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Bridging the Detroit divide

How people feel about Detroit seems to depend largely on where they are standing. Or so says Jana Cephas, who lived in that city for 12 years before moving to Boston to pursue a PhD at Harvard University’s Graduate School of Design in 2007.

When Detroit comes up as a topic among designers, architects, planners and historians, Cephas says she hears a lot of talk “very focused on decline, decay and vacancy as Detroit’s ‘problem.’” However, according to Cephas, one of Detroit’s biggest challenges is not that it has vacancy but that experts do not see the latent potential in that vacancy.

“What is sustaining a lot of people in Detroit today is their ability to use vacancy as an advantage,” she says.

Concerned with the wide gap between residents’ and outsiders’ perceptions of vacancy in Detroit, Cephas has secured a $2,000 BSA Research in Architecture grant to investigate the issue further. By documenting how residents use vacancy for financial gain, she hopes to help designers better understand how to accommodate informal economies in their redevelopment plans.

Cephas certainly isn’t contesting that Detroit has fallen on hard times. The poorest city in the United States, Detroit suffers from a high unemployment rate, with 33 percent of its residents living in poverty. And although no official vacancy rate exists, Cephas estimates that it would be around 35 to 45 percent based on anecdotal evidence. “If you drive around the city, any given block will be almost half empty,” she says.

But what piques her curiosity is the many ways—often unsanctioned or illegal—in which Detroit residents have begun to use vacant space as income-generating infrastructure.

While city residents’ use of vacant lots for urban farming has garnered publicity nationwide, many other Detroit practices have evaded mainstream attention. These include squatting and building reclamation, architecturally inspired art auctions and events, intentional co-housing and cooperative communities, illicit utility restructuring, and more.

For example, both formal and informal building deconstruction crews working throughout Detroit have generated a significant amount of economic activity in recent years.

“It’s anti-architecture in a way,” explains Cephas. “Residents have found ways to recycle vacant buildings and to create mini-economies around that recycling. They literally deconstruct the buildings by hand—taking them apart, piece by piece—and sell the parts.”

According to Cephas, this has spawned numerous smaller recycling businesses that do everything from recycling copper pipes to breaking down wood shingles into wood pulp that’s turned into other products to cleaning 19th-century doorknobs and pulls for resale through antique shops. “The unbuilding process has become a re-economy in the city—but one that hasn’t been tracked so far,” she says.

To better understand this kind of renegade reuse, Cephas has found herself turning to research methodologies drawn from disciplines outside architecture, such as anthropology and sociology.

“Part of what makes researching this topic so very challenging is that these activities are difficult to quantify. The information does not live in an archive or database somewhere, and there’s no clear way to access it. In fact, it’s impossible to know what exactly is happening unless you are living in the city and see what’s going on,” explains Cephas. “So a lot of what I do involves walking around and talking to people.”

When she finishes her research project in December, Cephas hopes to publish a peer-reviewed paper exploring how informal economies can serve as a legitimate catalyst for sustainable community development.

“Hopefully, the paper will help other designers understand not just Detroit, but this condition of lower economic layers and levels in general,” says Cephas.

Genevieve Rajewski is a Boston-based freelance writer who covers science, nature, animal issues, travel, food and passionate people for acclaimed publications such as Smithsonian, Washington Post Magazine, and the Boston Globe. Her website is

Beyond the branding: Designing a 21st-century Innovation District

“Innovation district” is an oxymoron. Today many innovators could be anywhere as long as they have a laptop and a place to get a good cup of coffee. But creativity does have a spatial component, which is why Boston; Barcelona, Spain; Portland, Oregon; and a host of other cities have pinned their hopes for urban renewal on areas branded as Innovation Districts.


Click image above to view slideshow.

Both academic studies and common sense suggest that dynamic clusters of people working together are the source of most social and technological breakthroughs. Boston Mayor Thomas Menino is trying hard to put this insight to work as new development on 800 acres of South Boston waterfront takes shape. He sees its tightly packed old warehouses on Fort Point Channel, a few newly built office and residential buildings, ongoing maritime industries and vast expanses of underused land as the place to be for the creative class.

But can an innovative spirit be built into a brand-new 6.5 million-square-foot speculative real estate deal proposed by the developers of Seaport Square and supporters in Boston City Hall? The corporate-size floor plates, distance from academic institutions and congested inner-city location don’t conform to successful Innovation District precedents. There is the potential for a clash of cultures—invention requires breaking down boundaries; renting property and collecting taxes is about erecting them.Historically, most centers of innovation have emerged organically in compact areas where complex webs of relationships grow over time. Fort Point Channel’s warren of brick-and-beam lofts, like parts of Brooklyn and San Francisco’s Mission District, have provided exactly the kind of small-scale, low-rent urban environment where innovators in hooded sweatshirts thrive. Rising rents have, unfortunately, been pushing these start-ups and artists out.

Across the river in Cambridge’s Kendall Square, MIT and new companies surrounding it offer a place for innovators in lab coats as they collaborate with compatriots in Palo Alto, California; Austin, Texas; and beyond. The well-furnished laboratories filled with PhDs and Nobel laureates create an environment where the next generation is mentored, and research can spin off profitable ventures down the street.

“Most successful centers of innovation have grown out of mission-driven institutions, like research universities, that create a kind of knowledge ecosystem in which new ideas and enterprises can take root,” says Janne Corneil, a principal at Sasaki Associates who has studied the relationship of institutions to their host cities. “They tend to have permeable boundaries that connect the public and private realms, link research to economic development and encourage collaboration between passionate people with diverse interests. Design needs to support these kinds of interactions.”

The Boston Redevelopment Authority worked with Seaport Square’s developers to get them to live up to the branding without an institution to jump-start the inspiration and Fort Point Channel’s hipster factor increasingly a thing of the past. Project permits require the inclusion of “innovation uses,” along with an “Innovation Center” cool-kid clubhouse, subsidized housing and space for start-ups, and ground-floor hangouts for cold beers and warm handshakes as part of the development deal. But the big, boxy buildings and formal streets and greens in preliminary drawings are the usual clichés of could-be-anywhere urbanism. The permeable, interconnected environments that might challenge orthodoxies and provide an architectural context for innovation don’t appear to be anywhere in sight. Subsidies for start-ups are terrific—but that brilliant kid in a T-shirt may prefer paying rent with friends in SoHo than accepting noblesse oblige in a corner of Boston with Dilbert.

The city may be better off mandating the kind of habitat in which an ecosystem of innovation can flourish—rather than the kinds of uses it thinks should inhabit them. Layered spaces, a multiplicity of entries and articulated volumes interwoven with delightful landscapes would embody an ethos of invention while allowing flexible rental space to adapt to market realities. Eight-hundred acres can accommodate some big, blocky buildings for the makers of blockbuster drugs but shouldn’t crowd out the small-scale spaces that will provide the habitat for the next generation.

While municipal officials focus on development within their borders, creative thinking—and financing— takes place across a much broader context. “Every city has its own unique set of strengths and weaknesses,” says development consultant Wig Zamore, who has worked on some of Boston’s biggest deals. “Historically, development efforts haven’t been coordinated, but working together, cities could develop policies that might benefit the entire region. Cambridge is filled with brilliant innovators who create revolutionary companies, but it has limited space for growth. Boston’s Innovation District can help relieve the pressure as companies become evolutionary and need more room and proximity to the airport.”

Cooperation would help keep businesses in the region as changing needs change the flavor of the neighborhood that works for them—without resorting to rebates and subsidies to get them to move from the city next door. The marketing efforts and money could focus on bringing in a mission-driven institution or satellite college that will help the area keep its edge.

Companies will come and go, and the uses in most buildings will change as innovation is redefined. Architecture and urban infrastructure endure. The creation of diverse types of interconnected spaces designed to inspire the imagination will create a district that supports innovation no matter what form it takes.

David Eisen AIA is a principal at Abacus Architects + Planners in Boston. He is the author of Boston Modern: The Spirit of Reinvention and writes frequently on design issues for a variety of publications. He received his architecture degree at Harvard University’s Graduate School of Design.


Top image: Seaport Square will occupy the heart of the South Boston Waterfront’s Innovation District adjacent to the old warehouses along Fort Point Channel. Preliminary design shows building massing and the distribution of open space. Courtesy of Boston Global Investors.

The key to sustainable farming: Cities

When people talk about being conscious of where their food comes from, they most likely are thinking of farms, and, for some, the zeal for local food leads to dreams of urban agriculture. But cities have a natural role in a sustainable food system, and a time-honored one: as markets. Cities are what make farms viable—whom else would farms sell their produce to? The growing appetite for local and regional foods is bringing many advocates’ and market operators’ attention to the urban infrastructure that is necessary to make local and regional foods a stable proposition for both growers and eaters.

The notion of a clear divide between the urban and the rural is itself a curious artifact of modernity. Because milk was too perishable to transport significant distances, milk production for cities was long concentrated in dairies within city centers, where cows munched swill from breweries and distilleries. Only with the railway was it possible to promote the sale in cities of “country milk” as a more wholesome alternative.

And it was the railway that created the nationwide food system that we all take for granted and that many now question. A monument to this system hides in plain sight. New York City’s High Line Park, created out of a disused elevated freight railway, is acclaimed as a graceful reclamation of an industrial relic. But the success of its repurposing has obscured its significance as the conduit that fed the country’s largest metropolis with produce from coast to coast. 

Architectural historian Patrick Ciccone has reconstructed the High Line’s decades as New York’s “life line,” illustrating the scale and complexity of a modern big city’s food-distribution needs. New York Central Railroad’s West Side line was the only freight railway that entered Manhattan, and the High Line, built between 1929 and 1934, lifted the tracks above grade level. This was done partly for safety reasons but also with a futuristic vision in which the whole of Manhattan’s West Side would be lined with enormous new buildings equipped with sidings for receiving shipments directly from cars on the elevated railway—a “new city within the city,” much of it dedicated to receiving the fruits of the “large producing areas” of the West, now connected by rail.

The High Line’s planners took for granted that local producers could never supply New York City’s food needs and celebrated the project’s ability to furnish foods “available in varieties and quantities that were unthinkable a hundred years ago,” regardless of the season. A 1930 study cited by Ciccone reported that the “average distance of haulage of foodstuffs to the markets of New York City is fifteen hundred miles.” New York Central ads for the Sheffield Farms 57th Street dairy plant and Cudahy Packing Co. Branch House vaunted the ability to directly transfer milk and meat horizontally into refrigerated storage and vertically onto local delivery trucks.

The full vision of the “new city” was never realized before the High Line declined in the 1960s with the growth of interstate trucking, but the legacy of the transcontinental food system, based on giant farms, remains. As Ciccone says, “It’s impossible to reverse the history, or we would starve.” Indeed, New York advocates of a decentralized food system don’t harbor illusions that small local farms can provide food for the entire city. However, the demand for regional foods has grown to the extent that the city’s market operators face the need to create their own infrastructure. Greenmarket, the city’s biggest farmers-market operator, runs a small wholesale farmers market—Wholesale Greenmarket—outdoors near the city’s main wholesale produce terminal at Hunts Point in the Bronx. But officials say that a building, a covered market, is indispensable for medium-size producers—those too big to rely on neighborhood retail-market stalls but too small for the mainstream wholesale system—to tap the demand that can keep them viable.

Greenmarket Director Michael Hurwitz and Wholesale Greenmarket Specialist Shayna Cohen note the features of a well-designed covered market: shelter from the elements for produce as well as for customers; loading docks that make it easy for both producers and buyers to load and unload food; and refrigerated storage to maintain the “cold chain” to preserve dairy and meat, the two categories of local food that Cohen says have the greatest unmet demand. (More slaughterhouses and live auction houses in upstate New York top Hurwitz’s list of additional regional infrastructural needs.)

More fundamentally, Cohen says, a permanent market building “formalizes” and “lends credibility” to the market “just by being there.” Without a firmly established wholesaling system, regional produce can’t be integrated into the fuller range of places most people get their food on a daily basis, including schools, hospitals and corner stores: “Farmers markets are not enough,” Hurwitz says.

Hurwitz points to the examples of the Ontario Food Terminal in Toronto, and the Rungis Market in Paris, general wholesale terminals with dedicated space for regional producers. He also invokes the covered public markets that you still find in European cities and that were once part of U.S. cities’ fabric, and often remain, even in disuse, cities’ most distinctive buildings. The public market is also the avowed inspiration for the New Amsterdam Market, also currently an open-air phenomenon, outside the defunct homes of the Fulton Fish Market, the 1907 Tin Building and the 1939 New Market Building. New Amsterdam’s president, Robert LaValva, a Harvard architecture graduate and former city planner, harbors the goal of a permanent covered facility that will reanchor a neighborhood that has been a point of face-to-face exchange since Dutch colonial times but hemmed in for decades by the high-rise financial district.

New York market officials note that some of the farmers who sell at the Wholesale Greenmarket belong to families that, a few generations before, tilled land within the city limits but later moved elsewhere in the region. Their farms have moved, but their point of sale remained the same: Little could better illustrate that distribution in the city is the nexus of any food system.

Jonathan_TaylorJonathan Taylor has written about places, buildings and food for publications including Print, The Believer, Bookforum and the blog Emdashes.

Urban Fabric: What happens when you let innovation lead

For many of us, graduating can often appear to be the end of romanticism and the beginning of practicality. After experiencing a period of enlightenment and conceptual thinking in school, we hang up our proverbial thinking caps and enter the working world, which seems, for the most part, cloaked in banal monotony. As we take our first steps toward professional practice, we sometimes leave our intellectual half unfulfilled and neglected, and often yearn for richer, more provocative experiences. Upon graduating from Harvard’s GSD and beginning work at Sasaki Associates in the summer of 2010, Alexis Canter and Eamonn Hutton took a conscious step to integrate these two seemingly distant worlds.

In October, after working full time for a few months, Canter and Hutton approached Gina Ford, a landscape principal at Sasaki, with the idea to conduct a research project that would investigate the declining quality of life in the American industrial city. Ford was highly receptive to their exploration and proposed that the firm play a strong supportive role in their research development and execution. In addition to their regularly scheduled workweek, Canter and Hutton spent countless hours conducting research, collecting data, meeting city officials and rigorously compiling information. They met monthly with principals and associates, all of whom contributed to the project’s ideas and research methods. Sasaki’s encouragement was not only crucial in the development of Canter and Hutton’s research but also critical in funding site visits, providing office resources and marketing the project. This collaborative effort and supportive environment created the opportunity for their research to evolve into what it has become to date—an exhibition and lecture series titled Urban Fabric: Strategies for American Cities.

Urban Fabric culminated into an investigative-research effort that closely examines three carefully chosen American industrial cities: Fall River, Massachusetts; Mobile, Alabama; and Newark, New Jersey. Each largely relied on one industry, textiles, to function. The initial investigation began as a means to discover the reason these once-thriving cities have become degraded and neglected. The exhibition profiles in great detail the political, social, cultural and economic characteristics of each city, presented in beautiful graphics and eloquent text.

During their travels, Canter and Hutton collected street interviews from the locals, providing emotional viewpoints to supplement the quantitative research. Listening to the personal accounts of life in American industrial “middle-cities” created a true understanding of the suppression the citizens living there felt.

After one of the Urban Fabric presentations, Ford explained the misconception that many people share, which is that the city is a self-healing entity and that, over time, things will recover. This simply is not true and has been proven through Canter and Hutton’s findings. They examined a large number of urban precedents, including the Five Borough Farm in Brooklyn, New York, by the Design Trust for Public Space, which begins to inform the elements of successful urbanism through inclusion and activation in once-stressed environments. Projects such as these offer insight into the possible design strategies that can be explored in the future. In their study of Fall River, for example, Canter and Hutton examined the effects on the city after local production had left and many of the residents and workers remained, regardless of the lack of work and uncertain economic growth. They began to question how the absence of industry continued to shape the city and contribute to its economics, politics and culture, and then how intervention could revitalize the afflicted area. They found that as a result of a rise in overseas production, many of Fall River’s mills became abandoned, leaving more than 10 million gross square feet of residual mill space within the city. They composed studies of realized mill renovation strategies that have contributed to the revitalization of inactivated sites around the country to begin discussion of how to move forward in these conflicted areas. Over the next several months, Canter, Hutton and the rest of Sasaki will continue to study and explore possibilities within these middle cities, most of which have lost their identities.

In addition to the exhibit, Sasaki has invited several landscape architects, research professionals and urbanists to give lectures and lead discussions every Wednesday and Friday, now until the beginning of May 2011. These lectures, coupled with Canter and Hunter’s research, have created a massive think-tank environment at Sasaki that has opened up discussion of how to cure these midtier cities from their economic demise.

With Canter and Hunter’s efforts and Sasaki’s support, provocative thought and practicality are harmonious, and academia has been successfully stitched with professionalism to create a brilliant thought-stimulating environment that nurtures progression.

Read more on “gateway cities” in ArchitectureBoston magazine.

Michael Paganetti received his MArch from Wentworth Institute of Technology in May 2010. He is currently working at DiMella Shaffer as an architectural intern and is aspiring to become licensed through the firm’s Intern Development Program. In addition to working, Paganetti enjoys traveling and visiting historic urban spaces and structures around the world.

Photo credit for exhibition triptych: Mary Lewey, Sasaki Associates.

Landscape urbanism: The challenge of implementation

Urban vs. rural, architecture vs. landscape, man vs. nature—these design dichotomies seem to have served professionals well. They are not only useful intellectual constructs dating back to Adam and Eve but also effective regulatory tools. By defining realms of authority in an understandable way, they allow complex projects to be funded, approved and built in an orderly fashion. 

Practitioners of landscape urbanism, however, question whether these distinctions remain meaningful in an era of limited resources and environmental threats, suggesting we can devise more-sustainable approaches to development by emphasizing the inter-relationships of ecological systems and urban construction. And they say no one is better equipped to distill a design direction from these fluid patterns than landscape architects. Recognizing environmental interconnections, however, challenges not only the usual architect-on-top hierarchy but also the property lines and regulatory sectors that define how we design and build.  

Stoss Landscape Urbanism’s Botanic Overlook on the Minneapolis riverfront uses waste heat from a nearby power plant to heat a series of communal pools, greenhouses and community facilities.

Chris Reed, founder of Boston-based Stoss Landscape Urbanism, says there is no choice. “We need to do more with less. Cities and public agencies are hungry for proposals that move multiple agendas forward. Flexible and productive open spaces that cleanse water, generate energy, structure development, create new habitat and adapt to climate change will be the only way to go for cash-strapped administrators.”  But, he acknowledges, turning bold ideas into buildable realities requires a commitment to research and experimentation, and a governance structure that will support ambitious proposals. 

Beneath the fluid forms and pastoral landscapes of Diller Scofidio + Renfro/James Corner Field Operations’ High Line are a vast array of drains, pipes, cables and beams that are engineered to make it all work.

To get traction within and beyond academia, landscape urbanism has developed an evocative language to convey its aspirations. And like most design “-isms,” it uses a family of forms to metaphorically suggest how those aspirations can be implemented. Sweeping curves, continuous ribbons and folded planes represent the kind of dynamic systems that landscape urbanists are trying to channel, with iconic projects such as Manhattan’s High Line (a park in New York City’s West Side that was formerly an elevated railroad track) offering tantalizing visuals. But without the High Line’s endless influx of high-society financing, can the landscape-urbanist principles of integrated design survive in a sliced-and-diced world?

Shauna Gillies-Smith ASLA of Ground Inc., a Somerville landscape practice, says a series of incremental improvements can add up to make meaningful changes—especially in dense urban environments. “With enough green-roof or groundwater-recharge projects done by individual landowners, we can make our cities more comfortable to live in and more compatible with the ecosystems they are part of.”  But, she adds, it may take zoning incentives or monetary subsidies to reach a critical threshold where we can provide a public return on private-sector investment.

For better or worse, vast bureaucracies stand between even the most-benevolent vision and its realization. In a democracy, public support is required for economic or development initiatives, and the public hardly speaks with a unified voice. Regulatory agencies moderate the debates and try to find common ground.

Ben Lynch, program chief for the Massachusetts Department of Environmental Protection’s Waterways Regulation Program, deals daily with the state’s forward-looking requirements for waterfront development. “Regulations and incentives are blunt instruments at best,” he admits. “If the public sector wants the private sector to pay for infrastructure improvements and the private players are trying not to lose their shirts, it will be a challenge to stay true to a landscape-urbanist agenda because there are so many agendas to balance.”

Although this agenda is at the cutting edge of land-use policy, many of its aspirations are firmly embedded in standard practice for engineers and bureaucrats. Fred Yalouris, director of architecture and urban design for Boston’s Central Artery/Tunnel Project, or “Big Dig,” says that the massive highway-burial project was in tune with the precepts of landscape urbanism, even if it plays down didactic ambitions. “A fifth of the project’s $15 billion was mitigation, ranging from the creation of 46 parks to over a billion for mass transit. We got rid of the rusting hulk of overhead highway and planted over 20,000 trees, and acres and acres of lawns and gardens. Rain gardens and urban agriculture can always be added as the icing on a pretty sustainable cake.” 

Landscape urbanism’s inspiring rhetoric and compelling forms provide a strong, poetic evocation of a more sustainable way to build. But if both the formal and practical ideals are to be implemented, they need to be harnessed to a more prosaic set of tools, such as building codes, zoning ordinances and engineering calculations. Designers will need to team up with scientists, sociologists and engineers—and bureaucrats and bean counters, too—if sustainable design solutions are to be pushed beyond the commonplace. The tendency to let poetic forms become stand-alone statements risks ceding the prosaic work of making real change to others.

David_Eisen_AIADavid Eisen AIA is a principal at Abacus Architects + Planners in Boston.  He is the author of Boston Modern: The Spirit of Reinvention and writes frequently on design issues for a variety of publications.  He received his architecture degree at Harvard Graduate School of Design.

Top image: Lighting, landscaping and pedestrian passageways are woven through an existing transportation infrastructure at the Queens Plaza Improvement Project by Wallace Roberts Todd, Margie Ruddick Landscape and Marpillero Pollak Architects.

Curious about landscape urbanism? Read more in the recent issue of ArchitectureBoston, Turf.

High-performance urban forestry for green infrastructure

The urban forest is perhaps the most conspicuous example of contemporary urbanism’s heartthrob, green infrastructure; witness the preponderance of “Million Tree” campaigns such as MillionTreesNYC, Million Trees LA, the Chicago Trees Initiative and Grow Boston Greener. After all, trees are good, especially a million trees, right? It depends. The planting techniques for most urban trees lag far behind what is necessary to steward them to old age and impressive size. 

The urban forest as green infrastructure, a primer
A robust urban forest produces myriad environmental, economic, social and cultural benefits, all while bolstering urban identity in ways no other infrastructure type can. As a biogenic public utility, it is unique in that it gains value over time rather than depreciating like most infrastructural assets.

The benefits of urban trees are well documented. Methods for assigning value to these benefits range from simple calculations, such as money saved on heating and cooling costs or increased property values to deeply contested and complex analyses. How does society determine the precise value, for instance, of the cleaner air and water or the increased biodiversity urban trees provide? The fields of environmental and ecological economics are hard at work creating metrics for such quandaries. At a minimum, it is widely accepted that the most important benefits the urban forest provides include a reduction of the heat island effect, improved stormwater management (which means higher water quality and reduced flooding), reduced air pollution, reduced energy use, increased property values, increased wildlife-habitat potential and a range of heightened aesthetic and spatial qualities.

Trees are remarkable biological machines that perform astounding feats of structural assembly and adjustment, self-defense and maintenance, organic chemistry, water pumping, atmospheric manipulation and power generation. The productive capacity of a tree increases in magnitude as it gets larger, and this is the key to understanding another maxim of urban trees: In terms of environmental and economic performance, bigger is better, by a long shot. 

The Center for Urban Forest Research calculates that large-canopy trees (greater than 50 feet in height and canopy spread) outperform small trees (less than 25 feet) by a factor of 15, and they do not start adding significant environmental performance until they reach 30 feet. Trees that do not reach this minimum will never be more than an aesthetic amenity. In the quest to make the urban forest into a high-performance green infrastructure, lots of big trees are required, especially in the most environmentally compromised zones: streets, plazas, parking lots, and commercial strips. These places have two things in common that make them hostile to trees: more than 90% impervious surface cover—what I like to call “extreme pavement”—and highly compacted soils.

An underground movement: soil resources
To grow large trees in the harshest urban conditions, a literal underground movement is necessary, and it’s all about the soil. Tree roots cannot penetrate the compacted soils of the urban environment; they need soil with lots of pore space and, ideally, organic matter. When a tree’s roots run out of space prematurely, one or more of the following happens: 1) The tree stops growing, 2) space-starved roots shove pavement and curbs aside in desperation and 3) the tree dies or is removed. Tree roots can and will break pavement, yet they cannot penetrate compacted soil. Because typical tree-root growth is relatively shallow and spreads laterally, roots need room to spread out. The eventual size and longevity of a tree depends on its ability to do that. 

A graph developed by landscape architect James Urban plots tree size, measured in crown spread and trunk diameter at breast height (DBH), as a function of available soil volume, measured in cubic feet. To grow a tree that achieves the minimum size for significant environmental performance, 800 cf of soil is required. A typical planting detail specifies a 4 feet by 10 feet tree pit (that is only 120 cf of soil!) carved out of highly compacted soil and surrounded by pavement. Trees planted in these conditions will be lucky to reach 15 feet in height, and the stormwater processing capabilities of that soil are negligible. High-compaction soil and extreme pavement are the dual enemies of urban tree growth and on-site stormwater management. Retooling underground infrastructure to accommodate high-quality, uncompacted soil enables the growth of large-canopy trees and the absorption of large volumes of stormwater.

Techniques to maximize soil
In pursuit of soil volumes required to grow environmentally productive urban trees (various experts recommend between 700 - and 1,000 cf), several techniques can be used that rely on the inventive use of space and augmented construction methods. Space permitting, the easiest way to achieve target volumes is an open planting area (1,000 cf = 10 feet by 34 feet by 3 feet tree pit, for example.) Since this is usually not possible in heavily paved areas, augmented techniques using covered soil in combination with open soil can be used. These include the use of root paths (narrow trenches of uncompacted soil under pavement to connect the planting area to nearby volumes of soil), structural soils and suspended-pavement systems. 

CU-Structural Soil™, developed by Professor Nina Bassuk and colleagues at Cornell University, solves the compaction problem by mixing angular one-inch crushed stone with planting soil, at a stone-to-soil ratio of 4:1. The stone pieces form a load-bearing “rigid lattice” that leaves space for uncompacted soil. CU-Structural Soil outperforms compacted soil, but the large proportion of stone in the mix means that 80% of the space is unavailable for root growth and water storage. Claiming a higher percentage of that space would boost performance.

Suspended-pavement systems offer the best combination of structural strength and large volumes of quality soil. A suspended-pavement system consists of an underground post-and-beam structure and a deck with pavement on top. The structure supports the weight of the pavement and additional loading by pedestrians and vehicles, leaving the space for large volumes of uncompacted soil for root growth and storm-water treatment. This approach also protects pavement and curbs from the rogue roots of cornered trees; they will always prefer expanding into tasty soil over pavement demolition. Storm water can be allowed to infiltrate the soil in several ways, such as via permeable pavements, drainage slots, curb-cut inlets and sheet flow to open planting areas. 

Providing that much high-quality soil opens the door to a much larger selection of species beyond the 10 or so that can survive in hostile urban soils. A greater mix of species helps fight pests and disease, and increases urban-habitat potential. This expanded planting palette may be one of the most significant ways to ensure the viability of the future urban forest.

San Francisco–based Deep Root Partners introduced its suspended-pavement system Silva Cell in 2007, and there are already hundreds of installations internationally, but performance data for mature trees is at least a decade away. Improvements in stormwater treatment can be measured immediately, however, and the benefits are clear. An installation in downtown Minneapolis intercepts stormwater for 6.6 acres with 179 trees planted in Silva Cells. Suspended-pavement systems are not new, and one of the best case studies is in Charlotte, North Carolina, where, in 1985, 170 trees were planted using custom suspended pavement along a 10-block stretch in the downtown business district. Each tree received 700 cf of soil, and the results have proved stunning. A 2009 survey found that the trees (167 of the 170 survived) have thrived, reaching an average height of 44 feet and 16 inches DBH.

The Achilles heel of suspended pavement is its high initial cost, adding as much as $10,000 per tree to install compared with conventional methods, a figure that will give pause to many! A life-cycle cost calculation goes a long way toward justifying this investment, and, in some cases, savings in up-front costs for traditional infrastructure can pay for it many times over. For instance, the City of Minneapolis chose a $1.5 million Silva Cell installation over a $7.5 million storm-sewer upgrade to meet the city’s storm-water goals. Still, the cost threatens to put suspended pavement out of reach for many smaller projects and out of the question for some private developers. 

Although many cities are writing minimum soil-volume standards into their zoning codes, cost is still a barrier. In Brookline, Massachusetts, the urban forestry budget is now part of the Capital Improvements Program, typically the domain of infrastructure construction and maintenance. By elevating the urban forest to public-infrastructure status, new funding possibilities emerge to offset the costs for suspended-pavement and other soil-intensive planting techniques. As a hypothetical, a city’s Department of Public Works could purchase materials and supplies such as Silva Cell in bulk and provide them at little or no cost to new projects that achieve stated environmental goals. As in the Minneapolis experience, the cost savings to the city could easily pay for such a program.

What about those million trees? Although a million is a great public-relations sound bite, the absolute number is not nearly as important as the quality of the plantings. Many trees will undoubtedly be planted in parks and open spaces where soil conditions are favorable, but thousands of trees are bound for those tough streets and parking lots. In that case, 100,000 healthy, large trees trumps 500,000 struggling or dead trees in every way. I, for one, hope that the program managers direct their resources to make this happen.

Case studies
Waterfront Toronto 
Waterfront Toronto is investing in a suspended-pavement system at an infrastructural scale, specifying SilvaCell for hundreds of its 2,000-acre waterfront revitalization project. (video)
Queens Quay (Toronto ON, Canada)
Waters Edge Promenade and Boardwalk  (Toronto ON, Canada)
Portland Slip
Bloor Street
DeepRoot case studies

Matthew Gordy is principal of On Land, a landscape and urban design practice based in Boston and in Memphis, Tennessee. He has been a design critic for studios at the Harvard Graduate School of Design and led graduate seminars at Northeastern University’s School of Architecture. He received the MLA from Harvard in 2005. Gordy previously practiced with Landworks Studio in Boston and Michael Van Valkenburgh Associates in Cambridge, Massachusetts.

Make no little plans

Director Judith Paine McBrien moderates a discussion among architects and planners following the screening of her film Make No Little Plans: Daniel Burnham and the American City. Before urban planning existed as a profession, Burnham shaped the modern city in America and abroad. For more information, see our full schedule of upcoming lectures.

Co-sponsored by Perkins + Will and Wentworth Institute of Technology.

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