Ice storms as a disturbance factor in Appalachian oak forests

Abstract

Ice (glaze) storms are frequent natural disturbances in eastern deciduous forests. Two opposing hypotheses exist in the literature regarding the effect of glaze on forest succession. In the first view, succession is said to be accelerated as pioneer species sustain greater damage than equilibrium species. The resistant equilibrium species would then fill canopy gaps, shifting the stand to a more advanced stage. Alternatively, extensive canopy damage allows more light to reach the forest floor perhaps favoring the germination and establishment of pioneer seedlings. Survival of these individuals would return the community to an earlier successional stage, or maintain pioneer communities. This study examined the response of the reproduction and susceptibility of tree species (by damage and mortality) two growing seasons after an ice storm, across a moisture and successional gradient. Four stands were studied: Liriodendron, mesic and xeric Pinus, and Quercus. Damage for most species was consistent across stands, with larger trees generally sustaining greater damage than smaller trees or saplings. Mortality increased with increasing stem size and severity of damage for most species. However, while damage to Liriodendron tulipifera was very high, actual mortality was low due to its ability to sprout. Also, because seedling reproduction of pioneer species was stimulated in this stand, succession appeared to be retarded. Succession was accelerated in the mesic Pinus stand where mortality of canopy trees was high and where removal of the canopy stimulated growth and sprouting of understory equilibrium species. Succession of the stands on drier sites (e.g. Quercus and xeric Pinus) appeared unaffected as the composition of tree seedlings remained essentially unchanged after disturbance. Thus, the response of a community to ice damage depends on the interrelated variables of vegetation composition, successional status, and topographic position.