The mountain birch forest and the autumnal moth

The mountain birch is a tree perfectly adapted to the cold and wintry mountain climate prevalent in this last forest before the tree line. For the mountain animals such as hare, grouse and other small rodents, the forest provides shelter and serves as a valuable source of food. In winter, the forest floor provides edible plant debris and when spring arrives, fresh buds contain valuable nutrition. The buds hold a substance that keeps them from freezing; sudden cold spells are weathered without damage to the trees' budding process. This means that mountain birch foliage develops early in the summer season. The autumnal moth is an insect typical to this region. About every ten years or so the forest is infested with this small moth. Its green larvae can at times decimate the entire forest's foliage during summer. After a couple of years, the number of autumnal moths declines again, and the mountain birch get a decade of peace and quiet before the next mass attack. Such fluctuations are common in nature. We are not always sure what causes them. Maybe one day there will not be enough food for the autumnal moths after they have eaten all the leaves? Many animals eat autumnal moths; maybe that will affect their population in a subsequent year? Perhaps the mountain birch has developed toxins to ward off the periodically occurring plague of the autumnal moths?