DOI: 10.5061/dryad.zcrjdfn6z
title: Long-term monitoring reveals forest tree community change driven by atmospheric sulfate pollution and contemporary climate change

description: Aim: Montane environments are sentinels of global change, providing unique
 opportunities to assess impacts on species diversity. Multiple
 anthropogenic stressors such as climate change and atmospheric pollution
 may act concurrently or synergistically in restructuring communities.
 Thus, a major challenge for conservation is untangling the relative
 importance of different stressors. Here, we combine long-term monitoring
 with multivariate community modeling to estimate the anthropogenic drivers
 shaping forest tree diversity along an elevational gradient. Location:
 Camels Hump Mountain, Vermont, USA Methods: We used Generalized
 Dissimilarity Modelling (GDM) to model spatial and temporal turnover in
 beta diversity along an elevational gradient over a 50-year period, and
 tested for spatiotemporal shifts in density and elevational distribution
 of individual species. GDMs were used to predict community turnover as
 non-linear functions of changes in elevation, climate and atmospheric
 pollution. Results: We observed significant shifts in elevational range
 and density of individual species, which contributed to an overall
 reduction in the elevational gradient in beta diversity through time. GDMs
 showed the combined effects of sulfate deposition and temperature as
 drivers of this temporal reduction in beta diversity. Spatiotemporal
 changes differed among species, with shifts observed both up and
 downslope. For example, in a reversal of a previous upslope range
 contraction, red spruce (Picea rubens Sarg.) increased in density and
 shifted downslope since the 1990’s, occupying warmer, drier climates. Main
 conclusion: Our results demonstrate that global change is impacting the
 stratification of forest tree diversity along elevational gradients, but
 the responses of individual species are complex and variable in direction.
 We suggest abiotic drivers may directly impact individual species while
 also indirectly altering species interactions along elevational gradients.
 Our approach modelling the drivers of compositional turnover quantifies
 the rate and amount of change in beta diversity along environmental
 gradients, and serves as a powerful complement to studying
 species-specific responses.
description: In 1964, a long-term forest monitoring study was established on
 Camels Hump, a 1248m peak in the Green Mountains of Vermont. Inventory
 stands were established at intervals of approximately 60m along an
 elevational gradient from 549 to 1,159m on the mountain’s western slope.
 At each stand (N=11), five to ten permanently marked survey plots, each
 3.0 x 30.5m, were placed parallel to each other and roughly perpendicular
 to the contour line. Within each plot (N=85), species identity and
 diameter at breast height (dbh; 1.37m above ground) of all woody stems
 &gt; 2cm dbh were recorded during each of nine census years (1965,
 1979, 1983, 1986, 1990, 1995, 2000, 2004, 2015).
description: This is a comma separated file containing counts of forest trees
 by species for each census year. There are no missing
 values in the dataset. diam: Diameter at breast height
 (dbh) of each tree elevation: elevation of plot
 measured in meters above sea level (a.s.l.)
 rounded_ele: elevation of plot measured in meters above sea level
 (a.s.l.) rounded to nearest ten meters species: unique
 value assigned to each species in dataset