Establishment and Early Development of Even-Age Shortleaf Pine-Hardwood Mixtures Using Artificially Regenerated Shortleaf Pine and Various Site Preparation and Release Treatments

Shortleaf pine (Pinus echinata)-hardwood mixtures were once a common forest type on upland sites throughout the southeastern United States. These forest types have declined throughout much of shortleaf pine's native range. Information on restoring shortleaf pine-hardwood types when a shortleaf pine seed source is not present is lacking. The objectives of this study were to investigate the effects of four site-preparation and release treatments (control, burn, herbicide, and herbicide and burn) on the development of even-aged mixtures of planted shortleaf pine and natural hardwoods located on the Highland Rim physiographic province of Tennessee, USA. Three years after study establishment, statistical differences among treatments occurred for shortleaf pine survival and basal diameter. Survival was greatest in the herbicide-only treatment. Height and basal diameter growth were greatest in the herbicide and burn treatment. Stem densities were greater in treatments that did not include a herbicide release than those where herbicide was used alone or combined with prescribed burning. The herbicide and burn treatment had the greatest potential after 3 years for developing into a balanced, mixed shortleaf pine-hardwood stand, whereas most treatments had an influx of exotic, invasive species such as Chinese privet (Ligustrum sinense) and callery pear (Pyrus calleryana). Study Implications: Conversion and restoration of shortleaf pine-hardwood mixtures from mixed hardwood stands with no available shortleaf pine seed source can be accomplished using fell-and-burn site preparation and planting shortleaf pine seedlings at low densities. Shortleaf pine growth may be improved by using herbicides labeled for woody release with shortleaf pine. Foresters and landowners interested in managing for shortleaf pine-hardwood mixtures should carefully assess vegetation on site prior to beginning operations to determine the type and level of site preparation and possible subsequent release treatments necessary to ensure adequate shortleaf pine seedling survival. Burning alone without applying herbicides may not improve natural hardwood and pine composition on previously forested sites. When invasive species occur on site prior to initiating silvicultural activities, more aggressive site-preparation treatments using appropriate herbicides should be used to improve natural hardwood and pine composition.