(A) Specific leaf area, (B) light- saturated assimilation rate, (C) leaf nitrogen content and (D) photosynthetic nitrogen use efficiency of the invasive and native species in the field. Specific leaf area (SLA, m2. kg-1), light-saturated assimilation rate (Amax, μmol CO2. m-2. s-1), leaf nitrogen content (Na, g. m-2 ) and photosynthetic nitrogen use efficiency (PNUE, μmol CO2. g-1 N. s-1 ) of the invasive species (A. negundo, full bars), the late-successional native species (F. excelsior, grey bars) and the early-successional native species (A. glutinosa, light-grey bars) as measured in situ. Values are means of 25 to 34 adult trees (± 1 SE of the mean). ANOVA were highly significant for all variables, respectively: F = 18.51 p < 0.0001; F = 26.85 p < 0.0001; F = 19.6 p < 0.0001; F = 6.96 p = 0.0016. Means with the same letters are not significantly different (α = 0.05).