Biometric Based Carbon Flux Measurements and Net Ecosystem Production (NEP) in a Temperate Deciduous Broad-Leaved Forest Beneath a Flux Tower

Abstract

Biometric based carbon flux measurements were conducted over 5 years (1999–2003) in a temperate deciduous broad-leaved forest of the AsiaFlux network to estimate net ecosystem production (NEP). Biometric based NEP, as measured by the balance between net primary production (including NPP of canopy trees and of forest floor dwarf bamboo) and heterotrophic respiration (RH), clarified the contribution of various biological processes to the ecosystem carbon budget, and also showed where and how the forest is storing C. The mean NPP of the trees was 5.4 ± 1.07 t C ha−1 y−1, including biomass increment (0.3 ± 0.82 t C ha−1 y−1), tree mortality (1.0 ± 0.61 t C ha−1 y−1), aboveground detritus production (2.3 ± 0.39 t C ha−1 y−1) and belowground fine root production (1.8 ± 0.31 t C ha−1 y−1). Annual biomass increment was rather small because of high tree mortality during the 5 years. Total NPP at the site was 6.5 ± 1.07 t C ha−1 y−1, including the NPP of the forest floor community (1.1 ± 0.06 t C ha−1 y−1). The soil surface CO2 efflux (RS) was averaged across the 5 years of record using open-flow chambers. The mean estimated annual RS amounted to 7.1 ± 0.44 t C ha−1, and the decomposition of soil organic matter (SOM) was estimated at 3.9 ± 0.24 t C ha−1. RH was estimated at 4.4 ± 0.32 t C ha−1 y−1, which included decomposition of coarse woody debris. Biometric NEP in the forest was estimated at 2.1 ± 1.15 t C ha−1 y−1, which agreed well with the eddy-covariance based net ecosystem exchange (NEE). The contribution of woody increment (Δbiomass + mortality) of the canopy trees to NEP was rather small, and thus the SOM pool played an important role in carbon storage in the temperate forest. These results suggested that the dense forest floor of dwarf bamboo might have a critical role in soil carbon sequestration in temperate East Asian deciduous forests.