Biogeosciences
www.biogeosciences.net
1726-4170
1726-4189
4
4
2007
10.5194/bg-4-597-2007
http://www.biogeosciences.net/4/597/2007/
http://www.biogeosciences.net/4/597/2007/bg-4-597-2007.html
http://www.biogeosciences.net/4/597/2007/bg-4-597-2007.pdf
597
612
2007-08-06
Scaling net ecosystem production and net biome production over a heterogeneous region in the western United States
D. P. Turner
david.turner@oregonstate.edu
W. D. Ritts
B. E. Law
W. B. Cohen
Z. Yang
T. Hudiburg
J. L. Campbell
M. Duane
Forest Science Department, Oregon State University, Corvallis OR 97331, USA
USDA Forest Service, PNW Station, Corvallis OR 97331, USA
Bottom-up scaling of net ecosystem production (NEP) and net biome production
(NBP) was used to generate a carbon budget for a large heterogeneous region
(the state of Oregon, 2.5×10<sup>5</sup> km<sup>2</sup>) in the western United States.
Landsat resolution (30 m) remote sensing provided the basis for mapping land
cover and disturbance history, thus allowing us to account for all major
fire and logging events over the last 30 years. For NEP, a 23-year record
(1980–2002) of distributed meteorology (1 km resolution) at the daily time
step was used to drive a process-based carbon cycle model (Biome-BGC). For
NBP, fire emissions were computed from remote sensing based estimates of
area burned and our mapped biomass estimates. Our estimates for the
contribution of logging and crop harvest removals to NBP were from the model
simulations and were checked against public records of forest and crop
harvesting. The predominately forested ecoregions within our study region
had the highest NEP sinks, with ecoregion averages up to 197 gC m<sup>−2</sup> yr<sup>−1</sup>.
Agricultural ecoregions were also NEP sinks, reflecting the
imbalance of NPP and decomposition of crop residues. For the period
1996–2000, mean NEP for the study area was 17.0 TgC yr<sup>−1</sup>, with strong
interannual variation (SD of 10.6). The sum of forest harvest removals, crop
removals, and direct fire emissions amounted to 63% of NEP, leaving a
mean NBP of 6.1 TgC yr<sup>−1</sup>. Carbon sequestration was predominantly on
public forestland, where the harvest rate has fallen dramatically in the
recent years. Comparison of simulation results with estimates of carbon
stocks, and changes in carbon stocks, based on forest inventory data showed
generally good agreement. The carbon sequestered as NBP, plus accumulation
of forest products in slow turnover pools, offset 51% of the annual
emissions of fossil fuel CO<sub>2</sub> for the state. State-level NBP dropped
below zero in 2002 because of the combination of a dry climate year and a
large (200 000 ha) fire. These results highlight the strong influence of
land management and interannual variation in climate on the terrestrial
carbon flux in the temperate zone.
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