TREE THROW EROSION IN WESTERN MASSACHUSETTS ASSOCIATED WITH THE DECEMBER 2008 ICE STORM

In December 2008, a severe ice storm affected portions of east-central New York and western New England. Ice accumulations ranged from around half of an inch up to an inch. Widespread tree and power line damage in populated areas underscore the social impact of the ice storm. The natural landscape, too, experienced extensive damage and modification. Here, we document tree throw erosion associated with the ice storm within the Roaring Brook watershed in Mt. Toby State Forest, Franklin Country, Massachusetts. Roaring Brook is a steep, forested, upland catchment typical of those in the northern Appalachians; it was logged between the late 18th and early 20th centuries and has since returned to a mixture of oak, northern hardwoods, and hemlock trees. Over 200 trees within the watershed uprooted and fell downslope during the ice storm event, many within clusters involving multiple trees or in lines suggesting that successive, cascading failure took place. No particular tree type appears to dominate those that fell during the event, and local slope does not seem to have strongly influenced the distribution of fallen trees. The average dimensions of the root ball displaced by individual fallen trees measured ~2 m in diameter, with a thickness of 0.5-1 m, indicating the average volume of soil distributed and transported downslope per tree fallen was ~2.4 m³. Nearby convex hilltops suggest that diffusive processes such as tree throw dictate the pace and style of post-glacial soil transport, erosion and hillslope evolution in the area. Soil transport and local erosion associated with this single ice storm/tree throw event therefore highlight the dominant processes and timescales involved in the landscape evolution of this watershed. Preliminary observations of downed tree clusters farther west in the Berkshires highlight the regional significance of this event.