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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. 

Both theory and observations suggest that tree intrinsic water use efficiency (iWUE)—the ratio of photosynthetic carbon assimilation to stomatal conductance to water—increases with atmospheric CO2. However, the strength of this relationship varies across sites and species, prompting questions about additional physiological constraints and environmental controls on iWUE. In this study, we analyzed tree core carbon isotope ratios to examine trends in, and drivers of, iWUE in 12 tree species common to the temperate forests of eastern North America, where forests have experienced changes in CO2, climate, and atmospheric pollution in recent decades. Across all site-species combinations, we found that tree iWUE increased 22.3% between 1950 and 2011, coinciding with a 25.2% increase in atmospheric CO2. iWUE trajectories varied markedly among tree functional groups and within species across sites. Needleleaf evergreen iWUE increased until circa 2002 before declining in recent years, while iWUE of broadleaf deciduous species continued to increase. The analysis of environmental controls on iWUE trends revealed smaller increases in iWUE in trees subjected to higher atmospheric pollution loads. Our results suggest that tree functional characteristics and atmospheric pollution history influence tree response to atmospheric CO2, with implications for forest carbon and water balance in temperate regions. 

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. 

Leaf area index (LAI) is commonly used to assess forest canopies, and is calculated as the area of all leaves per unit area of ground. In September 2004, LAI was measured in all Bartlett Experimental Forest stands (C1-C9) of the MELNHE study in New Hampshire, using an LAI-2000 Plant Canopy Analyzer. Variables reported are leaf area index (LAI), standard error of LAI (SEL), diffuse non-interceptance (DIFN), mean tip angle (MTA), standard error of mean tip angle (SEM), and sample size (SMP). 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. 

Abstract Stomatal density, stomatal length and carbon isotope composition can all provide insights into environmental controls on photosynthesis and transpiration. Stomatal measurements can be time-consuming; it is therefore wise to consider efficient sampling schemes. Knowing the variance partitioning at different measurement levels (i.e., among stands, plots, trees, leaves and within leaves) can aid in making informed decisions around where to focus sampling effort. In this study, we explored the effects of nitrogen (N), phosphorus (P) and calcium silicate (CaSiO3) addition on stomatal density, length and carbon isotope composition (δ13C) of sugar maple (Acer saccharum Marsh.) and yellow birch (Betula alleghaniensis Britton). We observed a positive but small (8%) increase in stomatal density with P addition and an increase in δ13C with N and CaSiO3 addition in sugar maple, but we did not observe effects of nutrient addition on these characteristics in yellow birch. Variability was highest within leaves and among trees for stomatal density and highest among stomata for stomatal length. To reduce variability and increase chances of detecting treatment differences in stomatal density and length, future protocols should consider pretreatment and repeated measurements of trees over time or measure more trees per plot, increase the number of leaf impressions or standardize their locations, measure more stomata per image and ensure consistent light availability. 

Successional, second-growth forests dominate much of eastern North America; thus, patterns of biomass accumulation in standing trees and downed wood are of great interest for forest management and carbon accounting. The timing and magnitude of biomass accumulation in later stages of forest development are not fully understood. We applied a “chronosequence with resampling” approach to characterize live and dead biomass accumulation in 16 northern hardwood stands in the White Mountains of New Hampshire. Live aboveground biomass increased rapidly and leveled off at about 350 Mg/ha by 145 years. Downed wood biomass fluctuated between 10 and 35 Mg/ha depending on disturbances. The species composition of downed wood varied predictably with overstory succession, and total mass of downed wood increased with stand age and the concomitant production of larger material. Fine woody debris peaked at 30–50 years during the self-thinning of early successional species, notably pin cherry. Our data support a model of northern hardwood forest development wherein live tree biomass accumulates asymptotically and begins to level off at ∼140–150 years. Still, 145-year-old second-growth stands differed from old-growth forests in their live ( p = 0.09) and downed tree diameter distributions ( p = 0.06). These patterns of forest biomass accumulation would be difficult to detect without a time series of repeated measurements of stands of different ages. 

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. 

Northern hardwood forests have long been assumed to be primarily nitrogen limited, but may often be co‐limited by multiple elements. Nutrient limitation can be inferred through responses of foliar and litter chemistry to nutrient addition over time. We compared community‐level foliar and litter chemistry and resorption efficiency in a long‐term, factorial nitrogen (N) and phosphorus (P) fertilization study across 10 forest stands at three sites in New Hampshire, where N and P were added annually. We measured N, P, calcium (Ca), magnesium (Mg), and potassium (K) in foliage from codominant trees and in fresh litter in 2008–2010 (pretreatment) and again in 2014–2016 and 2021–2022. Foliar N and P concentrations indicated co‐limitation in 2014–2016 based on reduced concentrations of one nutrient following addition of the other, suggesting a dilution effect. In 2021–2022, an interactive effect of N and P addition was observed: foliar P concentrations were lower under N+P addition, consistent with dilution following a greater growth response to N + P than to P addition, which was observed by 2015–2019. Changes in litter N and P concentrations with N and P addition mirrored those in foliar N and P. Resorption efficiency of N and P decreased with addition of these respective nutrients and P resorption efficiency was higher in the N+P treatment than the P treatment. Foliar Ca and litter Ca and K decreased with N addition but increased with P addition. Results indicated N and P co‐limitation and revealed biogeochemical interactions among N, P and base cations. 

Leaf temperature measurements were collected during the summer of 2020 within forested areas at the Thompson Farm Earth Systems Observatory in Durham, New Hampshire, USA. Located within the property is a registered Ameriflux site, Thompson Farm Forest (US-TFF), as well as experimental throughfall exclusion plots that are part of DroughtNet (experiment running since 2015). Leaf temperature measurements were made within the footprint of the eddy covariance flux tower as well as within both control and throughfall exclusion treatment plots. Upper canopy foliage was accessed using a bucket lift and in situ measurements made using a handheld thermal IR sensor. All data were paired with concurrent meteorological measurements from US-TFF or data from a co-located NOAA CRN station (NH Durham 2 SSW). Additionally, leaf chemical, physical, structure, and physiological traits have been measured at this site as well as canopy scale measures of structure and UAV-based spectral, thermal, and lidar imagery. Specific to this leaf temperature dataset, leaf-level light, temperature, and vpd photosynthetic response curves were measured. 

Standing trees and downed wood were inventoried in all of the chronosequence stands in the White Mountains, New Hampshire to characterize biomass. Live and standing dead trees were inventoried in the chronosequence stands in 1994, 2004, 2012, and 2021. Coarse (≥ 7.6 cm diameter) and fine woody debris (3.0 – 7.6 cm) were inventoried at the same stands in 2004 and 2020. Twigs (FWD < 3.0 cm) were inventoried in 2004 and 2020. The Bowl and Mt. Pond old-growth sites were inventoried (standing trees and downed wood) in 2021.