The deadly experiment that could save the American elm

Researchers in Vermont are deliberately infecting thousands of young American elms with Dutch elm disease, the fungus that has killed tens of millions of elms since it arrived in North America last century. The goal is to find the rare trees that can survive repeated exposure, then breed them into a new, genetically diverse population that could eventually repopulate river valleys and floodplains across the country.

American elms once lined Main Streets nationwide before the disease wiped most of them out. Past breeding efforts produced a few disease-tolerant varieties sold in nurseries, but they came from a narrow gene pool and aren't tough enough for the harsh, repeated exposure trees face in the wild over long lifespans. This new project pulled cuttings from dozens of surviving "parent" trees around New England, cross-bred them, and is now testing thousands of offspring by injecting them with the fungus directly. Early results, with hundreds of trees showing no symptoms so far, are promising, though researchers won't know which parent trees produced the hardiest offspring for at least two more years, and any resulting seed orchard is still a decade or more away from producing widely available trees.

For homeowners, there's no product or program to act on yet. But elms matter beyond looks: they tolerate shade and flooding better than almost any other floodplain tree, and healthier elm populations could help absorb storm water and reduce flood damage in the regions where they once grew. If this research succeeds, more resilient elms could eventually become available for planting on private property, though that's still years off.