Floodplain Forest Response to Multiple Large-Scale Inundation Events Survey Data From Eight Pools of the Upper Mississippi River Collected During the Growing Seasons of 1995 and 2021

Throughout the Upper Mississippi River System (UMRS), floods in 1993 and 2019 were record-setting events in terms of flood stage and duration of flooding. Floodplain tree species are adapted to survive moderate frequencies, intensities, and durations of inundation. These events generated interest in quantifying levels of tree mortality and presented an opportunity to study how differences in flood attributes may affect tree survivorship and forest community dynamics post-flood. In 1995, 547 plots randomly located within forested land cover were established within seven reaches on the Upper Mississippi River (Pool 4, Pool 8, Pool 13, Pool 17, Pool 22, Pool 26, Open River) and one reach of the Illinois River (La Grange Pool). In 2021, 39-46 sites (n = 342) from each of the eight reaches were navigated to using GPS coordinates from the original study and resurveyed using the same field sampling protocol used in 1995. In many cases (n = 287), the original posts and tree tags installed in 1995 could not be found and thus plots in 2021 were re-established by navigated as close to the original GPS coordinates as possible and referencing the 1995 data. In some of these cases (n = 24), plots were inaccessible (e.g., in a water body) due to landform changes that had occurred in the intervening years between field sample collections, and in these instances, plots were relocated to a nearby site with similar forest composition, elevation, and river geomorphology. Plots were re-established in order to maintain a consistent number of plots per reach for potential future monitoring, however, those that were moved were noted along with original 1995 coordinates in the provided ‘Plot_2021.csv’ file and can be included or removed in subsequent analyses depending on research questions and goals. Plots were sampled using a fixed radius sampling methodology with a radius of 10 meters, and data collected included: overstory species composition, diameters, and health status; canopy cover; seedling counts and composition; cover classes for different forest height strata; ground cover; and herbaceous cover. Seedlings, ground cover, and herbaceous cover were measured within ten randomly located 0.5 m x 0.5 m subplots.