tree sites: good, bad and ugly · design and installation by peter trowbridge and nina bassuk •...
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Tree Sites: Good, Bad and Ugly…or why is the tree you recommended tearing up my driveway?
Paula Peper, EcologistCenter for Urban Forest Research
Pacific Southwest Research Station,USDA Forest Service
Why site assessment?
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When they’re small, it is hard to imagine….
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…tall
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…crammed into
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…small spaces
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and weird places
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Our Job: Simple as This?
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Species Profiles
Benefits vs. Costs
Why is Knowing Mature Tree Size Important?
• Placement for tree health and longevity
• Maintenance requirements
• Planning for low maintenance costs
Don’t We Already Know All About Tree Size?
• Different resources classify trees as small, medium, large– Same tree classified as medium or
large depending upon resource• Example:
– Utah – large tree >40 feet– California – large tree > 50-60 feet
Define Size: Which direction?
Tree Height Crown Diameter
What Determines Size?
• Tree Height– Important under
utility lines– Vistas and view
clearance• Crown Diameter
– Site constraints• Leaf area
– Benefits
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Growth rate – how fast trees grow – what influences,
growth?
• Climate• Site• Management• Culture
Climate
• Climate– Precipitation– Temperature– Elevation– Wind
Northern Mountain & Prairie Growth Comparisons
Silver Maple
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
80.00
90.00
0 15 30 45 60 75
Years After Planting
Hei
ght (
ft)
Bismarck
Cheyenne
Ft Collins
65%
46%58%
85%
Silver Maple at 70
Bismarck
Cheyenne
Ft. Collins
Throughout the West
Cheyenne Climate and Environmental Factors
• Weather:– 4th windiest city– Highest incidence of hailstorms– Average 14.4 inches precipitation annually– Low humidity and higher altitude (6138 ft)
• Soils:– Alkaline– Low water-holding capacity
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What Influences Growth?
• Culture– Local mindset
• Management
Sweetgum
Sweetgum
02468
101214161820
0 5 10 15 20 25 30 35 40 45 50Years
Bol
e &
Tot
al H
eigh
t (m
)
Santa Monica
Modesto
Claremont
70%40% 26%
LiquidambarSweetgum in three cities at age 40
Claremont Santa Monica Modesto
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Consider the tree’s needs• Big trees need more
space• As many or more
roots below ground as there are branches above
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Water access and soil
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Pruning Requirements
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Pollen and Litter
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Species Needs
Match Site Conditions
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Resources:
• Sacramento Tree Foundation– Tree Advisory Committee Tree Matrix
• Selectree (caution on sizes)– http://selectree.calpoly.edu/
• Dirr’s Manual of Woody Landscape Plants
• Sunset Western Garden• Ed Gilman’s website
– http://hort.ifas.ufl.edu/woody/selection.html
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The Right Place
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Space to grow & space for other trees
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Learning from the past – size and conflicts
Development and RetrofitRecent plans for 2-way residential street
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Actual Two-way Streets
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Sacramento’s Park Neighborhoods
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Close Tree Spacing (20-30 feet)
• Advantages:1. quick shade2. cathedral-like canopy3. less pruning of
drooping branches required due to the upright canopy
4. more natural, upright form develops
5. trees are less susceptible to wind damage
• Disadvantages:1. outer trees bend away
from others and are one-sided
2. if one or several die, adjacent trees may be susceptible to wind damage
3. more costly than farther spacing
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Wider tree spacing (40-60 ft)
Advantages:
1. Less costly than close spacing
2. Larger trees
3. More stable as adjacent trees die and are removed
Disadvantages:1. except for trees with an
upright habit, drooping branches need regular removal
2. large lower branches often develop, requiring removal and creating a large wound that can initiate decay
3. longer time needed to form a closed canopy
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Larger space = longer life, larger tree
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Space for Successful Trees
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The Unseen: below ground
Soil Volume
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Soil Compaction
*Critical bulk density = maximum compaction allowed for healthy root growth
109.210195.590.585.5Very poorly graded sand
87.4103989387.4Heavy clay
87.410910498.693Lean silty clay
87.410610195.590.5Loessial silt
93.611510910497.4Lean sandy silty clay
106.1120114109102Med. Graded sandy loam
106.1128122115109Well-graded sandy loam
109.2136129122115Well-graded loamy sand
Critical Bulk Density*100%95%90%85%Soil Type
Dry bulk density of several soils (lb/ft3) at 85-100% relative compaction
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Site: Soil Compaction
• Remediation:– Replace– Cover it up (Gold
River example)– Amend it
Soil Texture and Structure
Soil texture refers to the distribution (%) of the different soil mineral particles - sand, silt and clay
High % clay - soils may compact and hold more waterHigh % sand - no soil compaction and limited water retention
Soil structure refers to the arrangement or aggregation of the soil particles
Soil pHMeasure of soil acidity or alkalinity.
Influences absorption of essential elements absorption from soil ( but not of essential elements carbon, oxygen and hydrogen from air and water).
The pH scale runs from 0 - 14 with 7 representing neutral. Below 7 is acid and above 7 is alkaline. Generally the recommended range for trees is slightly acid - 5.5 to 6.5.
Soil Maps
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Drainage
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Sacramento Region’s Past
Site History: Natomas
In Transition…Center for Urban Forest Research 48
Site History: Gold RiverBefore
After
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Space for successful trees
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Light and Slope
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Salt
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Wind
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Conflicts
Vandalism “Reward Offered In Roseville High Tree Vandalism
Vandals Cut Down 21 Trees At Roseville High School”
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Regulations• Regulations for
PLACEMENT OF OBSTRUCTIONS ON SIDEWALKS OR STREETS
Chapter 20.40 Street Tree and Other Public Tree Regulations
• E. At street intersections, trees shall not be located within 70 feet of the intersection of curb lines (or pavement edge where curbs do not exist) when planted along arterial streets, within 50 feet when planted along collector streets, nor within 30 feet of the intersection of local streets. (City Engineer is to calculate distances.)
What Citizens Value
• Santa Monica– Semi-tropical
influence– Sunshine– Ocean views
• Claremont & Modesto– Heat relief– Suburban life
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Tree + Site + Management + Education = Tree Longevity
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Additional Resources• Cornell:
http://www.hort.cornell.edu/uhi/outreach/recurbtree/index.html
• Trees in the Urban Landscape Site Assessment, Designand Installation by Peter Trowbridge and Nina Bassuk
• Tree Roots in the Built Environment – Centre for Ecology and Hydrology
• Reducing Infrastructure Damage by Tree Roots: A Compendium of Strategies
• Integrated Management of Landscape Trees, Shrubs, and Vines
Homework Photos
Homework
• Choose a photo and describe what items you would consider in choosing the right tree for the right place.
• My email: [email protected]• Snail mail: 1731 Research Park Dr.
Davis, CA 95618