Forests dominate the interannual variability of the North American carbon sink

Yoichi P. Shiga, Anna M. Michalak, Yuanyuan Fang, Kevin Schaefer, Arlyn E. Andrews, Deborah H. Huntzinger, Christopher R. Schwalm, Kirk Thoning, Yaxing Wei

Research output: Contribution to journalArticlepeer-review

23 Scopus citations


Understanding what drives the interannual variability (IAV) of the land carbon sink is crucial for improving future predictions of this important, yet uncertain, component of the climate system. While drivers of global and hemispheric-scale net ecosystem exchange (NEE) IAV have been investigated, our understanding of the drivers of NEE IAV at regional scales (e.g. sub-continental, biome-level) is quite poor. Here we explore the biome-level attribution and drivers of North American NEE using inverse estimates derived from a dense network of atmospheric CO2 observations. We find that deciduous broadleaf and mixed forests are the primary regions responsible for North American NEE IAV, which differs from the ecoregions identified for the globe and Northern Hemisphere. We also find that a suite of terrestrial biosphere models (TBMs) do not agree on the dominant biome contributing to NEE IAV, with TBMs falling along an apparent spectrum ranging between those with IAV dominated primarily by forested ecosystems to those with IAV dominated by non-forested ecosystems. Furthermore, this regional trade-off in TBM NEE IAV is found to be linked to differing regional responses to environmental drivers among TBMs. This work displays the importance of extra-tropical forests in driving continental NEE IAV and also highlights the challenges and limitations of using TBMs to inform regional-scale carbon flux dynamics.

Original languageEnglish (US)
Article numberaad505
JournalEnvironmental Research Letters
Issue number8
StatePublished - 2018


  • Atmospheric CO
  • Attribution
  • Carbon cycle
  • Drivers
  • Net ecosystem exchange
  • Regional scale

ASJC Scopus subject areas

  • Renewable Energy, Sustainability and the Environment
  • General Environmental Science
  • Public Health, Environmental and Occupational Health


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