The Harrison Experimental Forest

Pine genetics comes of age

Located in the lower Coastal Plain in southeastern Mississippi, the Harrison Experimental Forest (Harrison) was established on the Desoto National Forest in 1934. By that time, vast stands of southern pines, mostly longleaf pine, had been cut from the estimated 31 million acres that made up the southern Coastal Plain forest. Located just north of Gulfport, Mississippi, the 4,111-acre experimental forest continues to provide critical information about the genetics of longleaf and other southern pines.

Measuring tree roots for study on the Harrison. Photo by U.S. Forest Service.
Measuring tree roots for study on the Harrison. Photo by U.S. Forest Service.

In 1955, the SRS Southern Institute of Forest Genetics (SIFG) was located on the Harrison, with research studies focused on forest genetics and pathology. SIFG research on the genetics of growth, form, and pest resistance of forest trees has guided tree improvement programs across the South.

In 1961, researchers installed experimental plots on the Harrison to test responses to fertilization of three different pine species—longleaf, loblolly, and slash. Along with a surprisingly strong response to one-time fertilization in all three species, the long-term experiments showed that after about 25 years, longleaf pine catches up with loblolly pine in terms of growth and productivity. In 1999, at mean age 39, mean timber volume per acre was actually greatest in the longleaf pine plots.

When Hurricane Katrina hit the Harrison in 2005, the experimental plots took a beating. In 2006, researchers measured the damage, comparing their data to 1999 records. They found that the damage from Katrina was over 30 percent greater in the loblolly pine plots than in the longleaf pine and slash pine plots. Findings from the damaged plots have provided important information for land managers trying to decide how to replant hurricane-damaged areas along the Gulf Coast while taking into account the increased storm activity predicted under climate change.

During the same period, the SRS Forest Genetics and Ecosystems Biology team based in North Carolina started taking data from the Harrison plots as part of their research on carbon sequestration and tree species adaptation to climate change. In spring 2008,  then team leader Kurt Johnsen, research biological scientist, present team leader Chris Maier, and plant physiologist John Butnor drove out to the Harrison to map tree roots and measure soil respiration for research on the differences in carbon storage among the three pine species.

Johnsen and his team also started designing and preparing a companion study to the one established in 1961. Seedlings for the new study were grown from seeds harvested from the original study and from genetically improved seeds. Various fertilization and prescribed fire treatments have been applied, and instruments to measure carbon efflux installed on the site so that scientists can study the interplay among genetics, silviculture treatments, and carbon sequestration.

Together, the old and new studies will continue to provide land managers the science-based knowledge they will need to manage and adapt Coastal Plain forests as the climate changes over the next decades.

Read more about findings from the original plots and the design of the new study plan.

For more information, email John Butnor at

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