A STUDY ON THE FOREST SOlL CO2 RELEASE RATES IN CHINESE FIR PLANTATIONS Soil CO2 Release Rate and Its Effect Factors in Chinese Fir Plantation Characteristics of CO2 Flux in a Chinese Fir Plantation Ecosystem in Huitong County, Hunan Province Long-Term Effects of Harvest Residue Management on Soil and Foliar δ15N of Chinese Fir Plantations