Forest disturbance by ice storms in Quercus forests of the southern Appalachian Mountains, USA
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In 1994, two ice storms (major freezing rain events) disturbed forests on east- and southeast-facing slopes of the southern Appalachian Mountains, Virginia, USA. This study investigates impacts of the disturbance on Quercus forests, the predominant vegetation type in the Appalachians. Forests were sampled at six sites on two neighbouring mountains during 1997 and 1998. The two storms killed a significant number of trees, reducing basal area and density by 28.7% and 29.2%, respectively, in the transects sampled for this study. The storms also removed an estimated 43.7% of the canopy cover. Uprooting of trees disturbed 3.5% of the soil surface, on average. The ice storms eliminated some minor tree species from the sampled transects, reducing species richness; however, evenness increased. Both abiotic and biotic factors (mountain, slope, tree size, and species) influenced patterns of tree damage and mortality. Differences among species in susceptibility to ice storm damage seem particularly important for forest dynamics. The dominant Quercus prinus, along with Acer rubrum and Carya species, exhibited low mortality, whereas Pinus rigida had exceptionally high mortality. More generally, mortality was low in shade-tolerant and moderately shade-tolerant species, and high in those intolerant of shade. Periodic ice storms may contribute to the successional replacement of Pinus rigida and other susceptible species by less susceptible species.
