Can disturbance create refugia from herbivores: an example with hemlock regeneration on treefall mounds

We tested the hypothesis that tip-up mounds of exhumed roots and soil created by treefalls provide a better site for the survival and growth of hemlock (Tsuga canadensis L.) than the areas immediately surrounding the mounds. The xeric and unstable conditions of tip-up mounds may impede the establishment and growth of hemlock relative to surrounding areas. The size and steep walls of tip-up mounds, however, may deter deer from accessing the tops of mounds, thereby allowing hemlocks to escape browsing. Nine years after a catastrophic blowdown in the Allegheny National Forest in northwestern Pennsylvania, we found that hemlocks on the mounds were larger, more abundant, and browsed less often than hemlocks found off of the mounds. The increased growth and survival of hemlocks on tip-up mounds was likely caused by decreased browsing pressure.