Restoring the American Elm

By Hannah Phillips –

The flower buds from Mrs. Waters’ elm tree are 35,000 feet up in the stratosphere on an express flight to Ohio. The goal is to get them there before they dry up. When they arrive, scientists will lay them on wax paper, collect their pollen as it falls from the stamens, and use it to hand-pollinate the flowers of Ohio elms that are receptive and waiting in the lab. These buds may be the key to restoring the American elm to dominance in the floodplain forests of the Eastern United States, a focal project of The Nature Conservancy (TNC) and floodplain ecologist Christian Marks.

The buds’ progenitor, a four-foot diameter American elm in Charlotte, Vermont, named Henrietta, has beat the odds. Located merely a stone’s throw from four other elms, all of which have succumbed to Dutch elm disease (DED), Henrietta is noticeably larger and healthier. Though she (also a he—American elms bear “perfect” flowers, with both male and female parts) has signs of DED on two branches, the remainder of the tree is healthy enough to produce flowering buds, a luxury that the sick elms around it cannot afford. Normally, trees exposed to DED die within a year of exposure[i]. That this one has not– and that it continues to flower—suggests it may possess some degree of resistance.

After scientists cross-pollinate the Vermont and Ohio elms, they will tend the branches until they set seed. When the seeds mature into small, wafer-like samaras, evolved for wind dispersal, the Ohio scientists will airmail them back to Marks (wind dispersal by mechanized means) who will then grow them to seedlings and plant them in one of TNC’s floodplain forest restoration preserves. But that’s not all. What’s to say those young seedlings won’t succumb to the same fate as their not-so-fortunate relatives?

For Marks to know that Henrietta is a stalwart, he must subject her offspring to a potentially fatal injection of DED when they reach one inch in diameter. Though it will be some time before we find out if Henrietta is truly resistant, the offspring of buds collected from other trees in 2011 and 2012 are approaching the requisite diameter for testing. And while “absolute resistance” is the stuff of science fiction, previous studies conducted through Guelph University in Canada found a heightened level of resistance in 25% of lab-pollinated offspring reared from large, healthy elms[ii]. Marks is hopeful for a similar (or better) result from his Vermont/Ohio crosses, which were selected not only for their size, but also for their proximity to elms that have succumbed to DED.

If Marks and his colleagues succeed in cultivating a DED-resistant American elm, this stately canopy tree may eventually be restored to its position in the highest strata of the floodplain forests in the Eastern United States and Canada. And though we may not be alive to see it regain canopy dominance, we can celebrate that the elm’s capacity for water uptake may reduce the severity of future flooding events, bald eagles may return to nest in its branches, and our children will once again walk to school beneath trees for which many American streets were named.

Perhaps this dream begins with the plump red buds bound – at this moment – for Ohio.

[i], [ii] Christian Marks, personal communication, 9 March 2016.

Hannah Phillips is a first-year graduate student in the Ecological Planning Program. She is grateful to Christian Marks, Gus Goodwin, and The Nature Conservancy-Vermont, for welcoming her on this outing, to Mrs. Waters for offering samples from her tree, and to Chea Waters Evans for cleverly naming the tree Henrietta (after Henrietta Lacks).