Inter-annual variability of carbon fluxes in temperate forest ecosystems: effects of biotic and abiotic factors

Min Chen1, Prof. Trevor F Keenan2, Koen Hufkens3, J. William Munger3, Gil Bohrer4, Edward R Brzostek5 and Andrew D Richardson6, (1)University of Wisconsin Madison, Department of Forest and Wildlife Ecology, Madison, WI, United States, (2)Lawrence Berkeley National Laboratory, Berkeley, United States, (3)Harvard University, Cambridge, MA, United States, (4)The Ohio State University, Department of Civil, Environmental and Geodetic Engineering, Columbus, United States, (5)West Virginia University, Department of Biology, Morgantown, WV, United States, (6)Northern Arizona University, School of Informatics, Computing and Cyber Systems, Center for Ecosystem Science and Society, Flagstaff, AZ, United States
Abstract:
Carbon dynamics in terrestrial ecosystems are influenced by both abiotic and biotic factors. Abiotic factors, such as variation in meteorological conditions, directly drive biophysical and biogeochemical processes; biotic factors, referring to the inherent properties of the ecosystem components, reflect the internal regulating effects including temporal dynamics and memory. The magnitude of the effect of abiotic and biotic factors on forest ecosystem carbon exchange has been suggested to vary at different time scales. In this study, we design and conduct a model-data fusion experiment to investigate the role and relative importance of the biotic and abiotic factors for inter-annual variability of the net ecosystem CO2 exchange (NEE) of temperate deciduous forest ecosystems in the Northeastern US. A process-based model (FöBAAR) is parameterized at four eddy-covariance sites using all available flux and biometric measurements. We conducted a “transplant” modeling experiment, that is, cross- site and parameter simulations with different combinations of site meteorology and parameters. Using wavelet analysis and variance partitioning techniques, analysis of model predictions identifies both spatial variant and spatially invariant parameters. Variability of NEE was primarily modulated by gross primary productivity (GPP), with relative contributions varying from hourly to yearly time scales. The inter-annual variability of GPP and NEE is more regulated by meteorological forcing, but spatial variability in certain model parameters (biotic response) has more substantial effects on the inter-annual variability of ecosystem respiration (Reco) through the effects on carbon pools. Both the biotic and abiotic factors play significant roles in modulating the spatial and temporal variability in terrestrial carbon cycling in the region. Together, our study quantifies the relative importance of both, and calls for better understanding of them to better predict regional CO2 exchanges.
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