A New Way to Plant Urban Trees


At the 2010 GreenBuild, Peter MacDonagh, the Kestrel Design Group, James Urban, FASLA, Urban Trees + Soils, and Peter Schaudt, FASLA, Hoerr Schaudt Landscape Architects, argued that without new tree planting techniques that use healthy loam soils, major “one million” urban tree planting campaigns will fail, wasting lots of money in the process. MacDonagh said “urban forestry is broken. We need to remake with a different approach.”

Finding out What Works for Urban Trees

Urban trees are now understood to be a central part of green infrastructure systems and provide a range of benefits. They reduce the urban heat island effect, manage stormwater, and provide shade that lengthens the life of materials. In the summer, shadier streets also means lower neighborhood temperatures, which can reduce air pollution that increase asthma rates. “All of these benefits are great, but they won’t happen if we keep planting like we have. It will be a mirage,” argued MacDonagh.

MacDonagh said larger, older trees are far more valuable than youger ones, so work needs to be done to preserve these and use new techniques to enable younger trees to stay in place longer. Citing data, he argued that a 30-inch diameter breast height (DBH) tree provides 70 times the ecological benefits of a 3-inch DBH tree. For example, a large tree intercepts 79 percent of rain hitting the ground, providing the “best green infrastructure you can find.”

The key to preserving larger older trees and keeping younger ones in place up to 50 years or more is to use large amounts of loam or bioretention soils that are 65 percent sand, 20 percent compost and 15 clay silt. These soils are not only the best growing mix for trees, but also filter out heavy metals, phosphorous, and nitrogen most efficiently. Nitrogen runoff can cause algae blooms and kill other life if it’s allowed to get to the watershed in large amounts.

The rule needs to be two cubic feet of loam for one square feet of tree canopy. So, for a tree that provides a 700 square foot canopy a designer needs to use 1,400 cubic feet of high-quality soil. These soils can be combined with “silva cells” that prevent soil compaction to enable the growth of tall, healthy trees. To prove this, MacDonagh showed the work of Bartlett Tree Lab’s Urban Plaza study, which demonstrated that loam soil grew trees had 300 times more leaves and were 1.7 times taller than those grown in compacted soils. “This is important because the average street tree only lasts 13 years.”

To sum up, MacDonough said “codify minimum loam soil volumes, diversify tree species to prevent devastating blights, set minimum canopy targets, and plant small trees properly.” Otherwise, “those million tree campaigns will be exercises in futility.” 

Overcoming Obstacles in the Built Environment and Dealing with Increased CO2 Emissions  

James Urban, FASLA, said structural soils, which combine broken up rock and soil, have issues so urban tree planters came up with a new idea: suspended pavements. In a new project, Queens Quay, along the Toronto waterfront, these suspended pavements use 48-inch deep silva cells, which kind of look like rubber packing crates, and 1,680 cubic feet of loam per tree. Within the combined loam and silva cells are irrigation systems that move water to the trees. Given the Toronto government was concerned that this system wouldn’t work, Urban says they first tested in a small strip and demonstrated that the approach works.  

Here Urban complained about one major obstacle: low tree quality. He argued the “American nursery business isn’t doing its job” and one firm tried to deliver trees with “girdling roots, a fatal flaw that would have killed the tree in five years.” He added that the current nursery “stock of trees is horrible.” If we are going to do million tree campaigns, he asked, “How can we check each one?”

In another project, The Bosque on the new Lincoln Center roof in New York City, Urban worked with Diller, Scofidio + Renfro on planting 30 trees on a roof deck. “There were lots of obstacles — everything is going on in the built urban environment.” Urban navigated the shallow roof, elaborate lighting systems, and thin paving on top of the deck. He ended up adding in “geogrids” and gravel that helped ensure the new platform could provide a safe growing environment for trees and also bear the weight of a light pick-up truck or ambulance.

Urban added that in addition to the CO2 emissions created from hauling in those soils, there were also tons of emissions released from the trailers and cranes that were used to install the huge trees. “Are urban trees really sustainable? Our carbon footprint was so large that these trees will never be able to sequester the amount we just put into the atmosphere.” He argued landscape architects must stop pretending urban trees sequester carbon when they are actually net-producers of carbon if you factor in transportation and installation. Also, landscape architects may be specifying other unsustainable materials (see earlier post).

Still, many progressive city governments including New York City see massive tree planting campaigns as a core part of their climate adaptation plans (see earlier post). Perhaps the questions are: Is there a way to mitigate uban trees’ installation and transportation-related emissions in the short-term with a greener installation technique? If not, does improved long-term resiliency to climate change somehow make up for increased short-term CO2 emissions?

Urban Trees Are Key to Successful Public Spaces

Peter Schaudt outlined his firm’s well-regarded Uptown Normal traffic circle (see earlier post) in Normal, Illinois, which was funded by federal, state, and local governments, “so you can imagine the number of meetings.” Schaudt decided to create a “people space in the center of a roundabout,” which some government officials didn’t think would be safe.

Schaudt thinks the new space, which features a set of urban trees, outer lawn, bog water infiltration system, and circular stream filled with cleansed water, represents the “park of the future.” Instead of seeming dangerous, the circle interior offers a safe space in large part due to the trees, which separate the cars from the social space. Trees in the traffic circle and nearby streets were also supported by silva cells, loam and drip irrigation, using Urban’s approach but on a smaller scale.

The circle’s trees were set-up to live a long time – Schaudt says he plans for the “4th dimension — time,” and likes to show clients what the site will look like in 25 years.

Lastly, MacDonagh added that well-planted trees are not only more cost-efficient, they also provide more ecosystem benefits. To demonstrate cost-efficiency, he pointed to research conduced by Minneapolis’ government, which found that they could either spend $3.5 million on new stormwater conveyance pipes to deal with runoff or spend $1.5 million on silva cell systems. On ecosystem service benefits, another study showed that 13-year old trees planted in standard structured soils had a net cost of $3,000, while a 50-year old tree planted in bioretention soils and silva cells offered $9,000 in benefits over its total lifecycle.

Quantifying the Benefits of the Sustainable Sites Initiative


Barbara Deutsch, Landscape Architecture Foundation (LAF) and Jose Alminana, FASLA, and Tom Amoroso, Affiliate ASLA, of Andropogon Associates discussed how to quantify the ecosystem services provided by sustainable landscapes using the Sustainable Sites Initiative (SITES) prerequisites and credits and other tools and calculators (see earlier post) in a session at the 2010 GreenBuild.

SITES and LAF’s Landscape Performance Series

According to Barbara Deutsch, LAF’s Landscape Performance Series aims to make “landscape performance as well understood as building performance” among design professionals and also complement SITES. To quantify all the benefits of SITES projects, landscape architects must use a “collaborative, integrated, systems-based approach,” design for natural processes and use natural resources, collect performance data, and continually measure benefits over time. (see earlier post)

She implied the usual landscape architecture project brief, which often just lists a “set of features,” is pretty useless. “We actually need solutions so we need to communicate the benefits of these features.” For landscape architects, Deutsch said it’s important to just start “defining and quantifying benefits now. If we are going to start investing in sustainability, we need to show value, a return on investment.”

Quantifying Benefits in the Design and Development Phase of a SITES Pilot Project

Jose Alminana and Tom Amoroso of Andropogon, a Philadelphia-based landscape architecture firm, discussed a case study that demonstrate how to both apply SITES prerequisites and credits to projects in the design and development phase, and quantify the value of ecosystem services. Alminana said “any landscape can provide ecosystem services. It’s about putting a price tag on the value nature provides.”

Shoemaker Green, a 3.5-acre open space used often used for athletic events on the campus of University of Pennsylvania, was highlighted as an example of how to start quantifying benefits early in the design and development phase. The project, a SITES pilot project, is a hub for urban redevelopment and part of new UPenn leadership’s plans for preserving its network of open space and redeveloping underperforming areas.

Andropogon’s design is also expected to earn the project some 80 percent of SITES credits, said Alminana. SITES prerequisites 1.5 and 1.6, which relate to sustainably siting, were easily met because the project designers are redeveloping a brownfield site that already serves an existing community. “The site is next to existing transportation networks and amenities. This project is in a dense area with links to pedestrian paths and open spaces,” said Amoroso. 

To meet prerequisite 2.1, which asks project designers to “complete a pre-design site assessment,” Andropogon did in-depth studies of the site’s existing soils, vegetation, hydrology, and materials. On soils, Amoroso found that the existing site soils were “urban fill soils,” but the reference soils were “alluvial, common to floodplain areas.” Other studies were done by testing “soil borings, percolation rates, and levels of organic matter.” Soils are important for vegetation and water.

To determine water management capabilities on site, the team studied the hydrology and modeled the “aspect” in 3-D to determine the slope and path of water and the sun across the site, which will help determine which plants can be used. An inventory of existing materials was also conducted to determine how unearthed materials can be reused in the site to ensure the site has “zero-waste.”

In the “pre-design assessment,” the team said they would win credits for 2.3, “engaging users and other stakeholders in site design” because the team has set up regular meetings with user groups, a project steering committee, and clients. “We brought in a general contractor for pre-construction support,” to help streamline the design review process.

Moving into the actual design, the project team is expecting to earn credits by preserving open space networks, reducing potable water use by 75 percent (credit 3.2), and addressing stormwater management on site (credit 3.5). To store stormwater on site, Andropogon used a system of “silva cells” and tree trenches, porous pavers, and raingardens to deal with the first inch of rainwater and a cistern as a water storage depot. Finally, for major flood events, there is infrastrucuture to direct water to the combined sewer system.

Alminana said the site “can deal with runoff from adjacent buildings and store up to 87,000 gallons per year,” which translates into real economic value for the university given Philadelphia now has high stormwater run-off fees calculated based on impervious surface areas. Amoroso added that “previously, 70 percent of the site was impervious. We will flip this to 70 percent pervious.”

The project can accrue credits for its soil management plan (credit 4.3), preservation and restoration of moved trees (credit 4.6), and use of recycled materials (credit 5.5). The team plans to mimize excavation, but where it’s inevitable, reuse broken up asphalt in the site structure and achieve zero-waste. This means lots of avoided expense taking materials to landfill, as well as avoided CO2 emissions.

Unfortunately, because urban soils don’t work with a lot of the sustainable vegetation and water systems, new soils will need to be trucked in though, perhaps adding to the project’s carbon footprint. While sustainable soils, water, and plants are crucial to any restorative landscape, project estimates for C02 emissions should be included in the mix of what’s tracked.

Calculating Gains in Construction Efficiency and Learning from Monitoring and Evaluation Results

The Salvation Army community center in central Philadelphia was used to explain how SITES construction credits work. The 11-acre site was redeveloped on a brownfield and now includes an integrated water management system. “For 2-year storm events, we calculated we reduced run-off by 99 percent, and for 100-year storm events, reduced run-off by 79 percent.”

The project would win all the credits for using recycled content (5.5) because reused concrete was integrated into the site. To achieve zero-waste, Alminana said you first need to create a plan for dealing with the materials in the beginning. “We focused on material sorting, upcycling and material placement in the site, and then backfill and grading and planting soil mixes.”

He said this approach worked, but it was “hard to quantify this benefit.” They eventually calculated they saved $300,000 in truck hauling fees. However, avoided CO2 emissions from material transportation wasn’t calculated.

Lastly, Alminana discussed Thomas Jefferson University’s Luebert Plaza, which is “basically a green roof over a parking lot,” in the context of SITES credit 9.1, which calls for “monitoring performance of sustainable design practices.” In this case, they found the soils weren’t working as planned. The plaza had to be watered twice a day to keep the grasses alive.

“We had to use soils that dry quickly so they don’t soak up too much water and put strain on the green roof structure. As a result, the root systems didn’t need to grow all the way down and the soil wasn’t balanced.” Tests showed that the there was too much bacteria and not enough fungi. The project team came up with a “customized organic composting tea” that “favors this species,” which helped reduce irrigation by 40 percent, eliminate chemical fertilizers, increase root growth, and limit compaction. Soils are key to the functioning of the site. “This demonstrates that beauty isn’t skin deep, but, in fact, you need to dig below the surface.”

Learn more at the Sustainable Sites Initiative.

Applying the Sustainable Sites Initiative


At GreenBuild 2010, David Yocca, FASLA, Principal of Conservation Design Forum, explained how the Sustainable Sites Initiative™ (SITES®) is moving to the next step in its path towards becoming a functioning rating system: “receiving feedback from real projects.”

SITES, as Yocca explained, is an “interdisciplinary effort to create a voluntary national guideline and rating system that can encourage integrated, systems-based approaches to sustainable landscape” design and development. SITES will work at all landscape scales, with or without structures. “The goal is renew and restore places and move from just conservation to regeneration through performative landscapes.” Yocca also argued that SITES can be used to “restore degraded ecosystem services” found in brownfields and greyfields, creating new economic value in the process.

Sustainable landscapes can provide a range of ecosystem services:

  • Climate regulation
  • Clean air, soil, water
  • Water supply regulation
  • Soil erosion / sediment control
  • Habitat and pollination
  • Decomposed waste integration
  • Human health and wellbeing
  • Food and organic products
  • Culltural, educational, and aesthetic value
  • Flood impact mitigation, among others.

Status of the SITES Guidelines and Rating System

SITES will be in its pilot phase over the next two years. In November 2009, the guidelines and performance benchmarks were released, which include a set of 15 prerequisites and 51 credits. The documents released include “credit intent, requirements, submittal documentation, potential technologies or strategies, and links to other credits.”

The rating system is on a 250 point scale, with four certification levels from one star to four star. “The certification levels are based in performance criteria. We are asking people to demonstrate actual performance.” The 250 possible points that can be accrued are broken down into a few categories:

  • Site selection (21 points)
  • Pre-design assessment and planning (4 points)
  • Site Design: Water (44 points)
  • Site Design: Soils and Vegetation (51 points)
  • Site Design: Material Selection (36 points)
  • Site Design: Human Health and Wellbeing (32 points)
  • Construction (21 points)
  • Operations & Maintenance (23 points) “This is important for ensuring the site provides ecosystem services over the long-term.”
  • Monitoring & Evaluation (18 points).

Landscape projects can use SITES in three ways: They can certify with SITES, just use the guidelines without certification, or by 2012, certify their projects using LEED, which will integrate SITES.

SITES’ Pilot Projects

Some 163 projects were selected as pilots. “These will inform the development of the reference guide and also guide credit refinement.” Pilots are found in 34 U.S. states and Iceland, Spain, and Canada. Projects include mixed-use, commercial, residential, institutional / educational, industrial, government, transportation corridors, and open space parks and gardens. The parks category covers 25 percent of projects.

Some 65 percent of projects are greyfields, while 20 percent are greenfields and 15 percent are brownfields. Project scales range from less than one acre to more than 500 acres. There are also lots of project budgets: 59 percent are more than one million, but 15 percent cost less than $100,000.

Illustrating the Prerequisites and Credits Using Case Studies

A number of Conservation Design Forum projects are SITES pilots. The Tuthill Corporation Headquarters and Training Facility in Burr Ridge, Illinois, is “integrated sustainable site design in practice.”

Prerequisite 2.1, which asks projects to “conduct a pre-design site assessment,” was met. The project team found through an initial investigation that the Illinois site was a “high-quality remnant prarie.” To preserve the prarie as much as possible, the site designers convinced the client to move the planned parking lots under the building, which “also provides weather protection in the winter.”

Prerequisite 2.2, which asks project teams to “use an integrated site design process,” was also met and Yocca found that it helped forge a “close connection between the interior and exterior spaces.” In addition, this prerequisite “creates tangible efficiencies” in the form of streamlined schedules, costs and approval processes.

Another prerequisite, 3.3, which asks projects to “protect and restore riparian, wetland and shoreline ecosystems” where applicable, was achieved but took some finagling. Yocca said he “engaged in a dialogue” with local environmental regulatory bodies to convince them to “invest in systems health instead of just putting a ring around degraded areas.” Part of this involved ripping out invasive species so that native plants could take over. In another example, he also persuaded local officials to allow for controlled burnings, which help achieve 4.8, a credit that calls for “preserving and plant and soil communities native to the eco-region.”

One project mentioned is the well-known Kresge Foundation Headquarters in Troy, Michigan. Kresge, which reduces potable water use by 75 percent (earning SITES credit 3.2) and manages stormwater on site (credit 3.5) through green infrastructure systems, started with “a simple grass matrix but additional species were added in over time, resulting in increased biodiversity.” Michigan state government definitely agrees: it gave the project the highest rating in the Michigan Floristic Quality Index, which means the site has “exceptional biodiversity value.” (see a case study). The foundation staff also use the site to teach the public about sustainability, which earns more credits.

Lastly, in another pilot project, Shay’s Folly, in a Western Springs, Illinois housing community, Kevin Graham, ASLA, is using the SITES credits to create a “landscape retrofit,” which features a system of green infrastructure pavers and swales that diverts and captures low-quality water run-off from roofs and streets, and a central water retention basin that captures clean rainwater. This integrated approach only works because the green infrastructure restores the landscape’s natural water managment function: “This system would have failed if you had oil-slick run-off going into the detention basin.” This project is also focused on restoring soils, adding native plants, and integrated compost into the landscape.

Learn more at the Sustainable Sites Initiative Web site.

Christopher Gielen’s Aerial Photos of Sprawl


In one session at the TED Mid Atlantic conference, German photographer Christoper Gielen showed his startling aerial images of American sprawl, but asked viewers to consider them as an “aesthetic experience.” Shot while hanging out of a helicopter, Gielen’s photos demonstrate that very similar sprawl shapes appear across the country.

To find his sites, Gielen first examined statistical databases and honed in on areas with the highest foreclosure rates, which he said indicate where the most unsustainable development is. In Houston, he found perfect web-like networks of prefabricated houses with trees exactly in the same place. One community in Nevada (see image above) is “so perfect” incoming aircraft use it as a marker on their way to the airport. As for the community, “it’s sold as active living, but it’s isolated in the middle of the Nevada desert. It’s a prison of our own making. People are really inside their cars or homes watching TV.”  

The high foreclosure rates among communities in Florida and Arizona demonstrate that many of these sites are economically unviable, but Geilen says they are also environmentally destructive. In one Florida sprawl community (see image below), the wetland was drained then water was reintroduced into managed channels. “The flow of the Everglades is being slowly cut off by development.”


While land-use policymakers want to “reconnect the severed arteries of the Everglades” and create “archipelagos of development” in a sea of of untouched landscapes, many sprawl communities continue to be built.

On a more existential note, Gielen also asked why he was seeing the same forms over and over again in different parts of the country. “There must be some geometric sociology. Why do these shapes — circles, stars, or webs — come into form? Is there something deep in the human psyche?”

See Gielen’s photographs, which he will publish in a book next year.

Image credit: (1,2,3) Untitled / Christopher Gielen