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1. Short‐term effects of moderate severity disturbances on forest canopy structure

   https://doi.org/10.1111/1365-2745.14145  

   Choi, Dennis Heejoon ; LaRue, Elizabeth A. ; Atkins, Jeff W. ; Foster, Jane R. ; Matthes, Jaclyn Hatala ; Fahey, Robert T. ; Thapa, Bina ; Fei, Songlin ; Hardiman, Brady S. ( June 2023 , Journal of Ecology)

   Moderate severity disturbances, those that do not result in stand replacement, play an essential role in ecosystem dynamics. Despite the prevalence of moderate severity disturbances and the significant impacts they impose on forest functioning, little is known about their effects on forest canopy structure and how these effects differ over time across a range of disturbance severities and disturbance types.

   Using longitudinal data from the National Ecological Observatory Network project, we assessed the effects of three moderate severity press disturbances (beech bark disease, hemlock woolly adelgid and emerald ash borer, which are characterized by continuous disturbance and sustained mortality) and three moderate severity pulse disturbances (spring cankerworm moth, spongy moth and ground fire, which are associated with discrete and relatively short mortalities) on temperate forest canopy structure in eastern US. We studied (1) how light detection and ranging (LiDAR)‐derived metrics of canopy structure change in response to disturbance and (2) whether initial canopy complexity offsets impact of disturbances on canopy structure over time. We used a mixed‐effects modelling framework which included a non‐linear term for time to represent changes in canopy structure caused by disturbance, and interactions between time and both disturbance intensity and initial canopy complexity.

   We discovered that high intensity of both press and pulse disturbances inhibited canopy height growth while low intensity pulse disturbances facilitated it. In addition, high intensity pulse disturbances facilitated increases in the complexity of the canopy over time. Concerning the impact of initial canopy complexity, we found that the initial canopy complexity of disturbed plots altered the effects of moderate disturbances, indicating potential resilience effects.

   Synthesis. This study used repeated measurements of LiDAR data to examine the effects of moderate disturbances on various dimensions of forest canopy structure, including height, openness, density and complexity. Our study indicates that both press and pulse disturbances can inhibit canopy height growth over time. However, while the impact of press disturbances on other dimensions of canopy structure could not be clearly detected, likely because of compensatory growth, the impact of pulse disturbances over time was more readily apparent using multi‐temporal LiDAR data. Furthermore, our findings suggest that canopy complexity might help to mitigate the impact of moderate disturbances on canopy structures over time. Overall, our research highlights the usefulness of multi‐temporal LiDAR data for assessing the structural changes in forest canopies caused by moderate severity disturbances.

    

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2. Coarse Woody Debris of the Ice Storm Experiment (ISE) plots at the Hubbard Brook Experimental Forest

   https://doi.org/10.6073/pasta/775d52a7665cc35574bca97e79fdd3c3  

   Rustad, Lindsey ; Campbell, John ; Leuenberger, Wendy M ( January 2021 , Environmental Data Initiative)

   The ice storm experiment was a novel experimental approach creating a suite of ice storms in a mature hardwood forest in New Hampshire, USA. The experiment included five ice storm intensities (0, 6.4, 12.7, and 19.1 mm radial ice accretion) applied in a single year, and one ice storm intensity (12.7 mm) applied in two consecutive years. This dataset quantifies the coarse woody debris transferred from the forest canopy to the soil under the different icing conditions. In this forest, little damage occurred below 6.4 mm radial ice accretion, moderate damage occurred with up to 12.7 mm of accretion, and significant branch breakage and canopy damage occurred with 19.1 mm of ice. The icing in consecutive years demonstrated an interactive effect of ice storm frequency and severity such that some branches damaged in the first year of icing appeared to remain in the canopy and then fall to the ground in the second year of icing. These results have implications for National Weather Service ice storm warning levels, and they provide a quantitative assessment of ice-load related inputs of forest debris that will be useful to municipalities creating response plans for current and future ice storms. These data were gathered as part of the Hubbard Brook Ecosystem Study (HBES). The HBES is a collaborative effort at the Hubbard Brook Experimental Forest, which is operated and maintained by the USDA Forest Service, Northern Research Station. 

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3. Disentangling the long‐term effects of disturbance on soil biogeochemistry in a wet tropical forest ecosystem

   https://doi.org/10.1111/gcb.14027  

   Gutiérrez del Arroyo, Omar ; Silver, Whendee L. ( January 2018 , Global Change Biology)

   Climate change is increasing the intensity of severe tropical storms and cyclones (also referred to as hurricanes or typhoons), with major implications for tropical forest structure and function. These changes in disturbance regime are likely to play an important role in regulating ecosystem carbon (C) and nutrient dynamics in tropical and subtropical forests. Canopy opening and debris deposition resulting from severe storms have complex and interacting effects on ecosystem biogeochemistry. Disentangling these complex effects will be critical to better understand the long‐term implications of climate change on ecosystem C and nutrient dynamics. In this study, we used a well‐replicated, long‐term (10 years) canopy and debris manipulation experiment in a wet tropical forest to determine the separate and combined effects of canopy opening and debris deposition on soil C and nutrients throughout the soil profile (1 m). Debris deposition alone resulted in higher soil C and N concentrations, both at the surface (0–10 cm) and at depth (50–80 cm). Concentrations of NaOH‐organic P also increased significantly in the debris deposition only treatment (20–90 cm depth), as did NaOH‐total P (20–50 cm depth). Canopy opening, both with and without debris deposition, significantly increased NaOH‐inorganic P concentrations from 70 to 90 cm depth. Soil iron concentrations were a strong predictor of both C and P patterns throughout the soil profile. Our results demonstrate that both surface‐ and subsoils have the potential to significantly increase C and nutrient storage a decade after the sudden deposition of disturbance‐related organic debris. Our results also show that these effects may be partially offset by rapid decomposition and decreases in litterfall associated with canopy opening. The significant effects of debris deposition on soil C and nutrient concentrations at depth (>50 cm), suggest that deep soils are more dynamic than previously believed, and can serve as sinks of C and nutrients derived from disturbance‐induced pulses of organic matter inputs.

    

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4. Ecosystem Nitrogen Response to a Simulated Ice Storm in a Northern Hardwood Forest

   https://doi.org/10.1007/s10021-019-00463-w  

   Weitzman, Julie N. ; Groffman, Peter M. ; Campbell, John L. ; Driscoll, Charles T. ; Fahey, Robert T. ; Fahey, Timothy J. ; Schaberg, Paul G. ; Rustad, Lindsey E. ( November 2019 , Ecosystems)

   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 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. 

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5. Hubbard Brook Experimental Forest: Ice Storm Experiment (ISE) Canopy Hemispherical Photos

   https://doi.org/10.6073/pasta/aa1ec68480b0d83a0abe4b3552f28f77  

   Campbell, John L ; Rustad, Lindsey E ; Fahey, Robert T ; Driscoll, Charles T ( January 2022 , Environmental Data Initiative)

   Abstract An ice storm simulation was performed at the Hubbard Brook Experimental Forest to evaluate impacts of these extreme weather events on northern hardwood forests. Water was pumped from the main branch of Hubbard Brook and sprayed above the forest canopy in subfreezing conditions so that it rained down and froze on contact with trees. The experiment consisted of five treatments, including a control (no ice) and three target levels of radial ice accretion: low (6.4 mm), mid (12.7 mm), and high (19.0 mm). Two of the mid-level treatment plots (midx2) were iced in back-to-back years to evaluate impacts of consecutive storms. This dataset consists of hemispherical photographs of the forest canopy with leaves on and off the trees before and after the various ice treatments. These data were gathered as part of the Hubbard Brook Ecosystem Study (HBES). The HBES is a collaborative effort at the Hubbard Brook Experimental Forest, which is operated and maintained by the USDA Forest Service, Northern Research Station. 

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