Tree Alarm

Tree Alarm

Dutch elm disease and chestnut blight have long since routed New Haven’s native elms and chestnuts. Now American beech trees—a keystone species in eastern forests, distinguished by their smooth, elephant-gray bark and leaves lined with spike-tipped veins—are under siege, targeted by something first discovered stateside in Ohio in 2012: beech leaf disease (BLD). The symptoms? Leaves with dark green banding, especially visible from the underside, that may turn yellow or brown; “cupped and leathery” leaves even in spring and summer; and unnaturally thin leaf cover, among others. The prognosis? Death within six to 10 years—half that if the tree is infected before reaching maturity.

Robert E. Marra, a Connecticut Agricultural Experiment Station researcher and part of a BLD working group with scientists in Ohio, Pennsylvania, New York, Massachusetts, West Virginia and at the USDA, emphasized that “this is a brand new disease.” He’s spent considerable time on the phone with beech owners and admirers “who are angry more is not being done” to mitigate BLD. But because trees have relatively long life cycles and spans, research into the causes and effects of a disease like this can also take a long time.

Fortunately, by 2020, there was a crack in the case, with researchers confirming a “newly recognized nematode subspecies Litylenchus crenatae mccannii” as the culprit behind BLD. “At first,” Marra says, “no one thought of nematodes”—microorganisms also known as roundworms—“because there was no historical experience with foliar nematodes of trees.” Marra “developed a molecular marker that allowed us to demonstrate that nematodes are there,” a crucial tool as he monitors forested plots in every county in Connecticut. In the meantime, the parasites have spread so quickly and widely that the CAES has advised the public not to bother reporting any more sightings.

It’s now known that BLD’s telltale symptoms appear the year after the nematodes—which Marra likened to “Godzilla tramping over towns full of people”—infect a tree’s buds, causing “mechanical damage.” The nematode population explodes over the summer, and when there’s a “wet event”—anything from a brief shower to a downpour—they “swim out” of leaves and hitchhike to other trees on creatures like spider mites, leafhoppers, squirrels or jays. “Maybe it goes to a maple tree and end up dead,” Marra says, but “the randomness of nature means sometimes they hit the jackpot: another beech. If a female is ready to lay eggs, they’re all set.”

Most of the callers to the CAES are concerned about ornamental, non-native “specimen” beeches such as the copper European variety dotting the drive-up entrance to East Rock Park, which are also vulnerable to BLD. But those trees don’t occupy a role in our native ecology, so “the real horror show,” Marra says, “is in the forest, playing out in slow motion in our midst.”

Keystone species are the backbones of their ecosystems. In the case of beeches, their nuts provide an important food source for birds and other animals. Even more importantly, beeches “tend to provide a large percentage of the forest canopy,” Marra says. Their shade helps determine what grows on the forest floor, and less than a decade after BLD was first detected in Ohio, there’s already a “25% loss of canopy density than what we’d expect to see” in Connecticut, Marra says. To see this thinning for yourself, walk east along the flat White trail in East Rock Park, starting just past Eli Whitney’s shed, and continue to the East Rock Street Bridge.

What to do? While research suggests potassium phosphite treatment may be effective in protecting individual ornamental beeches, the far more important thing to do is contact your federal representatives in the House and Senate and ask them to specify and prioritize US Forest Service funding for American beeches and BLD. According to Marra, because BLD is so new, there’s still no money explicitly budgeted for it.

Funding, he says, is critical to learning more about beech leaf disease and, ultimately, how to effectively treat and prevent it. “We’re at the nascent stage of understanding this disease and have a lot to learn,” Marra says. “We have far more questions than answers.” One answer it seems we do have: To preserve native forests here and beyond, BLD has to be addressed, quickly.

Written by Heather Jessen and Dan Mims. Photographed by Heather Jessen.

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