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Urban Forest Hurricane Recovery Program. http://treesandhurricanes.ifas.ufl.edu. Dr. Edward F. Gilman and Traci Partin. Wind-resistant urban design. Could this have been prevented?. Photo credit: Chuck Lippi. The answer is yes!. Wind-resistant urban design.

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Urban Forest Hurricane Recovery Program

http://treesandhurricanes.ifas.ufl.edu


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Dr. Edward F. Gilman and Traci Partin

Wind-resistant urban design


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Could this have been prevented?

Photo credit: Chuck Lippi



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Wind-resistant urban design

  • Design conflicts that can cause tree failure

  • Design solutions that promote wind resistance - existing design situations - new design/construction

  • How to take action



What design conflicts cause trees to fail l.jpg

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!

What design conflicts cause trees to fail?


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Large maturing tree near curb

Photo credits: Brent Marable


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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


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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


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Lack of open soil space

Root flare is interrupted by curb and sidewalk


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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


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Roots cut during construction

Step two

Step one

3 x trunk rule

Step three

Photo credit: Andy Kittsley


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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. builder’s sand)

Photo credit: Jim Urban


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This is a familiar site for many who live in South Florida.

What can be done with shallow, rocky soil?



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Larger groupings are less damaged

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




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Selecting the wrong species for the site

Choose small trees for sites where soil space is limited.


What design conflicts cause trees to fail22 l.jpg

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!

What design conflicts cause trees to fail?



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Wind-resistant urban design

  • Design conflicts that can cause tree failure

  • Design solutions that promote wind resistance - existing design situations - new design/construction

  • How to take action


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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

Existing design situations

CUTTING ROOTS IS NOT AN OPTION!


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Install different surface material: rock dust

Spread rock dust

Remove slabs

Pack dust tightly

Photo credits:


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Final product:

looks attractive and is no longer a tripping hazard


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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




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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



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How do we make trees fit?

Parking lots

Planting islands

Road medians

Sidewalks

Streets

Buildings

New design situations


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Choose the right tree for the conditions of the site

Design the right place to fit the trees you want

Good design happens in two ways…


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Designing theright place

  • Plant trees in the open soil space available

  • If this is not possible, direct roots toward the open soil

  • If there is not open space for root growth, design appropriate soil space

  • Consider groupings vs. individual plantings


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“Appropriate” soil space

At least 1000 to 2000 cubic feet of soil for eachhealthy, large maturing tree

Open soil space 3 X wider than trunk diameter at maturity (dbh) to allow root flare development



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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


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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


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Suspended sidewalk

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


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Suspended sidewalk: Soil cells

This particular system provides structure to support the hardscape, filling in the remaining space with quality soil.

Pavement

Structure

Soil


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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


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    Porous paving surfaces

    Porous surfaces are a good design idea for areas prone to flooding:

    • reduce runoff

    • provide aeration to the soil


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    Designing theright place

    • Plant trees in the open soil space available

    • If this is not possible, direct roots toward the open soil

    • If there is not open space for root growth, design appropriate soil space

    • Consider groupings vs. individual plantings


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    The goal: A healthy urban forest

    Canopy cover

    Diversity of tree species grouped together


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    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.


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    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.


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    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.


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    Remember: small spaces do not support large trees!


    Solutions can happen in two ways l.jpg

    Choose the right tree for the conditions of the site

    Design the right place to fit the trees you want

    Solutions can happen in two ways…


    Small trees for small spaces l.jpg
    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)


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    Wind resistant species

    To get a comprehensive list of wind-resistant species, refer to our website:

    (http://treesandhurricanes.ifas.ufl.edu/index.html


    Do not over plant one species l.jpg
    Do not over-plant one species

    • Restrict one genera or species to < 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


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    Wind-resistant urban design

    • Design conflicts that can cause tree failure

    • Design solutions that promote wind resistance - existing design situations - new design/construction

    • How to take action


    Where to begin l.jpg
    Where to begin…

    • Get the right people involved

    • Set new building ordinances for the community

    • Become a Tree City USA


    Who should be involved in the planning process l.jpg
    Who should be involved in the planning process?

    • City engineer

    • Landscape architect

    • Urban forester/arborists

    • Builders & developers

    • Planners

    • Parks and Recreation

    • Power companies

    • Homeowner’s Association

    • City or county commissioners


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    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


    Contact your local county extension l.jpg
    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!


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