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Saving Seattle’s trees may mean saving their yards

A home in the University District Credit: Flickr user Wonderlane

Amidst all the noise over the city’s recently adopted Housing Affordability and Livability Agenda (HALA), scarcely a word has been spared for the 4.35 million Seattleites who have the most to lose in the push to create more housing. These aren’t just any residents. They clean the air and water, and protect Puget Sound from the tainted runoff that is the leading threat to salmon and other local aquatic critters. According to a 2012 inventory sponsored by the U.S. Forest Service, they store two million metric tons of carbon, sequester another 140,000 tons each year, and remove 725 metric tons of other pollutants from the air. They prevent mudslides and block piercing noise and searing sun.

These stalwart Seattleites do more than air conditioners to cool the city, saving it from becoming even more of a heat island. Even before Seattle’s weather took a turn toward Tucson, they reduced building energy use by $5.9 million a year by blocking sun and wind and fostering evaporation. They’re a main component of the “livability” that’s saluted in the HALA report’s title, but scarcely discussed in its text. Numerous studies show that being around them is good for not only physical but mental and emotional health, not to mention children’s learning abilities.

These are Seattle’s trees, and they’re squarely in development’s sights, whatever lip service developers may pay to them. To take a particularly poetic example: At the corner of South Willow Street and Seward Park Avenue, an enormous cottonwood and a thicket of other broadleafs – nothing fancy, but a lot of green – lined the oversized front yard of a modest older home on a double lot. A developer bought that yard and, through some deft shortplatting magic, turned it into three lots. The trees were replaced with three looming gray and white boxes that look like all the other contemporary lot-busters going up around town. One scraggly, much-thinned ash and a few sidewalk saplings still cling to the remaining dirt perimeter.

The company responsible for this arbor-cide is called Green Canopy Homes. On its website, the company boasts that “we are the only for-profit homebuilder (that we are aware of) in all of America that was intentionally and deliberately started to combat and lessen the negative impacts of climate change and resource scarcity via in-city homebuilding.” Green Canopy’s CEO and CMO participated in the HALA committee’s strategic workgroups.

Beyond their credits, the word “canopy” does not appear in the HALA report. Nor does the word “trees.” What happened to that patch of lower-case green canopy is happening everywhere houses and apartments are going up. That is to say, just about everywhere in Seattle.

Even with its most controversial provision – the elimination of single-family zoning – deferred, HALA is still a density agenda. And density, absent special protections, is the mortal enemy of trees. The city, in its development standards, has tried to defy the laws of geometry by allowing other mitigating measures that take less space but are less effective – setbacks, balconies, bioswales, green roofs – to substitute for the open space where trees can grow.

But trees get in the way when soaring prices induce developers to max out their lots, and the city to allow more housing units in the hope (vain so far) that supply will outrun demand and hold prices down. “The problem is lot coverage and setbacks,” says one veteran Seattle arborist who has fought for years on behalf of stricter tree protection, but insists on anonymity for professional reasons. As the city grows, “there simply isn’t enough space for existing large trees.”

The HALA agenda will accelerate this process by loosening coverage and setback restrictions, and upzoning targeted single-family areas near transit and city-designated urban villages. But the process is already proceeding apace under current zoning, as developers raze smaller homes and what few unbuilt private plots remain. Surging development has already stalled, maybe reversed the much-hailed growth of Seattle’s canopy during the preceding three decades.

canopy cover
Single family homes create more tree canopy than developed parks in Seattle. Source: City of Seattle Urban Forest Stewardship Plan (2013).

Seattle’s tree canopy has waned, waxed, and waned again in the nearly 170 years since Euro-Americans first settled here. Canopy coverage was nearly total then, and the trees were much, much bigger: 200-foot cedars, hemlocks, spruce, and Douglas firs. Cass Turnbull, the executive director of Seattle’s TreePac lobby, estimates that coverage fell to just 10 percent by 1900 but rebounded to 50 percent by 1950, as logged-over parkland regrew and trees planted around homes reached leafy maturity.

Around 1970, city officials and others began trying to measure canopy using the new technology of Landsat,. This was followed by aerial photography, LIDAR, GS, on-site surveys, and, inevitably, Google Maps. But such measurement is devilishly tricky and variable, as UW researchers Jeffrey J. Richardson and Ludmila Monika Muskal show in a 2012 paper, “Uncertainly in Urban Forestry Canopy.”Technology, sample point size, shadows, the fine-grained complexity of urban landscapes, and bias all skew estimates.

So do the statistical equivalent of urban legends. For decades, many media and even some official reports have declared, without attribution, that trees covered 40 percent of Seattle in 1972; that would support Turnbull’s estimate of 50 percent coverage in 1950. The meme persists, even though it’s an implausible outlier. That same year, using Landsat, the national research and advocacy group American Forests calculated Seattle’s coverage at just 15 percent.

“We spent quite a few staff hours trying to track that [40 percent figure] down,” says Sara Wysocki, a spokesperson for the city’s Office of Sustainability and Environment (OSE). “We think it came from a report released by American Forests recommending 40 canopy cover for Puget Sound cities. We think that got transposed into ‘Seattle has 40 percent’ and lived in some sort of document.”

In 1999, American Forests calculated that Seattle’s canopy coverage had declined to just 18 percent by 1996. Since then various researchers and city consultants have variously pegged Seattle’s coverage at 22.5 percent in 2002, 22.9 in 2007, 26.4 and 29.6 percent in 2009, 26.3 percent in 2010, and 28.5 percent in 2012.

From these estimates, a broad trend emerges: Canopy recovered somewhat in the 1990s and 2000s, as the city pushed for new street trees and existing trees filled out. A recovery in the 2000s has lately stalled as redevelopment, which lapsed during the last decade’s two recessions, accelerates. Today, American Forests and city resources managers estimate Seattle’s canopy at 23 percent – just slightly more than New York’s 21 percent and well behind two cities with which Seattle is frequently compared on other scores, Portland (30 percent) and Minneapolis (31 percent).

Meanwhile, the city seems to be quietly backing away from its determination, passed by its council and enshrined in its comprehensive plan, to “achieve no net loss of tree canopy coverage, and strive to increase tree canopy coverage to 40 percent.”

In its 2007 Urban Forest Management Plan, the city adopted an “interim goal” of 30 percent coverage by 2037, a goal reiterated in its 2013 Urban Forest Stewardship Plan. Now it is reviewing a proposed “Seattle 2035” update to the comp plan. Seattle 2035’s draft environmental impact statement notes that one of its “most significant policy components” is “adjusting” the 40 percent goal to “be consistent” with the 30 percent goal. The city’s Urban Forestry Commission decries this as backsliding.

Such downsizing may be realistic, but it reflects deflated aspirations: the best we can hope to do now is almost catch up with Minneapolis. Seattle will have a hard time reaching even 30 percent if redevelopment continues at today’s pace. Past analyses have found that average tree coverage on redeveloped single-family lots fell from 30 to 18 percent. On redeveloped multifamily lots, coverage declined from 18 to 5 percent.

Don’t look to parks and open space to fill the gap. Much of the public forest is in rough shape, beset by ivy and other invaders and by the natural senescence of maples, alders, and other short-lived broadleafs that grew up after the original conifers got logged. The city, working with the nonprofit Forterra, is chipping away at restoring those long-lived firs, cedars, and hemlocks and other native plants. But it will take much more investment. So far they’ve started on just 1,000 of the 2,500 acres targeted for restoration by 2025.

And there’s only so much parkland anyway. The 2007 Urban Forest Management Plan reported that nearly half Seattle’s trees grow on city parks and greenbelts and only about a third grow on single-family lots. But Wysocki notes that those figures, derived by extrapolating from an estimated “coarse tree size unit,” were shaky even then: “We have had a data challenge. Seattle’s [interagency] Urban Forestry Team has recognized that. We knew our data were out of date going into the recession, and then there was no money to do anything. It’s part of our work plan for the Office of Sustainability and Environment to conduct a thorough assessment and analysis of canopy coverage.”

She says the best available data come from an “Urban Tree Canopy Analysis” the Seattle Parks Department commissioned from the imaging firm NCDC in 2009. It found that most of the canopy growth in recent years occurred on single-family properties, and most of the loss accrued in city parks. All the city’s parks and greenbelts and their street frontage together held just 21 percent of its canopy acreage. Sixty-three percent grew on single-family lots and their street frontage, 49 percent on the parcels themselves.

The 2013 Urban Forest Stewardship Plan affirmed those findings, and reported others just as significant: 55 percent of the trees on single-family lots are in “excellent” condition, and only about 2 percent are dead, dying, or in “critical” condition. By contrast, only 20 percent of trees in parks and greenbelts are in excellent shape. About 20 percent are dead, dying, or critical.

condition
City of Seattle Urban Forest Stewardship Plan (2013).

So Seattle ‘s healthiest trees, and most of its urban forest, grow unheralded around its bungalows, cottages, mansions, and ramblers. Preserving them means preserving the spaces they grown in, which means preserving the structures they grow around rather than replacing them with lot-busting McMansions and McPartments.

Doing that will require both regulation and incentives. Effective regulation will mean finally adopting a permanent tree-protection code with more teeth than the current interim code – an effort stalled for years in an impasse between urban-forest advocates and development interests. (Advocates such as Turnbull urge that the task be transferred from the Department of Planning and Development, which they see as captive to developers, to the Office of Sustainability and Environment.)

Possible incentives range from free rain barrels for homeowners who plant street trees to property-tax breaks for those who preserve exceptional trees and high canopy coverage. Sustaining trees on private property has public benefits, just as historic preservation and affordable housing do; perhaps it deserves similar tax forgiveness.

Changes to the land-use code could effectively expand housing stock, increase human (if not building) density, and foster affordability without razing or building, by relaxing occupancy and use limitations on existing structures. Rental houses might be converted to duplexes and triplexes, duplexes and triplexes might be allowed to go condo, and homeowners might be allowed to sell, not just rent, accessory dwelling units.

Such measures would encourage fuller use of large houses as household sizes shrink, make it easier for owners of modest means to stay in their homes, and answer neighborhood concerns about too many rentals. And they would leave room in the yards outside for the trees to keep doing their good work.

This article was changed on Nov. 5, 2015 to present more representative data from the 2007 Urban Tree Canopy Analysis and a more reliable estimate of 1996 canopy coverage.

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