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1. Trajectories of forest composition, structure, and productivity following an experimental ice storm disturbance

   https://doi.org/10.1139/cjfr-2025-0044  

   Fahey, Robert T; Campbell, John L; Rustad, Lindsey E; Driscoll, Charles T; Schaberg, Paul G (November 2025, Canadian Journal of Forest Research)

   Disturbance creates structural legacies that are important drivers of functional and compositional stabilities in forested ecosystems. We used an experimental ice storm disturbance to evaluate effects of disturbance severity on structural legacies and their functional consequences. We evaluated canopy structural characteristics (height, density, openness, and complexity) before and after disturbance using data from terrestrial LiDAR. We compared trajectories of structural characteristics and functional outcomes (composition, mortality, and productivity) among treatments and relative to controls. We found significant post-disturbance change for all canopy structural characteristics especially at higher severity levels, with persistent legacy effects on mean canopy height and canopy complexity. There were limited changes in biomass, productivity, and composition, and mortality did not vary significantly among treatments. There was limited evidence for linkages between structural and functional responses, but plots that retained greater complexity had higher stability of net primary productivity. Our findings indicate persistent structural legacies associated with ice storm disturbance, but declining structural legacies over time may affect interactions with subsequent disturbance or stressors. Improved understanding of these trajectories could help with predicting outcomes of changing disturbance regimes associated with global change. 

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2. Dynamic subcanopy leaf traits drive resistance of net primary production across a disturbance severity gradient

   https://doi.org/10.3389/ffgc.2023.1150209  

   Haber, Lisa T.; Atkins, Jeff W.; Bond-Lamberty, Ben P.; Gough, Christopher M. (July 2023, Frontiers in Forests and Global Change)

   Across the globe, the forest carbon sink is increasingly vulnerable to an expanding array of low- to moderate-severity disturbances. However, some forest ecosystems exhibit functional resistance (i.e., the capacity of ecosystems to continue functioning as usual) following disturbances such as extreme weather events and insect or fungal pathogen outbreaks. Unlike severe disturbances (e.g., stand-replacing wildfires), moderate severity disturbances do not always result in near-term declines in forest production because of the potential for compensatory growth, including enhanced subcanopy production. Community-wide shifts in subcanopy plant functional traits, prompted by disturbance-driven environmental change, may play a key mechanistic role in resisting declines in net primary production (NPP) up to thresholds of canopy loss. However, the temporal dynamics of these shifts, as well as the upper limits of disturbance for which subcanopy production can compensate, remain poorly characterized. In this study, we leverage a 4-year dataset from an experimental forest disturbance in northern Michigan to assess subcanopy community trait shifts as well as their utility in predicting ecosystem NPP resistance across a wide range of implemented disturbance severities. Through mechanical girdling of stems, we achieved a gradient of severity from 0% (i.e., control) to 45, 65, and 85% targeted gross canopy defoliation, replicated across four landscape ecosystems broadly representative of the Upper Great Lakes ecoregion. We found that three of four examined subcanopy community weighted mean (CWM) traits including leaf photosynthetic rate ( p = 0.04), stomatal conductance ( p = 0.07), and the red edge normalized difference vegetation index ( p < 0.0001) shifted rapidly following disturbance but before widespread changes in subcanopy light environment triggered by canopy tree mortality. Surprisingly, stimulated subcanopy production fully compensated for upper canopy losses across our gradient of experimental severities, achieving complete resistance (i.e., no significant interannual differences from control) of whole ecosystem NPP even in the 85% disturbance treatment. Additionally, we identified a probable mechanistic switch from nutrient-driven to light-driven trait shifts as disturbance progressed. Our findings suggest that remotely sensed traits such as the red edge normalized difference vegetation index (reNDVI) could be particularly sensitive and robust predictors of production response to disturbance, even across compositionally diverse forests. The potential of leaf spectral indices to predict post-disturbance functional resistance is promising given the capabilities of airborne to satellite remote sensing. We conclude that dynamic functional trait shifts following disturbance can be used to predict production response across a wide range of disturbance severities. 

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3. Aboveground Wood Production Is Sustained in the First Growing Season after Phloem-Disrupting Disturbance

   https://doi.org/10.3390/f11121306  

   Grigri, Maxim S.; Atkins, Jeff W.; Vogel, Christoph; Bond-Lamberty, Ben; Gough, Christopher M. (December 2020, Forests)

   null (Ed.)

   Carbon (C) cycling processes are particularly dynamic following disturbance, with initial responses often indicative of longer-term change. In northern Michigan, USA, we initiated the Forest Resilience Threshold Experiment (FoRTE) to identify the processes that sustain or lead to the decline of C cycling rates across multiple levels (0, 45, 65 and 85% targeted gross leaf area index loss) of disturbance severity and, in response, to separate disturbance types preferentially targeting large or small diameter trees. Simulating the effects of boring insects, we stem girdled > 3600 trees below diameter at breast height (DBH), immediately and permanently disrupting the phloem. Weekly DBH measurements of girdled and otherwise healthy trees (n > 700) revealed small but significant increases in daily aboveground wood net primary production (ANPPw) in the 65 and 85% disturbance severity treatments that emerged six weeks after girdling. However, we observed minimal change in end-of-season leaf area index and no significant differences in annual ANPPw among disturbance severities or between disturbance types, suggesting continued C fixation by girdled trees sustained stand-scale wood production in the first growing season after disturbance. We hypothesized higher disturbance severities would favor the growth of early successional species but observed no significant difference between early and middle to late successional species’ contributions to ANPPw across the disturbance severity gradient. We conclude that ANPPw stability immediately following phloem disruption is dependent on the continued, but inevitably temporary, growth of phloem-disrupted trees. Our findings provide insight into the tree-to-ecosystem mechanisms supporting stand-scale wood production stability in the first growing season following a phloem-disrupting disturbance. 

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4. 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. (January 2023, Journal of Ecology)

   Abstract 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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5. Effects of an experimental ice storm on forest canopy structure

   https://doi.org/10.1139/cjfr-2019-0276  

   Fahey, Robert T.; Atkins, Jeff W.; Campbell, John L.; Rustad, Lindsey E.; Duffy, Meghan; Driscoll, Charles T.; Fahey, Timothy J.; Schaberg, Paul G. (February 2020, Canadian Journal of Forest Research)

   null (Ed.)

   Intermediate disturbances are an important component of many forest disturbance regimes, with effects on canopy structure and related functions that are highly dependent on the nature and intensity of the perturbation. Ice storms are an important disturbance mechanism in temperate forests that often result in moderate-severity, diffuse canopy damage. However, it has not previously been possible to distinguish the specific effect of ice storm intensity (as ice accretion) from predisturbance stand characteristics and physiographic factors. In this study, we utilized a novel experimental ice storm treatment to evaluate the effects of variable ice accretion levels on forest canopy structure. Our results verified significant impacts of ice storm disturbance on near-term canopy structural reorganization. Canopy openness, light transmission, and complexity increased significantly relative to predisturbance baselines and undisturbed controls. We documented variable impacts with disturbance intensity, as significant canopy changes largely occurred with ice accretion levels of ≥12.7 mm. Repeated ice storm disturbance (two consecutive years) had marginal, rather than compounding, effects on forest canopy structure. Our findings are relevant to understanding how ice storms can affect near-term forest canopy structural reorganization and ecosystem processes and add to a growing base of knowledge on the effects of intermediate disturbances on canopy structure. 

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