Thanks! Which of these would you recommend? Should it be perfectly perpendicular to the crack? Should I do a standard back cut coming straight in opposite the notch or come in at an angle as to make a hinge that would be more triangle shaped than rectangle shaped if that makes sense?
Let's get orientated here with some explanations. The tension is at 180° opposite the lean. The crack looks to be at 90° (which makes sense) that's the direction it is prone to splitting even if it didn't have a split
So by moving the undercut off the lean then the tension is where the top of hinge is now.
When cutting the tree the top of the hinge is now the high side. Opposite the direction of fall is the safe side. It is the only spot you should be working from. So with this there is no need for a triangle back cut or a bore cut.
You have a very high chance of getting the saw pinched in the bore cut or finishing out the cut.
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My concern is the condition of the roots behind the split? Looks like the tree is dead from looking at the lifting bark at the front
You get oxegen exchange from the open crack which invites rot I wouldn't work from the tension back side nor does it make working under the front a great option Don't even think about the pond side.
If you go 90° off the lean (as it looks to be what you pencilled in in your second illustration) you only have one safe side that you can work from with this unstable tree.
The whole tree will have to be cut with your tip so you want it to self feed. Set the undercut too far and you are doing a blind undercut through pinch points reaching in from the safe side unless you crawl under the front.
Also if you move the undercut too far to the side then you put to much tension on the top of hinge and sometimes tear out the back of the tree or you lose the natural swing and break the holding wood. Very well may happen anway with Ash. Probably as soon as it starts going it will rip off like a bandage to the lean direction. Which is fine.
You can do that as an option anyway once you cut the back cut then just thin the top some more and let it peel off with the lean.
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Undercut/Cut height?
Pros 'N' cons
A danger tree is usually at a comfortable waist height. Often you can get above the rot as well you are a smaller target standing erect and looking up,,also you are in the best position to exit
In this case there is nothing overhead unless the back roots pull out and go into a barber chair.
Another point concerning this tree is the compession is greatest at the bend. (Pinch concern)
-Fibires are also strongest at the bottom if rot is not present
Generally speaking, if you do get pinched or need to redirect the tree then you have room to do that without working too high.
- if you need to slice a tree off the stump then that is much safer lower to the ground.
Things for us all to consider.
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I would take a knee and get below the bend
Go at least greater than 45° to the pond side by reaching under. The more you can offset the U/C then the less you are taking out of the bottom (pinch point) 45 will mitigate the barber chair potential.
Slowly take the low side of the undercut out up to the split
Do the flat cut and hack out the angle cut as you inch in or inch in by alternating two saw kerfs wide. Just a chicken §hit little U/C is good enough. If it starts pinching instantly then chop the bottom in with an axe and clean it up with the saw
Now cut the top of the undercut in with the saw slowly. The lower part of the back split section may be compressed also. Take your time.
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Got the undercut in?
It's the hard part sometimes.
You can get pinched easy in the back cut if you get too excited The bottom of the tree and maybe the bottom of the split are your pinch points here
If it starts to lean outwards to the pond and then you will even get pinched above your undercut if you tip is sticking out . Don't over commit too far to the edge or the split or the bottom
Do it all with the tip by starting with the outer top closest to where you should be standing (safe side) Bring top section down close to the split go deeper and bring some more down.
Cut a bit of the outside split down with the tip if it seems good.
You are bringing the back cut in on an angle then bring the middle down then outside bottom should be ready to open up some.
You should clear out that snow and do a root inspection to see what you are dealing with.
You are going to take the small tree out in the water first and work under this tree???
I wouldn't suggest doing that.
I will also likely stop a barber chair if the back section roots poped out. The most dangerous barber chairs are when the tree is standing up a lot more.
If you and the tree are still standing then maybe we could modify that plan a bit.