A significant carbon sink in temperate forests in Beijing: based on 20-year field measurements in three stands

Abstract:

Numerous efforts have been made to characterize the forest carbon (C) cycles and stocks. However, long-term observation-based quantification on each component of the forest C cycle and its change is still lacking. We measured C stocks and fluxes in three permanent temperate forest plots (birch, oak and pine forest plots) during 2011–2014 and calculated the changes of the C cycle components related to the measurements during 1992–1994 in Mt. Dongling, Beijing, China. Our results showed that forest net primary production in birch, oak and pine plots were 5.32, 4.53 and 6.73 Mg C ha^-1 yr^-1, respectively. The corresponding net ecosystem production were 0.12, 0.43 and 3.53 Mg C ha^-1 yr^-1. The C stocks and fluxes in 2011–2014 were significantly larger than those in 1992-1994: the biomass C densities in birch, oak and pine plots increased from 50.0, 37.7 and 54.0 Mg C ha^-1 in 1994 to 101.5, 77.3 and 110.9 Mg C ha^-1 in 2014; soil organic C densities from 207.0, 239.1 and 231.7 Mg C ha^-1 to 214.8, 241.7 and 238.4 Mg C ha^-1; and soil heterotrophic respiration from 2.78, 3.49 and 1.81 Mg C ha^-1 yr^-1 to 5.20, 4.10 and 3.20 Mg C ha^-1 yr^-1. These results suggest that the mountainous temperate forest ecosystems are a carbon sink in the recent two decades. These observations of C densities and fluxes provided field-based data for long-term study of C cycling in temperate forest ecosystems.