Background/Question/Methods: Common gardens were established along an 8 degree (~900 km) latitudinal transect to examine extrinsic and intrinsic factors potentially limiting the current geographical distribution of boreal and temperate tree species in eastern North America. The boreal species were trembling aspen (Populus tremuloides Michx.) and paper birch (Betula papyrifera Marsh.), while the temperate species were eastern cottonwood (Populus deltoides Bartr ex. Marsh var. deltoides) and sweetgum (Liquidambar styraciflua L.). Carbon-use efficiency (CUE), the efficiency with which carbon acquired through photosynthesis is converted into biomass (calculated as the quotient of plant carbon gain and gross photosynthesis), was compared among the four species along the transect in 2007. Results/Conclusions: CUE generally declined with decreasing latitude and, correspondingly, it was negatively correlated with growth temperature. Decreases in CUE were associated with increases in the ratio between estimates of total nighttime respiration and daily net photosynthesis (Rleaf/Aleaf) in tree foliage. Overall, trends in CUE and Rleaf/Aleaf along the transect did not differ between boreal and temperate species. Our findings contradict previous evidence of a relatively constant CUE across different climates, and they point to negative consequences of anticipated climate warming for the carbon balance of temperate as well as boreal tree species