An Ice Storm Manipulation Experiment in a Northern Hardwood Forest.

Ice storms are an important natural disturbance within forest ecosystems of the northeastern United States.  Current models suggest that the frequency and severity of ice storms may increase in the coming decades in response to changes in climate.  Because of the stochastic nature of ice storms and difficulties in predicting their occurrence, most past investigations of the ecological effects of ice storms across this region have been based on case studies following major storms.  Here we report on a novel alternative approach where a glaze ice event was created experimentally under controlled conditions at the Hubbard Brook Experimental Forest, New Hampshire, US.  Water was sprayed over a northern hardwood forest canopy during February 2011, resulting in 7 to 12 mm radial ice thickness.  Although this is below the minimum cutoff for ice storm warnings (13 mm of ice) issued by the US National Weather Service for the northeastern US, this glaze ice treatment resulted in significant canopy damage, with 142 and 218 g C m^-2 of fine and coarse woody debris (respectively) deposited on the forest floor, a significant increase in leaf-on canopy openness, and increases in qualitative damage assessments following the treatment.  This study demonstrates the feasibility of a relatively simple approach to simulating an ice storm, and underscores the potency of this type of extreme event in shaping the future structure and function of northern hardwood forest ecosystems.