Treedweller wrote:

I disagree with the suggestion to prune the top severely. Leaves make
energy, and you tree will need energy to recover from the stress of
root loss. Pruning out live tissue will reduce this energy production
while requiring energy expenditures to recover from the pruning.
Build the well and then, if branches die back over time, prune them
out later..

But leaves also use water. As roots die, the top usually dies back to
what the roots can support. So it really doesn't matter if you prune
the top, it just is a choice of pruning out live material or dead
material. But if you wait to prune out dead material, more of the tree
will die because energy will have been wasted on branches that
eventually died. The energy that is produced by the leaves is stored in
the roots. If the roots are dying, then they won't store as much energy.

I girdled 3 walnut trees that were killing my rhododendrons. I was
shocked that there was enough energy stored in the roots to keep the
trees alive for 3 years. Then they died the next spring. So,in that
case, I needed more top to kill the roots. The top I had took 3 years
and I hadn't pruned these trees at all.
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