repair hollow area

I removed a 10 inch limb 9 years ago from a 40 inch diameter silver maple, taking care not to damage the branch collar. The cut seems to closing in and healing okay, there is only about a 4 inch hole left and will be closed over in the next year. The problem is that over the last few years, there is a hollow area developing behind the cut, it's about 10 inches back and 18 inches down behind the cut.
I'm concerned the hollow area will weaken the tree or allow disease, if it hasnt already. The rest of the tree seems fine. I've seen trees where folks have filled in hollow areas with concrete. Is there something that should be done to fill in this hollow area, or should it be left alone.
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Kevin wrote:

Leave it alone.
--

Travis in Shoreline (just North of Seattle) Washington
USDA Zone 8
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Travis Wrote:

I'm with Travis. Leave it alone. New
-- Newt
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I am with Travis and Newt. Leave it alone.
--
Mike LaMana, MS, CTE
NJDEP Approved Forester
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thanks for the info --
I'm new to tree physiology -- what becomes of the hollow area ? once the cut closes over does the hollow area fill itself in?
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Kevin Wrote:

Sometimes yes and sometimes no. Take a look here at picture #62. http://tinyurl.com/9swcn
You might also find this interesting. http://tinyurl.com/ddmtr
New
-- Newt
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