Projections of water, carbon, and nitrogen dynamics under future climate change in an old-growth Douglas-fir forest in the western Cascade Range using a biogeochemical model

Abstract

Statistically downscaled climate change scenarios from four General Circulation Models for two Representative Concentration Pathways (RCP)were applied as inputs to a biogeochemical model, PnET-BGC, to examine potential future dynamics of water, carbon, and nitrogen in an old-growth Douglas-fir forest in the western Cascade Range. Projections show 56% to 77% increases in stomatal conductance throughout the year from 1986–2010 to 2076–2100, and 65% to 104% increases in leaf carbon assimilation between October and June over the same period. However, future dynamics of water and carbon under the RCP scenarios are affected by a 49% to 86% reduction in foliar biomass resulting from severe air temperature and humidity stress to the forest in summer. Important implications of future decreases in foliar biomass include 1) 20% to 71% decreases in annual transpiration which increase soilmoisture by 7% to 15% in summer and fall; 2) decreases in photosynthesis by 77% and soil organic matter by 62% under the high radiative forcing scenario; and 3) altered foliar and soil carbon to nitrogen stoichiometry. Potential carbon dioxide fertilization effects on vegetation are projected to 1) amplify decreases in transpiration by 4% to 9% and increases in soil moisture in summer and fall by 1% to 2%; and 2) alleviate decreases in photosynthesis by 4%; while 3) having negligible effects on the dynamics of nitrogen. Our projections suggest that future decrease in transpiration and moderate water holding capacity maymitigate soilmoisture stress to the old-growth Douglas-fir forest. Future increases in nitrogen concentration in soil organicmatter are projected to alleviate the decrease in net nitrogenmineralization despite a reduction in decomposition of soil organic matter by the end of the century.

Citation

Dong, Zheng; Driscoll, Charles T.; Johnson, Sherri L.; Campbell, John L.; Pourmokhtarian, Afshin; Stoner, Anne M.K.; Hayhoe, Katharine. 2019. Projections of water, carbon, and nitrogen dynamics under future climate change in an old-growth Douglas-fir forest in the western Cascade Range using a biogeochemical model. Science of The Total Environment. 656: 608-624. https://doi.org/10.1016/j.scitotenv.2018.11.377.