The paradox of tropical forests is that they are simultaneously the most diverse, the least understood, and the most imperiled terrestrial ecosystem in the world. Dramatic increases in the atmospheric carbon dioxide (CO$ sb2$) concentration threaten to adversely affect fundamental climatic and ecosystem processes, gradually changing many things which we do not yet understand. Although the impacts of this rise have been studied in temperate areas, little research has investigated tree responses in the tropics, especially under natural frost conditions. This thesis examines three central issues in tropical ecophysiology and global change. First, it investigates the feasibility of in-situ measurements of several physiological traits under heterogeneous environmental conditions in a Panamanian rainforest. Second, it studies whether physiological traits differ among species and which traits are most consistent with ecological niche. Finally, it explores how variable species are in response to elevated CO$ sb2$. If ecologically-defined functional groups were to remain physiologically similar under increased CO$ sb2$, they could be used in accurately representing the variation at the species level in a global change model of system-level responses. (Abstract shortened by UMI.)

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