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  1. The winter-spring shoulder season, or vernal window, is a key period for ecosystem carbon, water, and energy cycling. Sometimes referred to as mud season, in temperate forests, this transitional season opens with the melting of snowpack in seasonally snow-covered forests and closes when the canopy fills out. Sunlight pours onto the forest floor, soils thaw and warm, and there is an uptick in soil respiration. Scientists hypothesize that this window of ecological opportunity will lengthen in the future; these changes could have implications across all levels of the ecosystem, including the availability of food and water in human systems. Yet, there remains a dearth of observations that track both winter and spring indicators at the same location. Here, we present an inquiry-based, low-cost approach for elementary to high school classrooms to track environmental changes in the winter-spring shoulder season. Engagement in hypothesis generation and the use of claim, evidence, and reasoning practices are coupled with field measurement protocols, which provides teachers and students an authentic research experience that allows for a place-based understanding of local ecosystems and their connection to climate change.
    Free, publicly-accessible full text available April 1, 2023
  2. Abstract
    Root damage, as relative electrolyte leakage, was assessed following winter freeze-thaw cycle experimental treatments in 2014 and 2015 on all Climate Change Across Seasons Experiment (CCASE) plots. Reference (or control) plots are shared with the collaborating Northern Forest DroughtNet experiment. There are six plots total (each 11 x 14m). Two are warmed 5 degrees C throughout the growing season (Plots 3 and 4). Two others are warmed 5 degrees C in the growing season and have snow removed during winter to induce soil freeze/thaw cycles (Plots 5 and 6). Four kilometers (2.5 mi) of heating cable are buried in the soil to warm these four plots. Two additional plots serve as controls for our experiment (Plots 1 and 2). Analysis and results from these data are presented in Sanders-DeMott 2018. 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. Sanders-DeMott, R., Sorensen, P.O., Reinmann, A.B. et al. Growing season warming and winter freeze–thaw cycles reduce root nitrogen uptake capacity and increase soil solution nitrogen in a northern forest ecosystem. Biogeochemistry 137,More>>
  3. Abstract
    Fine root nitrogen uptake capacity was measured on excised roots prior to experimental treatment in 2013 and throughout the growing seasons of 2014 and 2015 on all Climate Change Across Seasons Experiment (CCASE) plots. Reference (or control) plots are shared with the collaborating Northern Forest DroughtNet experiment. There are six plots total (each 11 x 14m). Two are warmed 5 degrees C throughout the growing season (Plots 3 and 4). Two others are warmed 5 degrees C in the growing season and have snow removed during winter to induce soil freeze/thaw cycles (Plots 5 and 6). Four kilometers (2.5 mi) of heating cable are buried in the soil to warm these four plots. Two additional plots serve as controls for our experiment (Plots 1 and 2). Analysis and results from these data are presented in Sanders-DeMott 2018. 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. Sanders-DeMott, R., Sorensen, P.O., Reinmann, A.B. et al. Growing season warming and winter freeze–thaw cycles reduce root nitrogen uptake capacity and increase soil solution nitrogenMore>>
  4. Abstract
    Resin available soil solution nitrogen was measured during seasonal incubations in 2014 and 2015 on all Climate Change Across Seasons Experiment (CCASE) plots. Reference (or control) plots are shared with the collaborating Northern Forest DroughtNet experiment. There are six plots total (each 11 x 14m). Two are warmed 5 degrees C throughout the growing season (Plots 3 and 4). Two others are warmed 5 degrees C in the growing season and have snow removed during winter to induce soil freeze/thaw cycles (Plots 5 and 6). Four kilometers (2.5 mi) of heating cable are buried in the soil to warm these four plots. Two additional plots serve as controls for our experiment (Plots 1 and 2). Analysis and results from these data are presented in Sanders-DeMott 2018. 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. Sanders-DeMott, R., Sorensen, P.O., Reinmann, A.B. et al. Growing season warming and winter freeze–thaw cycles reduce root nitrogen uptake capacity and increase soil solution nitrogen in a northern forest ecosystem. Biogeochemistry 137, 337–349 (2018). https://doi.org/10.1007/s10533-018-0422-5
  5. Abstract
    Foliage was collected in 2015 and 2017 from red maple trees at the Climate Change Across Seasons Experiment (CCASE) as part of the Hubbard Brook Ecosystem Study (HBES). Analyses of foliar metabolites include polyamines, amino acids, chlorophylls, carotenoids, soluble proteins, soluble inorganic elements, sugars, and total nitrogen and carbon. There are six (11 x 14m) plots in total in this study; two control (plots 1 and 2), two warmed 5 degrees (°) Celsius (C) above ambient throughout the growing season (plots 3 and 4), and two warmed 5 °C in the growing season, with snow removal during the winter to induce soil freezing and then warmed with buried heating cables to create a subsequent thaw (plots 5 and 6). Each soil freeze/thaw cycle includes 72 hours of soil freezing followed by 72 hours of thaw. Four kilometers (km) of heating cable are buried in the soil to warm these four plots. Together, these treatments led to warmer growing season soil temperatures and an increased frequency of soil freeze-thaw cycles (FTCs) in winter. Our goal was to determine how these changes in soil temperature affect foliar nitrogen (N) and carbon metabolism of red maple trees. These data were gathered asMore>>
  6. The ability to automatically delineate individual tree crowns using remote sensing data opens the possibility to collect detailed tree information over large geographic regions. While individual tree crown delineation (ITCD) methods have proven successful in conifer-dominated forests using Light Detection and Ranging (LiDAR) data, it remains unclear how well these methods can be applied in deciduous broadleaf-dominated forests. We applied five automated LiDAR-based ITCD methods across fifteen plots ranging from conifer- to broadleaf-dominated forest stands at Harvard Forest in Petersham, MA, USA, and assessed accuracy against manual delineation of crowns from unmanned aerial vehicle (UAV) imagery. We then identified tree- and plot-level factors influencing the success of automated delineation techniques. There was relatively little difference in accuracy between automated crown delineation methods (51–59% aggregated plot accuracy) and, despite parameter tuning, none of the methods produced high accuracy across all plots (27—90% range in plot-level accuracy). The accuracy of all methods was significantly higher with increased plot conifer fraction, and individual conifer trees were identified with higher accuracy (mean 64%) than broadleaf trees (42%) across methods. Further, while tree-level factors (e.g., diameter at breast height, height and crown area) strongly influenced the success of crown delineations, the influence of plot-level factorsmore »varied. The most important plot-level factor was species evenness, a metric of relative species abundance that is related to both conifer fraction and the degree to which trees can fill canopy space. As species evenness decreased (e.g., high conifer fraction and less efficient filling of canopy space), the probability of successful delineation increased. Overall, our work suggests that the tested LiDAR-based ITCD methods perform equally well in a mixed temperate forest, but that delineation success is driven by forest characteristics like functional group, tree size, diversity, and crown architecture. While LiDAR-based ITCD methods are well suited for stands with distinct canopy structure, we suggest that future work explore the integration of phenology and spectral characteristics with existing LiDAR as an approach to improve crown delineation in broadleaf-dominated stands.« less