TEP Seminar XI
London England
Soil management innovation,
planting & establishment:
A view of structural tree soil, planting
design innovation
James Urban, FASLA, ISA
Urban Trees + Soils
Annapolis, Maryland
LR
TEP Seminar XI
London England
Soil management innovation,
planting & establishment:
A view of structural tree soil, planting
design innovation
James Urban, FASLA, ISA
Urban Trees + Soils
Annapolis, Maryland
LR
Trees need
dirt!
Help !
Tree Source Books
www.treesource.co.uk
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Savannah, Georgia
60% canopy
Atlanta, Georgia
<20% canopy
London
??% Canopy
33 year old Limes near
Guild Hall, London
Urban trees and soil quality
Silva Cells
Tree in compacted clay soil
Milton Keynes
20 + year old Pear trees
Roots
Tree in compacted clay soil
Milton Keynes
How Much Soil
Larger Trees
20” (500 mm)
Trunk Diameter
More Soil
1200 CF (34 M3)
Soil Volume
20” (500mm)Trunk Diameter
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Tree size to
Soil volume
800 CF (22.6 M3) Soil
1200 CF (34 M3) Soil
400 CF (11.3 M3) Soil
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Soil trench
480 CF (13.55 M3)
Total usable soil
Tree space soil
Usable Soil
115 CF (3.25 M3)
365 CF (10.3 M3)
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400 CF (11.3 M3) TRENCH
AT YEAR 12
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400 CF (11.3 M3)
TRENCH
YEAR 16
YEAR 25
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STUCTURAL SOIL
Trees in open soil
trench
Trees in
Structural soil
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Leaf count
Source: Growth response of Ficus benjamina
to limited soil volumes and soil dilution in a
skeletal soil container study. Loh, Grabowsky,
and Bassuk
Urban Forest, Urban Green, 2 (2003)
Days of Study
Value of the soil in
structural soil
Large
structural
soil
Small
Loam
soil
Large
Loam
soil
Large structural soil and small loam
soil have equal amounts of loam soil.
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Structural soil
315 CF (8.9 M3)
Total usable soil
Rock
Tree space soil
Usable Soil
115 CF (3.25 M3)
200 CF (5.65 M3)
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6’ wide structural
soil trench
YEAR 12
Soil - 275 CF (7.8 M3) / tree
In open planter
Structural soil - 70 CF (2 M3) / tree usable soil
Plus 55 CF (1.6 M3) soil in tree opening
Total usable soil 125 CF (3.5 M3) / tree
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Pavement
Structure
Soil
Silva Cell
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Silva Cells
1005 CF (28.25 M3)
Total usable soil
Tree space soil
Usable Soil
115 CF (3.25 M3)
890 CF (25 M3)
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Aggregate
and paving
Decks and
geotextile
Silva Cell Installation
Cells and soil
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32,000 lb (14,500 kg)
Axel Weight
8,000 lb (3,630 kg /
Tire
AASHTO - American
Association of State
Highway and
Transportation Officials
Silva Cell Load Test
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Bartlett tree study
Charlotte, NC
THE FIRST BLOCK OF TREES ARE THREE SPECIES OF
TREES IN A MOCK UP OF STRUCTURAL CELLS. THE
REMAINING TREES ARE GROWING IN VARIOUS TYPES
OF STRUCTURAL SOILS. PHOTO TWO YEARS AFTER
PLANTING
SILVA CELL MOCK UP
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More Water Storage
How Much
Water Storage
240 CF (6.8 M3)
Water storage
More Soil
1200 CF (34 M3)
Soil Volume
20” (500mm)Trunk Diameter
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Trees / Rain Water
and Structural Cells
Evapo-transpiration
Parking areas
1200 CF (34 M3) Soil volume
Treats 300 CF (8.5 M3) Water
Manages
Pervious
surface
3,600 SF (335 M2) Impervious area
1” rain event
Impervious
surface
Structural Cells
and Water
Storage
Infiltration
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Water access
options through
pavements
Pervious Pavers
Curb inlets
Trench Drains
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Trees need
dirt!
In the UK from
Tree Source Books
www.treesource.co.uk
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www.isa-arbor.com
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TREES IN STRUCTURAL SOIL IN
NEW YORK, NY AFTER 12
YEARS
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Trees / Rain Water
and Structural Cells
Evapo-transpiration
Urban Streets
Pervious
surface
Impervious
surface
Structural Cells
and Water
Storage
Toronto Waterfront
Courtesy of
West 8 + DTAH
Infiltration
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Trees and lights
have
equal cost
and
equal value
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Tree size to
Soil volume and
Water volume
800 CF (22.6 M3) Soil
160 CF (4.5 M3) Water
1920 SF (178 M2)
Drainage area
Drainage area management
based on a 1” (25mm) rain
event
1200 CF (34 M3) Soil
300 CF (8.5 M3) Water
3600 SF (335 M2)
Drainage area
400 CF (11.3 M3) Soil
80 CF (2.3 M3) Water
960 SF (89 M2)
Drainage area
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Establish Reasonable Tree and Soil Budgets
Balance design quality of all elements in the landscape
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Cities with Big Trees and Diversity of Species
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MAIN STREET SAVANNAH
Why are urban street trees……
Sometimes Successful
and
Sometimes not
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FACTORS IN CANOPY SUCCESS
1. SPEED OF DEVELOPMENT
MODEREN EQUIPMENT AND SPEED OF DEVELOPMENT IMPACTS SOIL
AND RATE OF CANOPY LOSS
2.MAINTAINING MATURE TREES
TIME TO REPLACE LOST CANOPY IS SLOWER THAN CANOPY IS LOSS,
WHILE REGROWING CANOPY IS SLOWED BY SOIL CONDITIONS
3. BACKGROUND SOIL CONDITONS
COMPACTION RESISTANT SOIL AND REMNANT SOIL CONDITIONS VARY
4. DEGREE OF SOIL DISRUPTION
MODERN CONSTRUCTION DISTROYS MORE SOIL ATTRIBUTES
DECREASING EFFECTIVE VOLUME
For sale: baby shoes, never used.
Ernest Hemmingway