The ~60 year old mulberry tree in my back yard has developed two large
dead limbs. It's clear the tree will have to come out eventually, but
it still yields useful shade, so I'd like to keep it as long as possible.

Simply cutting off the limbs will badly unbalance the tree and so long
as they're not rotten they'll still provide support to the branches
cabled together. Tapping on the buttress roots and the trunks suggests
the is mostly solid, with a decayed core.

Are there any accepted tests for stability (pulling on lines to the
crown, or pushing on jacks applied to the trunk, for example) that
can be used to gauge the stability of the tree as a whole? Obviously,
if a tug on the crown tips the base of the trunk, it has to come out
now. If a pull or push on the upper part of the tree doesn't disturb
the root crown there's some hope of another year or two of shade.

A set of photos is at
http://www.zefox.net/~bp/mulberry/
The images can be laid out something like

westlimb eastlimb
crown
trunks
base
to get an overall view if you're curious.

I had the cables installed in 2009 and the tree grew vigorously until
the middle of this summer. Even now, the surviving limbs are well-leafed
and seem healthy, thus my desire to save what I can as long as I can.

Thanks for reading

bob prohaska