I wrote the attached 5 years ago; a diametrically opposed theory with excellent results. Hey Brian, next week I get to restoration prune that big big tall willow oak you pruned in Raleigh. I will take plenty of pics and measurements, and do a followup article as well. It'll be in the australian mag in march, but tci soon enough.
I love the UK veteran tree movement, but from all I know and have seen, coronet cuts are unnecessary. Reduction to nodes gets more stable sprouting, and quicker wound closure. But keep an open mind--Neville Fay is coming to the USA in June--Philly, Santa Rosa CA,and Asheville NC on the 16th.
geez whatta forum--you can cuss all you want, but not upload a doc or pdf? I must be missing something...
SELECTIVE HEADING CUTS AFTER STORM DAMAGE
SUMMARY
Storms remove branches that trees grew and used to make and store food and other essentials. If too many branches are lost, the tree dies. So the natural approach is to take as little as possible off of damaged trees. The normal rules of pruning back to lateral branches do not apply to damaged trees; you should instead cut back to the first good node behind the break. Removing dead and damaged tissue is known as crown cleaning; this is always Job #1.
Sometimes to keep the tree you must leave stubs, and some people will call you a hack, or a tree-topper, or worse. When they do, you may get them off your back by asking these questions:
Have you ever reviewed the literature behind those rules you are repeating?
Why do you think it’s good to cause deeper decay, sunscald, imbalance and instability?
Mother Nature just gave this tree a big dose of pruning—should I give it an overdose?
Years after heading cuts are made, thinning cuts must be made to restore the tree’s shape. Simply remove or reduce the sprouts that don’t seem to have a future. Try not to take off more than one-third of them at a time. In the end you will be left with a tree that is balanced, solid and good-looking. If the tree is lucky, you won’t be able to tell it was ever damaged.
OUR STORY BEGINS
December 5th, 2002 was a day that will live forever in tree infamy in Raleigh, NC. An inch and one-quarter of ice put a crushing load on the area’s arboreal resources. Huge limbs dangled like Damocletian swords, grotesque ornaments greeting their owners. Contractors were told that in the course of cleaning out broken branches they had to cut all the stubs back to a substantial lateral. This rule is called “Natural Target Pruning” or “making Shigo cuts”. They were also told, following FEMA guidelines, to remove trees with 50% crown loss. It was a Catch-23: obeying the first rule would remove so much more living crown, many trees would be removed that could simply be restored.
If arborists wanted to facilitate the coexistence of people and trees, they had to reread the directions, the ANSI Pruning Standards. In ANSI A300 4.20, heading is defined as “Cutting an older branch or stem back to a stub in order to meet a defined structural objective.” 5.5.6 states that “Heading should be considered an acceptable practice in shrub or specialty pruning to reach a defined objective.” Since restoration pruning is a type of specialty pruning, the standards seem to allow for leaving stubs in trees for the defined objective of preserving them.
Also, selective heading cuts are routinely made in vine, shrub and fruit tree pruning, bonsai, pollarding and other arboriculture. So how can all selective heading cuts in a big tree be considered improper? This exceptional storm challenged the simplified rules, which seem based on a Cliff’s-Notes reading of the literature. The old ISA seal says, “Science, Research, Preservation”; good words to work by. Preserving trees is the goal; preserving branches is the way to reach that goal. This may mean cleaning the crown of damaged tissue only down to the first good node. As Dr. Alex Shigo said in A New Tree Biology, p. 458, “Topping is done internodal; proper crown reduction is done at nodes, OR at crotches. So the first separation must be nodes—good, internodes—bad.”
NODES ARE NATURAL TARGETS
Cutting to large laterals prevents natural regrowth and takes stored resources away from the tree. Restorative heading cuts are not random or predetermined, like topping cuts, but selected according to biological criteria. But what is a node, and what does it look like? In A New Tree Biology Dictionary, Dr. Shigo defines “node” as “the position on a stem or trunk that was occupied by the terminal bud and its associated buds.” Some nodes contain fully formed buds that have been carried along in the cambium as the branch grew.
These buds are connected to the vascular stream and often anchored by compacted xylem, as shown on pages 238-9 of ANTB. Due to their vascular connection, the growth from these buds can be well nourished, and due to their xylem connection it can be well anchored. This dominant growth contrasts clearly with weak growth newly formed on the surface of the bark from adventitious buds. Some botanists also define these growth points as nodes, but terminal bud locations offer a clearer target.
What do target nodes look like on the outside? A bulge just before a decrease in diameter can indicate reduced branch growth beyond a terminal bud. A cut just outside a bulge will also leave a smaller wound, and retain more symmetry and structure. Some raised areas may contain dormant buds visible to the naked eye. Some bumps and bulges may be due to pests, so the surface of the cut should be examined to ensure that is not the case. Wrinkles on branches are often the same swollen collars that once formed around the base of lateral branches. If a scar indicates that a lateral branch was shed at these locations, there may already be preformed lateral buds on the outside. They may also already contain what Gilman and Lilly called the “unique chemical barrier called the branch protection zones” in Arborist News, August and October 2002. These articles are viewable online.
DANGEROUS DROP-CROTCHING
Locating nodes without laterals may seem sketchy at first, but consider the alternative. Reducing damaged branches back to the center of the tree can increase the danger of windthrow. In The Body Language of Trees, Mattheck and Breloer caution against removing more weight from the windward, storm-damaged side of the tree. “The crown shape and the wind then combine forces to lift the pruned side of the crown, so reducing the normal stress and indeed perhaps transforming it into tensile stresses (i.e., lift!). When this happens, the effective sliding surface between the root-ball and the ground is so severely reduced that the tree blows over far more easily.”
If drop-crotching exposes the remaining branches to more stress and strain, how is the tree safer than if heading cuts were made? The damping effect of limbs, for years thickened by torque, is altered while other branches thicken under the new load. The tree is vulnerable to disintegration while new reaction wood is formed in response to the new stresses. As Dr. Karl Niklas notes in the Tree Structure and Mechanics Proceedings, “When exposed by the removal of neighboring stems, previously sheltered and mechanically reliable body parts may deform or break even under wind conditions that are ‘normal’.”
Avoiding decay is another good reason to make nodal cuts just below the storm-caused wounds. Large wounds on trunks are unlikely to close before they start cracking and become what Schwarze, Engels and Mattheck refer to in Fungal Strategies of Wood Decay in Trees as “motorways for decay-causing fungi and bacteria racing into the heart of the tree.” Our strategy must be to minimize the infection courts we create. Retaining branches that Nature topped also avoids sun injury, defined by Shigo in ANTB Dictionary as “…when trees are suddenly exposed to direct sunlight…The bark cambium is affected and the outer bark plates are flattened”. These injuries are slow to seal because the tree’s interior bark is very thin, and the sun dries the tissue at the edge. Big pruning wounds and sun-damaged bark often never seal over; trees rot and die before their time.
Restore or remove? Where to make the cuts? It depends on:
• Species- good sprouters and good compartmentalizers
• Age and vigor of tree, which affects sprouting potential and wound closure
• Size of wound – smaller wounds = faster closure
• Available laterals or other obvious nodes with sound wood
• The need to retain a central leader and weight balance
THE TREE’S RESPONSE
Retaining stems and scaffolds by making heading cuts can minimize sprouting by leaving, much higher in the tree, a smaller surface from which they will arise. Cutting deeper to a lateral may result in the attempted formation of more leaders growing more vigorously from a larger wound. The greater the dose of pruning, the greater the shift in the auxin/cytokinin balance. A part of the cytokinin effect in relieving apical dominance when applied to the bud may be the stimulation of vascular development connecting the lateral with the main vascular system. In The Formation and Development of Dormant Buds in Sugar Maple, Church and Goodman observed that "Epicormic sprouting below the live crown increased as additional amounts of the woody crown were removed...”
When storms upset the balance between roots and canopy, the tree responds by sprouting to restore the balance. The more that is removed from the tree, the greater the imbalance and the reaction. At some point there will no longer be enough photosynthesis and the tree will decline. In The Practice of Silviculture, Smith notes that “Diameter growth may suffer if the live crown ratio…is reduced to 40 percent or less. Reduction in diameter growth slows wound closure.”
Aftercare is often very easy but it is important to communicate to all stakeholders that the restoration process requires additional work to complete. The dominant sprouts can be trained to become the new branches. On mature oaks, every three to five years seems about right. During each visit we prune out:
• Branch sections that have failed to sprout well.
• Branch sections with rapidly advancing decay.
• Sprouts that are crowded together and could develop included bark.
• Sprouts that are not forming a buttress.
• Suppressed sprouts that are declining or dead.
ON THEY GROW!
Some branches that were headed back in 1996 just got their second thinning. They now have three strongly attached, natural-looking branch ends to carry on the growth of the tree. What looked like ugly stubs at first grew into attractive, safe and symmetrical portions of our valuable tree canopy. Some observers initially object to the sight of reduced branches because they are reminded of topping cuts. It may be time for the anti-topping passion to cool a little, so we can consider selective heading cuts without worrying about them looking like topping cuts.
Canopy conservation is the ultimate reason for minimizing crown losses. When nature radically removes portions of our tree canopy, it’s up to the arborist to save what’s left. Trees are dynamic systems. The more of the tree we conserve, the more present and future benefits such as clean air and water we will conserve. As measured by American Forests’ CityGreen software, our urban tree canopy delivers high value that should not be removed without a very good reason. One mature willow oak can recycle over two hundred gallons of water per day. Selective heading cuts on damaged trees benefits the tree, the tree owner and the community.
So think about specifications that require enlarging the holes in damaged tree canopies and risking imbalance, decay, sunscald, and anchorage loss. A “compassionate conservative” approach calls for the arborist to aim for natural targets, so the tree owner conserves assets. For the cost of three pruning jobs, the expense of removal and replacement can be avoided. So if air masses collide and crush your canopy, you can guide your trees’ restoration by selectively heading for better form.
If you have any experiences related to selective heading cuts, I’d love to hear about them.
Guy Meilleur, Climbing and Consulting Arborist
GuyM@BetterTreeCare.com
PO Box 1287, Apex NC 27502
