I have a large (75 feet tall) old silver maple with a bout a 4 foot diameter base which splits into three 1-2 foot limbs. Several large (6" to 1') braches have broken off in the last few years which are hollow in the center. Any ideas as to why this occurred and how to treat it would be appreciated. Also the tree is close to my house and I'm considering having it lightened just in case.

Reply to post by bill wagers, on May 31, 2000 at 13:17:53:

Silver maple is a fairly brittle tree and often fails to "compartmentalize" against the advance of decay into the wood.
Hollow limbs have lost much of their strength, and thinning to lighten the load can help reduce the risk of breakage, if the limbs don't need to be removed completely.
As with other trees, proper pruning cuts can help to minimize the wounding and subsequent decay of the wood.
Smaller cuts/thinning cuts are better than large cuts or heading cuts.
And of course it is important to support the needs of the tree for water and good soil/root conditions.
It may be better to spread the pruning out in time, rather than do it all at once, as long as the risk breakage is adequately addressed.
That way the tree has more food producing reserves with which to fuel the growth of "wound wood".
Large old trees are especially sensitive to excessive thinning and branch removal.