Assimilation of NEON Observations Into a Process‐Based Carbon Cycle Model Reveals Divergent Mechanisms of Carbon Dynamics in Temperate Deciduous Forests

Abstract

AbstractTerrestrial ecosystems can potentially alleviate or exacerbate climate change by regulating atmospheric CO2 concentration. Divergent predictions of the terrestrial C sink by the Earth System Models (ESMs) indicate no unified mechanism regarding abiotic and biotic response to climate change. The amount and diversity of observations of the terrestrial C cycle create an opportunity to improve the predictive capacity of C‐cycle models. Modeling study with observations could provide valuable insights into the controls on interannual variability of the terrestrial C sink. In this study, we used data from three deciduous forest sites in the National Ecological Observatory Network (NEON) to do site‐specific parameterizations in the Terrestrial ECOsystem model (TECO), and explore controls of the net C uptake. Calibrated TECO explained 58%–83% of variation in leaf area index and 35%–40% in net ecosystem C exchange. Root mean square (percentage) errors were 131–436 gC/m2 (0.9%–3.3%) for wood C pool, 3–73 gC/m2 (0.5%–11.5%) for fine root C, and 170–763 gC/m2 (1.9%–8.0%) for soil C pool. Calibrated parameters revealed site‐specific processes in phenology and turnover of leaves, fine roots, slow‐decomposing soil C, and temperature sensitivity of organic matter decomposition among the three deciduous forest sites. These findings imply the presence of bias in models using parameters at plant functional type (PFT) level, which is the case for many ESMs relying on land surface components (i.e., PFTs), rather than site‐specific parameters. Lastly, the magnitude of the terrestrial C sink in deciduous forests increased with temperature and this increase was caused by the temperature‐driven stimulation of the gross primary production.