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1. Assessment of spongy moth infestation impacts on forest productivity and carbon loss using the Sentinel-2 satellite remote sensing and eddy covariance flux data

   https://doi.org/10.1186/s13717-024-00520-w  

   Hussain, Nur; Gonsamo, Alemu; Wang, Shusen; Arain, M Altaf (December 2024, Ecological Processes)

   Background Deciduous forests in eastern North America experienced a widespread and intense spongy moth (Lymantria dispar) infestation in 2021. This study quantified the impact of this spongy moth infestation on carbon (C) cycle in forests across the Great Lakes region in Canada, utilizing high-resolution (10 × 10 m2) Sentinel-2 satellite remote sensing images and eddy covariance (EC) flux data. Study results showed a significant reduction in leaf area index (LAI) and gross primary productivity (GPP) values in deciduous and mixed forests in the region in 2021. Results Remote sensing derived, growing season mean LAI values of deciduous (mixed) forests were 3.66 (3.18), 2.74 (2.64), and 3.53 (2.94) m2 m−2 in 2020, 2021 and 2022, respectively, indicating about 24 (14)% reduction in LAI, as compared to pre- and post-infestation years. Similarly, growing season GPP values in deciduous (mixed) forests were 1338 (1208), 868 (932), and 1367 (1175) g C m−2, respectively in 2020, 2021 and 2022, showing about 35 (22)% reduction in GPP in 2021 as compared to pre- and post-infestation years. This infestation induced reduction in GPP of deciduous and mixed forests, when upscaled to whole study area (178,000 km2), resulted in 21.1 (21.4) Mt of C loss as compared to 2020 (2022), respectively. It shows the large scale of C losses caused by this infestation in Canadian Great Lakes region. Conclusions The methods developed in this study offer valuable tools to assess and quantify natural disturbance impacts on the regional C balance of forest ecosystems by integrating field observations, high-resolution remote sensing data and models. Study results will also help in developing sustainable forest management practices to achieve net-zero C emission goals through nature-based climate change solutions. 

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2. Impacts of Drought on Water Fluxes and Water‐Use Efficiency in an Age‐Sequence of Temperate Conifer Forests

   https://doi.org/10.1002/hyp.70134  

   Arango_Ruda, Elizabeth; Arain, M Altaf (May 2025, Hydrological Processes)

   ABSTRACT Evapotranspiration (ET) from temperate forests plays a significant role in the regional and global water cycles. However, extreme weather events such as heat and drought are affecting the water use and water use efficiency (WUE) of these forests. Climate change impacts may be more severe in plantation forests where the age of the forest plays a significant role, causing differences in their responses to environmental stresses. This study presents 14 years (2008–2021) of water flux data measured using the eddy covariance technique in an age sequence (83, 48 and 20 years as of 2021) of eastern white pine (Pinus strobusL.) forests in the Great Lakes region in southern Ontario, Canada. The mean annual ET was 465 ± 41, 466 ± 32 and 403 ± 21 mm year⁻¹in the 83‐, 48‐ and 20‐year‐old stands, respectively, with the highest annual water flux observed in the 83‐year‐ old stand, which was similar to that of the 48‐year‐old stand. Mean annual gross ecosystem productivity (GEP) was 1585 ± 100, 1660 ± 115 and 1634 ± 331 g C m⁻² year⁻¹in the 83‐, 48‐ and 20‐year‐old stands, respectively, while mean annual WUE was 3.4 ± 0.4, 3.6 ± 0.4 and 4.0 ± 0.8 g C kg H₂O year⁻¹in the respective stands. Lower ET and relatively higher GEP resulted in the highest WUE in the youngest stand, even though the highest GEP was observed in the middle‐aged stand. Air temperature (Tair) was the dominant control on ET, GEP and WUE in all three different‐aged stands, while drought, characterised as the relative extractable water (REW) in the soil, had a significant impact on ET in the late summer. The results of this study further showed that forest age significantly influenced how forests responded to drought stresses. The younger stand was more efficient in carbon sequestration and water use despite exhibiting greater sensitivity to water stress and higher drought coupling. The long‐term eddy covariance measurements analysed in this study have helped to enhance our understanding of water exchange processes in the temperate conifer forest ecosystems in Eastern North America. Specifically, this work contributes to a better understanding of how different‐aged forests respond to extreme weather events, aiding in the development of new strategies for managing water resources and ensuring water security in the region under a changing climate. 

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3. Disturbance‐accelerated succession increases the production of a temperate forest

   https://doi.org/10.1002/eap.2417  

   Gough, Christopher_M; Bohrer, Gil; Hardiman, Brady_S; Nave, Lucas_E; Vogel, Christoph_S; Atkins, Jeff_W; Bond‐Lamberty, Ben; Fahey, Robert_T; Fotis, Alexander_T; Grigri, Maxim_S; et al (August 2021, Ecological Applications)

   Abstract Many secondary deciduous forests of eastern North America are approaching a transition in which mature early‐successional trees are declining, resulting in an uncertain future for this century‐long carbon (C) sink. We initiated the Forest Accelerated Succession Experiment (FASET) at the University of Michigan Biological Station to examine the patterns and mechanisms underlying forest C cycling following the stem girdling‐induced mortality of >6,700 early‐successionalPopulusspp. (aspen) andBetula papyrifera(paper birch). Meteorological flux tower‐based C cycling observations from the 33‐ha treatment forest have been paired with those from a nearby unmanipulated forest since 2008. Following over a decade of observations, we revisit our core hypothesis: that net ecosystem production (NEP) would increase following the transition to mid‐late‐successional species dominance due to increased canopy structural complexity. Supporting our hypothesis, NEP was stable, briefly declined, and then increased relative to the control in the decade following disturbance; however, increasing NEP was not associated with rising structural complexity but rather with a rapid 1‐yr recovery of total leaf area index as mid‐late‐successionalAcer,Quercus, andPinusassumed canopy dominance. The transition to mid‐late‐successional species dominance improved carbon‐use efficiency (CUE = NEP/gross primary production) as ecosystem respiration declined. Similar soil respiration rates in control and treatment forests, along with species differences in leaf physiology and the rising relative growth rates of mid‐late‐successional species in the treatment forest, suggest changes in aboveground plant respiration and growth were primarily responsible for increases in NEP. We conclude that deciduous forests transitioning from early to middle succession are capable of sustained or increased NEP, even when experiencing extensive tree mortality. This adds to mounting evidence that aging deciduous forests in the region will function as C sinks for decades to come. 

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4. Defoliation severity is positively related to soil solution nitrogen availability and negatively related to soil nitrogen concentrations following a multi-year invasive insect irruption

   https://doi.org/10.1093/aobpla/plaa059  

   Conrad-Rooney, Emma; Barker Plotkin, Audrey; Pasquarella, Valerie J; Elkinton, Joseph; Chandler, Jennifer L; Matthes, Jaclyn Hatala (December 2020, AoB PLANTS)

   Atkins, Jeff (Ed.)

   Abstract Understanding connections between ecosystem nitrogen (N) cycling and invasive insect defoliation could facilitate the prediction of disturbance impacts across a range of spatial scales. In this study we investigated relationships between ecosystem N cycling and tree defoliation during a recent 2015–18 irruption of invasive gypsy moth caterpillars (Lymantria dispar), which can cause tree stress and sometimes mortality following multiple years of defoliation. Nitrogen is a critical nutrient that limits the growth of caterpillars and plants in temperate forests. In this study, we assessed the associations among N concentrations, soil solution N availability and defoliation intensity by L. dispar at the scale of individual trees and forest plots. We measured leaf and soil N concentrations and soil solution inorganic N availability among individual red oak trees (Quercus rubra) in Amherst, MA and across a network of forest plots in Central Massachusetts. We combined these field data with estimated defoliation severity derived from Landsat imagery to assess relationships between plot-scale defoliation and ecosystem N cycling. We found that trees in soil with lower N concentrations experienced more herbivory than trees in soil with higher N concentrations. Additionally, forest plots with lower N soil were correlated with more severe L. dispar defoliation, which matched the tree-level relationship. The amount of inorganic N in soil solution was strongly positively correlated with defoliation intensity and the number of sequential years of defoliation. These results suggested that higher ecosystem N pools might promote the resistance of oak trees to L. dispar defoliation and that defoliation severity across multiple years is associated with a linear increase in soil solution inorganic N. 

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5. Robust filling of extra-long gaps in eddy covariance CO2 flux measurements from a temperate deciduous forest using eXtreme Gradient Boosting

   https://doi.org/10.1016/j.agrformet.2025.110438  

   Liu, Yujie; Lucas, Benjamin; Bergl, Darby D; Richardson, Andrew D (April 2025, Agricultural and Forest Meteorology)

   Eddy Covariance measurements are often subject to missing values, or gaps in the data record. Methods to fill short gaps are well-established, but robustly filling gaps longer than a few weeks remains a challenge. Marginal Distribution Sampling (MDS) is a standard gap-filling method, but its effectiveness for long gaps (> 30 days) is limited. We compared the performance of a machine learning algorithm, eXtreme Gradient Boosting (XGB) against MDS, using various artificial scenarios of gap lengths and locations. We gapfilled half hourly CO2 flux from a temperate deciduous forest, Bartlett Experimental Forest, from 2010 to 2022. Whereas the standard implementation of MDS uses a narrowly-prescribed set of predictor variables, with XGB we were able to include additional variables. The Green Chromatic Coordinate (GCC), derived from PhenoCam imagery, and diffuse photosynthetic photon flux density, emerged as two of the three most important predictor variables. Compared to MDS, the root mean square error (RMSE) of XGB decreased by 9.5 %, and the R2 increased by 2.7 % in a randomized 10-fold cross validation test. XGB outperformed MDS for both day and night times across different seasons. But annual NEE integrals varied across methods, with weaker annual net carbon uptake, by -110 ± 74 g C m-2 y-1 for XGB compared to MDS (214 ± 11 g C m-2 yr-1). In artificial gap experiments, when trained using the 13-year data record, XGB reliably filled gaps, showing little change in RMSE for gaps up to 240 days. In contrast, the performance of MDS steadily decreased as gap lengths increased. MDS was unable to fill gaps longer than 2 months. In summary, XGB demonstrates excellent performance as an alternative method to MDS, providing reliable predictions for temperate deciduous forest carbon fluxes under different gap lengths and location scenarios. Implementation of XGB is facilitated by easy-to-use packages. 

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