In Spirit Island, can the Defend value gained from a slow power be kept until the next major round to block Ravage?

In Spirit Island, during the Slow Phase: I played a slow card that provides "Defend 4" to a certain land. At this point, this round's Invader Ravage has already been resolved before the Fast Phase. Can this Defend 4 persist across rounds and be used to block the next round's Invader Ravage?