Controlling Woody Vegetation for the Underplanting and Reintegration of Shortleaf Pine into Upland Hardwood Forests of the Southeast

Shortleaf pine (Pinus echinata Mill.) has the widest distribution of any pine species in the southeastern United States. Shortleaf pine is an important softwood commercial timber species, second only to loblolly pine (Pinus taeda). The amount of shortleaf pine has diminished dramatically beginning in the early 19^th century.

The decline of shortleaf pine has been attributed to several, primarily societal factors. Old field abandonment has declined which provided optimum seed bed conditions for the establishment of shortleaf pine. The timber industry began to favor the faster-growing loblolly pine with shorter stand rotations at the expense of shortleaf pine (Bragg, 2016). The Smokey Bear campaign also played a role in the reduction of natural and anthropogenic-related wildfires that created the early successional habitat conditions necessary for the growth and natural regeneration of shortleaf pine (Smith, 2017). Along with southern pine beetle (SPB) infestations (Oswalt et al., 2016), these events led to the eventual decline of shortleaf pine.

Historically, shortleaf pine forest types were a common occurrence in the southeastern US uplands. After a wildfire occurrence in November 2016 on the University of Tennessee Cumberland Forest, within a subregion of the Cumberland Plateau, a research project was initiated in order to reintegrate shortleaf pine into the hardwood upland forests where shortleaf pine was once a dominant species. In February 2018, an herbicidal application of imazapyr was administered on an unburned adjacent stand to a burned section of the forest, followed by an underplanting of shortleaf pine seedlings on both treatment sites. The objective was to compare the amount of available light with the use of a ceptometer, measuring photosynthetic active radiation, provided by the treatments and how available light affected seedling survival, height growth, and root collar diameter growth.

Results from this study suggest that the establishment of underplanted shortleaf pine would benefit more from the use of herbicides rather than fire in mature upland stands. Root collar diameters were not statistically different, though the fire plots had numerically greater growth in diameter. Furthermore, PAR values had no significant effect on seedling height and seedling root collar diameter during the experiment.