The BOREAS group TE-05 collected measurements in the NSA and SSA on gas exchange, gas composition and tree growth. This documentation describes leaf carbon isotope data that were collected in 1993 and 1994 at the NSA and SSA OJP, OBS and NSA UBS sites. In addition, leaf carbon isotope data were collected in 1994 only at the NSA and SSA OA sites. These data were collected to provide seasonal integrated physiological information for 10 to 15 common species at these 6 BOREAS sites.