Using silvicultural practices to regulate competition, resource availability, and growing conditions for Pinus palustris seedlings underplanted in Pinus taeda forests
In the southeastern United States, many forest managers are interested in restoring longleaf pine (Pinus palustris Mill.) to upland sites that currently support loblolly pine (Pinus taeda L.). We quantified the effects of four canopy treatments (uncut Control; MedBA, harvest to 9 m2·ha-1; LowBA, harvest to 5 m2·ha-1; and Clearcut) and three cultural treatments (NT, no treatment; H, herbicide release of longleaf pine seedlings; and H+F, herbicide release plus fertilization) on resource availability and growing conditions in relation to longleaf pine seedling response for 3 years. Harvesting treatments reduced competition from canopy trees but resulted in greater abundance of understory vegetation. Harvesting shifted the interception of light from the canopy to the subcanopy vegetation layer; however, total light availability at the forest floor increased with the intensity of canopy removal. Soil moisture was not affected by harvesting or by the cultural treatments. Foliar nutrient concentrations (N, P, and K) of longleaf pine seedlings generally increased with the intensity of the harvest treatment. Of the plant resources measured, we found that light was most strongly correlated with longleaf pine seedling growth and that incorporating the interception of light by subcanopy vegetation improved the relationship over that of canopy light transmittance alone.