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Urban Design to Accommodate Trees: Introduction

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Urban Design to Accommodate Trees: Introduction by Dr. Edward F. Gilman, professor Department of Environmental Horticulture University of Florida, Gainesville – PowerPoint PPT presentation

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Title: Urban Design to Accommodate Trees: Introduction


1
Urban Design to Accommodate Trees Introduction
  • by Dr. Edward F. Gilman, professor
  • Department of Environmental Horticulture
  • University of Florida, Gainesville

http//hort.ufl.edu/woody/planting
2
Outline of topics
  • Introduction
  • Site evaluation
  • Species selection
  • Formula for success
  • Roots/hardscape conflicts
  • Trees/sidewalk solutions
  • Parking lot/buffer strip solutions
  • Structural soils

3
Urban design to encourage tree canopy
Introduction
  • Trees often grow poorly in urban areas unless the
    infrastructure has been specially designed to
    accommodate tree root growth
  • This presentation is designed to help guide you
    through the design and species selection process

4
Few citizens want cities without trees
Introduction
  • A city without trees is hotter in summer,
    receives less rainfall, has greater runoff
    following storms, has fewer shoppers, and is not
    inviting

5
Poor design leads to failure
Introduction
  • Trees struggle unless spaces are designed
    appropriately
  • When lots of money is thrown at tree projects
    without guidance from knowledgeable
    professionals, waste occurs and no one wins

6
Good design leads to success
Introduction
  • Trees thrive when good designs are executed
    properly
  • 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

7
Outline of topics
  • Introduction
  • Site evaluation
  • Species selection
  • Formula for success
  • Roots/hardscape conflicts
  • Trees/sidewalk solutions
  • Parking lot/buffer strip solutions
  • Structural soils

8
Site evaluation
  • A thorough site evaluation insures that you will
    select the right tree for your planting site

9
Examples of some of the components of site
evaluation
evaluation
  • Above ground
  • USDA hardiness zone
  • Light, heat, and wind exposure
  • Below ground
  • Soil volume is there enough root space?
  • Soil pH and drainage
  • Soil texture, compaction
  • Maintenance issues
  • Availability of regular irrigation
  • Pruning program in place or not

10
Other important site evaluation criteria
evaluation
  • What is the average annual rainfall in the area?
  • Will the tree be plantedin the ground, in
    containers or in above ground planters, or near
    the coast
  • What is the distance between the top of the water
    table and the soil surface?
  • How will the site be irrigated?.
  • Will the tree be planted in a tree lawn or
    streetscape (the grassy strip between the curb
    and the sidewalk)?
  • Will the tree be planted along a street without a
    sidewalk.
  • Will the tree be planted in a sidewalk cutout?
  • Will the tree be planted in a parking lot?
  • Will the tree be planted in an open lawn area or
    in a shrub bed? What is the approximate size of
    this area?
  • Will the tree be planted within 8 feet of a
    sidewalk, driveway or other hard surface?
  • Will an adjacent sidewalk or roadway receive
    deicing salts?
  • Is there a swimming pool, vegetable garden,
    masonry wall or septic tank or drain field within
    50 feet of the planting site?
  • Are overhead wires within 30 feet of the planting
    site?
  • Is there a street light or security-type light
    within 35 feet of the planting hole?
  • Is the planting site within 35 feet of a
    building?
  • Would you care to eliminate trees that could drop
    messy fruit, large leaves or twigs during an
    extended period?
  • Would you like to eliminate trees that are known
    to be susceptible to breakage?
  • What is your budget for pruning trees?
  • Would you care to plant only native trees?

11
Outline of topics
  • Introduction
  • Site evaluation
  • Species selection
  • Formula for success
  • Roots/hardscape conflicts
  • Trees/sidewalk solutions
  • Parking lot/buffer strip solutions
  • Structural soils

12
The dilemma
Selection
the design
  • Certain trees grow well in tough urban sites so
    we use them often..monoculture results
  • They grow well in small spaces but disrupt and
    destroy sidewalks/curbs, grow into wires
  • We fix the problem by cutting roots and
    resurfacing hardscape, or cutting tops
  • Trees decline or look ugly as a result and
  • ..our vision of the urban forest never develops
    because trees never make it more than 20 to 40
    years
  • We can do better with appropriate design

13
The dilemma continued
the trees
  • We could try different species or cultivars but
    they may perform poorly and besides no one else
    has tried these
  • And alternative trees may be difficult to find at
    nurseries, especially in the size and quantity
    you want
  • Sowe plant what we know will work i.e. what
    everyone else plants, because it is safe
  • We are more or less stuck in this pattern now

14
Solution be creative
  • Restrict one genera or species to lt 20 for few
    years
  • Develop a list of alternatives for each commonly
    planted tree
  • For example alternatives to live oak
  • Swamp chestnut, redbay, trident maple,
    sugarberry, ash, sweetgum, american elm, cedar
    elm, overcup oak,

15
Match species to site characteristics
Selection
  • Choose the right tree that will grow in the
    conditions present at the site use books,
    software, web sites, your experience
  • or
  • Design the right place to fit the trees you want
    this is covered in detail next

Dont try to shoehorn a tree you want into a site
not designed to support that tree, unless you are
a short term planner, in which case go for it
16
Examples of right tree in the right place
Selection
  • Small planting pit hardscape damage and poor
    growth so pick small, low O2 trees
  • Parking lot island drought, small space, heat
    so pick urban tough, drought tolerant trees
  • Park/campus/lawn plenty of soil space so pick
    large maturing trees
  • Soil pH 8.2 poor growth on many trees so pick
    alkaline soil tolerant trees
  • Compacted soil surface roots and hardscape
    damage likely so pick small trees tolerant of low
    oxygen
  • Wires or lights overhead regular pruning so
    pick small trees or move wires and lights
  • Poor drainage surface roots so pick small trees
    or design in more soil space
  • Narrow planting strip deflected roots and
    toppled trees so pick small trees or design in
    more space

17
Diversity can be the key to adversity
Selection
  • But, once it is discovered that a certain tree
    grows well in a situation, it tends to be used
    over and over again.what is wrong with that?
  • Perhaps nothing so long as a pest problem like
    Dutch elm disease, emerald ash borer, and others
    do not occur.
  • How lucky do you feel? Detroit is not feeling too
    lucky.
  • Your community has to make that decision

18
Species selection for hardscape compatibility
Selection
  • Trees that have a long life span generally
    compartmentalize decay well so they are resilient
  • Trees that are free of serious pest problems are
    good

19
Species selection for hardscape compatibility
Selection
  • Trees that develop a prominent root flare
    (swelling at the base of the trunk) can lift
    sidewalks and curbs soon after planting in many
    circumstances if special provisions are not
    incorporated into the design

20
Species selection for hardscape compatibility
Selection
  • Avoid planting trees with fleshy fruit to reduce
    the likelihood of people slipping and falling on
    walks and pavement

21
Species selection for hardscape compatibility
Selection
  • Avoid trees with long sharp thorns or spines
    unless the thorns will be well above the ground
    and out of the way of pedestrians

22
Species selection for hardscape compatibility
Selection
  • Trees tolerant of low soil oxygen conditions
    often perform better than other trees when placed
    in small restricted soil spaces with poor
    drainage

23
Other selection criteria
Selection
  • Showy flowers/bark
  • Canopy density/texture
  • Attracts wildlife/or not
  • Leaf size/messiness
  • Nice fall color
  • Single/multi-trunked
  • Pruning requirement
  • Canopy form/habit
  • And others.

24
Outline of topics
  • Introduction
  • Site evaluation
  • Species selection
  • Formula for success
  • Roots/hardscape conflicts
  • Trees/sidewalk solutions
  • Parking lot/buffer strip solutions
  • Structural soils

25
Trees can form a canopy over the street
Success
  • With appropriate spacing
  • Access to open soil space
  • Open soil space is soil that is not covered by a
    hard surface such as a sidewalk, pavement or a
    building

26
Complete canopy closure
Success
  • Trees were planted 40 to 50 feet apart in a
    planting strip 10 feet wide this spacing allowed
    for the crowns of individual trees to touch,
    encouraging development of a more natural upright
    form
  • The 10' wide planting strip allowed the trunk
    flare to develop appropriately

State College, Pennsylvania
27
Complete canopy closure
Success
  • Trees were planted about 30 feet apart this
    spacing allowed for the crowns of individual
    trees to touch when they were fairly young and
    encouraged a more natural upright form
  • Trees gained tremendous size due to the almost
    unlimited access roots had to soil space

Saint Augustine, Florida
28
Complete canopy closure
Success
  • Trees were planted 15 to 40 feet apart this
    spacing allowed for the crowns of individual
    trees to touch when they were fairly young
    encouraging a more natural upright form
  • Trees gained tremendous size due to the almost
    unlimited access roots had to soil space

Seattle, Washington
29
Barely complete canopy closure
Success
  • Trees were planted about 50 feet apart. Because
    trees were spaced this far apart, they began to
    grow aggressive lower limbs. Lower limbs are
    drooping, creating a more spreading habit than
    would have occurred with closer spacing

Miami, Florida
Trees gained tremendous size due to the almost
unlimited access roots had to soil space
30
No canopy closurespacing too far
Success
  • Trees were planted about 50 feet apart. Because
    trees were spaced this far apart, they began to
    grow aggressive lower limbs. Lower limbs are
    drooping, creating a more spreading habit than
    would have occurred with closer spacing
  • Trees gained tremendous size due to the almost
    unlimited access roots had to soil space

Charleston, South Carolina
31
No canopy closure
Success
  • Trees were planted about 60-70 feet apart.
    Because trees were spaced this far apart, they
    began to grow aggressive lower limbs.
  • The planting strip is twenty feet wide and roots
    can grow into the lawns of the homes along the
    street

Coral Gables, Florida
32
The formula
  • Plenty of root space
  • Closer spacing for canopy closure and reduced
    maintenance

33
Outline of topics
  • Introduction
  • Site evaluation
  • Species selection
  • Formula for success
  • Roots/hardscape conflicts
  • Trees/sidewalk solutions
  • Parking lot/buffer strip solutions
  • Structural soils

34
Roots can destroy hardscape with improper design
Conflicts
  • Tree roots grow under sidewalks and asphalt in
    many instances because that is where the soil
    oxygen and moisture are located
  • The hardscape is often inadvertently designed to
    encourage roots to grow there better urban
    design can reduce the likelihood of roots
    proliferating under hardscape

35
Root spread on shade trees
Conflicts
  • Shade trees extend their roots way beyond the
    tree canopy
  • Note the root that is growing in the lawn (two
    arrows) it is located well beyond the branch
    tips

36
Roots grow well beyond canopy edge
Conflicts
  • Trees that normally grow a very expansive root
    system can become stressed and grow poorly in
    urban landscapes where soil space is limited
  • The result can be poor tree health, damaged
    sidewalks and curbs, and other problems

37
Root flare needs room to expand
Conflicts
  • The swelling at the base of the tree (where the
    large roots meet the trunk) is commonly referred
    to as the root flare or buttress
  • Roots normally raise out of the ground as shown
    here
  • Adequate open soil space must be designed into
    the system to accommodate expansion of the root
    flare

Flare commonly 2.5 to 3.5 times trunk diameter
38
Misfits and poor design
Conflicts
  • The oaks planted in this narrow soil strip have
    two choices
  • grow poorly due to the limited amount of soil
    space available for root expansion, or
  • grow well by sending roots under the pavement
    which will quickly crumble the curb and asphalt

39
Misplacement of large maturing trees
Conflicts
  • The honeylocust planted between the walk and the
    wall are capable of growing to a large size. In
    order to thrive in this site, the trees roots
    will have to grow under the wall and into the
    lawn behind the wall
  • The wall is likely to be displaced as the root
    flare develops and the roots expand in diameter
    beneath the wall

40
Young trees likely to grow to disrupt hardscape
Conflicts
  • The trees planted in this three to four foot wide
    strip are likely to cause disruption to the curb,
    sidewalk, and driveways along this street
  • These repairs cost communities in the US
    approximately 2 billion dollars annually

41
Damage can result
Conflicts
  • Large maturing trees located too close to walks
    can cause structural damage that is costly to
    repair

42
Sidewalks lifted
Conflicts
  • Roots often grow just under the slab because that
    is where moisture and oxygen are abundant
  • Roots lift the walk as they grow in diameter

43
Picking slow growing trees can help
Conflicts
  • Trees that remain small at maturity often cause
    less damage than large trees
  • More small trees will be required (at a spacing
    of approximately 25 feet) to develop a closed
    canopy than if large maturing trees were planted

44
Outline of topics
  • Introduction
  • Site evaluation
  • Species selection
  • Formula for success
  • Roots/hardscape conflicts
  • Trees/sidewalk solutions (go to sidewalk
    solutions PP file)
  • Parking lot/buffer strip solutions
  • Structural soils

45
Urban Design to Accommodate Trees Introduction
  • by Dr. Edward F. Gilman, professor
  • Department of Environmental Horticulture
  • University of Florida, Gainesville

http//hort.ufl.edu/woody/planting
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