Iowa has lost an estimated 94 percent of its 1.4 million native butternut trees since 1990 to a disease causing fungus transported by rain splash, wind and insects.
There is no known treatment for the fungus so conservation efforts are focused on finding and protecting butternut trees that have survived among neighboring butternuts that are dead or dying.
Butternut, sometimes called white walnut in Iowa, is native to the eastern half of the state. It produced valuable wood products because it is softer than black walnut making it easier for carpenters to shape and carve cabinets, flooring and furniture.
People and many different forest wildlife species seek butternut seeds to eat. Losing this species reduces the diversity of Iowa forest ecosystems and affects wildlife species that use to use butternut seeds as a food source before winter.
Western Iowa marks the end of the natural range for butternut. Foresters with the Iowa DNR and the U.S. Forest Service are working to identify and grow pure strain butternuts in an effort to preserve the species in two locations - Yellow River State Forest and the Loess Hills.
The Loess Hills site serves as a conservation area, while the Yellow River site allows exposure of butternut trees to butternut canker to test if they are truly resistant.
The Forest Service has been collecting butternut branches for more than 20 years in locations in the northeast U.S., from trees that survived while other butternuts died from the disease, giving hope to finding a disease-resistant strain.
These branches were grafted on to black walnut root stock to help create seed orchards that can produce more seeds to maintain a viable population of native butternuts. Iowa has planted 150 of these seedlings in 2007 and 2008.
In 2009, Iowa, Indiana, Connecticut, Vermont and Pennsylvania partnered on a grant to fund more butternut surveys and research. The grant helps to find, mark with GPS coordinates, perform DNA testing, graft branches from native selections, perform canker resistance testing and plant orchards with more butternut trees that have the exact genetics of the forest grown survivors.
Iowa foresters are tracking down leads of known forest grown butternuts. So far, they have collected seed from 20 different trees for an orchard in the Loess Hills, which is outside of the native range, to try and protect those trees until resistance can be found or breed into this species. DNA testing has identified 12 pure native butternuts within Iowa with another 15 to 20 trees still to test.
"The health of our land is dependent on its diversity. From Dutch elm disease to the emerald ash borer, invasive species are destroying the vibrancy of our woodlands," said Jean Wiedenheft, land steward at the Indian Creek Nature Center in Cedar Rapids. "Our grove of nearly dead butternuts is an echo of what a woodland could and should be. The DNR's project to cultivate and restore this now rare species is important to the future health of the forest.
"I may never see a stand of mature, healthy butternuts in my lifetime and that makes what live butternuts we do have all the more valuable to the woodlands," Wiedenfeft said.
Woodland owners with a forest or woods-grown butternut who would like to add to the conservation effort should contact Aron Flickinger, special projects forester with the Iowa DNR's forestry bureau at 515-242-5966 or at firstname.lastname@example.org.