Document: HAN-3-59-91

Terrestrial carbon dynamics in North America from 1860 to 1992: Quantifying mechanisms responsible for carbon sink.

TIAN, H.* ¹, J.M.MELILLO ¹, D.W.KICKLIGHTER ¹, A.D.MCGUIRE ² and B.MOORE III ³

Marine Biological Laboratory, Woods Hole, MA02543, USA ¹
USGS, ACF & WRU, University of Alaska, Fairbanks, AK 99775, USA ²
University of New Hampshire, NH 03824, USA ³

Abstract:
The magnitude of the terrestrial carbon sink in North America (>15⁰N) remains uncertain. Estimates on carbon storage based on forest inventories are about a factor of six smaller than the estimate based on inverse modeling by Fan et al. in 1998. However, neither inverse modeling nor forest inventories identify the mechanisms underlying their estimates of the North American carbon sink. In this study, we investigate how climate variability, increasing CO₂ and land-use change have affected carbon storage in North America during 18601992, by using the Terrestrial Ecosystem Model (TEM). Our modeled results indicate that during 18601992 a combination of increasing CO₂, climate variability and land-use change causes a 5.4% (12.6 Pg C) decrease in terrestrial carbon storage in North America. The carbon dynamics in North America exhibited a large decrease from the mid19th century to the mid20th century, followed by a slow recovery. The large decrease in carbon storage during the first period is primarily due to the conversion of natural ecosystems to croplands. The slow recovery of carbon storage during the second time period is primarily due to increasing CO₂ and regrowth of natural vegetation after agricultural abandonment. Our modeled results also indicate that net carbon storage shows substantial interannual variations, ranging from a 1.4 Pg C per year net efflux to a 0.8 Pg C per year uptake. Simulated net carbon storage also shows substantial spatial variations across the North America. Thus proper scaling of the site-specific measurements of carbon fluxes from eddy covariance or other atmospheric techniques to produce regional estimates must take into account temporal and spatial variations in net carbon storage. Our modeled estimate for a carbon dioxide/climate/land use sink in North America during 19801992 is closer to forest inventory estimates, but much lower than the estimate by Fan et al. in 1998.

Keywords: Terrestrial carbon sink, North America, Carbon dioxide, Climate variability, Land use change, Scaling, Ecosystem modeling

This abstract is being presented at: 4:45 PM in session:
Oral Session #52: Carbon Storage in Ecosystems.