CHAPTER III: MISSISSIPPI’S ECOLOGICAL FRAMEWORK-ECOREGIONS OF MISSISSIPPI 67
phenomenon in which high water stages on the Mississippi River create a damming effect, preventing
tributary drainage into the mainstem and at times reversing tributary flow upstream. As a result, long-
duration flooding accompanied by sediment and nutrient deposition occurs throughout the associated
tributary watersheds.
Concomitant to these flooding mechanisms are the hydrogeomorphic processes associated with
meandering river systems. The high energy inherent in the Mississippi River and its tributaries once
sculpted the landscape, producing a surface geomorphology comprised of natural levees, meander scar
(oxbow) lakes, point bars and ridge and swale topography. Site conditions within MSRAP range from
permanently flooded areas supporting only emergent or floating aquatic vegetation to high elevation
sites that support climax hardwood forests. The distribution of bottomland hardwood communities
within the floodplains of the Mississippi River and its tributaries is determined by timing, frequency and
duration of flooding. Elevational differences of only a few inches result in great differences in soil
saturation characteristics and thus the species of plants that grow there. As a result, much variability
exists within a bottomland hardwood ecosystem, ranging from the bald cypress/tupelo swamp
community that develops on frequently inundated sites with permanently saturated soils, to the
cherrybark oak/pecan community found on the sites subjected to temporary flooding. Between these
rather distinct community types are the more transitional, less distinguishable overcup oak/water
hickory, elm/ash/hackberry and sweetgum/red oak communities.
In time, and in response to sediment texture, deposition rates and quantities, plant communities
characteristic of MSRAP undergo ecological succession from pioneer communities dominated by black
willow or cottonwood (depending on soil drainage characteristics) to red oak and finally white oak
dominated climax community. But other disturbances also influence plant community distribution.
Both human- and naturally-induced disturbances, such as ice storms, hurricanes, beaver activity,
hydrologic alteration and silvicultural practices, greatly influence the rate and direction of succession.
There is emerging thought that the dynamic nature of this water- and sediment-driven system, coupled
with frequent disturbance, historically precluded, in most cases, the development or long-term viability
of a closed canopy of senescent trees, or a community commonly thought of as old-growth. The pre-
settlement forests of MSRAP were likely a shifting mosaic of even-aged small patches of all-ages,
further defined by minute differences in elevation and tolerances among a large number of woody
plants.
The diversity of forests and other habitat characterizing the historic landscape provided an extraordinary
habitat for a range of species utilizing MSRAP. River floodplain systems are highly productive and
provide exceptional habitat for a variety of vertebrates including foraging and spawning fish,
amphibians and reptiles. Over 240 fish species, 45 species of reptiles and amphibians and 37 species of
mussels depend on the river and floodplain system of MSRAP. In addition, 50 species of mammals and
approximately 60 percent of all bird species in the contiguous United States currently utilize the