Hollow Tree: Remove or Prune?

[treeseer]

March 17, 2013 Nash Square Park in Raleigh, NC. A willow oak has a removal notice. At the main fork 25’ up is a tear-out wound where a branch was pulled out all the way to the core. The entire branch tore off at the trunk due to overextension. It was the branch growing to the south and to the open. There is also minor damage lower on the trunk from the branch falling. Otherwise the trunk shows exceptional structure with burls forming at points of stress. It has a lower center of gravity and more interior growth than many old willow oaks.

The press release said that “While we did not see the termites noted in the Moore Square tree, we observed that the broken or removed limbs in both trees exposed internal decay. It seems apparent that pruning or reducing the crown of these trees would not mitigate the failure potential the trees present, and the cost and appearance of such pruning efforts would be negative aesthetically and economically. The resistograph readings confirm the weakened structural condition of these trees.”pruning the tree enough to make the risk acceptable would not be economically or aesthetically acceptable. (However, it appears that 2 climbers could have it done in a short day, and the tree would look quite attractive.)

 

There was no link to the report and no other technical detail was given aside from the fact that they used a resistograph.

There is a substantial amount of living wood at the border of the tearout wound. Squirrels have taken up residence, if they weren't there before. The tearout is at the major junction, so the question becomes what part of the tree is most subject to failure and what risk will remain after pruning or other mitigation.

 

The top of the tree is dominant, slightly taller than the adjacent Willow Oaks, one to the south west and the other to the northeast. The leverage on the wound coming from the tree’s height may be the highest risk factor. Reduce height and spread and density of crown, removing 6-8’ branches with cuts less than 2” cuts, <25% of present crown volume.

 

At the same level as the wound are two other limbs. The one growing to the east is overextend and presses against the willow oak to the northeast. It has long horizontal branches that could be reduced, and the upward growing portion could come back 8 feet with a less than 2 inch cut. The lowest horizontal branch could be removed all the way. The northern horizontal branch that over tops the northeast willow oak could be reduced 50%, pruning to upright laterals.

The second limb coming off that main junction is a double land that forks out at 4 feet. The upper of these two branches goes out 6 feet and then puts out two laterals, then goes another 6 feet and sends out a substantial 4 inch lateral that grows straight to the south. This limb could be reduced at that point, because after that it crowds the branch below. The lower limb is larger than the upper, 16 inches compared to 12.

The lower limb goes out 10 feet from the union, then forks. The Western branch has braided reaction would a twisted pattern of xylem formation, and a sign of strength. It also has four very strong uprights, so that cut can be beyond the fourth, at a narrowing of diameter 2 feet before a major fork. This limb is over extended beyond this point, and interferes with a maple below it. This suppression is forcing the maple to grow crooked.

 

The branch that goes to the North has an upright form. The lowest branch goes horizontally into the adjacent Willow oak to the northeast. Right at that union is a very large upright. This is a natural pruning target. The rest of the limb is the tallest thing around, and could be reduced by 6 foot sections perhaps 10 to 20% of buds. Of the two lowest branches, one is growing to the south. It could be reduced by 10 feet, back to a lateral that grows to the Northeast.

The other lowest branch that grows to the north interferes with the same maple, so it should come back to a strong lateral that is a 4" cut, taking off a 20 foot piece. This is all the pruning needed for now. Prognosis is reasonable stability for at least 5 years. Recommend inspection after major storms and every 9 months. Anticipated re-pruning cycle is every 5 years.

 

Buttress roots look normal; the flare is continuous. The trunk is 2 feet from the sidewalk but no sign of damage or decay at the base.

These three consecutive willow oaks that have interlocking crowns and are the tallest things around. The proposed removal of the middle tree would turn the adjacent trees into “edge trees”, greatly increasing their exposure to storms and their risk of failure. This effect should be seriously considered before deciding on removal.

 

The oak to the southwest is much larger in diameter and spread. It has a codominant form, splitting off 12 feet from the ground. The change in the movement in the tree during a storm would be substantial. The tree has two cables high in the crown. One supports that major co-dominant, and the other also supports a sprawling side branch. Though that fork does not look too narrow or codominant, the side branch is overextended. It would be newly exposed to winds from the north and east, which is the direction that many of our hurricanes and ice storms have come from. The long side branches would move more and so would the major limbs that are held up now by the cables. The root system overlaps the sidewalk and its entire area is constricted by Davie Street.

 

The Willow Oak to the northeast would be subjected to the full brunt of the wind coming from the south or west. Its long limbs would move a great deal more. The tree has good angles in its forks, but it is in the center of the park and would be the tallest thing remaining It has had three large branches from the westward trunk removed recently. Scar tissue is developing symmetrically, despite a rip on one. They are all within a 12 foot stretch of the same sap stream, a major stressor as resources are needed to fight on three fronts at once.

[David Humphries]

From your reports perspective I would say the removal appears excessive.

 

I would imagine a tree like this with the type of history you describe would/could be retained with similar (or slightly greater) reduction where I work.

Of course that would be coupled with annual inspection of the condition.

 

How high up on their tree strategy is the ecology of this urban park?

 

Do you happen to know (apart from the extension) what the weather conditions were at time of failure?

 

Why the cable at the base?

 

 

 

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[treeseer]

"From your reports perspective I would say the removal appears excessive.

 

The perspective was as objective as I could make it.

 

"I would imagine a tree like this with the type of history you describe would/could be retained with similar (or slightly greater) reduction where I work.

 

How much greater?

 

"Of course that would be coupled with annual inspection of the condition.

 

9 months works biologically and politically; gets it viewed in all seasons, and communicates a higher concern.

 

"How high up on their tree strategy is the ecology of this urban park?

 

Ecosystem services aka air and water values that can get a $ sign can be raised with some success here. Saproxylics aka bugs and crud, not so much. I'll ask some of the wildlife chaps at the U but I would expect the same blank stares I am met with when I raise that value elsewhere.

Bear in mind the park is within 3 blocks of city hall, county courthouse, and state capitol. When lawyers stride beneath, "target rating" goes off the charts.

 

"Do you happen to know (apart from the extension) what the weather conditions were at time of failure?

 

Good question; I'll try to find out. The other Q phellos had 4--4!! separate limb tearouts, and still the light bulb did not go on. Like wow man maybe we could prune those limbs before any more crash down; wuddya say dood?? Branch reduction is anathema; we are frozen by twisted Shigovian anti-topping dogma imo.

 

"Why the cable at the base?

 

For the lights installed up the trunk and out the scaffolds. Purpose unclear; perhaps the homeless vagrants petitioned for night lights.

[Amelanchier]

When lawyers stride beneath, "target rating" goes off the charts.

 

So true.