An estimate of the terrestrial carbon budget of Russia using inventory-based, eddy covariance and inversion methods

We determine the net land to atmosphere flux of carbon in Russia, including Ukraine, Belarus and Kazakhstan, using inventory-based, eddy covariance, and inversion methods. Our high boundary estimate is -342 TgC yr(-1) from the eddy covariance method, and this is close to the upper bounds of the inventory-based Land Ecosystem Assessment and inverse models estimates. A lower boundary estimate is provided at -1350 TgC yr(-1) from the inversion models. The average of the three methods is -613.5 TgC yr(-1). The methane emission is estimated separately at 41.4 Tg C yr(-1). These three methods agree well within their respective error bounds. There is thus good consistency between bottom-up and top-down methods. The forests of Russia primarily cause the net atmosphere to land flux (-692 TgC yr(-1) from the LEA. It remains however remarkable that the three methods provide such close estimates (-615, -662, -554 TgC yr(-1)) for net biome production (NBP), given the inherent uncertainties in all of the approaches. The lack of recent forest inventories, the few eddy covariance sites and associated uncertainty with upscaling and undersampling of concentrations for the inversions are among the prime causes of the uncertainty. The dynamic global vegetation models (DGVMs) suggest a much lower uptake at -91 TgC yr(-1), and we argue that this is caused by a high estimate of heterotrophic respiration compared to other methods.