The conceptual framework for a simulation model of primary productivity, decomposition and nitrogen cycling in a shrub-dominated desert ecosystem in southern New Mexico is presented. This model is based on our previous attempt to simulate carbon allocation patterns in the desert shrub Larrea tridentata Cov., which demonstrated that moisture patterns alone are insufficient to predict desert productivity. These results, as well as others, suggest that mineral nutrients, especially nitrogen, may also be an important determinant of productivity in arid environments. Our current research in the Chihuahuan desert is directed towards elucidating the numerous biotic and abiotic interactions that determine the rates and directions of carbon, nitrogen and water fluxes in this ecosystem. The development of this working model will serve as a tool to accomplish three major objectives: (1) to synthesize the large amounts of existing data on decomposition and nitrogen cycling in deserts, (2) to quantify our present state of knowledge about the structure and function of ecosystem components important in carbon and nitrogen dynamics in deserts, and (3) to address hypotheses concerning the complex mechanisms of interactions and feedbacks among the organisms involved in carbon and nitrogen exchanges in deserts.