More about refugia from the book Refugia Faith by Debra  Rienstra:

When Mount Saint Helens erupted in May of 1980, it lost 1,300 feet of elevation and gained a new mile-and-a-half-wide crater. The debris and ashfall from the volcanic blast devastated the mountain and its surroundings for miles, crushing, burning, killing, and coating everything in hot ash. Everyone assumed life could return to this apocalyptic death zone only very slowly, maybe over several human lifetimes.

Instead, forty years later, the mountainsides are covered with lush grasses, prairie lupines, alders. Critters scamper, streams flow. It will take a few hundred more years for the vegetation to return to something like old-growth forest. But still. Why did life come back with such vigor, and so quickly? As Kathleen Dean Moore explains in her book Great Tide Rising, “What scientists know now, but didn’t understand then, is that when the mountain blasted ash and rock across the landscape, the devastation passed over some small places hidden in the lee of rocks and trees. Here, a bed of moss and deer fern under a rotting log. There, under a boulder, a patch of pearly everlasting and the tunnel to a vole’s musty nest.” These little pockets of safety are called refugia. They are tiny coverts where plants and creatures hide from destruction, hidden shelters where life persists and out of which new life emerges.