Assessing the potential impact of retaining native off-site tree species in woodland restoration

Reestablishing appropriate tree species is an important step in converting off-site monocultures into woodlands. Species conversion is often necessary, as off-site exotic species rarely function like woodland species. However, when off-site tree species are native, and functionally redundant to woodland species, conversion may be unnecessary. To explore this possibility in the southeastern United States, we reviewed the literature on trait differences among the primary southern pines and qualitatively assessed the effect of their identity at the species and stand-levels. In this region, woodland restoration focuses on removing loblolly (Pinus taeda) and slash pine (P. elliottii) to reestablish longleaf (P. palustris) or shortleaf pine (P. echinata). Our review found minimal variation among species in understory flammability, fire resistance at maturity, and Red-cockaded Woodpecker (Leuconotopicus borealis) habitat at the stand-level. Longleaf and shortleaf pine were generally more resistant to abiotic and pest disturbance at the tree-level; however, stand-level differences in wind, drought, and boring insect resistance among southern pines growing in open forests were considered minimal. Retaining loblolly and slash pine will improve stand-level productivity in the short term, but creates regeneration problems due to low juvenile fire resistance and resilience. Ice resistance and long-term carbon sequestration will also likely be reduced by retaining loblolly and slash pine. Collectively, these results suggest that southern pine species are generally interchangeable at the stand-level in woodlands; although woodlands featuring loblolly and slash pine may be less stable in the face of disturbance than those dominated by shortleaf and longleaf pine.