Species and landscape variation in tree regeneration and 17 years of change in forested wetlands invaded by emerald ash borer

Understanding variation in tree regeneration among species and sites, and how well forest size class distribution (seedlings, saplings, and trees) portends long-term species compositional change, may assist managing forests during contemporary global change rapidly altering forests, such as after invasion by introduced pests. In northwestern Ohio, one of the North American regions longest invaded by emerald ash borer (EAB, Agrilus planipennis), we 1) examined variation in size class abundance among tree species and sites in 22 forested wetlands in 2018 and 2021; and 2) assessed how closely size class distribution of tree species in 2005, at the onset of EAB invasion before Fraxinus trees died, forecasted observed forest change during the next 17 years. In 2018 and 2021, three major groups of tree species emerged with respect to their frequency across size classes: 1) species commonly in all three, or at least two, size classes on a site, 2) species frequent in only one size class, which varied but was often seedlings, and 3) species almost always present only as trees, with little advance regeneration. Shade tolerance correlated with species occurring in all three size classes. Among sites in 2018 and 2021, abundance of regeneration and similarity of species composition across size classes varied between years (largely from fluctuations in seedlings) and with site factors. Sites with the least regeneration had high soil available water capacity and high cover of graminoids. On long-term sites after the onset of EAB invasion in 2005, all seedling -to -sapling and sapling -to -tree advancements recorded through 2021 were from species already present in 2005, and only shade -tolerant species (e.g., Ulmus americana) advanced. Results suggest that there is substantial variation in advance regeneration availability among species and sites in forested wetlands across the EAB-invaded landscape. Portions of this variability were structured into well -demarcated groups of similarly responding species and sites, were associated with species traits such as shade tolerance and site factors such as soil texture, and were prognostic of forest changes within the first two decades after EAB invasion.