People have saved seeds since the dawn of agriculture, but scientists at the Southern Research Station (SRS) are doing something new–combining modern genetics and the silvicultural strategy of seed orchards to preserve the genetic heritage of the South’s most at risk- and most ecologically important trees. Trees across the Southeast face exotic pests, shrinking ranges and a changing climate, and must adapt to survive.
“Seed orchards used to focus on making trees more economically valuable,” says Craig Echt, a research geneticist with the SRS Southern Institute of Forest Genetics. “That focus is shifting towards growing ecologically valuable trees in seed orchards and getting good seeds for reforestation projects and for helping imperiled populations survive.”
One way tree populations adapt to unfamiliar environments is through their offspring. Reproduction shuffles the genetic deck, and each new generation can have a slightly different shape, strength or sensitivity than its parents. With more cards to shuffle–more genetic diversity–come better odds that some individuals will have what it takes to succeed in their changing world. Unfortunately, populations with few versions of a gene–what’s termed low genetic diversity–may not be able to stay abreast of their changing environments, and could become locally or globally extinct.
“Establishing conservation seed orchards, or Restoration Seed Reserves, that can produce genetically diverse seeds could give struggling species enough genetic diversity to survive in changing environments,” says Echt. To make the most of extant genetic diversity, Echt and SRS colleague Dana Nelson and Barbara Crane of the National Forest System propose collecting at least 200 seeds from each of 200 parent trees for each imperiled species. ForGRAS, an assessment tool developed by Crane and Kevin Potter, a researcher at North Carolina State University, was used to identify 12 species at risk of losing genetic diversity–table mountain pine, American chestnut, Carolina and eastern hemlocks, several oaks and others.
Ideally, parent trees would represent 20 to 40 different populations, although for species in decline, as many populations as possible would be sampled. Crane and her colleagues have already harvested seeds from Table Mountain pine, a fire-adapted native of the Appalachian Mountains. Seeds have been divvied up between the USDA National Center for Genetic Resource Preservation, for long-term storage; the Forest Service Ashe Nursery Seed Orchard, for short-term storage; and a Restoration Seed Reserve at the Forest Service Beech Creek Genetic Resource Management Area, where the trees will be grown.
“When these trees mature and reproduce, genetic material from isolated, declining wild populations will flow into the same pool,” says Echt. “That’s going to revive the former breadth of genetic diversity in their offspring, increasing the declining genetic diversity–and the environmental adaptability–of tomorrows seeds, as well as supporting reforestation and restoration projects on our national forests.”
For more information, go to page 46 of the Proceedings of the 31st Southern Tree Improvement Conference and read “Establishing Restoration Seed Reserves in National Forest System Seed Orchards.”