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1. Hubbard Brook Nitrogen Oligotrophication (HBNO): Leaf mass per area

   https://doi.org/10.6073/pasta/a62a4261c79ab2de38bc564828582de9  

   Fahey, Timothy J; Cleavitt, Natalie L (January 2024, Environmental Data Initiative)

   This data set encompasses leaf area and dry weights for collected freshly shot leaves (early August) and fallen leaves (entire leaf fall period) along the elevation gradient of 14 sites used for the nitrogen oligotrophication study at Hubbard Brook Experimental Forest. This data will be used to calculate nutrient resorption along the elevation gradient for sugar maple (collection years: 2020-2022) and American beech (2021-2022). 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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2. Foliar resorption of beech and maple along an elevation gradient in a northern hardwood forest

   https://doi.org/10.1016/j.fecs.2025.100304  

   Fahey, Timothy J; Cleavitt, Natalie L; Templer, Pamela H; Groffman, Peter M; Bailey, Amey S; Caron, Stephen B; Wilson, Geoffrey (June 2025, Forest Ecosystems)

   Foliar resorption is a principal nutrient conservation mechanism in terrestrial vegetation that could be sensitive to ongoing changes in climate and atmospheric nitrogen (N) deposition. We quantified N resorption in northern hardwood forests along an elevation gradient of decreasing temperature and increasing soil N availability to evaluate how this critical nutrient cycling process can be expected to respond to global and regional environmental changes. Foliar N resorption proficiency (NRP) increased significantly at lower elevations for both sugar maple and American beech, the dominant species in these forests. Foliar N resorption efficiency (NRE) also decreased with increasing elevation, but only in one year. Both species exhibited strong negative relationships between NRP and soil N availability. Thus, we anticipate that with climate warming and decreasing N inputs, northern hardwood forests can be expected to exhibit stronger N conservation via foliar resorption. Both species also exhibited strong correlations between resorption efficiency of N and C, but resorption of both elements was much greater for beech than sugar maple, suggesting contrasting mechanisms of nutrient conservation between these two widespread species. 

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3. Tree Seed Data at the Hubbard Brook Experimental Forest, 1993 - ongoing

   https://doi.org/10.6073/pasta/778d8e1d131ad064a925cc2ac6631b53  

   Fahey, Timothy; Cleavitt, Natalie (January 2024, Environmental Data Initiative)

   Tree seeds sorted and counted from long-term reference area litter traps are presented for 1993 until the present. These data are part of the LTER funded quantification of tree annual productivity. Our focal species for seed counts have been sugar maple, American beech and white ash. This data set allows comparison between seed production in reference sites (BB and TF) and the calcium addition watershed (W1) for these species. 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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4. Tree Seed Data at the Hubbard Brook Experimental Forest, 1993 - ongoing

   https://doi.org/10.6073/pasta/19e69d787124d60ccdfede1b5b813061  

   Fahey, Timothy; Cleavitt, Natalie (December 2025, Environmental Data Initiative)

   Tree seeds sorted and counted from long-term reference area litter traps are presented for 1993 until the present. These data are part of the LTER funded quantification of tree annual productivity. Our focal species for seed counts have been sugar maple, American beech and white ash. This data set allows comparison between seed production in reference sites (BB and TF) and the calcium addition watershed (W1) for these species. 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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5. Hubbard Brook Experimental Forest: Seedling bank – watershed 1 and watershed 6 (2018)

   https://doi.org/10.6073/pasta/f1c35455db94754db3146c1d90f52f54  

   Cleavitt, Natalie; Battles, John J (January 2022, Environmental Data Initiative)

   The understory layer is complex and includes groups of stems with distinctly different chances of survival and recruitment to the sapling size class. We explored how calcium amendment has impacted the trajectory of the seedling bank at Hubbard Brook Experimental Forest. The density of all tree stems in the seedling bank in 2018 (19 years after treatment) was greater in CAL (Watershed 1; calcium treatment) than REF (Waterhsed 6; reference) and beech was more abundant than sugar maple in both watersheds. In terms of relative abundance, the treatment had the opposite effects on the two species: the relative density of sugar maple was significantly greater in CAL than REF while the relative density of beech was significantly less. In terms of beech stem origin, Beech sprouts were more abundant than seedlings on both watersheds; however, beech stems of seed origin were more abundant on CAL (mean±1SE: 4.06±0.49 seedlings m-2) than REF (2.98±0.42), while sprouts were fewer (CAL: 14.4±1.30; REF: 20.5±1.47) resulting in the seedling to sprout ratio on CAL (1:3.5) being half that on REF (1:7). The influence on the seedling bank on future composition of these forests remains to be seen. 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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