I’m a day late on this, but the Seattle P-I had an interesting series on Seattle’s ailing urban forests. The principal threat is the rapid spread of invasive species, which essentially throttle standing trees and smother healthy new growth:

"At first glance, the most prolific tree-killers seem pleasant enough, aesthetically speaking—a splash of green on a bare tree trunk, a burst of pretty flowers on the ground. But tendrils of ivy, morning glory and clematis quickly spread up into the tree canopies, starving the trees by cloaking their leaves and blocking photosynthesis. Their weight breaks branches and bends tree tops, stunting growth. Blackberry thickets smother ferns and saplings."

Folks at the Seattle Urban Nature Project, along with scores of other groups, are in the frontlines of the battle against the aliens. Without their dedication, the city’s forests and parks would likely succumb to the greedy monoculture of ivy and blackberry that is already in evidence nearly everywhere. So as a nature-loving city-dweller I’m happy about the much-needed efforts to restore the ecology closest to us.

But the more I read, the more the series also raised some interesting questions—for me, anyway—about how we treat conservation priorities. How do we sort out competing environmental goods, such as increasing urban density and preserving an urban forest canopy? Is urban ecology really the best use of our resources?

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  • Now obviously, it’s a good thing to restore the forests and natural areas within our cities. And it’s also a good thing to protect and restore natural areas on the urban fringe as well as in more remote locations. But given the sad fact that we have scarce resources to devote to conservation, is urban ecological restoration really our best option?

    The analytical part of me says no. I’d argue that we can get more ecosystem bang for our buck by investing in natural areas that are in less dire need of assistance—areas that are capable of supporting a more diverse array of biota. It’s futile to pour money into the heavily degraded Duwamish River, for example, when we can protect and repair less-damaged waterways like the Cedar or the Snohomish. Similarly, I wonder whether the price tag of saving Seattle’s city park forests—an estimated $48 million over 20 years—couldn’t be better spent saving and restoring forests in, say, east King County that are threatened by sprawl. Those forests, while not pristine, could be treated to replicate old-forest conditions that can support a variety of species, including some endangered ones.

    But the rest of me says yes. City nature matters.

    Urban ecology may not be the best possible investment for regional biodiversity, but that doesn’t make it a waste of resources. While Seattle’s urban forests will likely never support spotted owls, they can and do support people. Hospitalized patients recover faster when they can see trees. In inner-city neighborhoods, academic studies show that children learn better and are less likely to become involved in crime if they are exposed to plants and trees. Nature in the city may even foster social capital.

    Most people experience nature primarily in city parks and public beaches, not on backcountry trails in national parks and forests. That’s especially true for children, the elderly, lower-income folks, and people without cars. And that experience of nature has a powerful psychological, even spiritual, effect on people. It’s so powerful, I’d argue, that it’s very difficult to put a price tag on it.

    If you don’t believe me, and you live in Seattle, I’ve got a challenge for you: Later this November see if you can find the chum salmon running up Piper’s Creek in Carkeek Park. When I visited twice last year, the natural phenomena of the salmon run, even in a tiny urban creek, was clearly transformative for us fish-watchers, and we were legion. An astonishing array of people stood for hours in the rain, cheering on the fish—literally cheering for them—as they struggled up over the stream’s little barriers. There’s no doubt that the Northwest’s salmon constituency swelled greatly that day. And equally, I don’t doubt that we watchers were immeasurably better off for it.

    And the benefits of urban ecology are not all anthropocentric. Even if urban ecological restoration is not the best non-human biodiversity investment available, it still winds up being a plus in nature’s scales. Native bird, fish, and plant diversity all flourish when we remove invasive species.

    Finally, there are also plenty of economic arguments in favor of urban forests. These are not my main reasons for wanting to restore city forests, but they are instrumentally useful for convincing skeptics that there’s value in city ecology.

    Trees may be good for business by increasing worker productivity and boosting retail profits. Plus, there are tangible services that urban forests and trees provide—services that we can quantify in dollars and cents. As the P-I article describes it:

    When it rains, trees capture some of the water and help it soak into the ground slowly, controlling erosion and stemming the flow of dirty stormwater rushing off driveways and roads into Puget Sound.

    If the city were to lose its urban forests, it would cost more than $220 million in new stormwater-treatment facilities and drainage systems, according to an environmental group’s analysis.

    City officials say the costs would be higher, possibly topping $1 billion.

    Three years ago, researchers with the University of California-Davis and the U.S. Forest Service released a study that put a price tag on the benefits of urban trees in the Northwest.

    Considering all of the good that trees provide—such as reduced energy costs because of shade and protection from wind, less pollution and higher property values—a small residential tree netted a $12 annual benefit, while a large tree was worth $53.

    So, while $48 million to restore Seattle’s park forests is certainly more than I can scrounge up in loose change from my couch, it seems like a darn good investment in the health of the city. And when you consider the benefits, both tangible and intangible, that urban nature brings to our lives, it’s a steal.