smart growth 4

Smart Streets for Smart Growth2009 New Partners for Smart Growth Conference

Albuquerque, NM

Putting the Green back into Streets: Some Ideas About What It Takes to Make

Trees Part of Successful Streetscapes

Andrew Lavallee, RLA, ASLA, CSISenior Associate Landscape Architect

Director of Technical ServicesEDAW New York


Albuquerque, NM

Given a limited budget, the most effective expenditure of funds to improve a street would probably be on trees. Assuming that trees are appropriate in the first place, and that someone will take care of them, trees can transform a street more easily than any other physical improvement. Moreover, for many people trees are the most important single characteristic of a good street. Alan Jacobs, Great Streets. Cambridge: MIT Press, 1993, p. 293

Trees Form the Backbone of Greenstreets


Albuquerque, NM

There is little disagreement about the value of green streets with healthy (green) trees

State College, PA (Photo by Ed Gilman) Bethesda, MD

Healthy trees increase property value, intercept air pollutants, buffer temperatures, reduce wind speed, cool the city, reduce runoff from storms, encourage people to visit and spend money at shops, and create a more inviting community


Albuquerque, NM

All too often the needs of trees have been left last in the design and construction process

•Declining tree health and longevity

•Tree mortality

•Infrastructure damage

•Unsustainable management including:

•Ongoing tree maintenance and replacement

•Extensive infrastructure repair and replacement.

Street trees are squeezed into whatever space is left after other functional, economic and engineering needs have been met.

The consequences:


Albuquerque, NM

Poor planning and misplaced priorities have caused the quality of our streetscapes to suffer

•We plant monocultures which are susceptible to disease and infestation.

•We rarely adequately fund construction or maintenance

•We plant the wrong trees in the wrong places and they destroy sidewalks and curbs, and grow into wires

•We “fix” the problem trees by hacking at offending roots and branches

•Trees decline or look ugly and deformed

•Our vision of a functioning urban canopy never develops because trees rarely survive more than 20 years.

e put the wrong trees in the wrong places

Photo by Ed Gilman


Albuquerque, NM

We need to rethink our strategies forgreening our streets with trees

Ely (2008) has suggested we adopt a “tree sensitive design framework” that would have the following objectives:

• Fully recognize the value of street trees

• Give street trees equal priority to other forms of infrastructure

• Design streets around the biological needs of trees

• Select the “right tree for the right place”

• Maximize available space for trees in streetscape design

• Provide the necessary resources for growth

• Minimize tree/infrastructure conflicts

• Integrate street trees with stormwater design initiatives

• Adopt an interdisciplinary, collaborative design approach


Albuquerque, NM

We need to approach street design from an ecological systems point of view

The biological needs of trees are often overlooked in design and construction process including the need for :

• Adequate soil volume

• Infiltration and available soil moisture

• Drainage

• Aeration

• Soil Fertility

• Establishment period care

Source: Urban, Architectural Graphic Standards 10th

Edition, New York: John Wiley and Sons, 2002.


Albuquerque, NM

Trees and Plants Need Adequate Soil Volume

A typical 5’ x 5’ tree pit only provides 60 cubic feet of soil!

Trees and plants rely on soil volume to provide adequate water, nutrients, and rooting space.

Source: Urban, Architectural Graphic Standards 10th Edition, New York: John Wiley and Sons, 2000.


Albuquerque, NM

Trees and Plants Need Adequate Soil Volume

Sample calculation for a mature tree with a 30’ crown projection (30’ diameter canopy size):

Assumption: Provide 2 cubic feet of soil available for rooting for each square foot of mature crown projection.

Calculate crown projection by taking the mature crown spread of the tree in feet, squaring it, and multiplying by .7854.

Crown projection (30 feet)2 = 900 x .7854 = 707 x 2 cu. ft. of soil per square foot of crown projection = 1,414 cubic feet of soil volume for root growth. Volume of the soil required at an average depth of 3 feet (recommended depth): 1,414 cubic feet ÷ 3’ depth = 471 square feet of projected surface area to achieve the necessary soil volume for the tree. Take the square root of 471 to calculate the approximate length and width of the soil volume: √471 feet = 22 feet. This means you'd need a soil volume with the approximate dimensions of 22' x 22' x 3' to ensure adequate below-ground space


Albuquerque, NM

Achieving adequate soil volume often requires a variety of design methods

The location of soil volumes must be carefully coordinated with pavement design, drainage requirements, and other utility needs.

Source: James Urban, 2004

Root Paths Soil Trenches Structural Soil Soil Cells


Albuquerque, NM

Trees need Adequate Room Above Grade TooThe root flare of a mature tree can reach up to 2.5 to 3 times the caliper of the tree trunk, destroying adjacent pavements and creating pedestrian hazards.

Photos above by Ed GilmanCentennial Park, Atlanta, GA, EDAW


Albuquerque, NM

Trees and Plants Need Time to Become EstablishedWhen a tree is transplanted from a nursery root loss can be as high as 90%, causing the tree to go into shock.

Image adapted from: the Virginia Department of Forestry, Landscape Manual for Louisa County . Website accessed 1/22/09


Albuquerque, NM

Trees and Plants Need Time to Become Established

Most contractor maintenance on public projects lasts only one year!

Establishment period: the time it takes for a tree to regenerate enough roots to stay alive without irrigation.

Plants require time to become established so that they can survive on their own without irrigation, frequent maintenance or undo risk of disease or infestation.

Source: Gilman, University of Florida IFAS Website "Planting" PowerPoint, website accessed 1/22/09


Albuquerque, NM

Trees and Plants Need Frequent Watering to Become Established

Most contractor watering only lasts until notice of acceptance!

In order for plants to be vigorous and well established they require frequent watering over the length of their establishment period.

Source: Gilman, University of Florida IFAS Website "Planting" PowerPoint, accessed 1/22/09


Albuquerque, NM

Communities Need to Plan for Tree DiversityFew communities bother with the expense of tree inventories, but they prove invaluable when trying to plan out tree planting strategies over periods of years. Lack of diversity leaves a community particularly vulnerable to large scale loss of trees due to disease or infestation.

The emerald ash borer is responsible for the loss of tens of millions of ash trees in Michigan, Indiana, Ohio and Illinois since 2002.


Albuquerque, NM

Street Trees Require Adequate Budgets for SuccessOne of the greatest obstacles to the success of street trees is adequate funding for installation and establishment period care. Too often budgets are prepared without a clear understanding of what is required, scope is divided among too many different consultants, and then budgets are reduced as “unreasonable”by uninformed managers despite the objections of consultants.

Consider the following example of a 3-3 1/2” caliper street tree with a projected 30’ radius canopy planted in structural soil on an existing sidewalk:


Albuquerque, NM

Good Design Leads to Successful Streets

The Peach Tree, Atlanta, GA, EDAW

X

Trees thrive when good designs are executed properly.


Albuquerque, NM


Freedom Center, Reston, VA, EDAW

X

Providing better soil and surface treatments often provides increased urban design opportunities and improves the pedestrian experience.


Albuquerque, NM


Verrado, Buckeye, AZ

X

Healthy dimensions for trees ensures they are protected from vehicle damage and can develop symmetrical roots and crowns. Increased vegetated areas also provide for increased stormwater management opportunities and ensure sufficient room for subsurface utilities.


Albuquerque, NM

Some Helpful ResourcesEly, Martin. PhD candidate University of Adelaide, Australia. “Thinking Like A Tree: Developing A Framework For Tree Sensitive Urban Design.” Presentation at The 9th National TREENET Symposium, September 4 &5, 2008. http://www.treenet.com.au/Files/symposia/2008PDFs/2008%20THINKING%20LIKE%20A%20TREE%20-%20DEVELOPING%20A%20FRAMEWORK%20FOR%20TREE%20SENSITIVE%20URBAN%20DESIGN%20Martin%20Ely.pdf

Ferguson, Bruce. Porous Pavements. Boca Raton, FL: CRC Press, 2005. Provides an in depth discussion of porous pavements design principles and engineering, pavement base designs requirements, and structural soils.

Gilman, Dr. Edward. University of Florida IFAS Extension - Multiple PowerPoint Presentations. Provides excellent visual presentations about trees in the urban landscape, planting techniques, plant selection, maintenance, hurricane strategies and much more. There are also extensive notes accompanying each presentation. http://hort.ifas.ufl.edu/woody/powerpoints.html

Trowbridge, Peter and Bassuk, Nina. Trees in the Urban Landscape: Site Assessment, Design and Installation. New Jersey: John Wiley and Sons, 2004. A great introduction to the problems and solutions associated with street tree plantings including soil design and plant selection.

Urban, James. Up By Roots: Healthy Soils and Trees in the Built Environment. Champagne, IL: International Arboriculture Society, 2008. Provides detailed examples about what does and does not work when planting trees in the urban landscape.

http://www.treenet.com.au/Files/symposia/2008PDFs/2008 THINKING LIKE A TREE - DEVELOPING A FRAMEWORK FOR TREE SENSITIVE URBAN DESIGN Martin Ely.pdf



http://hort.ifas.ufl.edu/woody/powerpoints.html

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