In 2012, Ohio authorities detected a new apparent disease attacking American beech (Fagus grandifolia) in Northeast Ohio. Initially they observed decline and mortality of beech saplings. Over the four years between 2012 and 2016, the apparent disease, termed beech leaf disease (BLD), spread from an estimated 84 ha to 2,525 ha within Lake County, Ohio (Ewing et al. 2018) (see also pages on beech bark disease [BBD] and beech leaf-mining weevil [BLMW]).
In December 2020, Daniel Volk with Cleveland Metroparks sent out this update via email to a list of stakeholders, “There was a tremendous effort to survey for BLD in 2020 and the (below) map is a product of these efforts. In total, we added four new states (Massachusetts, New Jersey, Rhode Island, and West Virginia) and 31 new counties, totaling 71 counties with BLD across the US and Canada.” In 2021, outbreaks were detected in Maine and Virginia (Gianino, 2021 and Smith, 2021). Maps and other information are available at https://www.clevelandmetroparks.com/parks/education/publications. An updated USFS Pest Alert is now available here: USFS Beech Leaf Disease Pest Alert
The rate of decline within beech stands varies, suggesting that trees differ in susceptibility. This is a promising for breeding resistance (Ewing et al.).
Most scientists now agree that the cause is a non-native nematode. Japanese researchers described a previously un-named nematode as Litlylenchus crenatae in May 2018 after studying it on Japanese beech F.crenata (Kanzaki et al.). The U.S. population (found by David McCann of the Ohio Department of Agriculture) was later described as a subspecies Litylenchus crenatae ssb mccannii by Lynn Carta. Thousands of live Litylenchus nematodes (at least 10,000) can swim out from a single infested leaf.
Symptoms
Early symptoms are dark striping on the leaves – best seen by looking upward into the backlit canopy. The striping is formed by a darkening and thickening of leaf tissue between leaf veins. Later, lighter, chlorotic striping may also occur. Eventually the affected foliage withers, dries, and yellows. Bud and leaf production is also affected. Drastic leaf loss does occur for heavily symptomatic leaves during the growing season, as early as June, but asymptomatic and mildly symptomatic leaves show no or minimal leaf loss respectively. Both fully mature and very young “emerging” leaves show symptoms.
Disease Progression
In Northeast Ohio, intensive monitoring of a subset of 13 plots in Cleveland Metroparks sites revealed a 7% mortality rate in 2018, primarily in saplings (Volk, pers comm). More than half of the plots now have dead trees that had previously been only symptomatic. While most of the dead trees are less than 4.9 cm dbh, some larger trees have died and others bear only a few leaves in summer. Sapling and pole-sized trees die within about three years after symptoms are observed. In areas where the disease is established, the proportion of American beech affected nears 100% (Pogachnik 2016).
Disease incidence does not appear to be influenced by slope, aspect, soil conditions, or weather. Also, while a wide variety of insects and pathogens is associated with symptomatic trees, these appear to be independent of beech leaf disease.
Leaves with light, medium, or heavy symptoms of infection – as well as asymptomatic leaves – can occur on the same branch of an individual tree.
The disease may spread through beech clone clusters along the interlocking roots, rain splash, and biotic vectors such as through contact with songbirds (external or via consumption of plant materials).
Long range spread of the disease is probably assisted by anthropogenic transport, especially of nursery stock. Both European (F. sylvatica) and Asian (F. orientalis) beech have shown symptoms (Ewing et al. 2018). In the past, an Ontario retailer received – and rejected – a shipment of diseased beech from an Ohio nursery.
Place of American Beech in the Forest
American beech, Fagus grandifolia, is one of the most widely distributed hardwoods in North America. Its range reaches from Nova Scotia to Texas, and in the north, west to the Mississippi River (Houston in USFS GTR NE-331; Beckman et al. 2021). Beech averages 2.3% of the total forest basal area within its range. Population densities are highest in a broad band of maximum abundance following the Appalachian Mountains from Kentucky to Maine. Beech constitutes 11.1% or more of basal area in this band, and up to 51% in parts of the Adirondack Mountains. While data from the Canadian range is spottier, in 2004 beech made up 17% of the forest in Quebec (Cogbill, 2004). In 2019, American beech comprised more than 50% of basal area in 17 plots and between 20-50% basal area in 16 additional plots in southwestern Ontario (Reed et al. 2022). In much of the southern and Midwestern portion of the range, beech constitute less than one percent of basal area (Cogbill in USFS GTR NE-331). Human actions even before the advent of non-native pests and pathogens had exacerbated a centuries-old reduction in beech. Population densities in the Northeast at the beginning of the 21st Century was only 30% of that at the beginning of the 19th Century. Still, despite overall reduction and regardless of past history, as of the beginning of the 21st Century, northern hardwood landscapes tended to have beech in 70 – 100% of stands; beech formed 5 – 25% of basal area (Cogbill, 2004). Even in Michigan, on the western edge of the species’ range, there were an estimated 138 million beech trees on 7.16 million acres of forest. About half of these forest areas had a beech basal area greater than 20% before arrival of beech bark disease (Heyd, 2004).
Fagus grandifolia is the only native member of the genus in North America (Beckman et al. 2021). There is a disjunct population in eastern Mexico (Beckman et al. 2021) – sometimes considered a separate subspecies, Fagus grandifolia var. mexicana (Cogbill, 2004).
Throughout its range, beech is found on most mesic sites which have escaped fire. Trees grow from sea level along the Atlantic and Gulf coasts up to 2000 m elevation in gaps of the southern Appalachian Mountains. At the northern edge of the range, beech occurs under locally moderated temperature and moisture conditions up to ~ 800 meters on mountain slopes. It is especially abundant on well drained soils in valley sides or on hardwood ridges. The western limit of the range appears to be tied to moisture availability (Cogbill, 2004). Due to its extensive distribution, the species has not been considered at risk by the International Union for the Conservation of Nature or The Nature Conservancy (Beckman et al. 2021).
Beech’s modern geographic pattern reflects the interaction of three major factors: the species’ background regional abundance, alterations due to land use changes (e.g., land clearance, regeneration of agricultural lands, forest management), and – since the mid-20th Century – the effects of beech bark disease. Past land use affects light levels. Canopy beech promote soil and forest floor conditions that favor regeneration by beech seedlings over competitors, e.g., sugar maple and hemlock (Beckman et al. 2021; Lovett et al. 2006). In some of these forests, white ash also comprised significant proportions of the forest (e.g., 5% of saplings, 16% of seedlings in plots in southwestern Ontario [Reed et al. 2023] and also present in Michigan forests [Kearney et al. 2004]) until succumbing to emerald ash borer. Still, beech seeds and sprouts are not dispersed far from the parent tree, which to some extent limits its ability to exclude other tree species availability of soil nutrients (especially nitrogen and calcium) (Canham, in USFS GTR NE-331). Soil moisture is important because beech is highly sensitive to drought stress. On moist, acidic soils, beech competes overwhelmingly in late-successional stands. Beech uninfected by beech bark disease are highly resistant to wind damage. American beech is often said to be long-lived, although Cogbill (2004) said field studies have found few trees over 250 years old. Beech foliar litter is high in lignin so it decomposes more slowly than that of its principal hardwood co-dominants, yellow birch and sugar maple. Litter quality influences the development of the forest floor and affects nutrient retention and cycling in the stands (Lovett et al. 2006).
Despite the decline of American beech historically (see above) and 100 years of impacts from beech bark disease, the species is expanding in regenerating forests across many parts of the Eastern Deciduous Forest (Ducey et al. 2023; Miller et al. 2023; Payne and Peet, 2023). One factor might be that deer browse beech leaves and twigs only when other food sources are scarce [see National Deer Association article here]. Deer are documented as playing a significant, if not always dominant, role in regeneration of forest tree species (Miller et al. 2023; Blossey et al. 2024). Deer do feed on the nuts, apparently heavily (Storer et al. 2004).
American beech has limited value as timber, but it is recognized as very important to wildlife. The tree’s large nuts are high in both protein (20% dry matter) and fat (50% dry matter) [see National Deer Association article here ], making them an important food source for at least 20 wildlife species, (perhaps as many as 40) including rodents, certain passerine birds, turkey, and bear among others (McNulty and Masters, 2004). The nuts’ importance is greatest in those parts of the northern hardwood forest where oaks are rare; there, beeches are the only species producing hard mast (Lovett et al. 2006). However, mast resources are apparently not as “reliable” as has often been said. In Maine and New York – after arrival of beech bark disease – large mast crops are produced on alternate years (Jakubas et al. 2004; McNulty and Masters, 2004). In Michigan, before arrival of beech bark disease, less than 10% of beech nuts examined were sound (Storer et al. 2004).
In addition to challenges from three non-native pests – beech bark disease, beech leaf disease, and European beech leaf weevil, beech might be struggling to adapt to elevated nitrogen deposited in eastern forests by air pollution (Latty, 2004).
Online references
Beech Leaf Disease Publications, Cleveland Metro Parks https://www.clevelandmetroparks.com/parks/education/educational-resources/publications
Ohio Department of Natural Resources, Division of Forestry, Beech leaf disease page https://ohiodnr.gov/wps/portal/gov/odnr/discover-and-learn/safety-conservation/about-ODNR/forestry/forest-health/insects-diseases/Beech-leaf-disease
Beech Leaf Disease, New York Department of Environmental Conservation, https://www.dec.ny.gov/lands/120589.html
Sources
Blossey, B., Hare, D., and Waller, D.M. 2024. Where have all the flowers gone? A call for federal leadership in deer management in the US. Front. Conserv. Sci. 5:1382132. doi: 10.3389/fcosc.2024.1382132
Cogbill, C.V. 2004. Historical Biogeography of American Beech. In USDA USFS NE Research Station General Technical Report NE-331 BBD: Proceedings of the BBD Symposium Saranac Lake, NY June 16 – 18, 2004
Connecticut Agricultural Experiment Station. 2019. CAES Announces First Report of Beech Leaf Disease in Greenwich, New Canaan, and Stamford Connecticut. Press Release. October 17, 2019.
Ducey, M.J, Fraser, O.L., Yamasaki, M., Belair, E.P., and Leak, W.B. 2023. Eight decades of compositional change in a managed northern hardwood landscape. Forest Ecosystems, 10(3) 100121. https://doi.org/10.1016/j.fecs.2023.10012
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John Pogacnik, Biologist, Lake Metroparks & Tom Macy, Forest Health Program Administrator, Ohio Department of Natural Resources Division of Forestry. Forest Health Pest Alert Beech Leaf Disease July 2016
McNulty, S.A. and Masters, R.D. 2004. Changes to the Adirondack Forest: Implications of Beech Bark Disease on Forest Structure and Seed Production. In USDA USFS NE Research Station General Technical Report NE-331 BBD: Proceedings of the BBD Symposium Saranac Lake, NY June 16 – 18, 2004
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Photo Credit: New York State Department of Environmental Conservation