Technical Abstract: Farm-level agroforestry simulations such as the Agroforestry Estate Model (AEM) use as yield inputs either tables developed for a particular system or simulations from forest modeling tools. Specific tables with data for relatively long periods are often unavailable for temperate agroforestry systems and predictive functions are needed. Forest models, on the other hand, rely upon a set of assumptions related to site index (i.e., dominant height at a base age), stem diameter (DBH) and wood product distribution, wood production and tree mortality, which may not apply to agroforestry systems. Differences may arise because of the effects on tree growth of different spacings and configurations, the understory component and fertilizer and grazing regimes. We examined data from published or ongoing field trials to determine trends in tree growth and understory yields in silvopastoral systems with southern pines (P. taeda, P. elliotti) in the United States. Tree DBH and height were generally higher in systems with improved pastures than in those with volunteer grasses. Effects of understory characteristics were more marked on DBH than on height. DBH-height relationships differed among systems. Sigmoidal models predicted that tree height will peak at different age depending on tree spacing. These changes may affect the accuracy and applicability to agroforestry systems of site indices and wood yield predictions generated by forest models.