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Upslope shifts in plant distributions are often attributed to warming climate and lengthening of the growing season; however, biotic interactions may also contribute. The impacts of pests and pathogens are often sensitive to climate change and can vary along the climatic gradient associated with elevation. American beech ( Fagus grandifolia) has moved upslope throughout the northeastern United States. Meanwhile, beech growth and longevity have decreased as a result of beech bark disease (BBD), a decline disease caused by the introduced European felted beech scale insect ( Cryptococcus fagisuga) and native fungi from the genus Neonectria. Within a forested landscape spanning 250–1150 m elevation, we examined the relationships between elevation, beech demography and BBD to explore whether release from BBD at higher elevation may contribute to the upslope expansion of beech. Beech has shifted upslope at a rate of 1 m⋅year −1 coincident with lower mortality, higher recruitment, faster growth, lower BBD severity, and higher sapling densities at higher elevations. We suggest that climatic constraints on the beech scale insect at high elevations has led to a lower impact of BBD, which contributed to higher rates of beech growth, survival, and recruitment and in turn facilitated the regional upslope shift of beech. 

Leaf area index (LAI) of the mature deciduous forest adjacent to WS6 at Hubbard Brook Experimental Forest is estimated on the basis of leaf litterfall collections; the raw data for litterfall are posted in the EDI data package – Fine Litterfall Data at the Hubbard Brook Experimental Forest, 1992 – present (https://portal.edirepository.org/nis/mapbrowse?scope=knb-lter-hbr&identifier=49). These plots are designated TF, referring to throughfall chemistry collections performed at these plots many years ago (Lovett et al. 1996). Leaf litterfall is collected in 0.097 m2 litter traps raised 1.5 m above ground level and is sorted by species. The number of leaves of each species is counted. The counts are multiplied by the average area per leaf for each species in each plot to estimate LAI. Litter traps are located randomly within each of three plots that are arranged along the elevation gradient within the deciduous forest zone. 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. Gary M. Lovett, Scott S. Nolan, Charles T. Driscoll, and Timothy J. Fahey. Factors regulating throughfall flux in a New Hampshire forested landscape. Canadian Journal of Forest Research. 26(12): 2134-2144. https://doi.org/10.1139/x26-242 

Leaf area index (LAI) of the mature deciduous forest on WS1 at Hubbard Brook Experimental Forest is estimated on the basis of leaf litterfall collections; the raw data for litterfall are posted in the EDI data package – Fine Litterfall Data at the Hubbard Brook Experimental Forest, 1992 – present (https://portal.edirepository.org/nis/mapbrowse?scope=knb-lter-hbr&identifier=49). This watershed was treated with a calcium silicate mineral (wollastonite) in 1999 to gradually replace Ca lost as a result of acid deposition. Leaf litterfall is collected in 0.097 m2 litter traps raised 1.5 m above ground level and is sorted by species. The number of leaves of each species is counted. The counts are multiplied by the average area per leaf for each species in each plot to estimate LAI. Litter traps are located randomly within each of three plots that are arranged along the elevation gradient within the deciduous forest zone. 

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. 

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. 

The forest inventory surveys in the bird area were initiated in 1981 and transects were made permanent in 1991 by Tom Siccama who created and designed this tree survey. The inventory is representative of approximately 2.5 km2 of mid elevation northern hardwood forest. The data set is particularly geared toward producing accurate mortality and recruitment estimates. It consists of a total inventory of all trees greater than or equal to 10 cm dbh within each of four 10 m wide belt transects. The parallel transects are placed approximately 200 m apart and 290° bearing in an east-west direction for 2200 to 2900 m. In 1991, each live stem greater than or equal to 10 cm dbh was tagged with a unique number. Tree vigor is assessed every two years and diameter is remeasured every ten years. Every two years, new tags are placed on stems that have grown into the 10 cm diameter class. A survey of smaller trees (greater than or equal to 2 to less than 10 cm dbh) was first taken in 1991 and is resurveyed every ten years. This dataset includes 1991 and subsequent samplings. Data from an earlier sampling in 1981 can be found in: Sherry, T., D. Holmes, and T. Siccama. 2019. Forest Inventory of a Northern Hardwood Forest: Bird Area at the Hubbard Brook Experimental Forest, 1981 ver 7. Environmental Data Initiative. https://doi.org/10.6073/pasta/206b98f6553f1ff95cf584dd2185554e (Accessed 2021-09-16). 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. These data have been used in the following publication: Siccama, T.G., Fahey, T.J., Johnson, C.E., Sherry, T.W., Denny, E.G., Girdler, E.B., Likens, G.E., and Schwarz, P.A. 2007. Population and biomass dynamics of trees in a northern hardwood forest at Hubbard Brook. Can. J. For. Res. 37(4): 737–749. doi:10.1139/X06-261. 

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. 

Leaf area index (LAI) of the mature deciduous forest in the Bear Brook watershed (west of WS6) at Hubbard Brook Experimental Forest is estimated on the basis of leaf litterfall collections; the raw data for litterfall are posted in the EDI data package – Fine Litterfall Data at the Hubbard Brook Experimental Forest, 1992 – present (https://portal.edirepository.org/nis/mapbrowse?scope=knb-lter-hbr&identifier=49). Leaf litterfall collected in 0.097 m2 litter traps is sorted by species. The number of leaves of each species is counted. The counts are multiplied by the average area per leaf for each species in each plot to estimate LAI. Litter traps are located randomly within each of four plots that are arranged along the elevation gradient within the deciduous forest zone. 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 valley-wide plots are a grid of 431 sites along fifteen N–S transects established at 500-m intervals spanning the entire Hubbard Brook Valley. The plot network was designed by Paul Schwarz for spatial analysis of tree species distribution patterns within the valley. Multiple above- and below-ground attributes have been measured on these plots. This dataset includes forest inventory data at 10 year intervals, for 1995, 2005, and 2015. The full survey takes three seasons to complete, with the datatable listing the exact measurement interval for each tree. Data are included for both trees and saplings on 371 core plots (all surveys) and 60 densified plots (1998, 2008). Locations of plots in this study can be found in the following dataset: Hubbard Brook Experimental Forest Valleywide Plots: GIS Shapefile (2022.) https://doi.org/10.6073/pasta/440b176372e0cdeb341731aea816b67c 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. These data have been used in a number of publications including: Schwarz, P.A., Fahey, T.J., Martin, C.W., Siccama, T.G., and Bailey, A. 2001. Structure and composition of three northern hardwood–conifer forests with differing disturbance histories. For. Ecol. Manage. 144(1–3): 201–212. doi:10.1016/S0378-1127(00)00371-6. Schwarz, P.A., Fahey, T.J., and McCulloch, C.E. 2003. Factors controlling spatial variation of tree species abundance in a forested landscape. Ecology, 84(7): 1862–1878. doi:10.1890/0012-9658(2003)084[1862:FCSVOT]2.0.CO;2. van Doorn, N.S., Battles, J.J., Fahey, T.J., Siccama, T.G., and Schwarz, P.A. 2011. Links between biomass and tree demography in a northern hardwood forest: a decade of stability and change in Hubbard Brook Valley, New Hampshire. Can. J. For. Res. 41(7): 1369–1379. doi:10.1139/X11-063. Cleavitt, NL; AB Clyne and TJ Fahey. 2019. Epiphytic macrolichen patterns along an elevation gradient in the White Mountain National Forest, New Hampshire. J. Torrey Bot. Soc. 146(1): 8-17. Cleavitt, NL; Battles, JJ, Fahey, TJ, and Blum, J. 2014. Determinants of survival over seven years for a natural cohort of sugar maple seedlings in a northern hardwood forest. Can. J. For. Res.44 (9): 1112-1121.