News

Urban Forests

Natural systems make environmental and economic sense

By Tim Johnson · Wednesday, February 24, 2010

Bellingham City Council recently delayed (again) the adoption of a spending plan for parks in the city’s Southside in the hopes that an important parcel south of the city may come available and be acquired intact as an urban forest. The 82-acre parcel known by fans as the Hundred Acre Wood may be spared from development as a result of the failure of Horizon Bank and the transfer of that asset to a second bank. Last time the property changed hands, Chuckanut Ridge sold for $14.3 million.

That number is likely outside the range of what the city would want to pay to acquire Chuckanut Ridge, Bellingham Mayor Dan Pike said, but he remains hopeful a deal may be struck with Washington Federal, which acquired Horizon’s assets when the Bellingham-based bank was closed in January by federal regulators.

Meanwhile, how do we assign a value to forests left standing as the city grows around them?

Urban forests found within city parks serve not only as recreational and social centers, but also as organic sponges for various forms of pollution and as storehouses of carbon dioxide to help offset global warming.

“The beauty of urban forests is there are so many co-benefits,” notes Dr. Faisal Moola of the David Suzuki Foundation. “They help us fight climate change by absorbing and storing carbon dioxide. They provide psychological benefits by providing a place where we can find quiet and solace in our busy day. They shelter and protect our wildlife. They provide a quality environment where kids can learn about nature and reconnect with nature. They help to filter our water and air.

“We must recognize that nature—and not just natural ecosystems like wilderness, but also remnant forests that are coming back in our urban and suburban areas—that these areas provide a suite of ecosystem services that have direct value in terms of sustaining the health and well-being of our communities,” Moola said. “The problem is that most policymakers have a poor understanding of the benefits we actually receive from nature. And they have an even worse understanding of how valuable these systems are. In some cases, they’re priceless.

“In consequence,” he continued, “there’s no incentive to steward them. And there’s no disincentive to degrade them.”

Moola is director of terrestrial conservation and science at Canada’s David Suzuki Foundation and is an adjunct professor of Forest Conservation at the University of Toronto. He leads a team of scientists, policy analysts and public outreach experts on a number of campaigns to educate the public and reform environmental policy in Canada, including legal protection of endangered wildlife, valuation of ecosystems services, protection of urban agribusiness, and mitigating and adapting to climate change through nature conservation.

The benefits of forests—what scientists refer to as “ecosystem services”—are measurable and quantifiable, even to the point where a monetary value may be assigned to them.

“Environmentalists and scientists are trying to assign a monetary value to these benefits that are simply treated as externalizes by mainstream economists,” Moola said. “Economists typically do not try to assign a value to what’s lost if we pave over another old growth forest to put up another shopping mall. We’re working to assign what we might term the ‘replacement cost’ for the loss of these systems.”

One way that might be determined, he explained, is by polling people to find out what they’d be willing to pay to see a grizzly bear or catch a wild salmon. Other methods might include factoring the health costs associated with degraded air, or what it might cost for an infiltration and treatment system to replace a degraded water supply.

“It’s a nascent science, it’s an immature science,” Moola admitted, “but we’re trying our best to come up with a monetary sense of how much nature is worth.”

One such study assigned a value to the greenbelt surrounding Ontario of $3,571 per hectare in annual non-market ecological services.

When it comes to urban forests, Moola observed, “Here’s the rub: We can’t have healthy economies and healthy human societies without healthy ecosystems and species diversity. The loss of species and ecosystems— like urban forests—affects not just the production of commodities that sustain our economy, like the food that we eat or the timber we get from these forests. The loss also affects many of these non-market services that sustain our communities—like clean air and clean water, and the role forests are playing in helping to solve the global warming problem. Urban forests,” he said, “sequester and store enormous amounts of carbon dioxide from the atmosphere and in doing so act as a hedge, or a brake, against climate change.”

As early as 1978 Congress first recognized the importance of urban forests by passing the Cooperative Forestry Assistance Act, which provided funds to promote the maintenance, expansion and preservation of urban tree cover while encouraging research and development of related technical skills at the local level. The legislation also called for tree-planting to complement existing urban forest and open space maintenance programs.

The Urban and Community Forestry Assistance Program of 1990 expanded aid to state foresters and nonprofit organizations working to promote and expand urban forest parklands.

“We’re blessed in places like Washington State and British Columbia in that we still retain today much of the original forest cover,” Moola explains. “But the loss of nature—and particularly the loss of forests—is having a dramatic impact on the direct benefits that sustain the health and well-being of human communities that live in close proximity with remnant bits of nature.”

Though scattered individual trees can absorb pollution, the size of urban forests provide the most bang for a city’s buck. Urban forests also play an important role in sequestering carbon dioxide, the potent greenhouse gas that is primarily to blame for global warming.

“Parks with higher proportions of their area covered by healthy trees will provide the greatest impacts,” agrees David Noway, project leader of the U.S. Forest Service’s Urban Forest Ecosystem Research Unit.
Each year in Chicago, for example, the urban tree canopy removes 15 metric tons of carbon monoxide, 84 metric tons of sulfur dioxide, 89 metric tons of nitrogen dioxide, 191 metric tons of ozone and 212 metric tons of particulates, according to noway. Trees absorb these gaseous pollutants via their leaf stomata (the tiny pores on leaves) and break them down into less-harmful molecules during photosynthesis.

But Moola feels it is inappropriate to attempt to define what constitutes an urban forest from, say, a stand of trees in a neighborhood.

“The reason i don’t make that distinction is because while we’ve placed a lot of emphasis as environmentalists on protecting natural, primary forests—old growth forests, for example—we have to understand that even the trees we plant and manage are providing net benefits for the health and well-being of our communities,” Moola explained. “Therefore, we need to provide incentives to keep those trees around, as well as create incentives to plant new forests in urban areas.

“I don’t think you can make an ecological case that a stand of trees in a particular town is of lesser value than a natural forest. That said, a forest that’s found within a town is going to be very different than a natural wilderness,” he said. “Such a forest is going to be embedded in a matrix of land uses that is oftentimes very intensive and can have deleterious effects on the health of that forest.”

The City of Sacramento, Calif., for example, in a public-private partnership called Sacramento Shade spearheaded the planting of more than 200,000 trees around the city in the mid-1990s. in a study assessing Sacramento’s bolstered tree cover, Greg McPherson of the Western Center for Urban Forest Research found that the region’s urban forest removes more than 200,000 metric tons of carbon dioxide from the atmosphere each year, saving taxpayers as much as $3 million annually in pollution mitigation costs.

“It’s cheaper to plant trees than to generate more electricity,” McPherson concludes.
Gary Moll, a vice president at the nonprofit group American Forests, asserts that trees are the “ultimate urban multitasking,” performing the functions of air filter, sponge, humidifier, heat shield, wind block and carbon sink.

According to Eric Beckers of the Texas Forest Service, tree-planting efforts in urban areas boost this process, as city trees are “15 times more capable of reducing carbon in the atmosphere” than rural trees.

“We want people to understand that trees are an important part of the city infrastructure,” Moll said. “There’s a hard part, and there’s a green part, and we should be planning for both. it’s just not good business to sacrifice trees.”

Some statistics cited in this article are courtesy of E, the Environmental Magazine.