Oaks are subject to many kinds of wounds and injuries, high winds and heavy loads, among other factors, result in branches or whole stems breaking away from the main trunk. Sometimes two stems grow together which encapsulates areas of bark which creates vulnerable weaknesses where not enough holding wood is established to deal with the forces at play and eventually the weight overcomes the strength and failure ensues. While some trees may die of this sort of wound many heal over and these wounds may become nesting habitat for many critters.
