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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 is published in support of a manuscript titled "Nitrogen and phosphorus co-limitation of forest growth in northern hardwood forests" and includes data and code used in the analysis. The primary diameter breast height dataset can be found in: Fisk, M.C., R.D. Yanai, and T.J. Fahey. 2025. Tree DBH response to nitrogen and phosphorus fertilization in the MELNHE study, Hubbard Brook Experimental Forest, Bartlett Experimental Forest, and Jeffers Brook ver 2. Environmental Data Initiative. https://doi.org/10.6073/pasta/fb8f8d5b903627bee9ad6aa4c32f2289. 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 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. 

Identifying which aspects of global environmental change are driving observed ecosystem process responses is a great challenge. Here, we address how long-term (10-25 year) alterations in soil moisture, and nitrogen (N) oligotrophication (i.e. decreases in soil N availability relative to plant demand), alter the production of plant-available N via net mineralization and nitrification in a northern hardwood forest. Our objectives were to determine whether soil moisture has changed over the past decade and whether N cycle processes have become less sensitive to soil moisture over time due to N oligotrophication. We used long-term data sets from several related studies to show: (i) increasing winter soil temperatures and declining summer soil moisture from late 2010 into 2024; (ii) reductions in sensitivity of N cycling rates to soil moisture, and (iii) declining moisture-adjusted N cycle processes (the ratio of rate of N process:soil moisture) over time in both summer and winter. These changes suggest continued reductions in N availability to plants in these forests, with potential effects on forest productivity and response to disturbance. 

The Multiple Element Limitation in Northern Hardwood Ecosystems (MELNHE) project studies N and P acquisition and limitation through a series of nutrient manipulations in northern hardwood forests. This data set includes net N mineralization measured in Oe, Oa, and mineral soil horizons in all 13 of the MELNHE study sites. Samples are collected every several years, beginning with pretreatment (2008 and 2009) through 2017, representing 3 years of N and P fertilization. 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 following papers describe and make use of these data: Kang H, Fahey TJ, Bae K, Fisk MC, Sherman RE, Yanai RD, See C. 2016. Response of forest soil respiration to nutrient addition depends on site fertility. Biogeochemistry 127:113-124. https://doi.org/10.1007/s10533-015-0172-6. Ratliff TJ, Fisk MC. 2016. Phosphatase activity is related to N availability but not P availability across hardwood forests in the northeastern United States. Soil Biology and Biochemistry 94:61-69. https://doi.org/10.1016/j.soilbio.2015.11.009. Bae B, Fahey TJ, Yanai RD, Fisk MC. 2015. Soil nitrogen availability affects belowground carbon allocation and soil respiration in northern hardwood forests of New Hampshire. Ecosystems 18:1179-1191. https://doi.org/10.1007/s10021-015-9892-7. Fisk MC, Ratliff TJ, Goswami S, Yanai RD. 2014. Synergistic soil response to nitrogen plus phosphorus fertilization in hardwood forests. Biogeochemistry 118:195-204. https://doi.org/10.1007/s10533-013-9918-1. 

Nutrient cycling in forest ecosystems can be sensitive to disturbances that change the availability of one nutrient relative to others, altering the synchrony in nutrient cycles that is expected to develop in undisturbed systems. We asked whether the relative availabilities of nitrogen (N) and phosphorus (P) differ with forest successional age after harvest, and tested effects of adding one nutrient on availability and recycling of the other, in a factorial nitrogen (N) × phosphorus (P) fertilization study in multiple early- and mid-successional and mature northern hardwood forest stands in central NH, USA. We did not find effects of forest age on resin-available N:P ratios, which varied widely among successional forest stands and were related to net N mineralization potentials in the forest floor of each stand. P addition suppressed resin-N availability by 31 % and lowered litterfall N recycling by 10 %, but we detected no effects on net N mineralization potentials. P addition also increased nitrification potentials in the organic horizon by up to 60 %, mostly in combination with added N. The effects of added N depended on P; lower resin-P in mature stands and lower litterfall P recycling in stands of all ages were detected only when P was added with N. We conclude that P limitation influences N recycling across forest age classes in these northern hardwoods, with some indication of stronger effects in successional stands. However, net N mineralization potentials better predicted the resin-N response to added P than did stand age. Our results suggest that alleviating P limitation promotes N limitation over time, especially in more rapidly growing successional forests, by increasing biotic demand for N, reducing its recycling in litterfall, and potentially by reducing net N mineralization. 

Although temperate forests are generally thought of as N-limited, resource optimization theory predicts that ecosystem productivity should be co-limited by multiple nutrients. These ideas are represented in the Multi-Element Limitation (MEL) model (Rastetter et al. 2012). To test the patterns of resource limitation predicted by MEL, we are conducting nutrient manipulations in three study sites in New Hampshire: Bartlett Experimental Forest (BEF), Hubbard Brook Experimental Forest (HBEF), and Jeffers Brook in the White Mountain National Forest. We are monitoring stem diameter, leaf area, sap flow, foliar chemistry, leaf litter production and chemistry, foliar nutrient resorption, root biomass and production, mycorrhizal associations, soil respiration, heterotrophic respiration, N and P availability, N mineralization, soil phosphatase activity, soil carbon and nitrogen, nutrient uptake capacity of roots, and mineral weathering. These data can be found in the EDI repository, using the search term "MELNHE" (http://portal.edirepository.org), and through the data catalog on https://hubbardbrook.org, using the same search term. This data package is referenced by the MELNHE datasets, and includes a datatable of site descriptions and a pdf file with the project description, and diagrams of plot configuration. 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. 

Functional balance theory predicts that plants will allocate less carbon belowground when the availability of nutrients is elevated. We tested this prediction in two successional northern hardwood forest stands by quantifying fine root biomass and growth after 5–7 years of treatment in a nitrogen (N) x phosphorus (P) factorial addition experiment. We quantified root responses at two different levels of treatment: the whole-plot scale fertilization and small-patch scale fertilization of ingrowth cores. Fine root biomass was higher in plots receiving P, and fine root growth was highest in plots receiving both N and P. Thus, belowground productivity did not decrease in response to long-term addition of nutrients. We did not find conclusive evidence that elevated availability of one nutrient at the plot scale induced foraging for the other nutrient at the core scale, or that foraging for nutrients at the core scale responded to addition of limiting nutrients. Our observations suggest NP co-limitation of fine root growth and indicate complex interactions of N and P affecting aboveground and belowground production in early successional northern hardwood forest ecosystems. 

This dataset describes litterfall mass collected in the Multiple Element Limitation in Northern Hardwood Ecosystems (MELNHE) study in New Hampshire from fall 2009 through summer 2022. Litter was collected three times per year: fall (late October or early November), spring (June), and summer (August). Fall litter was sorted by species in a subset of stands. This data package also includes the R code used to impute missing data for analysis, a manually edited data file used in the R code flow, and a file matching the labels for litterfall collectors from the original (pre Fall 2011) and current (Fall 2011 and onwards) labeling systems. All collectors have the most current label if known for all years of data. Additional detail on MELNHE, including a table of stand descriptions, project description, and a diagram of plot configuration can be found in this data package: Yanai, R.D., M. Fisk, and T.J. Fahey. 2024. Multiple Element Limitation in Northern Hardwood Ecosystems (MELNHE): Project description, plot characteristics and design ver 2. Environmental Data Initiative. https://doi.org/10.6073/pasta/6cc8a39d052834c030650fb29937bf4f (Accessed 2024-10-17). Litterfall chemistry data for a subset of these samples can be found in the following data package: Fisk, M.C., R.D. Yanai, S.D. Hong, C.R. See, and S. Goswami. 2022. Litter chemistry and masses for the MELNHE NxP fertilization experiment ver 1. Environmental Data Initiative. https://doi.org/10.6073/pasta/8b2975a3a02cbcfb1b0a12ac954576d4 (Accessed 2024-06-09). 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 MELNHE study looks at patterns of resource limitation through nutrient manipulations in three study sites in New Hampshire: Bartlett Experimental Forest, Hubbard Brook Experimental Forest, and Jeffers Brook, located in the White Mountain National Forest. The investigation is monitoring stem diameter, leaf area, sap flow, foliar chemistry, leaf litter production and chemistry, foliar nutrient resorption, root biomass and production, mycorrhizal associations, soil respiration, heterotrophic respiration, N and P availability, N mineralization, soil phosphatase activity, soil carbon and nitrogen, nutrient uptake capacity of roots, and mineral weathering. This data set includes phosphate, nitrate and ammonium availability measured using resin exchange strips. 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 following papers describe and make use of these data: Fisk MC, Ratliff TJ, Goswami S, Yanai RD. 2014. Synergistic soil response to nitrogen plus phosphorus fertilization in hardwood forests. Biogeochemistry 118:195-204. https://doi.org/10.1007/s10533-013-9918-1 Goswami S, Fisk MC, Vadeboncoeur MA, Johnston M, Yanai RD, and Fahey TJ. 2018. Phosphorus limitation of aboveground production in northern hardwood forests. Ecology 99: 438-449. https://doi.org/10.1002/ecy.2100 Shan S, Fisk MC, Fahey TJ. 2018. Contrasting effects of N on rhizosphere processes in two northern hardwood species. Soil Biology and Biochemistry 126: 219-227. https://doi.org/10.1016/j.soilbio.2018.09.007 Shan S, Devens H, Fahey TJ, Yanai RD, Fisk MC. 2022. Fine root growth increases in response to nitrogen addition in phosphorus-limited northern hardwood forests. Ecosystems, https://doi.org/10.1007/s10021-021-00735-4 Gonzales KE, Yanai RD, Fahey TJ, Fisk MC. 2023. Evidence for P limitation in eight northern hardwood stands: Foliar concentrations and resorption by three tree species in a factorial N by P addition experiment. Forest Ecology and Management 529: 120696. https://doi.org/10.1016/j.foreco.2022.120696 Li S, Fisk MC, Yanai RD, Fahey TJ. 2023. Co-limitation of root growth by nitrogen and phosphorus in early successional northern hardwood forest. Ecosystems. https://10.1007/s10021-023-00869-7 

The Multiple Element Limitation in Northern Hardwood Ecosystems (MELNHE) project studies N and P acquisition and limitation through a series of nutrient manipulations in northern hardwood forests. This data set includes net N mineralization measured in Oe, Oa, and mineral soil horizons in all 13 of the MELNHE study sites. Samples are collected every several years, beginning with pretreatment (2008 and 2009) through 2017, representing 3 years of N and P fertilization. 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 following papers describe and make use of these data: Kang H, Fahey TJ, Bae K, Fisk MC, Sherman RE, Yanai RD, See C. 2016. Response of forest soil respiration to nutrient addition depends on site fertility. Biogeochemistry 127:113-124. https://doi.org/10.1007/s10533-015-0172-6. Ratliff TJ, Fisk MC. 2016. Phosphatase activity is related to N availability but not P availability across hardwood forests in the northeastern United States. Soil Biology and Biochemistry 94:61-69. https://doi.org/10.1016/j.soilbio.2015.11.009. Bae B, Fahey TJ, Yanai RD, Fisk MC. 2015. Soil nitrogen availability affects belowground carbon allocation and soil respiration in northern hardwood forests of New Hampshire. Ecosystems 18:1179-1191. https://doi.org/10.1007/s10021-015-9892-7. Fisk MC, Ratliff TJ, Goswami S, Yanai RD. 2014. Synergistic soil response to nitrogen plus phosphorus fertilization in hardwood forests. Biogeochemistry 118:195-204. https://doi.org/10.1007/s10533-013-9918-1.