Howdy,
To seal a wound the poor man's way, just liberally paint it with tar. The more professional way is to use a wound heal that the professional arborists or orchardists use. You can get info from your local county extension agent, if all else fails.
The object is to seal the wound to keep out bugs. If the wound is not deep, weaking of the tree is not a factor. If the crack occured because the center of the tree has become a bug farm, you have a much deeper problem (pardon the pun). The only solution then is the professional, drilling and treating, if it is determined that the tree is not an irrevolcable hazard. (And these days, they generally seem to prefer to take out the tree).
Nature's way is to make the tree grow faster in areas where the wood grain has been strained. The wood then becomes even stronger and harder, called timber bind. This assumes a young vigorous tree, and assumes that the bugs have not gotten to it. I have seen these things get so hard, that the mill-saw will be going along, come to it, and then turn and go right out the side of the log! The roots react much the same way. In areas where the root wad has started to work loose, the roots then grow faster and into a larger area to strengthen the tree in the direction against the prevailing winds. If you build a house and leave only a few remaining trees out of a stand, guess what? Next wind they fall on the house, and everyone cusses the trees. It takes years for things to adapt.
Walt Galer