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 winters of 2016 and 2017, water was pumped from the Hubbard Brook and sprayed over the forest canopy during subfreezing conditions, causing the water to freeze on contact. The study occurred on ten 20 x 30 m plots and included two replicates of each of five icing treatments.
The icing treatments included targets of 0, 6, 13, and 19 mm radial ice accretion sprayed in winter 2016 (to evaluate the impacts of different intensities of ice storms), and 13 mm sprayed again in winter 2017 (to evaluate impacts of consecutive ice storms). Measured ice accretion on wooden dowels suspended in the canopy showed that a gradient of ice accretion was achieved (6, 10, and 13 mm in 2016; 11 mm in 2017). The winter 2016 treatments resulted in a gradient of fine and coarse woody debris commensurate with the treatments (8, 33, 73, and 124 g C/m2 fine woody debris and 5, 24, 133, and 685 g C/m2 coarse woody debris for the 0, 6, 13 and 19 mm treatments, respectively, in the first year following icing (2016). Experimentally created gaps in the canopy resulted in increased variability in soil temperature and moisture. Surprisingly, impacts on total soil respiration were only modest (with depressed rates in the high ice treatments), and no treatment effects were observed for soil solution nutrient concentrations or microbial nitrogen dynamics during for the first year following icing (2016). Results provide new insights on the ecological impacts of these catastrophic winter storms.