Functional structural models (FSMs) are valuable tools to explore relationships between plant form and function, yet they lack rigorous methods for development and assessment. We use multi-criteria assessment of an architectural FSM to show that both traumatic sequential and adaptive delayed reiteration (ADR) are necessary components of foliage maintenance in branches of old-growth Pseudotsuga menziesii. ADR has previously been established as a process that maintains foliage in old-growth P. menziesii. We use a simulation model of branch development in the species to evaluate morphogenesis in the context of this ADR. The structure of the model is a theoretical representation of how P. menziesii branch morphology develops throughout the branch lifespan, and this model structure is assessed with two criteria that are optimized simultaneously; the criteria measure foliage demography by the number of foliated shoots, and how those foliated shoots are organized into independent clusters. Assessment results indicated that improvements in model structure were required. Anomalous parameter vectors from the assessment search uncovered an inadequacy in the process of foliage maintenance, and the model was modified to include traumatic sequential reiteration in addition to ADR. The modes of the resulting parameter distributions were consistent with empirical observations. We discuss why the assessment of FSMs is an essential procedure that requires multiple criteria.