A friend at work has a maple tree that had some amateur pruning done on it. The limb was flush cut, and now has a cavity in it that fills with water. The cavity is probably 6 inches deep, and the tree about 24" in diameter. He is wondering whether he should fill the cavity. Another guy here starting to talk about cement and I just shook my head. What do you guys think? I'll see if I can get some pics. Here is a crude drawing of what the cavity is shaped like.