Prime Drivers of Forest Compositional Change in the United States
The interaction between drivers of composition change results in compounding effects on forest make-up over time. North America has experienced each of these drivers, and often in combination with each other. Major forest pests and diseases that have had lasting impacts on North American forests to present day include the emerald ash borer, the hemlock wooly adelgid, oak wilt disease, beech bark disease, chestnut blight, Dutch elm disease, and dogwood anthracnose. The emerald ash borer is a metallic green beetle, Agrilus planipennis, which larvae feed on the phloem and cambium of ash trees (Fraxis spp.) and was first detected in North America in 2002 (Cappaert et al. 2005). First identified in North America in 1985, the hemlock wooly adelgid, Adelges tsugae Annand, is an insect pest affecting the eastern hemlock tree (Tsuga canadensis Carriere) (McClure 1987). Oak wilt disease is caused by fungus Ceratocystis fagacearum (Bretz) Hunt (Gibbs and French. 1979). Oak wilt disease impacts oaks (Quercus spp.) in North America and was first recognized in Wisconsin in 1942 (Wilson 2005). Chestnut blight, caused by pathogen Cryphonectria parasitica, was first reported in 1904 on an American Chestnut (Castenea dentata) and has since functionally eradicated the species from its native range of eastern forests (Rigling and Prospero 2017). Impacting trees in the genus Ulmus, Dutch elm disease is a fungal disease first found in North America in 1930 (Strobel and Lanier 1981). Dogwood anthracnose, affecting dogwood species (Cornus spp.), is a fungus that was introduced to the United States in the late 1970s (Hibben and Daughtrey 1988).
American Beech
The American beech (Fagus grandifolia) is a large, deciduous climax species, a species which dominates in an ecosystem’s final stage of succession, with smooth, blue-gray bark and a dense crown (Milo 1991). With a native range spanning from Texas to Northern Florida to Nova Scotia, beech is part of 20 forest cover types and is a codominant species in the sugar maple-beech-yellow birch and sugar maple-beech forest types of the northeastern United States and southeastern Canada (Tubbs and Houston 1990). Under favorable conditions, the American beech can live upwards of 300 years (Burns and Honkala 1990) and is central to many of the ecosystems and economies it plays a role in. As a nut producing species, beech is important for a variety of wildlife; beech mast is consumed by an array of avian and mammalian species ranging from blue jays to black bears. Beech also provides essential cover for the Carolina chickadee (Parus carolinensis) and the black-capped chickadee (Parus atricapillus) (Milo 1991). Additionally, beech wood is harvested and used as veneer plywood, flooring, furniture, and other timber products and, owing to its high density and burning qualities, is an especially favored fuel wood variety (Milo 1991). Due to its economic and ecological significance, impact on beech’s status carries far-reaching implications for the economic and natural environment.
Beech Leaf Disease
Beech Leaf Disease (BLD) is an emerging forest epidemic affecting American and European beech (Fagus Sylvatica) trees. BLD was first identified in Lake County, OH, USA in 2012 and has subsequently been recorded in 15 US states and portions of Canada, reaching east to Maine and north to Ontario (as of the most recent data available, published in June, 2025) (Shepherd et al. 2025).
Manifestations of Beech Leaf Disease
One initial symptom of BLD is dark green, interveinal banding among the lower canopy leaves. Further disease progression presents as thickened, curled, crimped, and/or shrunken leaves (Ewing et al. 2018) as well as crown thinning and branch dieback (Carta et al. 2020).
The effects of BLD on beech trees have to do with both structure and functional processes. Thickening of the spongy and palisade mesophyll as well and the abaxial epidermis due to hyperplasia was observed in affected leaves (Fletcher et al 2023). In a sample group of 1-2 branches for each of eight trees at two sites in Connecticut, Fletcher et al. found leaf mass per area to be 45% higher and saturated water contents to be 25% higher in symptomatic leaves, while leaf dry matter contents was 12% lower in symptomatic leaves compared to asymptomatic leaves. Tertiary and minor veins were 51% and 96% wider and stomal density was approximately 50% lower in affected regions. Maximum photosynthetic rate and stomatal conductance were 61% and 67% lower, respectively. By limiting carbon assimilation capacity, thus depleting carbon stores, and changing and interfering with typical anatomy and physiological processes, BLD puts affected beech trees in a vulnerable position (Fletcher et al. 2023).
Ecological Implications of Beech Leaf Disease
Symptoms of BLD have been associated with Litylenchus crenatae mccannii ssp. n, a subspecies of the Japanese nematode Litylenchus crenatae. The population was first recorded by the United States Department of Agriculture in 2017 from diseased leaves sent by the Ohio Department of Agriculture (Carta et al. 2020). A study published in 2025 by Shepherd et. al., observed a mortality rate of 29.6% among trees infected with BLD. This study also found that saplings and pole class trees are disproportionately affected by BLD and are impacted in a shorter timeframe. A correlation between basal area (measure of stand density) and mortality rate was noted (Shepherd et al. 2025).
In addition to beech leaf disease, American beech trees contend with the impacts of combined scale-fungus canker disease, beech bark disease (BBD). Although BBD has been present in North America since approximately 1920 (Ehrlich 1934), the compounding stress of BBD and BLD leaves beech increasingly vulnerable. While BLD has been found to disproportionately affect saplings and small trees, BBD primarily infects large beeches (Shepherd et al. 2025).
When a prominent forest species such as beech begins to decline, the resulting compositional shifts can have substantial ecological impacts. These compositional alterations may be the result of forest pathogens, various forms of direct human development, or climate related factors. The process of urbanization is complex and often includes fast, major environmental transitions such as timber harvesting, agricultural use, infrastructural development, selective preservation, and suppression or changes of fire and other disturbance regimes (Flinn et al. 2018). Urbanization can thus drive composition change through proceeding processes like mesophication and homogenization. Climate-related changes and instability also have severe implications for plant life, especially for species that are drought- and flood-sensative, as beech is (Stephanson and Coe 2017). Changing weather patterns additionally impact soil chemistry, suitable species ranges, and potential for shifting species dynamics as the environment becomes more favorable to different species.
In Ohio, large-scale disturbances resulting from Euro-American settlement and subsequent activity has resulted in extensive shifts in forest compositional patterns over the past 300 years. A 2016 study by Deines et al. compared archival U.S. Public Land Survey maps to the U.S. Forest Service’s present day Forest Inventory Analysis of 27 Ohio counties. Deines found substantial beech decline in northwestern counties from 26.9% to 1.2% since presettlement. Northwest Ohio also saw a notable decrease in abundance of elm species (-8.3%), and increase in abundance of the taxonomic groups of hickory (+12.7%) and oak (6.7%). In southeast Ohio, the greatest changes in abundance was observed in the oak (-27.7%), maple (+11.5%), tulip poplar (+7.4%), beech (-6.8%), cherry (+5.7%), and pine (+5.2%) taxa. A trend of general decrease in the dominant taxa and compositional homogenization was found across the full study area (Deines 2016).
Committed settlement began in southeastern Ohio the late 1780s and in northwestern Ohio by the 1830s (Deines 2016; Boerner and Cho 1987). The presettlement statewide forestation estimate of 95% (Trautman 1977) reached a low for southeastern Ohio at 20% in 2010 (Dyer 2001). The estimate for this region now sits at approximately 65%. In northwestern Ohio, however, forests were largely cleared for agricultural purposes and forest cover remains generally below 10% (Fry et al. 2011). Although pests and diseases including Dutch elm disease and the Emerald ash borer can be attributed to causing some of the shifts over this time period, much of these changes are the result of land modification often in the form of logging and agriculture. This widespread upheaval favors colonizing and disturbance-adapted species and has led to large-scale homogenization of species distribution, age, and size class. It has also served to disassociate species from their optimal climate zones. Soil, climate, and environment now shape species distribution to a lesser degree throughout the state (Deines 2016). A 2018 study by Flinn et al. comparing habitat types, plant species composition, and tree species abundance in northeast Ohio between 1800 and 2014 found a significant decrease in beta diversity within the study’s 214 year timeframe (Flinn et al. 2018).
Land conversion relating to agricultural advancements altered the drainage systems and hydrology of major portions of Ohio, which has likely been the primary driver of the historic decline of American beech in the state (Deines 2016). Now, impacted by both beech bark disease and the emergence of beech leaf disease, beech is under significantly increased stress.
The disappearance of beech from forests has a myriad of potential ramifications, both projected and possibly unforeseen.
The elimination of the American chestnut throughout the mid 1900s resulting from the canker fungal chestnut blight provides a parallel case reference. The American chestnuts (Castanea dentata) was a dominant species across a similar range to that of the American beech today (Freinkel 2007). Chestnut blight, likely introduced in 1904 (Milgroom et al. 1996) quickly spread throughout the range of the chestnut, functionally eradicating the species (Anagnostakis 2001). The disappearance of chestnut led to job and economic loss amidst the Great Depression (Lutts 2004), ecological suffering for a wide range of species and ecosystems which relied upon chestnut (Elliston et al. 2005), and profound compositional changes throughout the chestnut’s range (Karban and Karban 2024).
As BLD progresses, reduction in foliage will make the dense beech canopy more light permeable, which is expected to alter forest floor plant communities (Volk et al. 2019). With increased beech mortality, the currently co-dominant sugar and red maples can be expected to take over distribution gaps. Additionally, shade-intolerant and invasive species may find opportunities to exploit newly-cleared space, leading to loss of tree diversity and forest resilience (Forrester et al. 2003). Beyond regional impacts on American beech, recent research has been exploring potential for impacts of European beech (Fagus sylvatica) (Ewing et al. 2018).
Northeast Ohio is the epicenter of beech leaf disease. Understanding and analysis of chestnut blight is limited by a lack of baseline compositional data (Karban and Karban 2024). In order to track the progression of this detrimental disease and make informed decisions for our forests both in the context of BLD and future pathogenic challenges, systematic, quantitative cataloging of current forest composition is essential.
Bibliography
Anagnostakis SL. 2001. The effect of multiple importations of pests and pathogens on a native tree. Biol Invasions. 3:245–254. https://doi.org/10.1023/A:1015205005751.
Boerner REJ, Cho DS. 1987. Structure and composition of Goll Woods, an old-growth forest remnant in northwestern Ohio. Bull Torrey Bot Club. 114(2):173–179. https://doi.org/10.2307/2996127.
Cappaert D, McCullough DG, Poland TM, Siegert NW. 2005. Emerald ash borer in North America: a research and regulatory challenge. Am Entomol. 51(3):152–165.
Carta LK, Handoo ZA, Li S, et al. 2020. Beech leaf disease symptoms caused by newly recognized nematode subspecies Litylenchus crenatae mccannii (Anguinata) described from Fagus grandifolia in North America. For Path. 50:e12580. https://doi.org/10.1111/efp.12580.
Cleveland Metroparks Technical Report 2019/NR-07. Parma (OH): Cleveland Metroparks, Division of Natural Resources.
Coladonato ML. 1991. Fagus grandifolia. In: Fire Effects Information System [Internet]. Fort Collins (CO): U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory. Available from: https://www.fs.usda.gov/database/feis/plants/tree/faggra/all.html [accessed 2025 Dec 5].
Deines JM. 2016. Changes in forest composition in Ohio between Euro-American settlement and the present. Am Midl Nat. 176(2):247–271. https://doi.org/10.1674/0003-0031-176.2.247.
Dyer JM. 2001. Using witness trees to assess forest change in southeastern Ohio. Can J For Res. 31(10):1708–1718. https://doi.org/10.1139/x01-111.
Ellison AM, Bank MS, Clinton BD, Colburn EA, Elliott K, Ford CR, Foster DR, et al. 2005. Loss of foundation species: consequences for the structure and dynamics of forested ecosystems. Front Ecol Environ. 3:479–486. https://doi.org/10.1890/1540-9295(2005)003[0479:LOFSCF]2.0.CO;2.
Ewing CJ, Hausman CE, Pogacnik J, Slot J, Bonello P. 2019. Beech leaf disease: An emerging forest epidemic. For Path. 49:e12488. https://doi.org/10.1111/efp.12488.
Freinkel S. 2007. American Chestnut: The Life, Death, and Rebirth of a Perfect Tree. Berkeley (CA): University of California Press.
Fletcher LR, Borsuk AM, Fanton AC, Johnson KM, Richburg J, Zailaa J, Brodersen CR. 2024. Anatomical and physiological consequences of beech leaf disease in Fagus grandifolia L. Forest Pathol. 54:e12842. https://doi.org/10.1111/efp.12842.
Flinn KM, Mahany TP, Hausman CE. 2018. From forest to city: Plant community change in northeast Ohio from 1800 to 2014. J Veg Sci. 29:297–306. https://doi.org/10.1111/jvs.12621.
Forrester JA, McGee GG, Mitchell MJ. 2003. Effects of beech bark disease on aboveground biomass and species composition in a mature northern hardwood forest, 1985 to 2000. J Torrey Bot Soc. 130(2):70–78. https://doi.org/10.2307/3557531.
Fry JA, George X, Jin S, Dewitz JA, Homer CG, Yang L, Barnes CA, Harold ND, Wickham JD. 2011. Completion of the 2006 National Land Cover Database for the Conterminous United States. Photogrammetric Engineering & Remote Sensing. 77(9).
Gibbs JN, French DW. 1979. The Transmission of Oak Wilt. St. Paul (MN): USDA Forest Service.
Karban R, Karban CC. 2024. Floristic changes following the chestnut blight may be delayed for decades. PLoS One. 19(10):e0306748. https://doi.org/10.1371/journal.pone.0306748.
Lutts RH. 2004. Like manna from God: the American chestnut trade in southwestern Virginia. Environ Hist. 9(3):497–525. https://doi.org/10.2307/3985770.
McClure MS. 1987. Biology and control of hemlock woolly adelgid. New Haven (CT): Connecticut Agricultural Experiment Station. Bulletin 851:1–9.
Milgroom MG, Wang K, Zhou Y, Lipari SE, Kaneko S. 1995. Intercontinental population structure of the chestnut blight fungus: Cryphonectria parasitica. 88(2):179–190.
Rigling D, Prospero S. 2018. Cryphonectria parasitica, the causal agent of chestnut blight: invasion history, population biology and disease control. Mol Plant Pathol. 19:7–20. https://doi.org/10.1111/mpp.12542.
Shepherd BL, Burke DJ, Stuble KL. 2025. Fagus grandifolia growth and mortality a decade after the emergence of beech leaf disease. Trees Forests People. 20:100836. https://doi.org/10.1016/j.tfp.2025.100836.
Stephanson CA, Ribarik Coe N. 2017. Impacts of beech bark disease and climate change on American beech. Forests. 8(5):155. https://doi.org/10.3390/f8050155.
Strobel GA, Lanier GN. 1981. Dutch elm disease. Sci Am. 245(2):56–67. http://www.jstor.org/stable/24964537.
Trautman MB. 1977. The Ohio Country from 1750 to 1977: a naturalist’s view.
Tubbs CH, Houston DR. 1990. Fagus grandifolia Ehrh. American Beech. In: Burns RM, Honkala BH, editors. Silvics of North America. Vol. 2. Washington DC: USDA Forest Service. p. 325–330.
Volk DR, Hausman CE, Martin DK. 2019. Beech leaf disease seasonal symptom progression.
Wilson DA. 2005. Recent advances in the control of oak wilt in the United States. Plant Pathol J. 4(2):177–191. https://doi.org/10.1674/0003-0031-176.2.247.