The genetics of shortleaf pine (Pinus echinata mill.) with implications for restoration and management

Shortleaf pine (Pinus echinata Mill.) is an important commercial timber resource and forest ecosystem component in the southeastern USA. The species occurs in mainly drier sites as an early- to mid-successional species, is fire-adapted, and it plays an important role in the fire ecology of the region. However, shortleaf pine genetics are not well-studied, especially in this era of molecular genetics and genomics. Most genetics research about the species has focused on provenance testing. Generally, shortleaf pine performs well in colder areas, when compared to loblolly pine (Pinus taeda L.), a close relative, which is faster growing and the most common plantation species in the region. Though not as advanced in genetic improvement as loblolly pine, tree breeders have improved shortleaf pine in one to two generations of selection, and diverse, genetically improved shortleaf pine materials are available to foresters and landowners throughout the southeastern USA. Researchers have also studied the genetic variation of shortleaf pine using various molecular markers and have found that shortleaf pine is generally a prolific outcrosser, a trait it shares with other non-isolated members of the family Pinaceae. In recent years, however, it has shared less genetic material across long ranges, probably because of habitat fragmentation. Various anthropogenic factors also affect shortleaf pine’s future, as recent studies show that shortleaf pine introgression with loblolly pine puts the species—and the resiliency of southeastern forests—at risk. Importantly, fire exclusion is a likely cause of the increase in introgression. Herein, we provide further details and up-to-date genetic information and resources for foresters and ecologists interested in the restoration and management of shortleaf pine.