Changes in trees, groundlayer diversity, and deer-preferred plants across 18 years in oak (Quercus, Fagaceae) forests of northwestern Ohio1,2

Abstract

The persistence of Quercus forest ecosystems in eastern North America is uncertain with replacement of Quercus spp. by other trees, invasion by nonnative plants, and alteration of native ground layers through deer herbivory and other factors. In northwestern Ohio, we examined changes in tree strata and ground layers (herbs, shrubs, and tree seedlings) at eight Quercus forest sites measured in 2002, 2015, 2018, and 2019. Mortality averaged 2.0% per year for small (1–40 cm in diameter at 1.4 m) and 0.7% per year for large (≥ 40 cm in diameter) Quercus trees. Assuming continued lack of recruitment and linear continuation of mortality rates, live Quercus trees would be absent on these sites by the year 2042 in the small size class and by 2165 in the large size class. Despite their density declining by half between 2002 and 2019, Acer rubrum, Sassafras albidum, and Prunus serotina remained the most abundant tree species in the understory (stems 1–10 cm in diameter). Contrasting with many studies, nonnative plants remained nearly absent, never exceeding 0.2% cover (compared with 27–48% average cover of native ground layer plants among years). A major change in the ground layer was a nine-fold increase in cover of deer-preferred, native forbs between 2015 and 2019. This increase coincided with deer management after 2015 and three consecutive wet early summers from 2017–2019. Based on the long-term dataset, we discuss five scenarios of future ecosystems under different potential conservation strategies, ranging from managing for forests with canopy gaps encouraging Quercus regeneration, to facilitating transitions to non-Quercus forests. Although lack of Quercus recruitment highlighted uncertainty in persistence of Quercus trees, trends in ground layer communities suggested sustained dominance by native plants.