Silvicultural treatments for converting loblolly pine to longleaf pine dominance: Effects on planted longleaf pine seedlings

A field study was installed to test silvicultural treatments for establishing longleaf pine (Pinus palustris Mill.) in loblolly pine (P. taeda L.) stands. Harvesting was used to create seven canopy treatments, four with uniformly distributed canopies at different residual basal areas [Control (16.2 m2/ha), MedBA (9.0 m2/ha), LowBA (6.4 m2/ha), and Clearcut (0 m2/ha)] and three circular gaps defined by area [LG (∼5281 m2), MG (∼3217 m2), and SG (∼1576 m2)]. Within each canopy treatment, we applied three cultural treatments designed to benefit planted seedling early growth: no treatment (NT), herbicide (H), and herbicide plus fertilization (H + F). Three growing seasons after planting, seedling survival significantly differed among canopy treatments; compared to Controls, Clearcut plots had higher survival (80.6%). H and H + F treatments did not affect seedling survival in the first two years after application. Canopy removal generally increased seedling root collar diameter (RCD) but interacted with cultural treatments. NT within Controls had the smallest RCD, and H + F within Clearcuts had the largest RCD. Canopy treatments significantly affected the percentage of seedlings in height growth (i.e., terminal bud >15 cm high); Control plots had a significantly lower percentage of seedlings in height growth than other canopy treatments. H and H + F treatments also significantly increased the percentage of seedlings in height growth when compared to NT. Our results indicate that canopy removal improves early establishment of longleaf pine seedlings and that herbicides may additionally be used to increase early longleaf pine seedling growth. Our results are similar to those reported in previous studies conducted in mature longleaf pine stands.

► Land managers are interested in converting loblolly stands to longleaf forests. ► Seven canopy and three cultural treatments are applied in the field. ► Canopy removal improves early establishment of planted longleaf pine seedlings. ► Herbicides may additionally be used to increase early longleaf pine seedling growth.