Wind-resistant urban design

1
Urban Forest Hurricane Recovery Program
http//treesandhurricanes.ifas.ufl.edu
2
Wind-resistant urban design

• Dr. Edward F. Gilman and Traci Partin

3
Could this have been prevented?
Photo credit Chuck Lippi
4
The answer is yes!
5
Wind-resistant urban design

1. Design conflicts that can cause tree failure
2. Design solutions that promote wind
   resistance - existing design situations -
   new design/construction
3. How to take action

6
How often do trees fall down due to poor design?
7
(No Transcript)
8
What design conflicts cause trees to fail?

• Large-maturing trees within 10 feet of a paved
  surface, without space designed for root growth
• Lack of open soil space
• Large roots cut during construction

• Poor soil conditions
• Single specimens (versus grouping trees)
• Wrong species selected for the site
• NOT ENOUGH ROOT SPACE!

9
Large maturing tree near curb
Photo credits Brent Marable
10
Space is needed for roots to spread
roots

• Fine roots can be found well beyond the canopy of
  the tree at full maturity
• These roots help anchor the tree under high winds

11
Soil depth is necessary for root stability

• Roots need adequate soil depth to anchor the tree
  under high winds.
• Soil should be at least 3 feet deep
• for large maturing trees

12
Lack of open soil space
Root flare is interrupted by curb and sidewalk
13
Open soil space allows root flare to develop

• 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
• The root flare provides balance and stability for
  the massive weight of a tree

Flare commonly 2.5 to 3.5 times trunk diameter
14
Roots cut during construction
Step two
Step one
3 x trunk rule
Step three
Photo credit Andy Kittsley
15
Poor soil conditions

• Compacted
• Shallow soil rocky high water table
• Drainage issues
• High clay content
• Alkaline soil/ Lime rock- inhibits uptake of
  essential nutrients
• Little to no organic matter (i.e. builders sand)

Photo credit Jim Urban
16

• This is a familiar site for many who live in
  South Florida.
• What can be done with shallow, rocky soil?

17
Single specimens vs. grouping trees
18
Larger groupings are less damaged

• This design did not suffer any tree damage when a
  hurricane blew through

19
Consider the natural setting for a tree
20
Notice the trees still standing
21
Selecting the wrong species for the site

• Choose small trees for sites where soil space is
  limited.

22
What design conflicts cause trees to fail?

• Large-maturing trees within 10 feet of a paved
  surface, without space designed for root growth
• Lack of open soil space
• Large roots cut during construction

• Poor soil conditions
• Single specimens (versus grouping trees)
• Wrong species selected for the site
• NOT ENOUGH ROOT SPACE!

23
Where do we grow now?
24
Wind-resistant urban design

1. Design conflicts that can cause tree failure
2. Design solutions that promote wind
   resistance - existing design situations -
   new design/construction
3. How to take action

25
Existing design situations

• Problem
• Mature tree with large roots interfering with
  hardscape.

• Solutions
• Install different surface material
• Add fill and re-pour walk
• Bridge over roots
• Re-route walk

CUTTING ROOTS IS NOT AN OPTION!
26
Install different surface material rock dust
Spread rock dust
Remove slabs
Pack dust tightly
Photo credits
27
Final product
looks attractive and is no longer a tripping
hazard
28
Install different surface material porous pavers

• To protect the root zone around the existing
  trees in this parking space at a botanical
  garden, porous pavers were selected

29
Add soil then re-pour over roots
30
Bridging over roots
31
Re-routing walk around tree

• When damaged sidewalks are repaired they can be
  re-routed around the tree trunks
• This can eliminate the need to prune roots that
  caused the walk to lift

32
Do not cut roots!
33
New design situations

• How do we make trees fit?

• Parking lots
• Planting islands
• Road medians
• Sidewalks
• Streets
• Buildings

34
Good design happens in two ways

• Choose the right tree for the conditions of the
  site

• Design the right place to fit the trees you want

35
Designing the right place

1. Plant trees in the open soil space available
2. If this is not possible, direct roots toward the
   open soil
3. If there is not open space for root growth,
   design appropriate soil space
4. Consider groupings vs. individual plantings

36
Appropriate soil space
At least 1000 to 2000 cubic feet of soil for each
healthy, large maturing tree
Open soil space 3 X wider than trunk diameter at
maturity (dbh) to allow root flare development
37
Planting strips in successful designs
38
Structural soilSmall aggregate material (angular
rocks 1 in. diameter) with enough soil to
almost fill the space between the rocks. Roots
grow well in the soil between the aggregates.
Illustration credit Jason Grabosky
39
Tree growth in structural soil

• These trees were planted into a strip of
  structural soil installed in this retrofitted
  parking lot between the blue arrows
• They have performed quite well

Photo credit Jason Grabosky
40
Suspended sidewalk

• Suspending the sidewalk avoids issues with soil
  compaction so that roots can spread without
  interrupting the hardscape

41
This particular system provides structure to
support the hardscape, filling in the remaining
space with quality soil.
Suspended sidewalk Soil cells
Pavement

• Structure
• Soil

42
Use alternate surface materials

• Materials other than concrete can be used as a
  wearing surface
• crushed granite
• gravel
• wood decking
• brick-in-sand
• porous pavers
• porous asphalt
• These materials allow oxygen to penetrate the
  soil and may encourage root growth

43
Porous paving surfaces

• Porous surfaces are a good design idea for areas
  prone to flooding
• reduce runoff
• provide aeration to the soil

44
Designing the right place

1. Plant trees in the open soil space available
2. If this is not possible, direct roots toward the
   open soil
3. If there is not open space for root growth,
   design appropriate soil space
4. Consider groupings vs. individual plantings

45
The goal A healthy urban forest

• Canopy cover
• Diversity of tree species grouped
  together

46
Plant trees closer for canopy closure

• Trees planted 60-70 feet apart grow large lower
  limbs due to wide spacing, and require pruning to
  allow clearance.
• Group trees 30 ft. apart to encourage an upright
  form.

47
Grouping vs. individual planting
Larger soil space shared by more trees
healthier trees!

• This is a sustainable design that will last many
  years.

In a few years, this tree will outgrow the space.
48
Example of sustainable parking lot design

• Trees are located only in the buffer strips
  surrounding this parking lot trees are not in
  small islands scattered throughout parking lot.
• This provides adequate space for tree roots to
  grow.

49
Remember small spaces do not support large trees!
50
Solutions can happen in two ways

• Choose the right tree for the conditions of the
  site

• Design the right place to fit the trees you want

51
Small trees for small spaces
When planting within 10 ft. of curbing Plant
small or medium sized trees (no greater
than about 35 ft. at maximum height)
52
Wind resistant species

• To get a comprehensive list of wind-resistant
  species, refer to our website
• (http//treesandhurricanes.ifas.ufl.edu/index.html

53
Do not over-plant one species

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

54
Wind-resistant urban design

1. Design conflicts that can cause tree failure
2. Design solutions that promote wind
   resistance - existing design situations -
   new design/construction
3. How to take action

55
Where to begin

1. Get the right people involved
2. Set new building ordinances for the community
3. Become a Tree City USA

56
Who should be involved in the planning process?

• City engineer
• Landscape architect
• Urban forester/arborists
• Builders developers
• Planners
• Parks and Recreation
• Power companies
• Homeowners Association
• City or county commissioners

57
What is Tree City USA?

• Program started by The National Arbor Day
  Foundation to promote communities that take care
  of their trees
• Provides a framework for starting a tree
  management program.

More information http//www.arborday.org/programs
/treeCityUSA.cfm
58
Contact your local county extension!

• Get information specific to counties across the
  state
• i.e. tree species that grow well in the area,
  local soil conditions, etc.
• Cuts time spent on looking up information in half!