Current understanding of the ecology of agroforestry practices, particularly traditional practices in the tropics, is frequently qualitative, sparse, and uncertain. Relevant information may be dispersed and complementary but not immediately compatible. Established approaches to decision support, which tend to be deterministic, demand more precise base information than is generally available for agroforestry practices. As a result, they are of limited utility in helping development professionals plan research and extension activities. In order to provide decision support at an appropriate level, domain-specific software was developed. This provides the user with an environment for creating knowledge bases by collating knowledge from a range of sources; facilitates the synthesis of that knowledge and its evaluation; and thereby facilitates its use in planning agroforestry research and extension. The software allows knowledge-base creation and exploration through text or diagram interfaces and incorporates a suite of inference mechanisms. A task language allows the combination of these mechanisms to be customized. This provides a powerful alternative to existing, less formal approaches to evaluating the current state of knowledge on interdisciplinary, problem-oriented topics as a basis for planning development activities.