Gas exchange and chlorophyll a fluorescence measurements of expanding and adult leaves of four plant species were compared under field conditions. The pioneer species (PS) tended to have thinner leaves with lower nitrogen content and higher stomatal density compared to forest species (FS). Expanding leaves featured lower photosynthetic pigment contents and gas exchange capacity than adult leaves consistent with an immature photosynthetic apparatus. At the time of maximum irradiance, sun-exposed leaves of both PS and FS showed alteration of initial, variable, and maximum fluorescence as well as their ratios indicating photoinhibition. However, leaves recovered to some extent at predawn, suggesting the activation of photoprotective mechanisms. Sun-exposed leaves had comparable responses to high irradiance.