We conducted this study in Upper Mississippi River Pools 4 and 8 to document the occurrence and cover of Phalaris arundinacea and other forest floor plants in UMR floodplain forests and relate measures of abundance of Phalaris, and community composition and diversity to estimates of flood duration which can exhibit high spatial heterogeneity. We used modeled inundation duration which allowed us to sample at randomly selected forest “places” across a large spatial scale in forest areas that had a range of tree canopy cover and basal area. We also evaluated changes in plant composition, Phalaris and wood nettle cover and silver maple seedling persistence between years relative to modeled inundation duration. From these repeated samples we also asked whether Phalaris and wood nettle cover the 1st year influenced plant composition the following year. Forest floor vegetation was quantified as percent cover within 5, 4m radius plots: one in the center and 4 others centered 25m from the center plot in the 4 cardinal directions. Percent cover was recorded to the nearest 5% for cover over 5%, to nearest 1 percent below 5%. We also noted species that were rare (1-5 individuals with less than 1%) as 0.1% cover, or numerous with insignificant cover (<1% cover), as 0.5% cover. Summing cover over all species in a plot could yield a number greater than 100, or greater than the total cover estimated for that plot if plant canopies overlapped. The species abbreviations (codes) follow the USDA Plants website conventions (https://plants.sc.egov.usda.gov/home).