Variations in speleothem C-13 values can reflect changes in overlying surface vegetation, which, over historical time scales, may represent the influence of human activities. Here, we examined C-13 variations in two stalagmites growing for the last 2200 years in Shennong Cave, Jiangxi Province, SE China. The two C-13 records corroborate well one another and show a prominent 6 parts per thousand enrichment of the C-13 values from AD 700 to 1100. The isotopic equilibrium for modern calcite and negative correlation between O-18 and C-13 values along the growth axis suggest that the influences of kinetic fractionation are negligible. Varied correlations between Mg/Ca and Sr/Ca ratios and divergent changes between C-13 values and Mg/Ca and Sr/Ca ratios from AD 700 to 1100 reveal that the prior calcite precipitation (PCP) and water-rock interaction did not dominate the increase of C-13 values. It is plausible that the obvious C-13 variation was largely influenced by the changes in vegetation cover overlying the cave. Our C-13 results, together with the records of climate and human activity from historical documentary records, suggest that: (i) prior to AD 700, small fluctuations in relatively light C-13 values reflect the presence of lush forest coverage above the cave, which was minimally disturbed by human activities; (ii) during AD 700-1100, the drastic increase in C-13 values indicates persistent and massive deforestation associated with large-scale immigration into northern Jiangxi after the Rebellion of An & Shi (AD 755-763) in the Tang Dynasty and the subsequent development of agriculture and economic activity; and (iii) since AD 1100, fluctuations in relatively high C-13 values suggest that local vegetation during the last millennium has been sparse. Since the Rebellion of An & Shi, southeastern China was progressively developed, coincident with deforestation and vegetation deterioration caused by human disturbance in the form of deforestation and cultivation.