Abstract: The xylem sap flows of two pioneer tree species, i.e., Acacia mangium and Schima superba, in degraded hill lands of South China, were continually monitored with Granier’s thermal dissipation probes during 2004-2007 and 2008-2012, respectively, and their seasonal transpiration changes at different tree age levels were compared. The results showed that the annual transpiration of both species increased with tree ages, and S. superba demonstrated a higher value than A. mangium. The average annual wholetree transpiration of S. superba (7014.76 kg) was higher than that of A. mangium (3704.97 kg). A. mangium (511.46-1802.17 kg) had greater seasonal variation than S. superba (1346.48-2349.35 kg). The standard regression coefficients (β) of transpiration (E_h), photosynthetically active radiation (PAR) and vapor pressure deficit (VPD) for both species increased with soil moisture, suggesting the increase of soil moisture generated a greater sensitivity of plants to environmental factors. Partial correlation analysis revealed that soil moisture played an important role in the seasonal variation of transpiration of both species. The optimum soil moistures of S. superba and A. mangium were 0.22-0.40 and 0.29-0.30 (V/V), respectively, indicating the native pioneer species S. superba better adapted to water deficit compared with exotic pioneer species A. mangium.