Simulating carbon flux over the Arctic tundra by incorporating remote-sensing data into a plant-level process-based model

Over the last three decades, warming temperatures have profoundly affected terrestrial ecosystems, especially in the Arctic tundra. Not only temperature-dependent processes have been altered by the temperature rise, but also widespread expansion of woody shrubs has appeared across the region. With a growing concern that tundra biome may become a carbon source, or a larger source, in coming years, there have been ongoing efforts to understand and simulate carbon balance over the Arctic region using various terrestrial ecosystem models. Most of the models, however, have a relatively-simplified vegetation representation such as a "big-leaf" scheme, and they may not adequately account for the effects of vegetation dynamics. Models that introduced canopy vertical stratification, such as the Ecosystem Demography Biosphere Model (ED2), have not yet been widely implemented in the study of carbon cycle at the Arctic region due to the limited information available regarding boundary conditions (e.g. vegetation height and density).

In this study, we simulated long-term changes in the carbon flux over the Arctic tundra using the ED2 model by incorporating vegetation structure information retrieved from remote sensing data. We initialized diameter at the breast height of the shrub species (height for graminoid) of the model using the Ent Global Vegetation Structure Dataset (Ent GVSD), which provides vegetation height and leaf area index (LAI) derived from remote sensing data (e.g. GLAS and MODIS). We optimized key model parameters using in-situ carbon flux measurements at two AmeriFlux sites in Alaska (Barrow and Atqasuk). We, then, analyzed the sensitivity of carbon flux to the climate change over the Arctic tundra ecosystem for the past two decades, and investigated the effect of local hydrological conditions on the response. Our result highlights the need to improve our understanding of the response of the tundra ecosystem to the ongoing climate change.

This study was funded by the Korea Polar Research Institute (KOPRI, grant number PE17900), Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning (2015R1C1A2A01054800), and the Korea Ministry of Environment as Climate Change Correspondence R&D Program (2018001310001).