Trees in the urban environment

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Trees in the urban environment benefits of
structural soil
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Limitations of conventional tree pits

• Compaction of subsoil and subbase eliminates
  macropores necessary for good root growth
• Decreases aeration and water movement
• Compaction increases the bulk density of the soil
  to the extent that root growth stops due to the
  physical barrier of the soil

From Using Cu-Structural Soil in the Urban
Environment
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Benefits of structural soil

• Preserves macropores in stone matrix which allows
  
• Space for root growth
• Proper levels of oxygen
• Allows necessary compaction levels for hardscapes
  subjected to intense vehicle and foot traffic

From Using Cu-Structural Soil in the Urban
Environment
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Structural soil components

• Uniformly graded angular stone (3/4 to 1.5)
• Clay loam or loam soil (min. 20 clay)
• 2 to 5 soil organic matter
• Hydrogel in small amount to hold soil to rock
• Ratios 100 20 0.03 by weight
• Soil volume must be less than pore space
  volume

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Tree pit detail

• Pit opening - min. 5
• Structural soil depth 3 optimum
• Irrigation line optional at edge of pit
• Drainage pipe connect to storm drain
• Geotextile fabric?
• Tree pit backfill
• Traditional Soil
• Structural Soil
• 2 cf SS/sf of canopy
• 20 diam. canopy 18 x 18 of structural
  soil _at_ 2-deep

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Connect pits together for expanded rooting volume
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No irrigation Concrete pavers on sand bed Drain
pipe cx. to storm
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Swamp White Oak on Lorimer Ave. Brooklyn, New
York Planted 1997 Structural Soil Trench
7 wide x 2 deep
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Cornell University 2006
Cornell University 2002
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Tree selection for structural soils

• Trees tolerant of alkaline environment
• Trees with moderate to good drought tolerance
• Trees that fit the aesthetic design criteria
• Height
• Texture
• Flowers
• Fruit
• Size
• Shape

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Brief list of suitable trees

• Acer miyabei State Street Maple
• Acer truncatum Shantung Maple
• Carpinus betulus European Hornbeam
• Catalpa speciosa - Northern Catalpa
• Celtis occidentalis Hackberry
• Cercis canadensis Redbud
• Corylus colurna Turkish Hazelnut
• Ginkgo biloba cv. Maidenhair Tree
• Gymnocladus dioicus Kentucky Coffeetree
• Maclura pomifera Osage Orange
• Platanus x acerifolia cv. London Planetree
• Robinia pseudoacacia Purple Robe Black
  Locust
• Syringa reticulata and cv. Japanese Tree Lilac
• Ulmus parvifolia and cv. Chinese Elm
• Zelkova serrata and cv. Japanese Zelkova
• Others
• Native MO tree

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Why buy structural soil

• Avoid having the contractor deal with something
  out-of-the-ordinary
• Uniformity of product
• Delivery as needed without worry of storage
• Guarantee to meet load bearing specifications

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Structural soil and storm water storage

• CU-Structural is about 31 macropores by volume
• Infiltration rate of greater than 24/hour
• With slight change in pit/trench construction,
  one can use the trench as storm water detention
• Must insure that retained water ends up where you
  want it

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Tree Pit Detail for storm water detention
Structural Soil Tree Pit Detail for Storm Water
Detention
Typical Structural Soil Tree Pit Detail
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Brady student center
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For more information

• Cornells Urban Horticulture Institute
• www.hort.cornell.edu/uhi
• Go to OutreachgtStructural Soil
• Brian Kalter _at_ Amereq, Inc. (bkalter_at_amereq.com)
• www.structuralsoil.com