# Hollow tree technique



## whatsup (Jun 2, 2006)

I have lurked on this forum for some time now and am grateful for the wealth of information and techniques its members willingly provide.

I'm a reasonably experienced amateur feller with a full compliment of equipment: Husky 55 saw, Echo pole saw, several 20-40' 3/8" high test chains, 1/4" airline cables, come-alongs, pulleys, full safety equipment and a track-loader. I don't do any climbing and will use the crawler to make challenging situations less-so whenever possible.

I had occasion last weekend to take down a tree that was more challenging than most I attempt. I got it down successfully,... not perfectly, but I think safely.

My hope, in making this post, is that some of the more experienced folks will review the precautions and technique I used and point out things I may have overlooked or provide other suggestions for improvement.

I wish now that I had taken some pictures of the setup... but a description will have to suffice. I do have some after-the-fact pictures showing the location and the stump here.

The situation was that I had a 16-18" diameter, 90-100' tall tree, located about four feet from the house, with a partially hollowed out base that has had significant carpenter ant activity for the last several years despite repeated treatments by an exterminator.

The tree's close proximity to the house made it easy to secure a 150' 1/4" airline pull cable about 25' up in the tree just over a substantial branch that prevented the cable from slipping downward when tightened with a come-along.

The tree had a slight lean away from the house in the direction I wanted it to fall. I cleared out a nearby 6" diameter tree that I wanted removed anyway and was in the intended direction of the fall.

Probing the hole in the tree with a stick revealed the hollowed out section was at least four feet in height. I opted to cut the tree higher than normal in the hope that there would be more wood there and so I would be in a better position to make a rapid exit if necessary.

To reduce the chance of a barber chair and prevent the trunk from moving towards my primary exit path I wrapped one of the 3/8" high test chains around the trunk several times, about a foot above where I was planning to cut and secured it the same way to a nearby 20"+ tree.

I carefully cut the notch intending that it be about 25% of the width of the tree hoping that would leave more wood for the hinge. That cut barely exposed some of the hollowed out center. I then cut the backcut. I reached a point where I began to be concerned about how much hinge I had left, despite the fact that the tree wasn't moving, so I stopped cutting and decided to use a second 200' cable/come-along to pull the tree over.

The tree was moving slightly and it was evident it was just a matter of time until it would come down. It fell, partially, before I was finished securing the second chain/come-along to a tree. When it fell, the right hinge broke and the tree fell about 20' to the left of my intended path causing it to get hung up in another tree. (Remember that I'm not closer than 200' or so to the tree at this point). I finished hooking up the 2nd cable, and within a couple minutes was able to easily pull the tree the rest of the way down.

You can see after-the-fact pictures of the cuts in the above link. My assessment is that I should have made the notch shallower (though I'm not sure how to know in advance how much wood you have to work with... drill it?) and that my backcut was a little sloppy resulting in a thinner right side hinge.

Besides that, I think this was done reasonably safely. I'd be interested in other's assessments... in particular with regard to safety things I might have overlooked and suggestions as to how this might have been done better.

Thanks!

- Mark


----------



## Ekka (Jun 2, 2006)

You did alright.

That was a pretty thick hinge you left.

Also, that was plenty of meat as far as the hollow is concerned. You could have gone deeper with your notch, dont panic just coz it's hollow.

Backing up with wedges is good practice too, it also helps take weight of the hinge in the early stages of the fall.

I've had large trees with not only hollows but half the tree missing (an opening). I have notched up the rams horn on one side only a few inches deep, gone over to the other side and done the same using good eye sight to line them up .... then done the back cut.

Good job, did you know that a 100mm dia pipe with a wall thickness of 10mm is exactly as strong as an 80mm solid rod? Did you know that it's commonly accepted that trees up to 70% hollow are relatively safe enough?


----------



## smokechase II (Jun 2, 2006)

*hollow not always bad*

I read somewhere here on arborsite where a guy by the name of Tim Ard was referenced and he was reported to have said something to the effect of "hollow trees are not a big deal, treat them like a regular and consider the hollow a face center bore."
That is if the face and hollow connect, as in your cut. The photo below shows where they didn't meet.
I think you'll find that many hollow trees are not that big a deal, provided they still have a reasonable amount of wood, and that they not only can be treated like a regular tree, but they actually can be safer. This because they are less likely to barber chair with the continuity of the hinge broken up by a face center bore.
This is important on your tree with you pulling it over with maybe more force than ideal. That force up high could be a sponsor of a barber chair. Except that with the face bore it is not that much of a statistical risk.

An exception to this regular tree thing is where there is too little wood left on a rotten/burned/hollow tree. About a month ago I started a thread on that titled something like "Can this tree be fell safely?"

I'd suggest that with a *gently* tapped in 'insurance wedge' and the lean being favorable and the up high rigging you could have found the tree not yet ready and then cut a skosh more of the back-cut. Rather than pull it over.

Your cuts look fine. Photos could use some better lighting.
I'd say don't make that face shallower. I think it's fine for depth. Remember that a deeper face, when working with a reasonable lean, is a superior release in that it can allow the tree to go over with less force needed from a rope pull or wedges or back-cut depth etc.


----------



## whatsup (Jun 2, 2006)

Thanks for the responses! I'm glad I asked... my inclination would have been to take a smaller notch next time, which sounds like the wrong thing to do. I was surprised at how strong the log was despite being hollowed out. I had expected it to crack/collapse when I pulled against the top of the cut off portion with the backhoe. It didn't and I was able to apply enough force to rip the (slightly loosened) roots out of the ground.

I suspect that I don't use wedges enough/properly. I pretty much don't use them unless I'm concerned about the possibility of the tree sitting back on the bar. I was taught to be deliberate about finishing things up once you've made the tree unstable. Stopping the cut to grab the wedge and sledge seems like it'd be taking my attention away from where it ought to be. I'm certainly open to suggestions though.

Smokechase, I saw your "Can this tree be felled safely" thread. My answer was "Sure"... by a guy in a big piece of equipment with a real strong ROPS. I was fascinated seeing how that guy approached it though.

- Mark


----------



## smokechase II (Jun 3, 2006)

*hollow tree strength*

Whatsup:
Goto http://www.arboristsite.com/showthread.php?t=25872&page=5
(The post big tree photo thread) and look over the photos in post # 69.

First photo shows how big the tree was.
Fourth photo shows how hollow it was.

Now the tree fell on its own, but it went over by pulling out roots, not stem failure. 

You wouldn't want to bank on that, but it is kinda impressive.


----------



## Freakingstang (Jun 3, 2006)

smokechase II said:


> Whatsup:
> Goto http://www.arboristsite.com/showthread.php?t=25872&page=5
> (The post big tree photo thread) and look over the photos in post # 69.
> 
> ...




I missed that the first time around. That is pretty impressive


----------



## Ekka (Jun 3, 2006)

Nice pics, that's the big question isn't it, how good are those roots holding?

The amount of times a customer wants a guarantee the tree wont blow over, and how many are cut down in the fear that they *might*


----------



## whatsup (Jun 3, 2006)

Impressive indeed!

In a nutshell then, it seems it really isn't necessary to modify one's technique much from normal to cut live hollowed out trees...

I make it a habit to wrap a heavy chain around the tree several times, above where I'm cutting, whenever I'm concerned about the possibility of a split/barber chair, though I've never seen/heard of a case where a wrapped tree has actually split. Still a wise precaution?

- Mark


----------



## smokechase II (Jun 3, 2006)

*still a concern*

I'm not an arborist. But I'd think most would recommend removal of that big guy because of its hollow condition. 
Yet that wasn't what brought it down.

If there is no root rot or fruiting bodies apparent. No lifting visible.
I haven't a clue as to how you guys could have predicted the root thing.

Whatsup:
We'll let Ekka dissect me on this.
I was surprised on the 100mm with a 10 mm 'rind' being as strong as an 80mm rod.
I think the strength he is referring to is force from a right angle, like putting it over a knee. If that is the case: A hollow pipe is only as strong as its weakest point. Very few trees seem to have a uniform rind from my experience. So having your size up be a bit longer on species you know to usually have a heart rot might be a wise move. 

Secondly, if the weakest link thought process is correct, think about your cuts creating that weak link. Then you're at the base of a tree when something could go wrong.

I don't think the Ekka's strength analysis is based on a vertical down force causing failure from some sort of compaction event. Although he could correct me on that. In any case, I think you need to consider a collapse of the tree vertically or an unpredicted early fell. 
If it feels wrong, step away and don't do it. 
If it feels OK, but is still at least a challenge, have multiple escape routes set up on the ground and in your mind.

Now, having said that. Without having seen the tree in your photos. It looks pretty solid and I suspect it was just fine. That appears to be a very decent amount of good wood to work with. 

Hollow trees are of course more prone to start over early and pinch your bar. So when you're trying for a reasonably deep face, keep that bar floating, don't be dogged in, and be ready to pull it out quickly.

Consider the type of rot that caused the hollow. At stump height, most rots come from below and usually shrink with altitude. One thought may be to move up the tree a foot or so and get better and more wood to work with.
On that "Can you fall this tree safely?" thread, note how that skilled cutter did move up a bit for that reason.

Think of your evaluation/size up of the tree as an on-going process. We can't do a CT scan on the tree base to get a precise reading of the interior. So if there isn't an opening, we bang a falling axe or do a vertical bore or two to check for rot. But be ready to still add to your evaluation with the face cut and possibly a face center bore revealing more. The face center bore cut is flat and can give you more info than a vertical test bore.
Granted, you generally can't change much, if anything at all, about your face and direction of fell at this point. But you can change your back-cut technique.

I would suggest that the boring back-cut techniques are not desireable on trees with substantial hollows. 

Another thread could be devoted to hollow sections above the ground. These are generally guessed at based on the number of conks (Fruiting bodies from some sort of rot going on inside). In my world, one Indian Paint fungus conk generally means the rot inside is going to be OK, two+ conks within 10 feet can mean imminent failure is possible, especially with the tree starting over in the fell. These guys can jacknife.


----------



## BlueRidgeMark (Jun 3, 2006)

smokechase II said:


> Hollow trees are of course more prone to start over early and pinch your bar. So when you're trying for a reasonably deep face, keep that bar floating, don't be dogged in, and be ready to pull it out quickly.




Floating? Short, quick cuts? As opposed to burying the bar and going all the way in one long cut?


----------



## smokechaser (Jun 3, 2006)

Remember: One half the volume of a board foot is in the outer 1/3 diameter of a tree. Hollow trees can be cut just like a solid one if the outer wood left is quality.


----------



## smokechase II (Jun 3, 2006)

*floating*

Have the bar moving back and forth somewhat slowly while cutting. This to allow the cutter to feel if it is starting to pinch.
If it even starts to feel like the movement is restricted. Remove it briskly and evaluate. I think you can feel any closing of the kerf, on smaller and mid sized timber, quicker than see the kerf close. Larger timber, with possibly a longer distance from bar to start of cut, I think you can either see or feel about the same.


----------



## smokechase II (Jun 3, 2006)

*volume strength*

I think Smokechaser meant to say, "One-half the volume is in the outer 1/3 of a tree."

That also backs the Ekka thoughts.
More strength by a surprising percentage of material. Strength in more than just design, but also by mass.

I've been taught by a bbzzillion people not to mess with the holding wood at the corners. (Exception; barber chair avoidance).
In a hollow tree or one where a face bore has been utilized, that is probably even more significant. The focus of those who have taught me has been strongly that you can cut the hinge wood in the center, in many instances, but don't mess with the outer hinge.

I don't want to stop you from binding if you feel it’s necessary. But I would suggest that on a hollow tree where the rot meets the face, that probably your greatest risk of a barber chair is from applying too much pulling force up high.

I've never seen a stump or heard a story that I can recall where a hollow tree barber chaired.
So, to hopefully stop myself from spouting ignorance, I think I'll start a new thread asking that question.


----------

