Mississippi Alluvial Valley
(Area - 11,461,500 ha)
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Location and physiography - This area includes the floodplain of
the Mississippi River that cuts into the Gulf Coastal Plain, extending north to and including the
delta at the confluence of the Mississippi and Ohio Rivers and south toward the Gulf of Mexico.
The Alluvial Valley includes most of eastern Louisiana, eastern Arkansas, northwest Mississippi,
small portions of west Tennessee and Kentucky, the bootheel of Missouri, and the Cache River
lowlands of Illinois. Nonforested marsh in southern portions of the floodplain is included in the
Coastal Prairie physiographic area. Water shaped this land. The ridges and swales, levees,
oxbows, and terraces of the Valley all resulted from meanderings and floods of the Mississippi
River. Small changes in elevation determine how wet a site is, the plant community that grows
there, and habitat conditions for birds.
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Conservation issues and recommendations - The Mississippi Alluvial Valley was entirely covered by bottomland hardwood forest at the time of European settlement, when it was the largest extent of that habitat type on earth. Since then, over 80% of the forest has been cleared for agriculture and other uses and the hydrology has been drastically altered, inhibiting many aspects of ecosystem function. Much of the remaining forest remains in small fragments, further reducing the capacity of the landscape to support bird populations. In recent years, however, forest clearing has essentially stopped and restoration has probably increased total forest coverage.
The area is mostly in private ownership, but there are numerous small to moderate-sized federal and state wildlife reserves. Much private forest land is owned by the forest products industry or limited partnership hunting clubs and is thus likely to remain forested. Well-drained land is valuable for agriculture and most current forested lands or areas likely to be restored are poorly-drained. This is the biological core of the Lower Mississippi Valley Joint Venture, and the focus of a good deal of reforestation effort. Because the remaining forest is so fragmented, conservation recommendations focus on retention or restoration of blocks of forest of sufficient size to support healthy populations of the suite of bottomland hardwood forest birds. In southern reaches, some of these should be 100,000 acres or more to support Swallow-tailed Kites and all associated species. To the north, 20,000 acres including at least some drier habitat should be sufficient for Cerulean Warblers and all other birds. Throughout, where blocks of that size are unattainable, a 10,000 block will support Swainson's Warblers and all other less area-demanding species. The total number of blocks to be retained or restored is about 70? and should include about one million reforested acres.
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