Carbon and nitrogen pools in Chinese fir and evergreen broadleaved forests and changes associated with felling and burning in mid-subtropical China

Abstract

A Chinese fir forest ( Cunninghamia lanceolata, CL) and a secondary evergreen broadleaved forest (BF) located in Fujian Province, south-eastern China, were examined before clear-cutting to compare their ecosystem carbon and nitrogen pools (above- and below-ground tree, understorey vegetation and forest floor biomass + 0–100 cm mineral soil layer). The ecosystem pools of C and N in the CL before clear-cutting were 257 Mg ha −1 and 8605 kg ha −1, respectively. The corresponding values for the BF were 336 Mg ha −1 of C and 10,248 kg ha −1 of N. For the two forests, most of the C was in the trees, whereas most of the N pool was in the soil. C and N pools in understorey vegetation and forest floor were small in the two forests (about 2% of ecosystem pools). During clear-cutting, 117 Mg ha −1 C and 307 kg ha −1 N in stem wood with bark and coarse branches (>2 cm) were removed from the CL compared to 159 Mg ha −1 C and 741 kg ha −1 N from the BF. Two days after slash burning, C removal from logging residues (including forest floor material) was estimated at 10 Mg ha −1 for CL and 23 Mg ha −1 for BF, and N removal was 233 and 490 kg ha −1 in the CL and BF, respectively. Compared with the pre-burn levels in the CL, contents of topsoil organic C and total N 2 days after burning were reduced by 17 and 19%, respectively. In the BF, the corresponding proportions were 27% (C) and 25% (N). Our results indicate that clear-cutting and slash burning had caused marked short-term changes in ecosystem C and N in the two forests. How long these changes will persist needs further study.