By Larry Lange
Seattle, WA (August 8, 2010)- Standing on a steep incline surrounded by tall alders, cottonwoods and maple trees, the two men in orange vests stretch out a measuring tape. Troy Beady lays one end on the forest floor at the higher elevation, then Jack Simonson stretches the other end straight ahead to a point where it meets the tree, about 5 feet above the descending ground.
Then Beady tilts a hand-held meter until he can see the top of the mature alder they’re surveying. He calls out the calculated figure, then Simonson adds on the length of the trunk below the tape and announces the tree’s estimated height, in meters: “Thirty-five-point seven-five,” he said. That’s more than 117 feet tall. Slowly, for the rest of this summer and maybe into next spring, the crew is circulating through Seattle, assessing city trees one plot at a time trying to answer a fundamental question: What is Seattle’s urban forest worth?
The study is being undertaken with the U.S. Forest Service, the University of Washington, Cascade Land Conservancy, King County and Seattle. It will ultimately estimate the trees’ economic worth to the city: how much pollution they absorb, how much summer cooling they provide and how much storm water they absorb in winter, showing how much they might save in energy and drainage costs.
The work advances beyond the estimates of the size of the city’s tree “canopy,” according to Ara Erickson of the Cascade Land Conservancy. It will be used to estimate the real-life economic benefits of having trees around. The answers might ultimately help the city decide how much more protections, if any, the city’s trees need. For the moment, tree-preservation advocates don’t have economic arguments to make “except to say we have approximately this many trees,” said Kathy Wolf, social scientist for the University of Washington and the U.S. Forest Service.
The new figures could provide tree advocates with more bottom-line suggestions, Wolf said. For example: “If we invest in more trees is that a favorable alternative to, say, investing in more light rail and investing in people car-pooling more?”
Erickson, the conservancy’s green-cities director, said, “there’s tons of benefits that are provided by urban forests” but it will help private landowners and development managers to have those quantified. Over the years, the city has estimated, the amount of land with an overhead tree canopy decreased from 40 percent in 1972 to 18 percent in 2006. The city now estimates the coverage has increased to nearly 23 percent, but efforts have begun to save the remaining trees and encourage the planting of new ones in hopes of increasing the total stock.
Tree-counting and analysis isn’t something people do every day, but federal stimulus money is financing an effort that started this summer in Seattle and will expand to include King County next year. A report on Seattle is expected by late next winter or early spring. Similar studies have been done in Chicago; Washington, D.C.; Milwaukee; Arlington, Texas; and Casper, Wyo. Local officials have wanted to do it in King County for some time and once the federal stimulus program was announced, “this was our shovel-ready proposal,” Wolf said.
In all, seven people are working either fulltime or part-time on the project, including two geographic-information systems experts hired for the project by the UW. This summer and next, Beady and Simonson will be among those working in the field. The rest of the year they’re King County employees who build and maintain back-country trails in county parks; while they’re paid for the forest-survey work with federal money the county can use its own money to replace them on the county jobs for the summer.
Inventorying trees is a labor-intensive effort. “One plot had 50 trees and that’s a day and a half” of work, said project coordinator Lisa Ciecko, who spends time in the field with the crews. Another plot was surrounded by blackberries so thick that “it took us longer to get to the plot than to (survey) it.”
Field crews will focus the work on 226 individual plots, each one-tenth of an acre, representing 9 different land-use zones around the city ranging from single-family residential to commercial and industrial areas and the downtown business district.
So far about 50 private single-family homeowners have agreed to let the crews onto their property for the survey, out of the 86 who were asked. Of those who’ve declined, “I don’t think we’ve received reasons why,” Erickson said. Organizers are still trying to reach single-family homeowners and “we’re hoping for more,” she said. The other 140 plots will be downtown and in other zones city-wide, and will include portions of parks.
Organizers said they aimed to be representative in the individual plots they’re surveying. “We’d expect the most variation in people’s yards,” Ciecko said. “Hopefully we’ve selected the right amount of plots to account for that.” In addition to measuring trees on each plot, crews will survey the overhead leaf cover, or “canopy,” by standing directly below its edges and measuring the distance across – then subtracting the open areas between branches where they see sky.
They’ll measure trees and shrubbery with branches one inch in diameter and larger. A computer model will estimate the amount of other ground cover based on the amount of leaves on each tree, to save time.
In all, crews will assess as many as 50 different variables in addition to tree size at each plot, including age and defects. There are challenges: try calculating the height of a tree with a bent top or one that leans at an angle. In that case, you stand directly under where the top ends and “then you’ve got to use a calculator,” Simonson said.
Erickson said, crews will assemble a picture of what the city’s forest looks like, what tree species it contains, what shape the plants are in and how old they are as well as its economic value. The Forest Service, using a computerized program it developed, will crunch numbers to estimate environmental benefits the city’s forest offer, and whether it’s old or diseased enough to require replanting or other attention. The results could also get thrown into the growing debate about Seattle’s trees. There are varying views of the value of the assessment.
Elizabeta Stacishin-Moura, chairwoman of Seattle’s advisory Urban Forestry Commission, said the work will help the discussion. “The more we know about the makeup, the density, the quality of the forest we have the better we can assess its value and we’re more prepared to protect it,” she said. But tree advocates have been critical of the city’s tree-preservation efforts. Kirk Prindle, another member of the forestry commission, said he applauds the new survey but “I am concerned about how any data collected…may be used.”
The conservancy, which works to preserve rural land, sees the urban tree project as ultimately helping make cities like Seattle more attractive by preserving more city trees, reducing the development pressures on rural land beyond the city limits. “We’re hoping that’s another benefit,” Erickson said.
Seattle Post-Intelligencer- Study’s goal: Finding out how much Seattle’s trees are worth
Cascade Land Conservancy
Human Dimensions of Urban Forestry and Urban Greening