In 2003, when SRS research forester Dave Haywood and plant physiologist Mary Anne Sword Sayer were working on the Palustris, they noticed that an unusual number of longleaf pine saplings had toppled when wind storms came through. They heard similar reports from industry and from university scientists across the southern region. Comparing notes, researchers suspected that the saplings were container-grown, and that their taproots were too deformed or their lateral roots too unevenly distributed around the taproot to hold against the wind.

SRS plant physiologist Susana Sung decided to go back to plots on the Palustris where artificial regeneration experiments had been established three decades before. In 2006, Sung started digging up longleaf pine trees 12 to 35 years old to look more closely at their root systems. She sampled trees regenerated by direct seeding, bare-root seedlings, and containergrown seedlings.

“As expected, trees from direct seeding had the longest taproots and more evenly distributed woody lateral roots,” says Sung. “Container-grown seedlings had the shortest taproots and the most uneven distribution of woody lateral roots.”

From these and other results, Sung recommended that those growing seedlings focus more on root development—and that copper-treated containers, though more expensive, offer the most “bang for the buck.” Copper (in miniscule amounts) essentially “zaps” roots as they grow towards the container walls; however, once these seedlings are outplanted, the lateral roots resume growing into their natural architecture.

What Sung found from digging up old studies reinforced findings from a study Sword Sayer and Haywood had installed on the Palustris in 2004 in an effort to improve container stock for hurricane zones. They found an increase in taproot weight, a change in lateral root morphology, and a shift in root growth potential along the outside of root plugs in response to copper. By year three, the saplings from the copper-treated containers were larger, with increases in height and diameter at ground level relative to container size.

So what’s the latest recommendation? “Use a coppercoated container that’s at least 5.7 cubic inches—a medium size—for longleaf pine seedlings,” says Sung. “Our research shows that the copper coating supports accelerated growth of longleaf seedlings out of the grass stage and less of the lateral root spiraling that can lead to saplings toppling from high wind conditions.”

For more information:
Susana Sung at 318–473–7233 or ssung@fs.fed.us