Pruning Young Street Trees, Using Pole Tools

Dr. Ed Gilman and Traci Jo Partin, adapted by Guy Meilleur, Guy@HistoricTreeCare.com

Pruning improves stability

Reduction pruning reduces trunk bend in high winds.

Not pruned

Reduced by pruning

Proactive Pruning: young trees

• Set the objectives: health, safety, longevity

• Frequency? (pruning cycle)

• Inspect structure—forks!

• Locate permanent branches• Keep temporary branches as

long as they are needed

Over-raising = Giraffe Pruning

Select and train lowest permanent branches.

Keep temporary branches as long as they are needed!

Poor form Good form

Principles of strong structure:• One (or more)dominant trunks• Strong branch unions• Balanced crown

Mitigate structural issues: avoid failure

• Codominant stems: stems of equal size originating from the same point on the tree

• Included bark: bark pinched between two stems = weakness in the union

• Unbalanced crown:one side heavier = asymmetric heavy ends = overextended Large low branches:

Collar

Strong connection: Subdominant

Weak connection: bark inclusion, codominants

ANSI Z60 NURSERY STANDARD:

1.3.2 Minimum quality requirement All nursery stock transacted within the terms of the Standard shall, at time of shipment, be substantially free of damaging insects and diseases, in good living condition, and typical in habit for the species in the region of the country in which it is grown.1.3.3 Co-dominant stems - Type 1 and Type 2 shade trees Unless specified as multi-stem trees (see Section 1.2,

above), Type 1 and Type 2 shade trees (see Section 2) with co-dominant stems occurring within the lower half of the crown do not meet the minimum quality requirement set forth in Section 1.3.2 (see Figure 6, below).

1.4.3 Lowest branch height for street trees Bid specifications for trees to be used as street trees shall include the minimum height of the

lowest branch, or the height to which the trunk shall be free of branches, which shall bear a relationship to the size and kind of tree so that the crown of the tree is in good balance with the trunk. Examples: Acer platanoides, 2 in. cal., 12 to 14 ft., trunk free of branches 6 ft. Quercus rubra 3½ in. cal., 14 to 16 ft., lowest branch 7 ft.

Soil above the root flare, from being deeply planted in the nursery as a young plant, as a result of maintenance practices in the nursery, or added during

harvest, shall not be included in ball depth measurement, and should be removed.

Tearout failures of codominants with included bark

Split failure due to bark inclusion

Unbalanced canopy

Liontailing: trees with overextended branches after inner branches were removed.• Susceptible to breakage• Restoring requires ‘stubs’•Large trunk wound will decay the attachment point

Liontailed trees failed

No laterals to cut back to after damage

Large lower limb will be removed for 14’ clearance.

Overpruning: small limbs removed instead

of reduced

8

Big cuts can result in decay and cracks and sunscald and imbalance and starvation and loss of contributions and...

Structural Pruning Strategies:1. Develop or maintain dominant leader(s)

2. Identify lowest permanent branches

3. Reduce temporary branches below the permanent crown to build and protect trunk, nourish roots

4. Space scaffold branches along dominant trunk(s)

5. Keep all branches ~< ½ trunk diameter

6. Subordinate codominants with included bark

Trees require about 25 years of training to develop strong

structure.

Objective: Promote strong structure

Trace included bark to inosculate(From an “innie” to an “outie”)

14 months later: re-clean

1 year later: Fini! From included bark to a bark ridge in 2 seasons.

Preventive Pruning: young trees

• Set the objectives: health, safety…

• Frequency and amount (cycle and dose)

• Prioritize structure• Locate permanent branches• Keep temporary branches

as long as they are needed

Pruning cycle: the time between each pruning event

• Depends on quality of nursery stock, growth rate, climate, species, availability of technicians.

• Shorter for faster-growing or defective trees.

• “Longer cycles force larger cuts to correct structural issues”: ??Theory, or fact?? This can be mitigated by avoiding horizontal cuts. Extrapolating research on small trees to the care of big trees does NOT work!

Determine a pruning cycle

Pruning cycle: (very generally)- more than 3-5 years = higher pruning dose- every 1-2 years = smaller pruning dose

Suggested program:

- At planting: Despite the myth to avoid this!- Year two or three- Year five or six- Year ten- Year fifteen

Pruning dose: the amount of live tissue removed at one pruning

• Depends on customer expectations, the size of the stems, and the pruning cycle.

Low pruning dose( < than 20%)

Higher pruning dose( > than 20%)

Mature or recently planted trees

(Veterans: <10%)

Young, established trees

(or even at planting time)

Cooler climates with short growing season

Warm climates where trees have longer growing season

Decay prone species Good compartmentalizers

Appropriate Pruning Dose for Specific Applications

Large Pruning Dose Small Pruning Dose

Municipality with no money or volunteers available.

Residences, commercial properties

Long pruning cycle Short pruning cycle

Aesthetics of less concern Aesthetics are a concern

Effects on the Tree from Applying Pruning Doses

Large Pruning Dose Small Pruning Dose

Larger pruning wounds Smaller pruning wounds

Larger void in canopy Smaller void in canopy

Greatly encourages growth in unpruned portions of tree

Encourages some growth in unpruned portions of the tree

Impact of pruning dose on co-dominant stem growth

before after 75% dose

Impact of pruning dose on co-dominant stem growth

Foliage removed for 75% dose

Maximum critical diameter: the largest diameter pruning cut you are willing to make on a certain species

• This limit should be specified in advance

• Should be smaller for decay-prone species.

• Is controlled by the pruning cycle *and angle: horizontal cuts should be smaller*

• The amount of heartwood or growth rings exposed

Branch size: - proportion relative to trunk - actual diameter of stem

Branch size Consequences of Removal

Recommended Action

Less than ½ trunk diameter

Few consequences Remove if needed

1/3 to ½ trunk diameter

Some trunk defects could result

Consider shortening instead

More than ½ trunk diameter

Defects likely Reduce instead of removing

Large enough to have heartwood

Defects likely Reduce instead of removing

Proactive Pruning: young trees

• Set the objectives: health, safety…

• Frequency and amount (cycle and dose)

• Prioritize structure• Locate permanent branches• Keep temporary branches

as long as they are needed

Make good cuts

Step Shorten the branch to get the weight off. When using a saw, undercut first. **Image wrong: 2nd cut should align with the first**

Step 2Pull away the cut section.

Step 3Remove the stub, outside the wrinkles. Do not cut flush against the trunk. Leave the collar intact.

Branch bark ridge

Collar: swollen area at the base of the branch where it joins the trunk. The wood is denser and rich in energy reserves and defensive chemicals. These same qualities exist at all growth points (nodes, forks). Good pruning cuts are made where diameter (taper) narrows.

Collar

Bad- flush cut

Wound wood does not develop evenly.

Obsolete Illustration

of Reduction Cut

Too big a woundToo close to another wound

Reduce further out!

Prioritize:Structural pruning not as important on these

Temporary vs. permanent branch management

14’

8’

0’-8’

A Hook is Handy

Pull down branch to stabilize and position for precise cutting

Pull out webworms, balloons, cats…

Pruning Plan: First 5 years

Identify architectural type and select leader(s)

Do not remove more than 35% of live foliage at a pruning visit.

Reduce all branches greater than ½ trunk diameter.

Reduce or remove all branches or stems competing with the one(s) selected to be the leader.

Reduce or remove large, low vigorous branches and broken, cracked, and damaged branches.

Reduce growth rate of low aggressive branches

Push Push

Before After

Year two

Pushback

AfterBeforeStructural pruning is a three

step process:

1. Identify the stem(s) that will make the best leader(s).

2. Identify which stems are competing with the leaders.

3. Decide where to shorten these competing stems.

AfterBefore

Pruning Plan: 5 – 20 years

Do not remove more than 25-35% of live foliage.

Reduce all branches greater than ½ trunk diameter.

Identify lowest scaffold limbs of the permanent canopy and reduce all aggressive lower branches.

Reduce branches with included bark.

Reduce or remove competing leaders (if there are more than 3 competing leaders, this can be done in stages).

Reduce branches within 18’’ of largest limbs.

Before After

Push

Two years later

Before after

Before After

Dominant leader structure after two

pruning visits

Before pruning After pruning

Transforming a bush into a tree

Two years later

Pruning Plan: 20 – 30 years

Identify 5 to 10 permanent scaffold limbs and reduce branches within 18-36’’ to avoid clustered branches.

Space permanent scaffold limbs to reduce wind resistance.

Remove many or all of the branches below the first permanent limb.

Reduce codominants with included bark.

Reduce and/or remove competing leaders.

Pruning at planting time and 10 years later built good form. In the mature tree, a stable skeleton of scaffolds are developed.The left image shows large uprights removed, which makes the ends heavier and the branch more likely to fail. Another way to subordinate large limbsIs to remove downright laterals, and reduce or retain uprights.

Reduce growth on branches below permanent

canopy

2 years later After

before after

Here is a tree that was damaged in a storm. As a result, many stems are growing upright

Remove two upright, interior stems

After removing right codominant stem

Before

Before - year 8

After

Debris

Before - year 8

After

Debris

One year after pruning

Before - year 8One year after pruning

18 months after pruning

With dedication to a management plan, your community can become a model for others