I don't agree with some of what Ken says. The tree is significantly damaged in a way that rot is likely. Rot can significantly weaken the trunk and create a tree that is much more likely to fail. As the tree ages and grows, the rot is likely to spread and the tree may be more likely to collapse, especially in windy conditions. Whether the tree will be able to successfully encapsulate and block off the rot is an unknown, so a variety of outcomes is possible. It appears that the tree was planted incorrectly, and this has likely contributed to the problem your tree now faces. The exact, and complete, cause may be unknowable, but at least some of the problem (improper planting) is fairly clear. Where I do agree with Ken, is that there isn't much you can do, at this point, to "fix" the situation. Your choices at this point are to either wait and see and enjoy the tree while you can, or, cut it down and replace it (not necessarily in that order - you could plant a replacement and let it get a start before removing the existing tree). If the tree poses a danger to your home or safety, I would consider keeping an eye on it and removing it before it's likely to cause a problem.

I found a conversation that someone detailed a similar issue http://forums2.gardenweb.com/forums/load/trees/msg0117425514243.html

Yes there are ways to save it and the "rodding" is one solution ....It looks to me as if it will not split since it's so far down the trunk I might have a differnt opinion if it were higher up...but i wouldn't guarantee it!! Silver maples are not that soft( even though they are considered soft maples and REALLY fast growers) and I rarely see limbs down after storms of silver maples but they are NOT sugar maple hardness. If it were mine and I wanted to keep it( silver maples are not "great trees" but if it's sentimental that's NOT important) I'd just have it properly trimmed and leave it but keep your insurance policy up to date and consider having it rodded as the other postie said.... David

I'm not sure there is a general rule, but the presence of fruiting bodies (mushrooms or bracket fungi) protruding from tree trunks is indicative of internal decay. These fungi are not killing the tree per se, but are simply opportunists setting up shop for an easy meal. Ranger, with one exception-that being wounds on oak trees in regions experiencing oak wilt disease, and which for whatever reason have had pruning cuts or other wounds happen to them during the growing season, the use of so-called tree paint, tree wound "sealant" etc. has been long discredited. Simply put, trees have had to manage various wounding processes since long before us hairless monkeys showed up on the scene, and they do this by the C.O.D.I.T. process, which stands for compartmentalization of decay in trees. That is, they do their own walling off of wounds when they can, and when they can't, there is nothing we can add to make things better. Nothing. Now if Spruceman still hung out on this forum, he might disagree with me in that he developed his own formulation of "liquid copper fungicide" that he used even on some very large wounds -at the time of making these wounds (pruning cuts), but that's a specialized case and all that notwithstanding, there is simply no evidence that applying tars, paints, orange shellac (lol!) or any other material does one bit of good. Incidentally, the reason trees get so much larger than other living organisms is this very C.O.D.I.T. process. It enables them to go on living after significant injury, to wall off these injuries, and not have them end up leading to whole-plant failure. Grass, herbs, flowers, etc. can't do this. They have essentially no means to cope with injury, at leas tin terms of retaining permanent structures. And this process is not "healing". In healing...let's say I cut my finger....new cells will replace the old, damaged ones. Trees don't replace cells like that, they wall off-both chemically and physically-the damage, so that it doesn't go on to spread throughout the plant. If one were to somehow wound the trunk of a young tree, but not so badly that the tree was destroyed, that wound will remain with the tree for its entire life (and beyond-you can see this stuff in lumber), and as the tree puts on girth, the old wound ends up buried deep inside. But it's still there.