TY - JOUR
T1 - Coupling between carbon cycling and climate in a high-elevation, subalpine forest
T2 - A model-data fusion analysis
AU - Sacks, William J.
AU - Schimel, David S.
AU - Monson, Russell K.
N1 - Funding Information:
Acknowledgments Rob Braswell provided much of the impetus for the SIPNET modeling and helped us develop many of the ideas that led to this study; we are grateful for his intellectual contributions. We are also grateful for Ernst Linder’s help with the statistics underlying the parameter estimation. We thank Sean Burns, Andrew Turnipseed, Laura Scott-Denton and others who were instrumental in the data collection. Thanks also to Galina Churkina for insights into growing season length. Finally, we thank three anonymous reviewers for their constructive comments. This work was supported by grants from the National Aeronautics and Space Administration (TE/02-0000-0015 & NAG5-12876), the National Science Foundation (2003108), the National Oceanic and Atmospheric Administration (2002192), and a grant from the South Central Section of the National Institute for Global Environmental Change (NIGEC) through the US Department of Energy (BER Program) (Cooperative Agreement No. DE-FC03-90ER61010). The National Center for Atmospheric Research is funded by the National Science Foundation. The experiments performed for this study comply with the current laws of the United States of America.
PY - 2007/2
Y1 - 2007/2
N2 - Fundamental questions exist about the effects of climate on terrestrial net ecosystem CO2 exchange (NEE), despite a rapidly growing body of flux observations. One strategy to clarify ecosystem climate-carbon interactions is to partition NEE into its component fluxes, gross ecosystem CO2 exchange (GEE) and ecosystem respiration (RE), and evaluate the responses to climate of each component flux. We separated observed NEE into optimized estimates of GEE and RE using an ecosystem process model combined with 6 years of continuous flux data from the Niwot Ridge AmeriFlux site. In order to gain further insight into the processes underlying NEE, we partitioned RE into its components: heterotrophic (RH) and autotrophic (RA) respiration. We were successful in separating GEE and RE, but less successful in accurately partitioning RE into RA and RH. Our failure in the latter was due to a lack of adequate contrasts in the assimilated data set to distinguish between RA and RH. We performed most model runs at a twice-daily time step. Optimizing on daily-aggregated data severely degraded the model's ability to separate GEE and RE. However, we gained little benefit from using a half-hourly time step. The model-data fusion showed that most of the interannual variability in NEE was due to variability in GEE, and not R E. In contrast to several previous studies in other ecosystems, we found that longer growing seasons at Niwot Ridge were correlated with less net CO2 uptake, due to a decrease of available snow-melt water during the late springtime photosynthetic period. Warmer springtime temperatures resulted in increased net CO2 uptake only if adequate moisture was available; when warmer springtime conditions led into mid-summer drought, the annual net uptake declined.
AB - Fundamental questions exist about the effects of climate on terrestrial net ecosystem CO2 exchange (NEE), despite a rapidly growing body of flux observations. One strategy to clarify ecosystem climate-carbon interactions is to partition NEE into its component fluxes, gross ecosystem CO2 exchange (GEE) and ecosystem respiration (RE), and evaluate the responses to climate of each component flux. We separated observed NEE into optimized estimates of GEE and RE using an ecosystem process model combined with 6 years of continuous flux data from the Niwot Ridge AmeriFlux site. In order to gain further insight into the processes underlying NEE, we partitioned RE into its components: heterotrophic (RH) and autotrophic (RA) respiration. We were successful in separating GEE and RE, but less successful in accurately partitioning RE into RA and RH. Our failure in the latter was due to a lack of adequate contrasts in the assimilated data set to distinguish between RA and RH. We performed most model runs at a twice-daily time step. Optimizing on daily-aggregated data severely degraded the model's ability to separate GEE and RE. However, we gained little benefit from using a half-hourly time step. The model-data fusion showed that most of the interannual variability in NEE was due to variability in GEE, and not R E. In contrast to several previous studies in other ecosystems, we found that longer growing seasons at Niwot Ridge were correlated with less net CO2 uptake, due to a decrease of available snow-melt water during the late springtime photosynthetic period. Warmer springtime temperatures resulted in increased net CO2 uptake only if adequate moisture was available; when warmer springtime conditions led into mid-summer drought, the annual net uptake declined.
KW - Ecosystem respiration
KW - Eddy covariance
KW - Gross primary productivity
KW - Net ecosystem exchange
KW - Parameter estimation
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U2 - 10.1007/s00442-006-0565-2
DO - 10.1007/s00442-006-0565-2
M3 - Article
C2 - 17013598
AN - SCOPUS:33846588931
SN - 0029-8549
VL - 151
SP - 54
EP - 68
JO - Oecologia
JF - Oecologia
IS - 1
ER -