 2013.

Information on the Green Cities Research Alliance is online. The Seattle report can be viewed or downloaded on the Forterra website. A more detailed General Technical Report will be provided by the US Forest Service in 2013.

Editor’s note: Lisa Ciecko, and Kathleen Wolf, Ph.D., represent Environmental Non-profit Organizations and the College of Forest Resources at the University of Washington, on the Washington Community Forestry Council.