Humans adores trees. But humans also migrate and trade, habits that led to the accidental introduction of insects and diseases that harm trees and alter the landscape. Examples are easy to find and may be outside your front door: American elms that once dotted streets across America succumbed to Dutch elm disease. Now all colors of ash species – black, green, white, pumpkin, and blue – are threatened by emerald ash borer. The already uncommon butternut tree, also known as white walnut, faces the possibility of extinction from a mysterious attacker.
Many invasive insects and fungi come from regions where native trees have evolved to resist their attacks. When these species enter the United States, they find trees that lack this resistance. There’s no immediate end to this dismal pipeline, but there is hope on the horizon.
After a pest has moved through a forest, inquisitive scientists scour the woods looking for survivors. There is a chance that no trees will survive, but those that do may be worth studying. Scientists at the USDA Forest Service’s Northern Research Station work with the agency’s Reforestation, Nurseries, and Genetics Research program, also known as RNGR. They have identified lingering green ash trees that are demonstrating resistance. So far, 16 selectively bred varieties of American elm are on the market, and scientists at the Northern Research Station are breeding trees to improve resistance even further. Resistance in butternut remains elusive, but scientists in the United States and Canada, including those at the Hardwood Tree Improvement Regeneration Center, are embarking on a new plan to help save the species. Today, the search for ash and elm trees with resistance to emerald ash borer and Dutch elm disease continues.
Finding survivors is the first step toward improving resistance. Scientists acquire a branch or bud from surviving trees, then transport and study these survivors to their lab for assessments and controlled studies. Surviving trees can be cross-pollinated to increase resistance in the offspring. Eventually, as resistant material becomes available, you can check the national nursery and seed directory at the RNGR website.
Citizen scientists can contribute to this important work. If you find a surviving elm or ash tree in the woods, upload the information to Treesnap, a free app that you can download to your phone. Hard-working scientists and trained citizen-scouts are needed to conserve seed, graft survivors, and breed for resistance. These efforts may be our best bet to prevent the wholesale loss of our most beloved, and valued, forest trees.
