Growth model for uneven-aged loblolly pine stands : simulations and management implications
A density-dependent matrix growth model of uneven-aged loblolly pine stands was developed with data from 991 permanent plots in the southern United States. The model predicts the number of pine, soft hardwood, and hard hardwood trees in 13 diameter classes, based on equations for ingrowth, upgrowth, and mortality. Projections of 6 to 10 years agreed with the growth of stands between the last two inventories. In 300-year simulations of undisturbed growth, softwood species were replaced by hardwoods, in accord with previous knowledge. Soft hardwood species became dominant on good sites and hard hardwoods on poor sites. Basal areas oscillated over time, converging slowly towards a steady state. Changes in tree size diversity were correlated positively with basal area. Without disturbance, species diversity would decrease. For economic analysis, equations were developed to predict total tree height, sawlog length and volume, pulpwood volume, and volume of top sawtimber, as functions of tree diameter and stand basal area. Simulations of three cutting regimes showed that management would lead to a steady state faster than would natural growth. Management aimed at maintaining the current average distribution would result in size and species diversity similar to that of an unmanaged stand. From a financial point of view, the q-factor guide and a 13-in.- (330-mm-) diameter-limit cut would be superior to the average current management regime. The diameter-limit regime would have the greatest effect on lowering tree size diversity and an effect on species diversity similar to that of the q-factor guide. A computer program, SOUTHPRO, was developed to simulate the effects of other management alternatives.