Rising atmospheric CO2 and the need to understand potential impacts on terrestrial ecosystems has become increasingly recognized. Models can play a beneficial part in this research to enhance understanding of ecosystem responses to changing conditions like elevated CO2. In this study, data from a long term elevated CO2 experiment in a native forested ecosystem in east central Florida were employed to assess the utility of a multi-layer canopy photosynthesis model as a tool to better understand the responses to elevated CO2 in this ecosystem. Model results compared satisfactorily with the canopy gas exchange measurements in this ecosystem for the period modeled. Sensitivity analyses were used to evaluate the robustness of the model and understand the effects that changing model parameters had on model results, i.e. carbon assimilation in the system. The parameters evaluated included canopy height, leaf area density profile, number of canopy layers, maximum rate of carboxylation (Vcmax), and canopy species composition. Results of the sensitivity analyses point to structure and species as being important to carbon assimilation in this ecosystem. Although only an initial examination, this model could be a valuable tool to further understanding of the response of this important ecosystem to increasing CO2 and indicates that further work is certainly warranted.