Effects of longleaf pine restoration management on ground layer vegetation in existing loblolly pine forests of the southeastern United States

Background/Question/Methods

Longleaf pine (Pinus palustris) forests of the southeastern United States provide high quality habitat for many rare and endangered species and can support high levels of floral diversity. Efforts to restore longleaf pine to upland sites often include removal of the existing canopy, along with cultural treatments designed to benefit planted longleaf pine seedlings.  Managers need information on how such treatments affect ground layer vegetation, a component that is critical to ecosystem structure and function.  We established a randomized complete block, split-plot field experiment to test the effects of harvesting and cultural treatments on ground layer vegetation response at Fort Benning, GA. Main plot treatments were applied in 2007 and included an uncut Control (basal area ~ 15 m²/ha), MedBA (single tree selection to residual basal area of ~ 9 m²/ha), LowBA (single tree selection to residual basal area of ~ 5 m²/ha), and Clearcut (complete canopy removal); split-plot treatments included a control, an herbicide release treatment and an herbicide plus fertilizer treatment.  Treatments were replicated in six blocks. We measured vegetation cover by functional group in three growing seasons following canopy removal, and we recorded species composition during the third growing season.

Results/Conclusions

Regardless of the canopy treatment, the ground layer vegetation included a higher proportion of herbaceous cover than woody cover, which is generally a desirable characteristic in the longleaf pine ecosystem.  During the third growing season, canopy density significantly affected total vegetation cover (p = 0.0010), herbaceous vegetation cover (p = 0.0452), and woody vegetation cover (p = 0.0236), with increased vegetation cover associated with canopy removal.  Herbicide release treatments reduced total vegetation cover immediately following treatment (p = 0.0043), but the effect was transient and no longer significant during the third growing season (p = 0.4650).  Species richness (number of species/m²) during the third growing season was not significantly affected by canopy density (p = 0.7416) or cultural treatment (p = 0.5599), with approximately 13 species/m².  Non-metric multidimensional scaling indicated that the study block (site location) had greater control on composition than did study treatments when considered at the landscape level.  Overall, we found that canopy removal increased growth of ground layer vegetation, but there were few negative effects of the study treatments on the condition of the ground layer, suggesting that various restoration treatments may be suitable for longleaf pine restoration in loblolly pine stands.