[Carbon storage and its allocation in karst forest at different stand ages in Guangxi, China].

Based on a survey of 45 plots (1000 m each) of five different stand ages, i.e., young, middle-aged, pre-mature, mature, and over-mature plantations in the main production area of karst forest in Guangxi, carbon (C) storage and its allocation in vegetation and soil were studied. The results showed that the carbon storage of karst plantations in Guangxi changed in an increasing order of young plantation (86.03 t·hm), near-mature plantation (110.63 t·hm), middle-aged plantation (112.11 t·hm), mature plantation (149.1 t·hm), and then over-mature plantation (244.38 t·hm). The carbon storage distribution varied in both different vegetation la-yers and different stand ages. Tree layer was found to store the greatest amount of carbon by accounting for up to 92.3%-98.7% of total vegetation carbon. The proportion of carbon stored in the tree layer increased with stand age. The proportions of carbon stored in the shrub layer, herb layer, litter and root were 0.3%-1.9%, 0.3%-1.2%, 0.3%-2.5% and 0.3%-3.3%, respectively. Soil organic carbon density decreased as soil depth increased. The soil organic carbon storage over the whole soil profile ranged from 51.75 t·hm to 81.21 t·hm. The proportion of soil organic carbon in total ecosystem carbon in karst forest ranged from 33.2% to 66.2%, which decreased with stand age. The carbon storage for aboveground and underground parts were 22.80-141.72 t·hm and 62.30-102.66 t·hm, respectively. Total ecosystem carbon storage was greater in underground part than in aboveground part except mature plantation. The carbon storage in aboveground part carbon increased with stand age but that in underground part changed insignificantly with the carbon storage of soil. The soil and tree layer were the major carbon pools of the forest ecosystems in the karst region, and the sum of carbon stored in soil and tree accounted for more than 96% of total ecosystem carbon storage.