Series Description

Floodplain forests were investigated along two major rivers in Minnesota -the Red River of the North from Breckenridge to the Canadian border and the Minnesota River from Granite Falls to Mankato. Both systems are located in watersheds dominated by intensive agriculture and both systems are subject to dramatic flooding, primarily in the spring. Floodwaters are temporarily retained in small depressions and former river channels, providing important habitat for amphibians and aquatic invertebrates.

The Red River flows north through the Glacial Lake Agassiz basin - an expansive area with little relief. The fertile soils of this region have been mostly converted to agricultural crops, especially small grains, sunflower, and sugar beets. The presettlement vegetation was mainly tallgrass prairie with forest restricted to the narrow floodplain of the river and nearby upland. Only small, scattered patches of forest remain. In general, the river channel is narrow with a narrow flanking floodplain bounded by slopes that rise quickly to the upland. Where still forested, typical tree species in the floodplain are green ash (Fraxinus pensylvanica), American elm (Ulmus americana), box elder (Acer negundo) and willow (Salix spp.) The river is minimally regulated with flood control alterations in urban areas.

The Minnesota River originates at Big Stone Lake on the western border of the state, and flows southeasterly until it reaches Mankato, where it turns northeast. Tributaries to the river flow through a watershed dominated by corn and soybean crops and livestock farms, through level to gently rolling terrain. The terrain drops rapidly through steep hills that mark the edge of the wide river valley and floodplain. This landscape was formed during glacial times by the River Warren, which carried tremendous volumes of glacial meltwater runoff, carving a wide and deep valley through the land. While much of the rich alluvial soils of the floodplain have been put to agricultural use, large tracts of intact floodplain forest sitll remain in some areas. Typical tree species there include silver maple (Acer saccharinum), cottonwood (Populus deltoides), and green ash (Fraxinus pensylvanica). In other areas, the original floodplain has been reduced to a narrow fringe or, in urban areas, replaced altogether by riprap and floodwalls. The river itself has been dammed and channelized in a few urban area, but is otherwise fairly unaltered along its length.

A total of 35 floodplain sites were evaluated in summer 1995. These potential study sites were identified by consulting with local Department of Natural Resources Area Wildlife managers, Natural Resource Conservation Service staff and from National Wetland Inventory maps. Twenty sites were rejected after initial evaluation; most because they were located along small tributaries to the major rivers or because they were another kind of wetland, such as a marsh. A few sites were rejected because they had only minimal floodplain area. The fifteen sites selected were those that best-represented a gradient from least disturbed to highly degraded, with respect to human land use. Sites with extensive intact floodplain forest and unengineered channels were considered to be least disturbed. These criteria were applied to both river systems, though the Red River does not have as extensive of floodplain forest development as the Minnesota River. Sites representing the least degraded end of the gradient were Chamberlain Woods Scientific and Natural Area (CW) and Minneopa State Park (MI). Other than a railroad at Minneopa, both sites are large with relatively little human impact (although historic logging likely occurred). The adjacent uplands of both sites also had minimal cultural development. Two of the most degraded sites were Mankato (MA) and Breckenridge (BR). Mankato is a site located within that city that was formerly floodplain forest but has been converted to to a rip rap bank below a floodwall. The Breckenridge site is located on a golf course that has been diked along the river to prevent flooding and is pumped if it does flood. Typical sites were represented by Boesch WMA (BO) on the Minnesota River and Hanson (HA) on the Red River. Both sites are much smaller floodplain forest fragments than Chamberlain Woods and Minneopa. The adjacent land use of both sites is agriculture.

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