The relationships between leaf area index, photosynthetically active radiation, canopy nitrogen status, and stem growth in loblolly pine stands of different planting densities

Limitations to stem growth with increases in planting density were examined by ascertaining the relationships between stem growth and projected leaf area index (LAI), annual photosynthetically active radiation (PAR) capture, foliar nitrogen concentration, and canopy nitrogen content. Canopy variables were measured during the fourth growing season in stands of loblolly pine (Pinus taeda L.) ranging in planting density from 740 to 4440 trees ha-1. While stem growth rates increased significantly with planting density from 12.0 to 35.2 m3 ha-1 y-1, increases were not proportional, indicating the presence of competition-induced limitations to growth. Stem growth rates were best correlated to annual PAR capture (r2=0.90). This, in addition to the fact that annual PAR capture per unit LAI increased significantly with planting density, suggests that factors affecting PAR capture were of primary importance in limitations to growth rates with increasing planting density.