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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. 

Coarse litterfall (woody litter greater than 2 cm diameter) was collected from cleared plots in the same sites as fine litterfall to quantify total aboveground litterfall in the reference forest. These collections are for quantifying CWD inputs from live standing trees rather than all CWD inputs. Tree mortality and fall rates are used for dead tree inputs. All together these data are used to calculate aboveground production and forest carbon and nutrient budgets. 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. 

In order to evaluate the role of Ca supply in regulating the structure and function of base-poor forest and aquatic ecosystems, the Ca content of soil was increased through the application of wollastonite (CaSiO3) in October 1999. The watershed is forested by typical northern hardwood species (sugar maple, beech and yellow birch) on the lower 90 % of its area, and by a montane boreal transition forest of red spruce, balsam fir and white birch on the highest 10%. Forest inventory surveys were initiated in 1996 and repeated at 5 year intervals. This data set includes 2016 inventory measurements. The data consists of a total inventory of all trees ≥10 cm diameter-at-breast-height (dbh) on the whole of the watershed (11.8 ha), as measured in each of the 200 25 m x 25 m plots. Trees ≥ 2 to ≤10 cm dbh were subsampled using a 3 meter wide strip along one edge of each 25 m x 25 m plot. With the addition of tree tags in 2006 on all trees ≥10 cm dbh, tracking of individual trees is now possible and trees that grow into the ≥10 cm dbh size class are tagged each survey. The data consist of the diameters (dbh) of all the trees ≥10 cm dbh, live and dead, in the whole of the watershed (about 9000 individual stems) and an additional 3000-4000 saplings. 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. 

A whole-tree harvest was conducted during the dormant season of 1983-1984 in order to assess ecosystem response to whole-tree logging operations. Pre-harvest forest inventory surveys were conducted in 1982 on the whole of the watershed. Post-harvest surveys were conducted in 1990, 1994 and every 5 years thereafter. This data set includes data for 1982 – 2019 surveys. The hydrology has been monitored since 1962 and stream water chemistry monitored since 1963. In 1982, before the clearcut, the watershed was forested by typical northern hardwood species (sugar maple, beech and yellow birch) on the lower 85 % of its area and by a montane boreal transition forest of red spruce, balsam fir and white birch on the highest 15%. 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 watershed is forested by typical northern hardwood species (sugar maple, beech and yellow birch) on the lower 90% of its area and by a montane boreal transition forest of red spruce, balsam fir and white birch on the highest 10%. Forest inventory surveys were initiated in 1965, repeated in 1977, and repeated at 5 year intervals after that. This data set includes all inventories from 1965 to 2022 (11 surveys). The inventory consists of a total inventory of all trees ≥10 cm diameter-at-breast-height (dbh) (over 11,000 individual stems overtime) on the whole of the watershed (13.23 ha, 549−792 m in elevation), as measured in each of the 208 grid cells (= plots; 25 m x 25 m, 625 m2). Trees ≥2 to <10 cm dbh were subsampled using a 3 meter wide strip along one edge of each 25 m x 25 m plot. While the specifics of the inventory design varied between watersheds and over time, the core measurements were consistent. Differences between exact inventory methods over time are detailed in the Methods. The surveys include 6000 – 7000 live trees and another 2000-3000 dead standing trees. These data were gathered as part of the Hubbard Brook Ecosystem Study (HBES) and funded largely through the Long-term Ecological Research (LTER) program through NSF since 1988. 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. 

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. 

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. 

Fine litterfall (leaves, twigs, fruits, seeds, etc.) is collected in Watershed 1, Watershed 5, the Throughfall plots and the Bear Brook Watershed reference forest, located to the west of Watershed 6, to quantify carbon and nutrient flux associated with this important pathway. These measurements have facilitated quantification of ice storm effects and species declines (paper birch, sugar maple). 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. 

Overstory foliage is collected in late summer from a reference forest to the west of Watershed 6 (also referred to as Bear Brook Watershed). Concentrations of C, N, P, K, Ca, Mn, Mg, and the natural abundance of N and C isotopes (delta-15N and delta-13C) in foliage are measured. These measurements, in combination with litterfall estimates of foliar biomass, allow us to estimate the pool of nutrients in foliage. They also allow us to estimate nutrient retranslocation, using measurements of leaf litterfall chemistry. Long-term measurements continue with the aim of detecting disturbances in nutrient cycling and trends in foliar chemistry over long time scales. 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.