The American Elm and its importance for warblers
The American Elm as a specimen tree is so diminished now due to the decades-long problem of Dutch Elm Disease (DED). From the 1960’s on, when the disease was first introduced in Minnesota, the devastating loss of these stately, grand trees has scarred many people who grew up enjoying them in their neighborhoods. Because the American Elm is no longer considered a desirable tree, homeowners are reluctant to try and plant some of the newer “disease-resistant” strains and often remove any volunteer elms that sprout naturally in their backyard. What is being overlooked are the natural benefits of the American Elm when it is actively growing and thriving, often for years, before it succumbs to DED.
I first noticed the importance of the American Elm when looking for warblers during the spring migration. Two species of trees in my backyard always seem to host the most feeding warblers at one time - oaks and elms. American elms host a small grub in their seed heads that the warblers prize. These small yellowish grubs eventually drop to the ground where they overwinter and will develop into midges (small flies). The following spring they emerge to mate and the females fly back to the elm when flowering to deposit eggs which rapidly grow into grubs in time for the migrating warblers to eat. This midge is specific to the American Elm which has creates this springtime relationship with the warblers.
Maybe someday the American Elm will overcome DED. There are plenty of young to med-sized elm trees around - it is not like what is now happening with the Emerald Ash Borer where it does not seem any ash trees are safe regardless of their health, age or size. Elm trees grow between one to two feet a year so they can quickly get to a decent size to provide shade and food for birds. And if isolated or lucky, an American Elm can live decades in the backyard before coming in contact with DED.
Now is not the time to give up on this distinctly American tree with its long history of providing food for migrating warblers as well as being a host plant for several butterfly species including Painted Lady, Eastern Comma, Mourning Cloak, Question Mark Butterfly, and the Red Spotted Purple Butterfly.