A new long-term study from The Holden Arboretum reveals just how devastating beech leaf disease (BLD) has become. After tracking 263 American beech trees over a 10-year period, researchers found that 30% have died since the disease appeared in northeast Ohio in 2014, with the worst impacts coming in the last three years.
“We saw an exponential increase in mortality in just the last three years,” said Brianna Shepherd, lead author of the study and a research specialist at Holden Forests & Gardens. “Saplings were hit especially hard, with mortality rates as high as 14% in 2022 alone.”
A Slow, Worsening Threat
BLD, first noticed in Lake County, Ohio in 2012, is linked to a non-native nematode (Litylenchus crenatae subsp. mccannii) that causes dark, curled leaves and can reduce a tree’s ability to photosynthesize by up to 60%. It has now spread to 15 U.S. states and Ontario, Canada.
Though the disease doesn’t kill trees immediately, its long-term effects are compounding. Trees grow more slowly, lose energy, and gradually decline over time. “This is a slow-moving crisis,” said David Burke, co-author and Vice President for Science and Conservation at Holden. “Especially in a forest where beech is dominant, these effects will ripple out.”
Tree Crowding and Soil Conditions Matter
Interestingly, the study found higher mortality in areas with dense beech populations, suggesting that crowded conditions may increase disease transmission or stress. But in plots that had been treated with limestone or phosphate, the mortality was somewhat lower. This hints that soil chemistry may play a role in how this beech leaf disease affects trees.
Unique Data Gives Rare Insights
What sets this study apart is the long-term dataset. The research plots were set up back in 2009 at Case Western Reserve University’s Squire Valleevue Farm in Hunting Valley, Ohio before BLD even arrived. That gave scientists a rare before-and-after view of the disease’s impact.
“Many forest disease studies don’t have access to this kind of baseline data,” said Katie Stuble, co-author and Director of Research at Holden. “It gives us a much clearer picture of what this disease is doing.”
A Warning for the Future
The team warns that as BLD continues to spread and combines with other threats like beech bark disease and climate change. It could dramatically change the makeup of eastern North American forests.
“We’re watching the decline of a foundational species in real-time,” said Shepherd. “It’s sad, but as we learn more, we get closer to possible solutions.”
