Adapting gePSi (Generic Plant Simulator) for modeling studies in the Jasper Ridge CO₂ project

In order to conduct modeling studies on the effects of elevated atmospheric carbon dioxide concentration ([CO₂]) on plant and ecosystem processes at the Jasper Ridge grassland in northern California, the generic plant simulator (GePSi) (Chen, J.-L. and Reynolds, J.F., 1997. Ecol. Model., 94:53-66), is modified to simulate grass dynamics. This modification was attempted by the authors of this paper, who had no prior experience with the model. Prior to this project, GePSi, which is implemented in the object-oriented programming (OOP) language. C+ +, had only been used to model trees and woody shrubs. This exercise addressed several of the concepts presented in this volume concerning the purported benefits of genericness, modularity, and OOP in plant modeling. The objective of this paper is to briefly summarize the extent to which these benefits were realized and some of the problems encountered. Our evaluation is presented in terms of: (1) design considerations, including the importance of how the modules in GePSi were defined: and (2) the implementation phase, which critiques the use of OOP for facilitating the transfer of the model. This study suggests that generic, modular models such as GePSi will facilitate the interactions of model developers and users and reduce duplication of effort in model development.