Polycultural agroecosystems, such as rangelands, are too complex and poorly understood to permit precise numerical simulation. Management decisions that depend on behavioral predictions of such ecosystems therefore require a variety of knowledge sources and reasoning techniques. Our approach to designing a computer system that provides advice concerning such ecosystems is to incorporate various reasoning paradigms and apply whatever paradigm is most appropriate to each task arising in the advice process. This approach is based on a particular process description of expert human problem solving that uses four different reasoning paradigms: model-based reasoning; case-based reasoning; rule-based reasoning; and statistical reasoning. The process description is implemented in CARMA, a computer system for advising ranchers about the best response to rangeland grasshopper infestations. CARMA attempts to emulate the human ability to integrate multiple knowledge sources and reasoning techniques in a flexible and opportunistic fashion. The goal of this approach is to enable computer systems to optimize the use of the diverse and incomplete knowledge sources and to produce patterns of reasoning that resemble those of human decision-makers.

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CARMA is an advisory and research support tool for grasshopper infestations. Designed with usability as a primary goal, CARMA presents an interface so intuitive that it completely eliminates the need for a user manual. To achieve this goal, CARMA interacts with the user through a goal-oriented, guided style reminiscent of a natural conversation between an advice seeker and an expert. Usability is furthered by its modeling of four important characteristics of human expert problem solving (speed, graceful degradation, explanations, and opportunism). In order to gain non-biased user feedback about CARMA's interface, we surveyed a group of novice users not previously familiar with CARMA. Positive survey results suggest that CARMA's approach to usability is a success. Furthermore, our survey approach illustrates a simple anonymous online technique which elicits candid non-biased feedback from participants about a product, and is particularly applicable to practitioners short on staff or time.

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