Abstract: Soil samples at 0-30 cm depth were collected from the primary spruce (Picea asperata) forest and its plantations at different succession stages (22-, 47-, and 65-year-old) in subalpine zone of western Sichuan Province to study the dynamic changes of soil organic carbon stock and labile organic ca
rbon content. The soil total organic carbon (TOC) stocks in 0-10, 10-20, and 20-30 cm soil layers decreased from 95.87, 79.08, and 71.55 t·hm^-2 in 22-year-old plantation to 56.12, 34.75, and 31.06 t·hm^-2 in 65-year-old plantation, respectively, and the TOC stocks in these soil layers in 47 and 65-year-old plantations were less than those (88.08, 71.16 and 64.81 t·hm^-2, respectively) in primary forest. The easily oxidizable organic carbon (EOC) ontents in 0-10, 10-20, and 20-30 cm soil layers decreased from 35.89, 26.91, and 26.00 g·kg^-1 in primary forest to 20.25, 14.50, and 12.36 g·kg^-1 in 65-year-old plantation, the microbial biomass carbon (MBC) contents decreased from 524.44, 273.26, and 257.97 mg·kg^-1 in primary forest to 312.41, 186.95, and 152.18 mg·kg^-1 in 65-year-old plantation, and the particulate organic carbon (POC) contents decreased from 40.23, 27.10, and 19.55 g·kg^-1 in rimary forest to 12.33, 7.31, and 5.32 g·kg^-1 in 65-year-old plantation, respectively. The results suggested that within the long succession period of primary P. asperata forest to its plantations in the subalpine zone of western Sichuan Province, soil TOC and labile organic carbon were in the state of net consumption.

Key words: subalpine forest soil, easily oxidizable organic carbon, microbial biomass carbon, particulate organic carbon, fuel moisture, Canadian fire weather index system (FWI), Tahe, litter.