A site- and density-dependent matrix growth model for naturally-regenerated stands of mixed shortleaf pines (Pinus echinata Mill.) and hardwoods was developed. The data came from 1,047 re-measured plots in seven states in the southern United States. Growth, mortality and recruitment equations gave the parameters to predict the number of shortleaf pine, soft hardwood, and hard hardwood trees per unit area in each of 13 diameter classes. Equations to calculate the volume of trees growing in different stand conditions are also presented. The model predictions were tested on observations on 209 random plots not used in model estimation. Long-term simulations of the model suggested that, with natural succession and without major disturbance, hardwood trees would gradually replace the currently dominant softwood trees.