It is increasingly evident that human-induced climate change is altering the prevalence and severity of extreme weather events. Changes in climate extremes can have greater impacts on ecosystems than a more gradual change in mean climate conditions. Ice storms are an example of an extreme weather event that can have profound and lasting impacts on the structure and function of temperate forest ecosystems. 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 have been based on case studies following major storms. Here we present results from a novel alternative approach where a glaze ice event was created experimentally under controlled conditions at the Hubbard Brook Experimental Forest, New Hampshire, USA. During winter of 2016, water was pumped from the Hubbard Brook and sprayed over the forest canopy during sub-freezing conditions, causing the water to freeze on contact. The study occurred on ten 20 x 30 m plots and included two replicates of each icing treatment.
The target levels of icing included an unsprayed reference, and three different amounts of radial ice thickness (6, 13, and 19 mm). Two of the mid-level treatment plots (13 mm) will be sprayed again during winter of 2017 to evaluate impacts of consecutive ice storms. Results from the first year of treatment show that a gradient of ice accumulation was achieved (6, 10, and 13 mm as measured on dowels that were suspended in the canopy), albeit slightly less than the target values. Ecological response variables that are being evaluated include (a) tree damage assessment; (b) biogeochemical pools and cycling of nutrients with a focus on C and N cycling (microbial biomass and transformations, soil solution chemistry and trace gas losses); (c) tree physiology (e.g., woody growth and wound closure); and (d) stand demographics. This experiment is the first full ice storm manipulation ever conducted in a mature forest ecosystem, and one of a growing number of experiments worldwide to investigate the effects of extreme weather events on ecosystems. Results of this work are relevant to many types of extreme events that damage tree crowns and alter forest structure and could fundamentally transform scientific understanding of these and analogous events.