The U.S. Carbon budget: contributions from land-Use change

Area of Science:

• Environmental Science
• Ecology
• Climate Science

Background:

• Historical land use, including clearing, abandonment, and wood harvesting, significantly impacts terrestrial carbon storage.
• Understanding these historical land use dynamics is crucial for accurate carbon cycle modeling.

Purpose of the Study:

• To reconstruct historical land use changes in the United States from 1700 to 1990.
• To quantify the net carbon flux to and from terrestrial ecosystems as a result of these land use changes.

Main Methods:

• Reconstruction of historical land use rates (clearing, abandonment, harvesting, burning) using available data.
• Application of a terrestrial carbon model to simulate annual changes in ecosystem carbon storage.

Main Results:

• Land use changes released an estimated 27 +/- 6 petagrams of carbon (PgC) to the atmosphere before 1945.
• After 1945, terrestrial ecosystems accumulated 2 +/- 2 PgC, primarily due to fire suppression and afforestation of abandoned farmlands.
• In the 1980s, carbon fluxes from land management offset 10-30% of U.S. fossil fuel carbon emissions.

Conclusions:

• Historical land use has been a major driver of atmospheric carbon over the past three centuries.
• Modern land management, particularly fire suppression and forest regrowth, has shifted the U.S. terrestrial ecosystem from a net carbon source to a sink.
• Land management plays a significant role in modulating national carbon budgets and climate change mitigation efforts.