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This dataset provides comprehensive measurements of nutrient concentrations and fluxes in foliage, fine roots, wood, litterfall, and throughfall in hardwood and conifer stands across temperate forest stands at three long-term ecological research sites in the northeastern United States: Cone Pond, NH, Hubbard Brook, NH, and Sleepers River, VT. These sites vary in bedrock composition, parent material, and soil chemistry, but share similar climatic characteristics. Tissue nutrient concentrations were determined in leaves, fine roots, wood, and branches using site- and tissue-specific methods, with additional quality control through certified standards and duplicate sampling. Nutrient fluxes via litterfall and throughfall were measured over multiple years. Nutrient fluxes in roots were estimated from minirhizotron-based turnover rates and fine root biomass. Annual nutrient accumulation and uptake were calculated by integrating biomass production and nutrient concentrations. This dataset supports cross-site comparisons of forest biogeochemistry and provides a basis for evaluating nutrient limitations, cycling processes, and ecosystem responses to environmental gradients in northeastern temperate forests. 

In the northeastern United States, both hardwood and conifer forests have developed on sites with contrasting soils, allowing an examination of the effect of site and forest type on ecosystem nutrient cycling. We measured biomass production and nutrient fluxes in northern hardwood and conifer stands at three sites differing in soil fertility. We found that leaf, root, and wood concentrations of calcium (Ca), magnesium (Mg), and potassium reflected differences in soil base cation availability, while concentrations of nitrogen (N) and phosphorus (P) were more consistent across sites. Nutrient uptake was calculated as the sum of litterfall, net throughfall (throughfall minus precipitation), root turnover, and accumulation in perennial tissues (wood). We propose a novel metric of nutrient cycling, the nutrient retention fraction (NRF), defined as the proportion of annual nutrient uptake retained in biomass accretion. Because the NRF is unitless, it can be compared across nutrients; Ca and Mg had the highest NRF and P the lowest ( p = 0.05). Across sites and elements, NRFs were lower for conifers (5.0 ± 0.6%) than for hardwoods (7.2 ± 0.5%), associated with their lower productivity. Nutrient-use efficiency (biomass production divided by nutrient uptake) tended to be high where foliar concentrations indicated low availability of that nutrient. Nutrient retention of N and P was higher where availability of the other element was high, which could be a mechanism contributing to N and P co-limitation. 

The Multiple Element Limitation in Northern Hardwood Ecosystems (MELNHE) project studies N and P acquisition and limitation of forest productivity through a series of nutrient manipulations in northern hardwood forests. This data set includes tree diameters at breast height (DBH) collected pre-treatment (2008, 2009, and 2010), and post-treatment (2011, 2015, 2019, and 2023). Additional detail on the MELNHE project, including a datatable of site descriptions and a pdf file with the project description and diagram of plot configuration can be found in this data package: https://portal.edirepository.org/nis/mapbrowse?scope=knb-lter-hbr&identifier=344. 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. 

Soil respiration in 15 stands across 3 sites within the White Mountain National Forest was measured between 2008 and 2020. Stands included in the dataset are part of the Multiple Element in Northern Hardwood Ecosystems (MELNHE) study, a full-factorial NxP fertilization experiment. Pre- and post-treatment data are included, with treatment beginning in 2011. Soil temperature, soil moisture, and relative air humidity at the time of measurement were also recorded next to or above the soil respiration collar at the time of the soil respiration measurement. Having been cut between 1883 and 1990, stands are representative of different successional stages. 

Soils in our northeastern forests were formed in parent materials deposited by glaciers. The direction and distance of glacial movement can be used to predict the source of glacial till at “downstream” points on the landscape (Bailey 1992). The goal of this project was to identify the rocks excavated from the soil pits in each of the plots and then to use that data to validate the glacial till model. The minority of rocks in the soil pits matched the bedrock, showing the importance of glacial movement. Additional detail on the MELNHE project, including a data table of site descriptions and a pdf file with the project description and diagram of plot configuration can be found in this data package: https://portal.edirepository.org/nis/mapbrowse?scope=knb-lter-hbr&identifier=344. 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. Literature cited: Bailey, S.W., 1992. Lithologic composition and rock weathering potential of forested, glacial-till soils (Vol. 662). US Department of Agriculture, Forest Service, Northeastern Forest Experiment Station. 

Sugar maple (Acer saccharum Marsh.) sap sweetness and elemental concentrations, foliar gas exchange, and foliar elemental concentrations were measured in 2013 in Bartlett Experimental Forest stands C6, C8, and C9 and Jeffers Brook stands JBM and JBO. In February and March 2013, sugar maples were sampled for sap sweetness and elemental concentrations of potassium (K), aluminum (Al), calcium (Ca), magnesium (Mg), manganese (Mn), phosphorus (P), and strontium (Sr). In July 2013, leaves from four sugar maple trees per plot, representing the two highest and lowest sap sugar concentrations, were sampled for foliar gas exchange and foliar elemental analyses of Ca, K, Mn, P, nitrogen (N), and silicon (Si). Additional detail on the MELNHE project, including a datatable of site descriptions and a pdf file with the project description and diagram of plot configuration can be found in this data package: https://portal.edirepository.org/nis/mapbrowse?scope=knb-lter-hbr&identifier=344 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. 

The project reports the flux of biomass and nutrients in leaf litterfall in 14 stands (the “Federer Chronosequence”) of northern hardwood forests. These 14 stands are located in the White Mountains of New Hampshire. Monitoring occurred from August 1993 through summer 1997 and again from August 2003 through summer 2006. The litterfall year is defined as starting in August (when we first set out baskets) and ending in August of the following year, years are named by the fall (in which most litter falls). In some years, we have litter mass by basket (3 per transect): 1993, 1994, 1995, 2003, 2005. In other years, we have only transect means: 1996, 2004. Seasonal masses are provided for 2005. Litterfall was sorted by species in all years except for 2005. Twig mass is reported only for 2005. Litter chemistry was measured in fresh litter samples collected in the same stands from 1994 through 2004. Raw, unedited data sorted by season can be found in “Other Entities”, though note the substantial changes that occurred between these values and the processed values published in this dataset. 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. Related publications: Yanai, R. D., Arthur, M. A., Acker, M., Levine, C. R., & Park, B. B. (2012). Variation in mass and nutrient concentration of leaf litter across years and sites in a northern hardwood forest. Canadian Journal of Forest Research, 42(8), 1597-1610. Acker, M. 2006.Base cation concentration and content in litterfall and woody debris across a northern hardwood forest chronosequence. MS Thesis. Lexington, KY: University of Kentucky. Yang, Y., Yanai, R. D., See, C. R., & Arthur, M. A. (2017). Sampling effort and uncertainty in leaf litterfall mass and nutrient flux in northern hardwood forests. Ecosphere, 8(11), e01999. 

Freshly senesced leaf litter was collected during autumn in New Hampshire at the Bartlett Experimental Forest, Hubbard Brook Experimental Forest, and Jeffers Brook as part of the Multiple Elementation Limitation in Northern Hardwood Ecosystems (MELNHE) study. Leaf litter was collected in October 2021 and 2022 at peak litterfall (i.e., mid-October) during a rain-free period. These leaf-litter samples were analyzed for nutrient concentrations for use in resorption analyses. This dataset includes photos of all of the leaf-litter samples used for chemical analysis. For the corresponding chemistry data, please see the following data package: Zukswert, J., K. Gonzales, S. Hong, C. See, B. Quintero, and R.D. Yanai. 2025. Multiple Element Limitation in Northern Hardwood Ecosystems (MELNHE): Fresh Litter Chemistry ver 3. Environmental Data Initiative. https://doi.org/10.6073/pasta/f52a613213855e4b4a03fa4a0e2f2922 (Accessed 2025-01-14). These leaf litter samples correspond with green foliage samples collected in late July and early August of the same years: the green foliage data can be found in the following data package: Zukswert, J.M., S.D. Hong, K.E. Gonzales, C.R. See, and R.D. Yanai. 2025. Multiple Element Limitation in Northern Hardwood Ecosystems (MELNHE): Foliar Chemistry 2008-2022 in Bartlett, Hubbard Brook, and Jeffers Brook ver 4. Environmental Data Initiative. https://doi.org/10.6073/pasta/ef3696a753150d0a420fd9009f73b1e9 (Accessed 2025-01-14). Photos of the corresponding foliage samples can be found in the following data package: Zukswert, J.M. 2024. Multiple Element Limitation in Northern Hardwood Ecosystems (MELNHE): Foliage Scans and Photographs ver 2. Environmental Data Initiative. https://doi.org/10.6073/pasta/7d93f50f9f2e848805b4aac9ed24689c (Accessed 2025-01-14). Additional detail on the MELNHE project, including a datatable of site descriptions and a pdf file with the project description and diagram of plot configuration can be found in this data package: https://portal.edirepository.org/nis/mapbrowse?scope=knb-lter-hbr&identifier=344 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. 

The functioning of mycorrhizal symbioses is tied to soil nutrient status, suggesting that nutrient availability should influence the reproduction of mycorrhizal fungi. To quantify the effects of nitrogen (N) and phosphorus (P) availability on ectomycorrhizal fungal fruiting, we collected >4000 epigeous sporocarps representing 19 families during the course of a season in a full factorial NxP addition experiment in six replicate forest stands. Nutrient effects on fruiting shifted as the season progressed, with early fruiting species responding more to P and late-fruiting species responding more to N. The composition of species fruiting in young successional forests differed more with nutrient addition than in mature forests. Sporocarp abundance and species richness were suppressed by N addition. This work shows that N and P availability affect ectomycorrhizal fungal fruiting, with these effects taking place within a context defined by stand age and the progression of fruiting across the season. 

Root cores were obtained in 2010 (pre-treatment) from two soil depths, 0-10 cm and 30-50 cm, in two MELNHE stands, C5 and C7, at Bartlett Experimental Forest. Arbuscular mycorrhizal (AM) and ectomycorrhizal (EM) colonization and root length were quantified in each core to determine if AM or EM was more prevalent in shallow or deep soils. Detailed description and analyses of these data can be found in: Nash, J.M., Diggs, F.M. & Yanai, R.D. Length and colonization rates of roots associated with arbuscular or ectomycorrhizal fungi decline differentially with depth in two northern hardwood forests. Mycorrhiza 32, 213–219 (2022). https://doi.org/10.1007/s00572-022-01071-8 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.