Shortleaf Pine: What’s in the Genes?
Fundamental Knowledge for Land Managers and Researchers
Despite shortleaf pine’s importance, relatively little is known about its genetics. “The lack of knowledge is especially apparent in this era of molecular genetics and genomics,” says U.S. Forest Service research geneticist Dana Nelson.
Nelson and his colleagues recently reviewed shortleaf pine genetics, and their implications for restoration and management. The research team included Oklahoma State University post-doctoral fellow and lead author John Stewart as well as Rodney Will, a professor at the university. Barbara Crane, the Forest Service Region 8 geneticist, also contributed to the study, which was published in the journal Tree Genetics and Genomics.
Shortleaf pine has an inherent ability to adapt to different temperature and moisture gradients, according to the research Nelson and his colleagues reviewed. Much of this research, which is known as provenance testing, also suggests that shortleaf pine has great potential for adapting to future environments.
Shortleaf pine once had the largest range of any southern pine. Historically, genes flowed across the entire range, meaning that a shortleaf pine in Arkansas could have similar genes as a Florida tree. However, as shortleaf pine’s range has contracted, the flow of genes across different areas has also decreased. “Shortleaf pine forests are becoming more genetically isolated,” says Nelson.
Shortleaf pine is an important timber species, and tree breeders have recently developed faster-growing strains. However, the improved strains – especially as seedlings and saplings – do not grow as fast as loblolly pine, which has been the subject of genetic studies and intensive tree breeding activities for more than 60 years. Loblolly pine is the most common plantation species in the southeast, and dominates the timber industry.
Like other members of the pine family, shortleaf pine and loblolly pine can hybridize. In some areas, shortleaf-loblolly hybrids are so common that shortleaf pine’s existence as a genetically distinct species is in jeopardy. Hybrids have also infiltrated seed orchards, and the Forest Service is currently genotyping trees and eliminating hybrids.
Outside the seed orchard, land management plays an important role in the rates of hybridization. In earlier studies, Nelson and his colleagues have found that shortleaf pine restoration requires fire. “Fire can help remove hybrids, and potentially protect the genetic integrity of shortleaf pine,” says Nelson. “The window of opportunity to kill shortleaf-loblolly pine hybrids is when they are young – hybrid seedlings and saplings are sensitive to fire.”
In addition to prescribed fire, shortleaf pine also responds well to other common management approaches, although some, such as mid-rotation thinning, can disproportionately affect the slower-growing young shortleaf pine and inadvertently promote loblolly pine or other faster growing species.
Once shortleaf pine matures, it grows faster than loblolly pine. Shortleaf pine can live for centuries, is naturally more resistant to fusiform rust and other diseases. The species also effectively resists drought, ice, cold, and fire.
Ecologically, shortleaf pine anchors many types of forests. “It’s often a foundational species for ecosystem restoration,” says Nelson. The Forest Service is currently restoring approximately 250,000 acres of shortleaf pine-bluestem savanna on the Ouachita National Forest and is beginning similar projects in the southern Appalachians and on other national forests such as the Ozark National Forest.
“The time to protect shortleaf pine is now,” says Nelson. “Without this species, forests will be less resilient to future disturbances and climate regimes.”
Visit the Shortleaf Pine Initiative for tools and resources that managers or landowners can use to restore and manage shortleaf pine.
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For more information, email Dana Nelson at dananelson@fs.fed.us.