Understanding Beech Leaf Disease

by | Botany, Environment

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When the first warm days arrive, spring bursts at the seams with greenery and the forest comes alive as native trees emerge from dormancy. The American Beech, an iconic part of the New England landscape, (Fagus grandifolia) showcases its brilliant green leaves.

New England is known as one of the most forested regions in the country with 80% total forest cover. (1, 2, 3) The majority of that land consists of maple-beech forest, an important northern hardwood community that supports a complex ecosystem of native plants and wildlife.

Image: D. K. Berard. Diseased leaves showing yellow banding in autumn.

The dense beech canopy provides habitat, shelter, and food for an estimated 235 species of birds, caterpillars, mammals, and insects.

Some species depend almost exclusively on beech trees, such as the imperiled Early Hairstreak butterfly (Erora laeta) which lives and lays eggs in the canopy, feeding on beech leaves in its larval stage.

In fall, beech trees create a stunning display of brilliant yellows and produce nuts, a critical source of fat that helps wildlife survive the winter. Beechnuts are so nutritious that they can predict next years’ wildlife populations from black bears to wood ducks. (4) “A key determinant of animal numbers is food availability,” says Stacy McNulty from the Adirondack Ecological Center.

“A key determinant of animal numbers is food availability,”

Stacy McNulty, SUNY ESF

Beech is also an economically important source of wood for plywood, veneer, furniture, and firewood. Humans have used beech for centuries, favoring its smooth grey bark and soft wood. Beech bark tablets were used as paper in early literature, and historians believe the Germanic word for beech (Buche) gave us the modern word for “book”. (5)

With such an intertwined history, it’s no wonder that beech is still a forest favorite, inspiring the musings of poets and catching the admiration of hikers.

Image: Destynnie K. Berard, HerbSpeak author, selecting diseased leaves from beech trees for further research.

The broad leaves shrivel and turn leathery as branches die, becoming inedible to the Early Hairstreak and other caterpillars that feed on the leaves.

This reduces canopy cover to as little as 10%, halting nut production as the tree spends all its energy producing new leaves.

Without beechnuts to depend on, wildlife must find alternate sources of food or starve.

Without its leaves, beech trees cannot exchange oxygen or photosynthesize. These are the tree’s dying breaths. Age does not protect them, as even mature trees can succumb within 2-7 years of initial infection.

Image: D. K. Berard. One of the few remaining healthy beech leaves. Shown sprouting at the first sign of Spring.

How Did Beech Leaf Disease Start?

In 2012, Lake Metroparks biologist John Pogacnik first discovered Beech Leaf Disease in Lake County, Ohio. At first, it wasn’t clear to John that the trees were diseased. “It was found when it was a really dry year, so […] you thought maybe they were drought related, because it’s so dry.”

He soon discovered more diseased saplings at other parks and alerted the U.S. Department of Agriculture and the Ohio Department of Natural Resources. These agencies began searching for clues that could point them to the cause.

Identifiable by darkened bands in the canopy of otherwise translucent-green leaves, this disease affects photosynthesis, which limits the nutrients the tree can produce and store. “Diseased stands can suffer from defoliation and canopy dieback, which tends to increase in severity following multiple years of infection,” says Dr. Cameron McIntire, a research pathologist for the USDA Forest Service. (6)

Image: D. K. Berard, Unidentified nematodes found under microscope with infected beech leaves.

The Cause Revealed

In 2017, the Ohio Department of Agriculture made a breakthrough, discovering an invasive nematode in infected samples.

Nematodes are microscopic worms that live in soil or plant tissues. Most nematodes play an essential role in the ecosystem by feeding on organisms that hurt plants or by making nutrients available for the roots. Some nematodes, however, can cause significant damage.

The USDA Agricultural Research Service in Maryland compared DNA samples of the nematode to confirm the discovery as the first observation of the Litylenchus crenatae, a shrub nematode, in the western hemisphere. Due to its new range and choice of host, it was given a subspecies: Litylenchus crenatae ssp. mccannii. (7)

Soon after identification, symptoms of Beech Leaf Disease appeared in New England forests. Connecticut first reported symptoms in 2019, and by 2021, the nematodes had reached as far north as Maine. (8)

As a foliar nematode, L. crenatae moves on water films, meaning it may spread through irrigation, rain, or snowmelt; but that doesn’t explain such rapid expansion.

 

In a race against the clock, an increasing number of scientists, state agencies, and citizens are all working together to find the answers. Despite this effort, little is known about how they spread or why they target beech trees.

 

 

The USDA Forest Service works with states to gather data from a bird’s eye view, monitoring and documenting the spread to aid research. This requires all-hands in each state, surveying state properties to monitor for signs of progression.

Meanwhile in labs across the country, researchers are trying to determine how the nematodes, which reside entirely in the leaf and bud tissue, make the jump from one tree to another miles away.

Researchers at Ohio State University are taking samples from insects and birds to determine if they are unwittingly carrying the nematode, while others are assessing environmental patterns. Current hypotheses include transmission by windborne mites, or by birds that eat beech buds.

Scientists are also tackling the issue from a management perspective. The University of Rhode Island is building on the work done in Ohio by testing fungicides as a potential management solution for individual trees.

Landscaping arborists are conducting research into whether mulching or irrigation can help individual trees, and citizens are getting involved by submitting photographic reports of both healthy and infected trees.

 

The Fate of American Beech Trees

The fate of the American Beech tree hangs in the balance, but the resilience of nature and the determination of those invested in its preservation offer a glimmer of hope. Researchers, scientists, and citizens are banding together to protect these trees and the intricate web of life they support. Some people are saving the beechnuts that fall on their property, while others look for alternative plants to support wildlife and investigate treatments. 

Image: GIF showing visual timeline of beech leaf disease spread by county 2012-2022. Original Feb 2023 map and data © Ontario, USDAFS, Ontario. Map modified into animated format on HerbSpeak.

While it is tempting to remove beech trees before they are infected, healthy trees could hold the key to resistance. “We have to give beeches a chance to adapt,” says Joe Orefice, from the Yale School of the Environment. Some trees appear to be naturally resistant to infection, which could hold clues to preventing the disease from progressing.

 

The story of the American Beech and its battle against Beech Leaf Disease serves as a powerful reminder of the interconnectedness of humans and nature, impressing the importance of stewardship and safeguarding the biodiversity that sustains us all. By sharing knowledge with a sense of collective responsibility, future generations may still marvel at the vibrant green beech canopy on the New England landscape for years to come.

 

What Can You Do?

Like our own communities, a forest requires diversity and complex relationships to thrive. Healthy forests support wildlife and humans by providing food and shelter while stabilizing the local climate.

Beech Leaf Disease is spreading across beech forests at a critical time of biodiversity loss around the globe, driving wildlife from their homes and damaging our climate security.

Active awareness is the first step to protecting our native New England landscape. Community reports of both injured and healthy trees are a critical component of ongoing scientific research.

Reports can be sent through state and university extension forms, or through free community apps like iNaturalist.org. This citizen science data is used to measure forest health, helping scientists track down the cause of the disease – and hopefully, a cure.

Recommended Next Article: How to Use iNaturalist

References
References
  1. Butler, Brett J., Forests of Massachusetts (2016), retrieved from: https://www.fs.usda.gov/research/treesearch/54870# doi: https://doi.org/10.2737/FS-RU-138
  2. New England Forestry Foundation, Keeping New England Forested, https://drive.google.com/file/d/1AP7V8stptjfcJkFRjhE0KTSdqBU3uska/view?usp=sharing
  3. Wikipedia, Forest Cover By State and Territory in the United States, https://en.wikipedia.org/wiki/Forest_cover_by_state_and_territory_in_the_United_States
  4. Adirondack Almanack, Stacy McNulty: Beech Nuts, Mice, and Bears, https://www.adirondackalmanack.com/2012/08/stacy-mcnulty-beech-nuts-mice-and-bears.html
  5. Pierce, M. (2006). The Book and the Beech Tree Revisited: The Life Cycle of a Germanic Etymology. Historische Sprachforschung / Historical Linguistics, 119, 273–282. http://www.jstor.org/stable/40849386
  6. Research Brief: Surveying for Beech Leaf Disease, https://www.nps.gov/articles/research-brief-surveying-for-beech-leaf-disease.htm
  7. Carta, Lynn Kay; Handoo, Zafar A.; Li, Shiguang; Kantor, Mihail; Bauchan, Gary; McCann, David; Gabriel, Colette K.; Yu, Qing; Reed, Sharon; Koch, Jennifer; Martin, Danielle; Burke, David J. 2020. Beech leaf disease symptoms caused by newly recognized nematode subspecies Litylenchus crenatae mccannii (Anguinata) described from Fagus grandifolia in North America. Forest Pathology. 50(2): e12580. 15 p. https://doi.org/10.1111/efp.12580.
  8. Mapping the Environmental Risk of Beech Leaf Disease in the Northeastern United States, Yongquan Zhao, Dr. Pierluigi Bonello, and Prof. Desheng Liu, Plant Disease 0 0:ja https://doi.org/10.1094/PDIS-12-22-2908-RE

 

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About Destynnie K. Berard
I am a lifelong naturalist who believes a good sense of humor is essential to staying happy. ★ After traveling for years, I settled in New England, falling in love with the diverse landscape the Northeast has to offer, and began pursuing conservation in earnest. ★ My career background is in enterprise marketing and communications, which provides me with a unique perspective of ecological relationships.

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