Structural pruning

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Structural pruning
http//hort.ufl.edu/woody

• University of Florida
• Dr. Ed Gilman, professor

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A brief introduction

• How trees are put together
• What makes them strong

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Codominant stems form far up into the canopy on
most forest trees
Asking lots from these low branches
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Its party time for all
Its all about access to sunlight
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Its party time for all
Its all about access to sunlight
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Spreading crown with terrible structure
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Close-up of base of tree
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Eleven years later inclusion failed
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Strong vs. weak
No reaction woodNo stem taperHeavy end
weightNo damping in wind
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In storms Upright broken, horizontal OK
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Where has it been used?
Photo credit unknown
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After the wind storm
Photo Norm Easey
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Storm damage observations tell us to minimize
occurrence of upright stems
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Codominant stems
branch
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Later in the growing season
In spring
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Courtesy Dr. Shigo
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Photo credit unknown
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This research tells us how to manage trees

• That is, with branches that are small compared to
  the trunk
• With branches more horizontal than vertical
• But there are limits to the horizontal
  orientation as well

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We manage trees by pruning them
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Structural pruning

• What, where, how, why its used
• What is a removal cut and reduction cut
• Canopy response to structural pruning

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Structural Pruning

• Changes the relative size of parts by managing
  growth rate and sunlight

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Objective Prune to promote strong structure
Trees require about 25 years of training to
develop strong structure.

• Structural Pruning Strategies
• Develop or maintain a dominant leader
• Identify lowest branch in the permanent canopy
• 3. Prevent branches below the permanent canopy
  from growing too large
• 4. Space main branches along dominant trunk
• Keep all branches less than ½ the trunk diameter
• Suppress growth on branches with included bark

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A more appealing approach Reduce growth rate of
low aggressive branches
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Without pruning 14 years later low aggressive
limbs develop that are in the way
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Without pruning 14 years later low aggressive
limbs develop that are in the way
E
E
D
D
C
C
A
B
A
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Now we have this hugh cut that invites decay to
move into the trunk
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Tree Growth Cycle
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Tree Growth Cycle
RaisingStructuralRoot management
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Tree Growth Cycle
CleaningStructuralThinningRestorationSoil
managementSupport systems
RaisingStructuralRoot management
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Reduction cut is the key
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Trees with good structure at planting
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Several years later, without pruning
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From the nursery
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What would you do?
Photos Peter Kaseman-Wold, Goodland Tree Works
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One year later
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One year later
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Remove competing stems
Photos Brian Kempf
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Before
After
Push
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After
2 years later
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Paulownia at Longwood
1991
2007
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Six leaders
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Before
After
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After
Before
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6 years after initial pruning
8 years after
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First treat the biggest problems
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Then work the mid-canopy
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2 reduction cuts at arrows
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Now work the top
Lots of upright stems
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Before - year 8
After
Debris
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Before - year 8
One year later
After
Debris
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Before - year 8
One year later
After
Debris
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One year later
Before - year 8
After
Two years later
Debris
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One year later
Before - year 8
After
Two years later
Close-up
Debris
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One year later
Before - year 8
Three years later
After
Two years later
Close-up
Debris
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One year later
Before - year 8
Three years later
After
Two years later
Four years later
Close-up
Debris
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One year later
Before - year 8
Three years later
After
Two years later
Four years later
Close-up
Debris
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14 years of pruning
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after
after
before
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3 years later
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Fabulous low maintenance structure in a shade tree
Climbers comment to me Ed, that tree was
really easy to climb
2005
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Way cool - a live oak with a dominant leader
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Before
2005
After raising and structural
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Chinese elm
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Declining leader
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Young enough to fix
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What should we do?
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First cut
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3.5 inch stem removed
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Second cut
First cut
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After pruning
Before pruning
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After pruning
One year later
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Tree shifted
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Florida champion Quercus virginiana
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reduce
reduce
Visible crack - some branches have hidden cracks
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Reduce entire canopy
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We now have good evidence that reducing length of
long stems and those competing with leader
significantly reduces storm damage
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Structural pruning

• What, where, how, why its used
• What is a removal cut and reduction cut
• Canopy response to structural pruning

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Removal cut removes the smaller
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Morphology Fewer vessels Narrower vessels Turned
vessels Physiology More parenchyma Starch - rich
zone Fungi-toxins
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Two branch protection zones
Photo credit Dr. Shigo
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This all happensinside the collar
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Big cuts
canresultin decay
andcracks
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Reducing back to a live lateral
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September 2007
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4 cuts on one tree
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Reduction cut size guidelines on permanent
branches
in routine temperate tree care .
Good compartmentalizers 2 to 4
Poor compartmentalizers 1 to 2

• Horsechestnut
• Red maple
• Beech
• Shumard oak
• Poplar

• White oak
• Walnut
• Red oak
• Taxus
• Elms

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Then theres this
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Structural pruning

• What, where, how, why its used
• What is a removal cut and reduction cut
• Canopy response to structural pruning

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Effects of pruning on trees in wind

• Ed Gilman
• Environmental Horticulture Department
• University of Florida
• Forrest Masters
• Civil and Coastal Engineering Department
• University of Florida
• Jason Grabosky
• Forest and Ecology
• Rutgers University

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The Wind Machine 1.0 (AKA its a start)
Testing the wind field
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Increasing pruning dose reduced canopy movement
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Trunk movement 54 in. above top most root
(averaged across dose)
Pruning type 15mph 30mph 45mph 60mph -------------
--------------------------------------------------
------------------- Structural NS NS 1.3a 2.1a
Raise NS NS 1.5a 2.3a Liontail NS NS 1.5a 2
.4a Reduce NS NS 1.8ab 2.6a Thin NS NS 3.1b
3.3b
Thinning was least effective its the only type
that did not reduce profile area of the canopy
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The wind machine 2.0 (AKA wall of wind)
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5 Thinned
5 treesraised
5 treesnot pruned
5 treesreduced
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Three incline devices on each tree
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Increasing foliage removal reduced movement in
straight line winds
Study funded by TREE Fund
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Thinning removed 33 of foliage
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Reducing 33 foliage removed resulted in less
than half the trunk movement
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Show videos
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Bending angle by treatment
Top device Bottom device

• Not pruned 46 a 29 a
• Raised 31 ab 15 b
• Thinned 23 bc 12 b
• Reduced 17 c 12 b

Reduced thinned Not pruned raised
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Wind machine 3.0 now were gettin serious
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TREE Fund purchased the rudders
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Largest portable wind tunnel in the world
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December 2007
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We compared pruning types in real gusty-wind
conditions up to 100 mphWind measured in real
storms

• No pruning
• Reducing
• Thinning

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thinned
reduced
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Go to gopher cam
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Looks like we found similar results as with
non-gusty wind
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Fourth study

• Impact of subordination structural pruning on
  stresses and motion
• Funded by the TREE Fund

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December, 2008 study
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Show video
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So, what did we learn

• Prune your trees to reduce or thin defective
  branches
• Reduce by making one cut 2 to 4 diameter
• Thin by removing 6 to 15 foot long 1.0 to 2.5
  diameter branches

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Three main research-based reasons to keep
branches small compared to trunk
Structural pruning

• Less likely to split small branches from trunk
• Less decay should limb require removal
• More resistant to wind and perhaps ice damage

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Thinning
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Good
Proper thinning reduces tree damage in storms and
preserves the trunk
But foliage simply grows back
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Thinned
Not thinned
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Lions-tailing causes drooping
After pruning
2 years later
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before
4 months
after
12 months