backup a tree?

If you are building a multi pitch anchor or even a top rope anchor to a tree and back it up with another tree, gear, or anything else, if the tree is sizable is it really a backup? If the tree uproots surely the falling tree will break the cord between the other gear. If the tree uproots and does not get pulled off whatever belay ledge you are on, then it could still be anchoring you and perhaps hasn't "failed"..

So it almost seems like if you going to anchor off any object large enough to break the rest should it fall, then only anchor off that, else choose two lighter weight objects or gear. What would be a case where the large object should be paired up?

I thought about that, but I assumed if you are anchoring to one object you would be using a doubled cordelette or some such redundant cordage and biners.

But your point is valid, however backing up the cord on the tree with another anchored object still poses the risk of the tree falling. And if the tree isn't going to fall then obviously no backup is necessary, given you backup the tree cord and such like you pointed out...

I am very surprised I haven't seen this mentioned in any books and especially since I see most books recommend two trees for top rope anchors.

Am I way off base in the logic?

Find a book on rescue rigging and read about "back tensioning" a tree anchor. In layman's terms, trees don't explosively uproot. They get pulled over by tension, and tying the tree back to another anchor e.g. a second BF tree, will stop that.

I back up the anchor or toprope with double cords or slings, and double biners to the same massive unmovable tree. I'f talking over a foot in diameter. If it decided to 'uproot' or tip over, just its massive weight alone would be enough to still hold the climber I'd say. I think one would feel the sag and give as the tree gave way and you could lower off before it got dragged over the edge. This is why I always pick massive boulders or trees for anchors.

John Marsella wrote:What if you consider not the tree itself failing/uprooting, but the sling or cord breaking, or a carabiner unclipping or a bomber knot untying itself, etc?

^^^^^^^^^^^^^^^^^^^^ +1
Redundancy isn't just about the objects you are anchored to. Especially when building a top rope anchor that you're going to walk away from. Any number of things can go wrong including tourists F'in with your rig.