Abstract:Foliar δ13C values, an indicator of long-term intercellular carbon dioxide concentration and, thus, of long-term water use efficiency (WUE) in plants, were measured for Pinus massoniana Lamb., P. elliottii Engelm., Cunninghamia laceolata (Lamb.) Hook., and Schima superba Gardn. et Champ. in a restored forest ecosystem in the Jiazhu River Basin. Seasonal variation and the relationship between the foliar δ13C values of the four species and environmental factors (monthly total precipitation, monthly average air temperature, relative humidity, atmospheric pressure, and monthly total solar radiation and evaporation) were investigated. The monthly δ13C values and WUE of the four species increased with increasing precipitation, air temperature, solar radiation, and evaporation, whereas δ13C values of the four species decreased with increasing relative humidity and atmospheric pressure. Despite significant differences in δ13C seasonal means for the four species, our results demonstrate a significant convergence in the responses of δ13C values and WUE to seasonal variations in environmental factors among the species investigated and that the δ13C signature for each species gives a strong indication of environmental variables.