Ice storms as a successional pathway for Fagus grandifolia advancement in Quercus rubra dominated forests of southern New England

摘要

On 11 December 2008, a severe ice storm affected large portions of southern New England. We report the results of a study investigating differential damage among tree species. Past studies surveying ice-damaged forests have relied heavily on ocular estimations of canopy damage. We compare this method with damage estimates based on the cross-sectional area of downed woody material and quantitative comparisons of tree height and canopy projection in damaged and undamaged stands. Ocular estimates and changes in canopy height and projection were unreliable. Estimates based on the amount of woody debris provide a more robust measure of storm damage. We assess damage in two forest tracts with a dominant red oak (Quercus rubra L.) canopy (42% of total basal area) and an American beech (Fagus grandifolia Ehrh.) dominated understory (50% of all stems > 1.3 m). Species' standing basal area was well correlated with the amount of newly downed woody debris (r = 0.69, p 0.001); accordingly, oak species constituted approximately 57% of all newly downed woody debris, and ANOVA showed that oak species were significantly more impacted by ice damage than other species present (p 0.001). Our findings indicate that canopy species provide an "umbrella effect", shielding less dominant lower strata trees from the worst effects of ice load. Oak was also the largest contributor to older downed woody debris, indicative of a recurrent historical pattern of differential canopy disturbance driven by strata and relative dominance. These findings suggest that periodic ice events play an important role in facilitating the advancement of shade-tolerant tree species into the canopy from lower strata.