Arkansas Post National Memorial is in the Lower Mississippi Riverine Forest ecoregion.
Land-surface form. The ecoregion consists of a flat to gently sloping broad floodplain and low terraces made up of alluvium (water transported sediment) and loess (windblown and deposited sediment). From near sea level in the south, altitude increases gradually to about 660 feet in the north. Most of the area is flat, with an average southward slope of less than 8 inches per mile. The only noticeable slopes are sharp terrace scarps and natural levees that rise sharply to several meters above adjacent bottomlands or river channels. This is the land of oxbow lakes and cutoff meanders.
Climate. Winters are warm, with temperatures ranging from 50 to 60 degrees F, and summers are hot, with temperatures ranging from 70-80 degrees F. Rain falls throughout the year, with a minimum amount in autumn. Temperature and precipitation decrease as one moves northward.
Vegetation. Before cultivation, this area was covered by bottomland deciduous forest with an abundance of green and Carolina ash, elm, cottonwood, sugarberry, sweetgum, and water tupelo, as well as oak and bald cypress. Pecan is also present, associated with eastern sycamore, American elm, and roughleaf dogwood. Vines are prolific along water courses.
Soils. The soils are a mosaic of Inceptisols (in alluvial bottomland), Alfisols (in areas of loess), and Mollisols (in areas with swampy vegetation).
Fauna. Among the numerous bird species found here are the prothonotary warbler, white-eyed vireo, wood duck, yellow-billed cuckoo, Louisiana water thrush, and all the species found in the Southeastern Mixed Forest Province. Racoons, opossum, and deer can be seen in the Memorial unit. Nutria and alligators are found in the waterways surrounding the park.