Dissected Till Plains
(Area - 22,394,200 ha)
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Location and physiography - The Dissected Till Plains occupy
much of Iowa, eastern Nebraska, northwest Missouri, and small parts of northwest Illinois,
southern Minnesota, and northeast Kansas. This area was glaciated, uplifted, and subsequently
eroded into a flat-to-rolling terrain that slopes gently toward the Missouri and Mississippi River
Valleys. Natural vegetation is a mosaic of tallgrass bluestem prairie and oak-hickory forest with
oak savannahs characteristic of transition zones. Bottomland hardwoods grow in river
valleys.
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Conservation issues and recommendations - This former upland prairie/savannah/forest complex is now one of the most heavily altered physiographic areas in the country. Agriculture dominates the uplands, fire suppression and urbanization encourage trees where there was once prairie, and reservoirs have flooded many of the more extensively wooded bottomlands.
About half of the agricultural lands are hay field or pasture which offer some potential for use by priority grassland birds. Dominance of fescue and early mowing for hay, however, greatly reduces much of the area's value. Protection or restoration of a series of grassland Bird Conservation Areas each consisting of a 2000-acre core surrounded by a mile-wide matrix containing at least 2000 additional acres of grassland may be the best hope for perpetuation of the grassland species suite. Where prairie-chickens are not an issue, such a large central core may not be necessary as long as patch sizes exceed minimum area requirements of other priority birds and the percentage of grassland in the Bird Conservation Area remains 40% or greater. Smaller grasslands specially managed or enrolled under the Conservation Reserve Program may support one or a few priority species, especially if they help bring the total amount of grassland in a landscape above some critical threshold. Restoration of riverine corridors offers promise for forest birds if patches are large enough that predation and parasitism rates are minimized. PIF suggests management of small upland woodlots for in-transit migrants.
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