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Title: Ecosystem Nitrogen Response to a Simulated Ice Storm in a Northern Hardwood Forest
Ice storms are important but understudied disturbances that influence forest structure and function. In 1998, an ice storm damaged forest canopies and led to increased hydrologic losses of nitrogen (N) from the northern hardwood forest at the Hubbard Brook Experimental Forest (HBEF), a Long-Term Ecological Research (LTER) site in New Hampshire, USA. To evaluate the mechanisms underlying this response, we experimentally simulated ice storms with different frequencies and severities at the small plot scale. We took measurements of plant and soil variables before (2015) and after (2016, 2017) treatments using the same methods used in 1998 with a focus on hydrologic and gaseous losses of reactive N, as well as rates of soil N cycle processes. Nitrogen cycle responses to the treatments were insignificant and less marked than the responses to the 1998 natural ice storm. Pools and leaching of inorganic N, net and gross mineralization and nitrification and denitrification rates, and soil to atmosphere fluxes of nitrous oxide (N2O) were unaffected by the treatments, in contrast to the 1998 storm which caused marked increases in leaching and watershed export of inorganic N. The difference in response may be a manifestation of N oligotrophication that has occurred at the HBEF over the past more » 30 years. Results suggest that ecosystem response to disturbances, such as ice storms, is changing due to aspects of global environmental change, challenging our ability to understand and predict the effects of these events on ecosystem structure, function, and services. « less
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