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Research Project: Understanding Water-Driven Ecohydrologic and Erosion Processes in the Semiarid Southwest to Improve Watershed Management

Location: Southwest Watershed Research Center

Title: Declines in northern forest tree growth following snowpack decline and soil freezing

Author
item Reinmann, A.c. - Boston University
item Susser, J.r. - Boston University
item Demaria, Eleonora
item Templer, P.h. - Boston University

Submitted to: Global Change Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/24/2018
Publication Date: 8/1/2018
Citation: Reinmann, A., Susser, J., Demaria, E.M., Templer, P. 2018. Declines in northern forest tree growth following snowpack decline and soil freezing. Global Change Biology. 25:420-430. https://doi.org/10.1111/gcb.14420.
DOI: https://doi.org/10.1111/gcb.14420

Interpretive Summary: Projected declines in snow cover due to a warmer atmosphere will have adverse effect on forest productivity in northern climates. Using snow and sugar maple trees productivity measurements from an experimental site in New Hampshire, U.S.A, this study shows that when snow cover declines there is increased soil freezing and this reduces root vitality and nutrient uptake by the trees. Additionally, the loss of forest insulation, when snowpack reduces, will likely decrease carbon sequestration by forestsvin the Northeastern U.S. along the Canadian border.

Technical Abstract: The northern forest is projected to experience declines in winter snowpack depth and duration that will increase soil frost severity over the next century. Though adverse effects of these changes in winter climate on tree physiology have been well documented, the response of forest aboveground net primary productivity (ANPP) is unknown. We use a 5-year snow removal experiment, tree species distribution data, and projected changes in snowpack over the next century to document the effects of reduced snowpack and increased soil freezing on ANPP of Acer saccharum (sugar maple), a dominant tree species in northern temperate forests, and its implications for forest carbon (C) sequestration. Sugar maple trees previously exposed to a reduced winter snowpack and greater soil freezing in these experimental plots have reduced root vitality, nutrient uptake and terminal shoot elongation. Here we show that these adverse impacts on tree physiology are accompanied by a 40% reduction in sugar maple ANPP with no indication of growth recovery one year after cessation of the experiment. The combination of high sugar maple biomass (22% of forest aboveground biomass) and large projected declines in snowpack (up to 95% of the northern forest will lose its insulating snowpack; defined as 20 cm depth) make the 3.3 million ha of deciduous forest in the Northeastern U.S. along the Canadian border particularly vulnerable to changes in winter climate. Our study demonstrates the important, but often overlooked, impacts of changes in snowpack and soil frost dynamics on tree growth and northern forest C storage, and shows that studies focusing on growing season climate likely overestimate rates of tree growth and C storage in response to climate change.