Differential responses of tree species to a severe ice storm and their implications to forest composition in the southeast United States

The unique terrain, geography, and climate patterns of the eastern United States encourage periodic occurrences of catastrophic ice storms capable of large-scale damage or destruction of forests. However, the pervasive and persistent effects of these glaze events on regional forest distribution and composition have rarely been studied. In the southeastern US, ice storm frequency and intensity increase with increasing latitude and along the complex gradients from the coast (low, flat, sediment controlled and temperature moderated near the ocean) to the interior (high, rugged, bedrock controlled, distant from warming ocean). To investigate the potential influence of this disturbance gradient on regional forest composition, we studied the differential responses of trees (canopy position, lifeform group, and species group) to a particularly severe ice storm. Our results indicated that tree mortality and damage (canopy damage, bent bole, snapped bole, and uprooted) varied significantly between overstory and understory trees, and among species and lifeform groups. Overstory trees were more prone to glaze damage than understory trees, and evergreen broadleaf species were the most susceptible to glaze damage, while deciduous species were the least susceptible. Among the pine species studied, slash pine (Pinus elliottii Engelm.) and longleaf pine (P. palustris Mill.) suffered more severe damage and mortality than loblolly pine (P. taeda L.). Further, ice damage was correlated with distribution-based differences in injury susceptibility among pine and deciduous tree species. The most ice storm-tolerant pine species, loblolly pine, had the most northerly distribution (39.51°N), while the least resistant species were those with more southerly distribution (e.g., 33.29°N for slash pine). These results support hypotheses that the distributions of evergreen tree species are regulated by periodic catastrophic ice storms. Therefore, predicting future distributions of tree species in response to climate change should consider the role of ice storms in shaping the forest composition.