Shrub Expansion Can Counteract Carbon Losses From Warming Tundra

Journal Article · Mon Jul 28 00:00:00 EDT 2025 · Journal of Geophysical Research. Biogeosciences

DOI:https://doi.org/10.1029/2024JG008721· OSTI ID:3002754

Yazbeck, Theresia ^[1]; Bohrer, Gil ^[1]; Sonnentag, Oliver ^[2]; Qu, Bo ^[2]; Detto, Matteo ^[3]; Hould‐Gosselin, Gabriel ^[2]; Graveline, Vincent ^[2]; Alcock, Haley ^[2]; Lecavalier, Bruno ^[2]; Marsh, Philip ^[4]; Cannon, Alex ^[5]; Riley, William J. ^[6]; Zhu, Qing ^[6]; Yuan, Fengming ^[7]; Sulman, Benjamin ^[7]

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1. The Ohio State Univ., Columbus, OH (United States)
2. Univ. of Montreal, QC (Canada)
3. Princeton Univ., NJ (United States)
4. Wilfrid Laurier Univ., Waterloo. ON (Canada)
5. Environment and Climate Change Canada, Victoria, BC (Canada)
6. Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
7. Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)

Arctic warming is causing substantial compositional, structural, and functional changes in tundra vegetation including shrub and tree-line expansion and densification. However, predicting the carbon trajectories of the changing Arctic is challenging due to interacting feedbacks between vegetation composition and structure, and surface characteristics. We conduct a sensitivity analysis of the current-date to 2100 projected surface energy fluxes, soil carbon pools, and CO₂ fluxes to different shrub expansion rates under future emission scenarios (intermediate—RCP4.5, and high—RCP8.5) using the Arctic-focused configuration of E3SM Land Model (ELM). We focus on Trail Valley Creek (TVC), an upland tundra site in the western Canadian Arctic, which is experiencing shrub densification and expansion. We find that shrub expansion did not significantly alter the modeled surface energy and water budgets. However, the carbon balance was sensitive to shrub expansion, which drove higher rates of carbon sequestration as a consequence of higher shrubification rates. Thus, at low shrub expansion rates, the site would become a carbon source, especially under RCP8.5, due to higher temperatures, which deepen the active layer and enhance soil respiration. At higher shrub expansion rates, TVC would become a net CO₂ sink under both Representative Concentration Pathway scenarios due to higher shrub productivity outweighing temperature-driven respiration increase. Our simulations highlight the effect of shrub expansion on Arctic ecosystem carbon fluxes and stocks. We predict that at TVC, shrubification rate would interact with climate change intensity to determine whether the site would become a carbon sink or source under projected future climate.

• Research Organization: Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States); Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
• Sponsoring Organization: National Science Foundation (NSF); US Department of Energy; USDOE; USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23), Climate and Environmental Sciences Division (SC-23.1 )
• Grant/Contract Number: AC02-05CH11231; AC05-00OR22725; SC0021067; SC0023084
• OSTI ID: 3002754
• Alternate ID(s): OSTI ID: 2587927
• Journal Information: Journal of Geophysical Research. Biogeosciences, Journal Name: Journal of Geophysical Research. Biogeosciences Journal Issue: 8 Vol. 130; ISSN 2169-8953; ISSN 2169-8961
• Publisher: American Geophysical Union
• Country of Publication: United States
• Language: English