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Dryad

Long-term monitoring reveals forest tree community change driven by atmospheric sulfate pollution and contemporary climate change

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Dec 09, 2020 version files 1.29 MB

Abstract

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.