image: Brianna Shepherd, research specialist at Holden Forests & Gardens, measures the diameter of an American beech tree as part of a long-term study on the impacts of beech leaf disease. First observed in northeastern Ohio over a decade ago, the disease is now rapidly spreading across the species’ range. In a new report, researchers near the epicenter share long-term monitoring data that quantify its effects for the first time. They found 30% of beech trees have died, and growth of surviving trees has slowed. The scientists warn the emerging threat could reshape eastern forests.
Credit: Brandon Younan/Holden Forests & Gardens
KIRTLAND, OH — A decade after the emergence of beech leaf disease (BLD) in northeast Ohio, a new study by researchers at The Holden Arboretum reveals that American beech (Fagus grandifolia) is experiencing significant mortality and reduced growth—signs that the disease may bring lasting changes to eastern North American forests. The study is the first to quantify the extent of the damage.
Published in the scientific journal Trees, Forests and People, the study quantified the long-term impacts of BLD on individual trees, using a unique data set collected annually since before the disease was first detected in the region. Of 263 American beech trees tracked at the Cuyahoga County research site, 30% have died since BLD was first observed in the area in 2014, with the most severe losses occurring in recent years.
“We saw an exponential increase in mortality in just the last three years,” says Brianna Shepherd, a research specialist at Holden Forests & Gardens, who led the study. “Saplings were hit especially hard, with mortality rates as high as 14% in 2022 alone.”
The disease, which is associated with the non-native nematode Litylenchus crenatae subsp. mccannii, causes darkened, distorted leaves that can reduce photosynthesis by up to 60%. These symptoms, first noticed in Lake County, Ohio, in 2012, now stretch across 15 U.S. states and into Ontario, Canada.
In addition to increased mortality, the study found that beech trees in the affected plots grew significantly more slowly after BLD arrived.
“This is a slow-moving crisis,” says David Burke, co-author and Holden’s Vice President for Science and Conservation. “Beech leaf disease doesn’t kill trees as quickly as some pests, but the cumulative impacts—slower growth, energy loss, increasing mortality—add up. Especially in a forest where beech is dominant, these effects will ripple out.”
The researchers also found that tree mortality was higher in plots with denser beech populations, suggesting that crowding or disease transmission may be compounding stress on the trees. In contrast, mortality was somewhat lower in plots amended with limestone (to lower acidity) or phosphate (to increase nutrients)—an experimental treatment from a separate study—hinting at possible links between soil chemistry and mortality.
The findings are based on long-term data from research plots at Case Western Reserve University’s Squire Valleevue Farm in Hunting Valley, Ohio, just miles from the epicenter of the BLD outbreak, which were serendipitously established in 2009. Originally established to study the effects of soil nutrients and acidification, the plots offered a rare opportunity to observe progression of the disease over time. BLD symptoms were readily observed on trees at the site by 2017.
“Our long-term dataset let us track exactly what happened, from before the disease was here through nearly a decade of spread,” says Katie Stuble, co-author and Director of Research at Holden. “Many forest disease studies don’t have access to this kind of baseline data, so it gives us a much clearer picture of what this disease is doing.”
The team emphasizes the need for continued monitoring, particularly as BLD continues expanding its range and intersects with other stressors such as beech bark disease and climate change. Together, these pressures could reshape the composition and structure of eastern forests.
“We’re watching the decline of a foundational species in real time,” Shepherd says. “It’s sad, but as we learn more and more about the disease through studies like this one, we get closer to possible solutions.”
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Citation: Shepherd, Brianna L., David J. Burke, and Katharine L. Stuble. "Fagus grandifolia growth and mortality a decade after the emergence of Beech Leaf Disease." Trees, Forests and People (2025): 100836.
About Holden Forests & Gardens: Holden Forests & Gardens is made up of two of Northeast Ohio’s most important environmental and cultural institutions—the Holden Arboretum and Cleveland Botanical Garden—whose mission is to connect people with the wonder, beauty, and value of trees and plants, to inspire action for healthy communities. One of the largest public gardens in the country, Holden Forests & Gardens has 21,000 member households and an annual attendance of nearly 350,000 for whom we strive to provide inspirational and educational visitor experiences. For more information, visit holdenfg.org.
Journal
Trees Forests and People
Method of Research
Observational study
Subject of Research
Not applicable
Article Title
Fagus grandifolia growth and mortality a decade after the emergence of Beech leaf disease
Article Publication Date
21-Mar-2025
COI Statement
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.