As frosts touch the earth and the reds and yellows of fall creep down the mountainsides, oaks, hickories, beeches, and other trees shed their fruits. Many animals will join in the harvest of this fruit, but several, especially bear, deer, wild boar, gray squirrel, chipmunk, turkey, and ruffed grouse, are particularly dependent on this mast, as it is called, for their autumn and winter welfare. With the chestnut gone these animals must rely mostly on acorns. Oaks, unlike the chestnut, do not produce consistently, but fruit abundantly some years and fail in others. In the poor years, when competition for mast is keen, the effects are starvation, wandering, and mass migrations. The appearance and multiplication of European wild boars in the park have only added to the pressure on the native animal species. Acorn shortages bring into sharp focus the life styles and survival systems of the mast-dependent animals. From among these the wild boar emerges as an ecological villain, although we should perhaps cast man, who introduced the boar here, in that role. The loss of the chestnut illustrates how a change in one element can irrevocably alter an entire ecosystem. As the chestnuts of the Smokies died, their place was taken primarily by chestnut oak, northern red oak, red maple, hemlock, and silverbell. The annual mast crop suffered from this change in two ways. First, only about half of the replacement trees were mast-bearing oaks. Second, oaks are not dependable mast-bearers. Mast failures seem to result mainly from spring freezes during the pollinating and fertilization of oak flowers. Chestnuts bloomed in the first two weeks of June when the danger of frost was slight and so they bore well nearly every year. This difference in flowering time has had reverberations throughout the animal world within these mountains. By looking into the life histories and population dynamics of some of the acorn eaters we may get some idea of the nature and extent of those reverberations.