Hemlock Seed Banking

Identifying Collection Locations for Future Hemlock Restoration

Eastern and Carolina hemlock trees in more than 400 counties across 19 states are dead, dying, or threatened by infestation of the invasive hemlock woolly adelgid.

Eastern hemlock
Maps show prioritized locations for seed collection from eastern hemlock populations. Red indicates the highest priority.

As the aphid-like pest continues to spread throughout the ranges of these economically and ecologically important trees, scientists, managers, and other specialists from North Carolina State University’s (NCSU) Camcore program are racing to collect and store seeds with support from the U.S. Forest Service.

New maps can help them and other conservationists prioritize locations for seed collection, necessary for off-site plantings and breeding programs designed to restore hemlocks in the future.

“Once successful adelgid management techniques are in place, the availability of diverse genetic material for planting and breeding is critical for successful hemlock restoration,” says Kevin Potter, a cooperating scientist with the U.S. Forest Service Eastern Forest Environmental Threat Assessment Center, “because genetic diversity provides a basis for adaptation and resilience to environmental stress and change.”

Potter and NCSU researchers John Hastings, Robert Jetton, and Mark Megalos as well as  Eastern Threat Center research ecologist Frank Koch applied a novel approach known as multi-attribute frontier mapping to identify priority seed collection locations across the entire range of both hemlock species.

The researchers combined information on density of seed collection to date, climate data, measures of hemlock abundance and population isolation, and four genetic diversity measures from previous studies. Then, for each cell on maps depicting where eastern and Carolina hemlock occur, the combined information was compared and ranked. Results were recently published in the journal New Forests.

Carolina hemlock
The highest priority locations for Carolina hemlock seed collection are shown in red.

For eastern hemlock, results suggest that all isolated populations—which Potter and his colleagues previously found to be genetically distinct when compared to populations in the main range—should be prioritized for seed collection. Eastern hemlocks in northern regions where the adelgid has recently or not yet established should also be prioritized.

For Carolina hemlock, which is much rarer, tends to exist only in isolated populations, and is subject to inbreeding due to isolation, most of the main range in the Southern Appalachians should be prioritized. The researchers also stress the need for more genetic sampling of Carolina hemlock.

Since 2003, the Forest Service and Camcore have collected about 2.5 million eastern and Carolina hemlock seeds from 76 and 24 populations, respectively, and hope is already in the ground: seed orchards of genetically diverse trees have been established in North Carolina, Chile, and Brazil. With this new way to focus seed collection efforts, hope for the future of hemlocks will continue to grow. And, researchers say that multi-attribute frontier mapping can be applied to other species that are dying due to the spread of insects and disease, such as green ash and butternut, as well as trees that are still perfectly healthy today.

“This kind of genetic conservation prioritization analysis is a critically important response to destructive pests and a potential solution for the efficient and effective application of limited conservation resources in the face of an uncertain future,” says Hastings, who coordinated the project as part of his master’s degree work in the Department of Forestry and Environmental Resources at NCSU. “Regardless of species imperilment, these kinds of studies can help inform proactive conservation strategies so that genetic diversity is maintained in the event of a pest attack and other threats.”
Read the full text of the article.

For more information, email Kevin Potter at kevinpotter@fs.fed.us.

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